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// Copyright 2014 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package runtime
import (
"internal/abi"
"internal/cpu"
"internal/goarch"
"runtime/internal/atomic"
"runtime/internal/sys"
"unsafe"
)
// set using cmd/go/internal/modload.ModInfoProg
var modinfo string
// Goroutine scheduler
// The scheduler's job is to distribute ready-to-run goroutines over worker threads.
//
// The main concepts are:
// G - goroutine.
// M - worker thread, or machine.
// P - processor, a resource that is required to execute Go code.
// M must have an associated P to execute Go code, however it can be
// blocked or in a syscall w/o an associated P.
//
// Design doc at https://golang.org/s/go11sched.
// Worker thread parking/unparking.
// We need to balance between keeping enough running worker threads to utilize
// available hardware parallelism and parking excessive running worker threads
// to conserve CPU resources and power. This is not simple for two reasons:
// (1) scheduler state is intentionally distributed (in particular, per-P work
// queues), so it is not possible to compute global predicates on fast paths;
// (2) for optimal thread management we would need to know the future (don't park
// a worker thread when a new goroutine will be readied in near future).
//
// Three rejected approaches that would work badly:
// 1. Centralize all scheduler state (would inhibit scalability).
// 2. Direct goroutine handoff. That is, when we ready a new goroutine and there
// is a spare P, unpark a thread and handoff it the thread and the goroutine.
// This would lead to thread state thrashing, as the thread that readied the
// goroutine can be out of work the very next moment, we will need to park it.
// Also, it would destroy locality of computation as we want to preserve
// dependent goroutines on the same thread; and introduce additional latency.
// 3. Unpark an additional thread whenever we ready a goroutine and there is an
// idle P, but don't do handoff. This would lead to excessive thread parking/
// unparking as the additional threads will instantly park without discovering
// any work to do.
//
// The current approach:
//
// This approach applies to three primary sources of potential work: readying a
// goroutine, new/modified-earlier timers, and idle-priority GC. See below for
// additional details.
//
// We unpark an additional thread when we submit work if (this is wakep()):
// 1. There is an idle P, and
// 2. There are no "spinning" worker threads.
//
// A worker thread is considered spinning if it is out of local work and did
// not find work in the global run queue or netpoller; the spinning state is
// denoted in m.spinning and in sched.nmspinning. Threads unparked this way are
// also considered spinning; we don't do goroutine handoff so such threads are
// out of work initially. Spinning threads spin on looking for work in per-P
// run queues and timer heaps or from the GC before parking. If a spinning
// thread finds work it takes itself out of the spinning state and proceeds to
// execution. If it does not find work it takes itself out of the spinning
// state and then parks.
//
// If there is at least one spinning thread (sched.nmspinning>1), we don't
// unpark new threads when submitting work. To compensate for that, if the last
// spinning thread finds work and stops spinning, it must unpark a new spinning
// thread. This approach smooths out unjustified spikes of thread unparking,
// but at the same time guarantees eventual maximal CPU parallelism
// utilization.
//
// The main implementation complication is that we need to be very careful
// during spinning->non-spinning thread transition. This transition can race
// with submission of new work, and either one part or another needs to unpark
// another worker thread. If they both fail to do that, we can end up with
// semi-persistent CPU underutilization.
//
// The general pattern for submission is:
// 1. Submit work to the local run queue, timer heap, or GC state.
// 2. #StoreLoad-style memory barrier.
// 3. Check sched.nmspinning.
//
// The general pattern for spinning->non-spinning transition is:
// 1. Decrement nmspinning.
// 2. #StoreLoad-style memory barrier.
// 3. Check all per-P work queues and GC for new work.
//
// Note that all this complexity does not apply to global run queue as we are
// not sloppy about thread unparking when submitting to global queue. Also see
// comments for nmspinning manipulation.
//
// How these different sources of work behave varies, though it doesn't affect
// the synchronization approach:
// * Ready goroutine: this is an obvious source of work; the goroutine is
// immediately ready and must run on some thread eventually.
// * New/modified-earlier timer: The current timer implementation (see time.go)
// uses netpoll in a thread with no work available to wait for the soonest
// timer. If there is no thread waiting, we want a new spinning thread to go
// wait.
// * Idle-priority GC: The GC wakes a stopped idle thread to contribute to
// background GC work (note: currently disabled per golang.org/issue/19112).
// Also see golang.org/issue/44313, as this should be extended to all GC
// workers.
var (
m0 m
g0 g
mcache0 *mcache
raceprocctx0 uintptr
)
//go:linkname runtime_inittask runtime..inittask
var runtime_inittask initTask
//go:linkname main_inittask main..inittask
var main_inittask initTask
// main_init_done is a signal used by cgocallbackg that initialization
// has been completed. It is made before _cgo_notify_runtime_init_done,
// so all cgo calls can rely on it existing. When main_init is complete,
// it is closed, meaning cgocallbackg can reliably receive from it.
var main_init_done chan bool
//go:linkname main_main main.main
func main_main()
// mainStarted indicates that the main M has started.
var mainStarted bool
// runtimeInitTime is the nanotime() at which the runtime started.
var runtimeInitTime int64
// Value to use for signal mask for newly created M's.
var initSigmask sigset
// The main goroutine.
func main() {
mp := getg().m
// Racectx of m0->g0 is used only as the parent of the main goroutine.
// It must not be used for anything else.
mp.g0.racectx = 0
// Max stack size is 1 GB on 64-bit, 250 MB on 32-bit.
// Using decimal instead of binary GB and MB because
// they look nicer in the stack overflow failure message.
if goarch.PtrSize == 8 {
maxstacksize = 1000000000
} else {
maxstacksize = 250000000
}
// An upper limit for max stack size. Used to avoid random crashes
// after calling SetMaxStack and trying to allocate a stack that is too big,
// since stackalloc works with 32-bit sizes.
maxstackceiling = 2 * maxstacksize
// Allow newproc to start new Ms.
mainStarted = true
if GOARCH != "wasm" { // no threads on wasm yet, so no sysmon
systemstack(func() {
newm(sysmon, nil, -1)
})
}
// Lock the main goroutine onto this, the main OS thread,
// during initialization. Most programs won't care, but a few
// do require certain calls to be made by the main thread.
// Those can arrange for main.main to run in the main thread
// by calling runtime.LockOSThread during initialization
// to preserve the lock.
lockOSThread()
if mp != &m0 {
throw("runtime.main not on m0")
}
// Record when the world started.
// Must be before doInit for tracing init.
runtimeInitTime = nanotime()
if runtimeInitTime == 0 {
throw("nanotime returning zero")
}
if debug.inittrace != 0 {
inittrace.id = getg().goid
inittrace.active = true
}
doInit(&runtime_inittask) // Must be before defer.
// Defer unlock so that runtime.Goexit during init does the unlock too.
needUnlock := true
defer func() {
if needUnlock {
unlockOSThread()
}
}()
gcenable()
main_init_done = make(chan bool)
if iscgo {
if _cgo_thread_start == nil {
throw("_cgo_thread_start missing")
}
if GOOS != "windows" {
if _cgo_setenv == nil {
throw("_cgo_setenv missing")
}
if _cgo_unsetenv == nil {
throw("_cgo_unsetenv missing")
}
}
if _cgo_notify_runtime_init_done == nil {
throw("_cgo_notify_runtime_init_done missing")
}
// Start the template thread in case we enter Go from
// a C-created thread and need to create a new thread.
startTemplateThread()
cgocall(_cgo_notify_runtime_init_done, nil)
}
doInit(&main_inittask)
// Disable init tracing after main init done to avoid overhead
// of collecting statistics in malloc and newproc
inittrace.active = false
close(main_init_done)
needUnlock = false
unlockOSThread()
if isarchive || islibrary {
// A program compiled with -buildmode=c-archive or c-shared
// has a main, but it is not executed.
return
}
fn := main_main // make an indirect call, as the linker doesn't know the address of the main package when laying down the runtime
fn()
if raceenabled {
runExitHooks(0) // run hooks now, since racefini does not return
racefini()
}
// Make racy client program work: if panicking on
// another goroutine at the same time as main returns,
// let the other goroutine finish printing the panic trace.
// Once it does, it will exit. See issues 3934 and 20018.
if runningPanicDefers.Load() != 0 {
// Running deferred functions should not take long.
for c := 0; c < 1000; c++ {
if runningPanicDefers.Load() == 0 {
break
}
Gosched()
}
}
if panicking.Load() != 0 {
gopark(nil, nil, waitReasonPanicWait, traceEvGoStop, 1)
}
runExitHooks(0)
exit(0)
for {
var x *int32
*x = 0
}
}
// os_beforeExit is called from os.Exit(0).
//
//go:linkname os_beforeExit os.runtime_beforeExit
func os_beforeExit(exitCode int) {
runExitHooks(exitCode)
if exitCode == 0 && raceenabled {
racefini()
}
}
// start forcegc helper goroutine
func init() {
go forcegchelper()
}
func forcegchelper() {
forcegc.g = getg()
lockInit(&forcegc.lock, lockRankForcegc)
for {
lock(&forcegc.lock)
if forcegc.idle.Load() {
throw("forcegc: phase error")
}
forcegc.idle.Store(true)
goparkunlock(&forcegc.lock, waitReasonForceGCIdle, traceEvGoBlock, 1)
// this goroutine is explicitly resumed by sysmon
if debug.gctrace > 0 {
println("GC forced")
}
// Time-triggered, fully concurrent.
gcStart(gcTrigger{kind: gcTriggerTime, now: nanotime()})
}
}
//go:nosplit
// Gosched yields the processor, allowing other goroutines to run. It does not
// suspend the current goroutine, so execution resumes automatically.
func Gosched() {
checkTimeouts()
mcall(gosched_m)
}
// goschedguarded yields the processor like gosched, but also checks
// for forbidden states and opts out of the yield in those cases.
//
//go:nosplit
func goschedguarded() {
mcall(goschedguarded_m)
}
// goschedIfBusy yields the processor like gosched, but only does so if
// there are no idle Ps or if we're on the only P and there's nothing in
// the run queue. In both cases, there is freely available idle time.
//
//go:nosplit
func goschedIfBusy() {
gp := getg()
// Call gosched if gp.preempt is set; we may be in a tight loop that
// doesn't otherwise yield.
if !gp.preempt && sched.npidle.Load() > 0 {
return
}
mcall(gosched_m)
}
// Puts the current goroutine into a waiting state and calls unlockf on the
// system stack.
//
// If unlockf returns false, the goroutine is resumed.
//
// unlockf must not access this G's stack, as it may be moved between
// the call to gopark and the call to unlockf.
//
// Note that because unlockf is called after putting the G into a waiting
// state, the G may have already been readied by the time unlockf is called
// unless there is external synchronization preventing the G from being
// readied. If unlockf returns false, it must guarantee that the G cannot be
// externally readied.
//
// Reason explains why the goroutine has been parked. It is displayed in stack
// traces and heap dumps. Reasons should be unique and descriptive. Do not
// re-use reasons, add new ones.
func gopark(unlockf func(*g, unsafe.Pointer) bool, lock unsafe.Pointer, reason waitReason, traceEv byte, traceskip int) {
if reason != waitReasonSleep {
checkTimeouts() // timeouts may expire while two goroutines keep the scheduler busy
}
mp := acquirem()
gp := mp.curg
status := readgstatus(gp)
if status != _Grunning && status != _Gscanrunning {
throw("gopark: bad g status")
}
mp.waitlock = lock
mp.waitunlockf = unlockf
gp.waitreason = reason
mp.waittraceev = traceEv
mp.waittraceskip = traceskip
releasem(mp)
// can't do anything that might move the G between Ms here.
mcall(park_m)
}
// Puts the current goroutine into a waiting state and unlocks the lock.
// The goroutine can be made runnable again by calling goready(gp).
func goparkunlock(lock *mutex, reason waitReason, traceEv byte, traceskip int) {
gopark(parkunlock_c, unsafe.Pointer(lock), reason, traceEv, traceskip)
}
func goready(gp *g, traceskip int) {
systemstack(func() {
ready(gp, traceskip, true)
})
}
//go:nosplit
func acquireSudog() *sudog {
// Delicate dance: the semaphore implementation calls
// acquireSudog, acquireSudog calls new(sudog),
// new calls malloc, malloc can call the garbage collector,
// and the garbage collector calls the semaphore implementation
// in stopTheWorld.
// Break the cycle by doing acquirem/releasem around new(sudog).
// The acquirem/releasem increments m.locks during new(sudog),
// which keeps the garbage collector from being invoked.
mp := acquirem()
pp := mp.p.ptr()
if len(pp.sudogcache) == 0 {
lock(&sched.sudoglock)
// First, try to grab a batch from central cache.
for len(pp.sudogcache) < cap(pp.sudogcache)/2 && sched.sudogcache != nil {
s := sched.sudogcache
sched.sudogcache = s.next
s.next = nil
pp.sudogcache = append(pp.sudogcache, s)
}
unlock(&sched.sudoglock)
// If the central cache is empty, allocate a new one.
if len(pp.sudogcache) == 0 {
pp.sudogcache = append(pp.sudogcache, new(sudog))
}
}
n := len(pp.sudogcache)
s := pp.sudogcache[n-1]
pp.sudogcache[n-1] = nil
pp.sudogcache = pp.sudogcache[:n-1]
if s.elem != nil {
throw("acquireSudog: found s.elem != nil in cache")
}
releasem(mp)
return s
}
//go:nosplit
func releaseSudog(s *sudog) {
if s.elem != nil {
throw("runtime: sudog with non-nil elem")
}
if s.isSelect {
throw("runtime: sudog with non-false isSelect")
}
if s.next != nil {
throw("runtime: sudog with non-nil next")
}
if s.prev != nil {
throw("runtime: sudog with non-nil prev")
}
if s.waitlink != nil {
throw("runtime: sudog with non-nil waitlink")
}
if s.c != nil {
throw("runtime: sudog with non-nil c")
}
gp := getg()
if gp.param != nil {
throw("runtime: releaseSudog with non-nil gp.param")
}
mp := acquirem() // avoid rescheduling to another P
pp := mp.p.ptr()
if len(pp.sudogcache) == cap(pp.sudogcache) {
// Transfer half of local cache to the central cache.
var first, last *sudog
for len(pp.sudogcache) > cap(pp.sudogcache)/2 {
n := len(pp.sudogcache)
p := pp.sudogcache[n-1]
pp.sudogcache[n-1] = nil
pp.sudogcache = pp.sudogcache[:n-1]
if first == nil {
first = p
} else {
last.next = p
}
last = p
}
lock(&sched.sudoglock)
last.next = sched.sudogcache
sched.sudogcache = first
unlock(&sched.sudoglock)
}
pp.sudogcache = append(pp.sudogcache, s)
releasem(mp)
}
// called from assembly.
func badmcall(fn func(*g)) {
throw("runtime: mcall called on m->g0 stack")
}
func badmcall2(fn func(*g)) {
throw("runtime: mcall function returned")
}
func badreflectcall() {
panic(plainError("arg size to reflect.call more than 1GB"))
}
//go:nosplit
//go:nowritebarrierrec
func badmorestackg0() {
writeErrStr("fatal: morestack on g0\n")
}
//go:nosplit
//go:nowritebarrierrec
func badmorestackgsignal() {
writeErrStr("fatal: morestack on gsignal\n")
}
//go:nosplit
func badctxt() {
throw("ctxt != 0")
}
func lockedOSThread() bool {
gp := getg()
return gp.lockedm != 0 && gp.m.lockedg != 0
}
var (
// allgs contains all Gs ever created (including dead Gs), and thus
// never shrinks.
//
// Access via the slice is protected by allglock or stop-the-world.
// Readers that cannot take the lock may (carefully!) use the atomic
// variables below.
allglock mutex
allgs []*g
// allglen and allgptr are atomic variables that contain len(allgs) and
// &allgs[0] respectively. Proper ordering depends on totally-ordered
// loads and stores. Writes are protected by allglock.
//
// allgptr is updated before allglen. Readers should read allglen
// before allgptr to ensure that allglen is always <= len(allgptr). New
// Gs appended during the race can be missed. For a consistent view of
// all Gs, allglock must be held.
//
// allgptr copies should always be stored as a concrete type or
// unsafe.Pointer, not uintptr, to ensure that GC can still reach it
// even if it points to a stale array.
allglen uintptr
allgptr **g
)
func allgadd(gp *g) {
if readgstatus(gp) == _Gidle {
throw("allgadd: bad status Gidle")
}
lock(&allglock)
allgs = append(allgs, gp)
if &allgs[0] != allgptr {
atomicstorep(unsafe.Pointer(&allgptr), unsafe.Pointer(&allgs[0]))
}
atomic.Storeuintptr(&allglen, uintptr(len(allgs)))
unlock(&allglock)
}
// allGsSnapshot returns a snapshot of the slice of all Gs.
//
// The world must be stopped or allglock must be held.
func allGsSnapshot() []*g {
assertWorldStoppedOrLockHeld(&allglock)
// Because the world is stopped or allglock is held, allgadd
// cannot happen concurrently with this. allgs grows
// monotonically and existing entries never change, so we can
// simply return a copy of the slice header. For added safety,
// we trim everything past len because that can still change.
return allgs[:len(allgs):len(allgs)]
}
// atomicAllG returns &allgs[0] and len(allgs) for use with atomicAllGIndex.
func atomicAllG() (**g, uintptr) {
length := atomic.Loaduintptr(&allglen)
ptr := (**g)(atomic.Loadp(unsafe.Pointer(&allgptr)))
return ptr, length
}
// atomicAllGIndex returns ptr[i] with the allgptr returned from atomicAllG.
func atomicAllGIndex(ptr **g, i uintptr) *g {
return *(**g)(add(unsafe.Pointer(ptr), i*goarch.PtrSize))
}
// forEachG calls fn on every G from allgs.
//
// forEachG takes a lock to exclude concurrent addition of new Gs.
func forEachG(fn func(gp *g)) {
lock(&allglock)
for _, gp := range allgs {
fn(gp)
}
unlock(&allglock)
}
// forEachGRace calls fn on every G from allgs.
//
// forEachGRace avoids locking, but does not exclude addition of new Gs during
// execution, which may be missed.
func forEachGRace(fn func(gp *g)) {
ptr, length := atomicAllG()
for i := uintptr(0); i < length; i++ {
gp := atomicAllGIndex(ptr, i)
fn(gp)
}
return
}
const (
// Number of goroutine ids to grab from sched.goidgen to local per-P cache at once.
// 16 seems to provide enough amortization, but other than that it's mostly arbitrary number.
_GoidCacheBatch = 16
)
// cpuinit sets up CPU feature flags and calls internal/cpu.Initialize. env should be the complete
// value of the GODEBUG environment variable.
func cpuinit(env string) {
switch GOOS {
case "aix", "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd", "illumos", "solaris", "linux":
cpu.DebugOptions = true
}
cpu.Initialize(env)
// Support cpu feature variables are used in code generated by the compiler
// to guard execution of instructions that can not be assumed to be always supported.
switch GOARCH {
case "386", "amd64":
x86HasPOPCNT = cpu.X86.HasPOPCNT
x86HasSSE41 = cpu.X86.HasSSE41
x86HasFMA = cpu.X86.HasFMA
case "arm":
armHasVFPv4 = cpu.ARM.HasVFPv4
case "arm64":
arm64HasATOMICS = cpu.ARM64.HasATOMICS
}
}
// getGodebugEarly extracts the environment variable GODEBUG from the environment on
// Unix-like operating systems and returns it. This function exists to extract GODEBUG
// early before much of the runtime is initialized.
func getGodebugEarly() string {
const prefix = "GODEBUG="
var env string
switch GOOS {
case "aix", "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd", "illumos", "solaris", "linux":
// Similar to goenv_unix but extracts the environment value for
// GODEBUG directly.
// TODO(moehrmann): remove when general goenvs() can be called before cpuinit()
n := int32(0)
for argv_index(argv, argc+1+n) != nil {
n++
}
for i := int32(0); i < n; i++ {
p := argv_index(argv, argc+1+i)
s := unsafe.String(p, findnull(p))
if hasPrefix(s, prefix) {
env = gostring(p)[len(prefix):]
break
}
}
}
return env
}
// The bootstrap sequence is:
//
// call osinit
// call schedinit
// make & queue new G
// call runtime·mstart
//
// The new G calls runtime·main.
func schedinit() {
lockInit(&sched.lock, lockRankSched)
lockInit(&sched.sysmonlock, lockRankSysmon)
lockInit(&sched.deferlock, lockRankDefer)
lockInit(&sched.sudoglock, lockRankSudog)
lockInit(&deadlock, lockRankDeadlock)
lockInit(&paniclk, lockRankPanic)
lockInit(&allglock, lockRankAllg)
lockInit(&allpLock, lockRankAllp)
lockInit(&reflectOffs.lock, lockRankReflectOffs)
lockInit(&finlock, lockRankFin)
lockInit(&trace.bufLock, lockRankTraceBuf)
lockInit(&trace.stringsLock, lockRankTraceStrings)
lockInit(&trace.lock, lockRankTrace)
lockInit(&cpuprof.lock, lockRankCpuprof)
lockInit(&trace.stackTab.lock, lockRankTraceStackTab)
// Enforce that this lock is always a leaf lock.
// All of this lock's critical sections should be
// extremely short.
lockInit(&memstats.heapStats.noPLock, lockRankLeafRank)
// raceinit must be the first call to race detector.
// In particular, it must be done before mallocinit below calls racemapshadow.
gp := getg()
if raceenabled {
gp.racectx, raceprocctx0 = raceinit()
}
sched.maxmcount = 10000
// The world starts stopped.
worldStopped()
moduledataverify()
stackinit()
mallocinit()
godebug := getGodebugEarly()
initPageTrace(godebug) // must run after mallocinit but before anything allocates
cpuinit(godebug) // must run before alginit
alginit() // maps, hash, fastrand must not be used before this call
fastrandinit() // must run before mcommoninit
mcommoninit(gp.m, -1)
modulesinit() // provides activeModules
typelinksinit() // uses maps, activeModules
itabsinit() // uses activeModules
stkobjinit() // must run before GC starts
sigsave(&gp.m.sigmask)
initSigmask = gp.m.sigmask
goargs()
goenvs()
parsedebugvars()
gcinit()
// if disableMemoryProfiling is set, update MemProfileRate to 0 to turn off memprofile.
// Note: parsedebugvars may update MemProfileRate, but when disableMemoryProfiling is
// set to true by the linker, it means that nothing is consuming the profile, it is
// safe to set MemProfileRate to 0.
if disableMemoryProfiling {
MemProfileRate = 0
}
lock(&sched.lock)
sched.lastpoll.Store(nanotime())
procs := ncpu
if n, ok := atoi32(gogetenv("GOMAXPROCS")); ok && n > 0 {
procs = n
}
if procresize(procs) != nil {
throw("unknown runnable goroutine during bootstrap")
}
unlock(&sched.lock)
// World is effectively started now, as P's can run.
worldStarted()
// For cgocheck > 1, we turn on the write barrier at all times
// and check all pointer writes. We can't do this until after
// procresize because the write barrier needs a P.
if debug.cgocheck > 1 {
writeBarrier.cgo = true
writeBarrier.enabled = true
for _, pp := range allp {
pp.wbBuf.reset()
}
}
if buildVersion == "" {
// Condition should never trigger. This code just serves
// to ensure runtime·buildVersion is kept in the resulting binary.
buildVersion = "unknown"
}
if len(modinfo) == 1 {
// Condition should never trigger. This code just serves
// to ensure runtime·modinfo is kept in the resulting binary.
modinfo = ""
}
}
func dumpgstatus(gp *g) {
thisg := getg()
print("runtime: gp: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n")
print("runtime: getg: g=", thisg, ", goid=", thisg.goid, ", g->atomicstatus=", readgstatus(thisg), "\n")
}
// sched.lock must be held.
func checkmcount() {
assertLockHeld(&sched.lock)
if mcount() > sched.maxmcount {
print("runtime: program exceeds ", sched.maxmcount, "-thread limit\n")
throw("thread exhaustion")
}
}
// mReserveID returns the next ID to use for a new m. This new m is immediately
// considered 'running' by checkdead.
//
// sched.lock must be held.
func mReserveID() int64 {
assertLockHeld(&sched.lock)
if sched.mnext+1 < sched.mnext {
throw("runtime: thread ID overflow")
}
id := sched.mnext
sched.mnext++
checkmcount()
return id
}
// Pre-allocated ID may be passed as 'id', or omitted by passing -1.
func mcommoninit(mp *m, id int64) {
gp := getg()
// g0 stack won't make sense for user (and is not necessary unwindable).
if gp != gp.m.g0 {
callers(1, mp.createstack[:])
}
lock(&sched.lock)
if id >= 0 {
mp.id = id
} else {
mp.id = mReserveID()
}
lo := uint32(int64Hash(uint64(mp.id), fastrandseed))
hi := uint32(int64Hash(uint64(cputicks()), ^fastrandseed))
if lo|hi == 0 {
hi = 1
}
// Same behavior as for 1.17.
// TODO: Simplify ths.
if goarch.BigEndian {
mp.fastrand = uint64(lo)<<32 | uint64(hi)
} else {
mp.fastrand = uint64(hi)<<32 | uint64(lo)
}
mpreinit(mp)
if mp.gsignal != nil {
mp.gsignal.stackguard1 = mp.gsignal.stack.lo + _StackGuard
}
// Add to allm so garbage collector doesn't free g->m
// when it is just in a register or thread-local storage.
mp.alllink = allm
// NumCgoCall() iterates over allm w/o schedlock,
// so we need to publish it safely.
atomicstorep(unsafe.Pointer(&allm), unsafe.Pointer(mp))
unlock(&sched.lock)
// Allocate memory to hold a cgo traceback if the cgo call crashes.
if iscgo || GOOS == "solaris" || GOOS == "illumos" || GOOS == "windows" {
mp.cgoCallers = new(cgoCallers)
}
}
func (mp *m) becomeSpinning() {
mp.spinning = true
sched.nmspinning.Add(1)
sched.needspinning.Store(0)
}
var fastrandseed uintptr
func fastrandinit() {
s := (*[unsafe.Sizeof(fastrandseed)]byte)(unsafe.Pointer(&fastrandseed))[:]
getRandomData(s)
}
// Mark gp ready to run.
func ready(gp *g, traceskip int, next bool) {
if trace.enabled {
traceGoUnpark(gp, traceskip)
}
status := readgstatus(gp)
// Mark runnable.
mp := acquirem() // disable preemption because it can be holding p in a local var
if status&^_Gscan != _Gwaiting {
dumpgstatus(gp)
throw("bad g->status in ready")
}
// status is Gwaiting or Gscanwaiting, make Grunnable and put on runq
casgstatus(gp, _Gwaiting, _Grunnable)
runqput(mp.p.ptr(), gp, next)
wakep()
releasem(mp)
}
// freezeStopWait is a large value that freezetheworld sets
// sched.stopwait to in order to request that all Gs permanently stop.
const freezeStopWait = 0x7fffffff
// freezing is set to non-zero if the runtime is trying to freeze the
// world.
var freezing atomic.Bool
// Similar to stopTheWorld but best-effort and can be called several times.
// There is no reverse operation, used during crashing.
// This function must not lock any mutexes.
func freezetheworld() {
freezing.Store(true)
// stopwait and preemption requests can be lost
// due to races with concurrently executing threads,
// so try several times
for i := 0; i < 5; i++ {
// this should tell the scheduler to not start any new goroutines
sched.stopwait = freezeStopWait
sched.gcwaiting.Store(true)
// this should stop running goroutines
if !preemptall() {
break // no running goroutines
}
usleep(1000)
}
// to be sure
usleep(1000)
preemptall()
usleep(1000)
}
// All reads and writes of g's status go through readgstatus, casgstatus
// castogscanstatus, casfrom_Gscanstatus.
//
//go:nosplit
func readgstatus(gp *g) uint32 {
return gp.atomicstatus.Load()
}
// The Gscanstatuses are acting like locks and this releases them.
// If it proves to be a performance hit we should be able to make these
// simple atomic stores but for now we are going to throw if
// we see an inconsistent state.
func casfrom_Gscanstatus(gp *g, oldval, newval uint32) {
success := false
// Check that transition is valid.
switch oldval {
default:
print("runtime: casfrom_Gscanstatus bad oldval gp=", gp, ", oldval=", hex(oldval), ", newval=", hex(newval), "\n")
dumpgstatus(gp)
throw("casfrom_Gscanstatus:top gp->status is not in scan state")
case _Gscanrunnable,
_Gscanwaiting,
_Gscanrunning,
_Gscansyscall,
_Gscanpreempted:
if newval == oldval&^_Gscan {
success = gp.atomicstatus.CompareAndSwap(oldval, newval)
}
}
if !success {
print("runtime: casfrom_Gscanstatus failed gp=", gp, ", oldval=", hex(oldval), ", newval=", hex(newval), "\n")
dumpgstatus(gp)
throw("casfrom_Gscanstatus: gp->status is not in scan state")
}
releaseLockRank(lockRankGscan)
}
// This will return false if the gp is not in the expected status and the cas fails.
// This acts like a lock acquire while the casfromgstatus acts like a lock release.
func castogscanstatus(gp *g, oldval, newval uint32) bool {
switch oldval {
case _Grunnable,
_Grunning,
_Gwaiting,
_Gsyscall:
if newval == oldval|_Gscan {
r := gp.atomicstatus.CompareAndSwap(oldval, newval)
if r {
acquireLockRank(lockRankGscan)
}
return r
}
}
print("runtime: castogscanstatus oldval=", hex(oldval), " newval=", hex(newval), "\n")
throw("castogscanstatus")
panic("not reached")
}
// casgstatusAlwaysTrack is a debug flag that causes casgstatus to always track
// various latencies on every transition instead of sampling them.
var casgstatusAlwaysTrack = false
// If asked to move to or from a Gscanstatus this will throw. Use the castogscanstatus
// and casfrom_Gscanstatus instead.
// casgstatus will loop if the g->atomicstatus is in a Gscan status until the routine that
// put it in the Gscan state is finished.
//
//go:nosplit
func casgstatus(gp *g, oldval, newval uint32) {
if (oldval&_Gscan != 0) || (newval&_Gscan != 0) || oldval == newval {
systemstack(func() {
print("runtime: casgstatus: oldval=", hex(oldval), " newval=", hex(newval), "\n")
throw("casgstatus: bad incoming values")
})
}
acquireLockRank(lockRankGscan)
releaseLockRank(lockRankGscan)
// See https://golang.org/cl/21503 for justification of the yield delay.
const yieldDelay = 5 * 1000
var nextYield int64
// loop if gp->atomicstatus is in a scan state giving
// GC time to finish and change the state to oldval.
for i := 0; !gp.atomicstatus.CompareAndSwap(oldval, newval); i++ {
if oldval == _Gwaiting && gp.atomicstatus.Load() == _Grunnable {
throw("casgstatus: waiting for Gwaiting but is Grunnable")
}
if i == 0 {
nextYield = nanotime() + yieldDelay
}
if nanotime() < nextYield {
for x := 0; x < 10 && gp.atomicstatus.Load() != oldval; x++ {
procyield(1)
}
} else {
osyield()
nextYield = nanotime() + yieldDelay/2
}
}
if oldval == _Grunning {
// Track every gTrackingPeriod time a goroutine transitions out of running.
if casgstatusAlwaysTrack || gp.trackingSeq%gTrackingPeriod == 0 {
gp.tracking = true
}
gp.trackingSeq++
}
if !gp.tracking {
return
}
// Handle various kinds of tracking.
//
// Currently:
// - Time spent in runnable.
// - Time spent blocked on a sync.Mutex or sync.RWMutex.
switch oldval {
case _Grunnable:
// We transitioned out of runnable, so measure how much
// time we spent in this state and add it to
// runnableTime.
now := nanotime()
gp.runnableTime += now - gp.trackingStamp
gp.trackingStamp = 0
case _Gwaiting:
if !gp.waitreason.isMutexWait() {
// Not blocking on a lock.
break
}
// Blocking on a lock, measure it. Note that because we're
// sampling, we have to multiply by our sampling period to get
// a more representative estimate of the absolute value.
// gTrackingPeriod also represents an accurate sampling period
// because we can only enter this state from _Grunning.
now := nanotime()
sched.totalMutexWaitTime.Add((now - gp.trackingStamp) * gTrackingPeriod)
gp.trackingStamp = 0
}
switch newval {
case _Gwaiting:
if !gp.waitreason.isMutexWait() {
// Not blocking on a lock.
break
}
// Blocking on a lock. Write down the timestamp.
now := nanotime()
gp.trackingStamp = now
case _Grunnable:
// We just transitioned into runnable, so record what
// time that happened.
now := nanotime()
gp.trackingStamp = now
case _Grunning:
// We're transitioning into running, so turn off
// tracking and record how much time we spent in
// runnable.
gp.tracking = false
sched.timeToRun.record(gp.runnableTime)
gp.runnableTime = 0
}
}
// casGToWaiting transitions gp from old to _Gwaiting, and sets the wait reason.
//
// Use this over casgstatus when possible to ensure that a waitreason is set.
func casGToWaiting(gp *g, old uint32, reason waitReason) {
// Set the wait reason before calling casgstatus, because casgstatus will use it.
gp.waitreason = reason
casgstatus(gp, old, _Gwaiting)
}
// casgstatus(gp, oldstatus, Gcopystack), assuming oldstatus is Gwaiting or Grunnable.
// Returns old status. Cannot call casgstatus directly, because we are racing with an
// async wakeup that might come in from netpoll. If we see Gwaiting from the readgstatus,
// it might have become Grunnable by the time we get to the cas. If we called casgstatus,
// it would loop waiting for the status to go back to Gwaiting, which it never will.
//
//go:nosplit
func casgcopystack(gp *g) uint32 {
for {
oldstatus := readgstatus(gp) &^ _Gscan
if oldstatus != _Gwaiting && oldstatus != _Grunnable {
throw("copystack: bad status, not Gwaiting or Grunnable")
}
if gp.atomicstatus.CompareAndSwap(oldstatus, _Gcopystack) {
return oldstatus
}
}
}
// casGToPreemptScan transitions gp from _Grunning to _Gscan|_Gpreempted.
//
// TODO(austin): This is the only status operation that both changes
// the status and locks the _Gscan bit. Rethink this.
func casGToPreemptScan(gp *g, old, new uint32) {
if old != _Grunning || new != _Gscan|_Gpreempted {
throw("bad g transition")
}
acquireLockRank(lockRankGscan)
for !gp.atomicstatus.CompareAndSwap(_Grunning, _Gscan|_Gpreempted) {
}
}
// casGFromPreempted attempts to transition gp from _Gpreempted to
// _Gwaiting. If successful, the caller is responsible for
// re-scheduling gp.
func casGFromPreempted(gp *g, old, new uint32) bool {
if old != _Gpreempted || new != _Gwaiting {
throw("bad g transition")
}
gp.waitreason = waitReasonPreempted
return gp.atomicstatus.CompareAndSwap(_Gpreempted, _Gwaiting)
}
// stopTheWorld stops all P's from executing goroutines, interrupting
// all goroutines at GC safe points and records reason as the reason
// for the stop. On return, only the current goroutine's P is running.
// stopTheWorld must not be called from a system stack and the caller
// must not hold worldsema. The caller must call startTheWorld when
// other P's should resume execution.
//
// stopTheWorld is safe for multiple goroutines to call at the
// same time. Each will execute its own stop, and the stops will
// be serialized.
//
// This is also used by routines that do stack dumps. If the system is
// in panic or being exited, this may not reliably stop all
// goroutines.
func stopTheWorld(reason string) {
semacquire(&worldsema)
gp := getg()
gp.m.preemptoff = reason
systemstack(func() {
// Mark the goroutine which called stopTheWorld preemptible so its
// stack may be scanned.
// This lets a mark worker scan us while we try to stop the world
// since otherwise we could get in a mutual preemption deadlock.
// We must not modify anything on the G stack because a stack shrink
// may occur. A stack shrink is otherwise OK though because in order
// to return from this function (and to leave the system stack) we
// must have preempted all goroutines, including any attempting
// to scan our stack, in which case, any stack shrinking will
// have already completed by the time we exit.
// Don't provide a wait reason because we're still executing.
casGToWaiting(gp, _Grunning, waitReasonStoppingTheWorld)
stopTheWorldWithSema()
casgstatus(gp, _Gwaiting, _Grunning)
})
}
// startTheWorld undoes the effects of stopTheWorld.
func startTheWorld() {
systemstack(func() { startTheWorldWithSema(false) })
// worldsema must be held over startTheWorldWithSema to ensure
// gomaxprocs cannot change while worldsema is held.
//
// Release worldsema with direct handoff to the next waiter, but
// acquirem so that semrelease1 doesn't try to yield our time.
//
// Otherwise if e.g. ReadMemStats is being called in a loop,
// it might stomp on other attempts to stop the world, such as
// for starting or ending GC. The operation this blocks is
// so heavy-weight that we should just try to be as fair as
// possible here.
//
// We don't want to just allow us to get preempted between now
// and releasing the semaphore because then we keep everyone
// (including, for example, GCs) waiting longer.
mp := acquirem()
mp.preemptoff = ""
semrelease1(&worldsema, true, 0)
releasem(mp)
}
// stopTheWorldGC has the same effect as stopTheWorld, but blocks
// until the GC is not running. It also blocks a GC from starting
// until startTheWorldGC is called.
func stopTheWorldGC(reason string) {
semacquire(&gcsema)
stopTheWorld(reason)
}
// startTheWorldGC undoes the effects of stopTheWorldGC.
func startTheWorldGC() {
startTheWorld()
semrelease(&gcsema)
}
// Holding worldsema grants an M the right to try to stop the world.
var worldsema uint32 = 1
// Holding gcsema grants the M the right to block a GC, and blocks
// until the current GC is done. In particular, it prevents gomaxprocs
// from changing concurrently.
//
// TODO(mknyszek): Once gomaxprocs and the execution tracer can handle
// being changed/enabled during a GC, remove this.
var gcsema uint32 = 1
// stopTheWorldWithSema is the core implementation of stopTheWorld.
// The caller is responsible for acquiring worldsema and disabling
// preemption first and then should stopTheWorldWithSema on the system
// stack:
//
// semacquire(&worldsema, 0)
// m.preemptoff = "reason"
// systemstack(stopTheWorldWithSema)
//
// When finished, the caller must either call startTheWorld or undo
// these three operations separately:
//
// m.preemptoff = ""
// systemstack(startTheWorldWithSema)
// semrelease(&worldsema)
//
// It is allowed to acquire worldsema once and then execute multiple
// startTheWorldWithSema/stopTheWorldWithSema pairs.
// Other P's are able to execute between successive calls to
// startTheWorldWithSema and stopTheWorldWithSema.
// Holding worldsema causes any other goroutines invoking
// stopTheWorld to block.
func stopTheWorldWithSema() {
gp := getg()
// If we hold a lock, then we won't be able to stop another M
// that is blocked trying to acquire the lock.
if gp.m.locks > 0 {
throw("stopTheWorld: holding locks")
}
lock(&sched.lock)
sched.stopwait = gomaxprocs
sched.gcwaiting.Store(true)
preemptall()
// stop current P
gp.m.p.ptr().status = _Pgcstop // Pgcstop is only diagnostic.
sched.stopwait--
// try to retake all P's in Psyscall status
for _, pp := range allp {
s := pp.status
if s == _Psyscall && atomic.Cas(&pp.status, s, _Pgcstop) {
if trace.enabled {
traceGoSysBlock(pp)
traceProcStop(pp)
}
pp.syscalltick++
sched.stopwait--
}
}
// stop idle P's
now := nanotime()
for {
pp, _ := pidleget(now)
if pp == nil {
break
}
pp.status = _Pgcstop
sched.stopwait--
}
wait := sched.stopwait > 0
unlock(&sched.lock)
// wait for remaining P's to stop voluntarily
if wait {
for {
// wait for 100us, then try to re-preempt in case of any races
if notetsleep(&sched.stopnote, 100*1000) {
noteclear(&sched.stopnote)
break
}
preemptall()
}
}
// sanity checks
bad := ""
if sched.stopwait != 0 {
bad = "stopTheWorld: not stopped (stopwait != 0)"
} else {
for _, pp := range allp {
if pp.status != _Pgcstop {
bad = "stopTheWorld: not stopped (status != _Pgcstop)"
}
}
}
if freezing.Load() {
// Some other thread is panicking. This can cause the
// sanity checks above to fail if the panic happens in
// the signal handler on a stopped thread. Either way,
// we should halt this thread.
lock(&deadlock)
lock(&deadlock)
}
if bad != "" {
throw(bad)
}
worldStopped()
}
func startTheWorldWithSema(emitTraceEvent bool) int64 {
assertWorldStopped()
mp := acquirem() // disable preemption because it can be holding p in a local var
if netpollinited() {
list := netpoll(0) // non-blocking
injectglist(&list)
}
lock(&sched.lock)
procs := gomaxprocs
if newprocs != 0 {
procs = newprocs
newprocs = 0
}
p1 := procresize(procs)
sched.gcwaiting.Store(false)
if sched.sysmonwait.Load() {
sched.sysmonwait.Store(false)
notewakeup(&sched.sysmonnote)
}
unlock(&sched.lock)
worldStarted()
for p1 != nil {
p := p1
p1 = p1.link.ptr()
if p.m != 0 {
mp := p.m.ptr()
p.m = 0
if mp.nextp != 0 {
throw("startTheWorld: inconsistent mp->nextp")
}
mp.nextp.set(p)
notewakeup(&mp.park)
} else {
// Start M to run P. Do not start another M below.
newm(nil, p, -1)
}
}
// Capture start-the-world time before doing clean-up tasks.
startTime := nanotime()
if emitTraceEvent {
traceGCSTWDone()
}
// Wakeup an additional proc in case we have excessive runnable goroutines
// in local queues or in the global queue. If we don't, the proc will park itself.
// If we have lots of excessive work, resetspinning will unpark additional procs as necessary.
wakep()
releasem(mp)
return startTime
}
// usesLibcall indicates whether this runtime performs system calls
// via libcall.
func usesLibcall() bool {
switch GOOS {
case "aix", "darwin", "illumos", "ios", "solaris", "windows":
return true
case "openbsd":
return GOARCH == "386" || GOARCH == "amd64" || GOARCH == "arm" || GOARCH == "arm64"
}
return false
}
// mStackIsSystemAllocated indicates whether this runtime starts on a
// system-allocated stack.
func mStackIsSystemAllocated() bool {
switch GOOS {
case "aix", "darwin", "plan9", "illumos", "ios", "solaris", "windows":
return true
case "openbsd":
switch GOARCH {
case "386", "amd64", "arm", "arm64":
return true
}
}
return false
}
// mstart is the entry-point for new Ms.
// It is written in assembly, uses ABI0, is marked TOPFRAME, and calls mstart0.
func mstart()
// mstart0 is the Go entry-point for new Ms.
// This must not split the stack because we may not even have stack
// bounds set up yet.
//
// May run during STW (because it doesn't have a P yet), so write
// barriers are not allowed.
//
//go:nosplit
//go:nowritebarrierrec
func mstart0() {
gp := getg()
osStack := gp.stack.lo == 0
if osStack {
// Initialize stack bounds from system stack.
// Cgo may have left stack size in stack.hi.
// minit may update the stack bounds.
//
// Note: these bounds may not be very accurate.
// We set hi to &size, but there are things above
// it. The 1024 is supposed to compensate this,
// but is somewhat arbitrary.
size := gp.stack.hi
if size == 0 {
size = 8192 * sys.StackGuardMultiplier
}
gp.stack.hi = uintptr(noescape(unsafe.Pointer(&size)))
gp.stack.lo = gp.stack.hi - size + 1024
}
// Initialize stack guard so that we can start calling regular
// Go code.
gp.stackguard0 = gp.stack.lo + _StackGuard
// This is the g0, so we can also call go:systemstack
// functions, which check stackguard1.
gp.stackguard1 = gp.stackguard0
mstart1()
// Exit this thread.
if mStackIsSystemAllocated() {
// Windows, Solaris, illumos, Darwin, AIX and Plan 9 always system-allocate
// the stack, but put it in gp.stack before mstart,
// so the logic above hasn't set osStack yet.
osStack = true
}
mexit(osStack)
}
// The go:noinline is to guarantee the getcallerpc/getcallersp below are safe,
// so that we can set up g0.sched to return to the call of mstart1 above.
//
//go:noinline
func mstart1() {
gp := getg()
if gp != gp.m.g0 {
throw("bad runtime·mstart")
}
// Set up m.g0.sched as a label returning to just
// after the mstart1 call in mstart0 above, for use by goexit0 and mcall.
// We're never coming back to mstart1 after we call schedule,
// so other calls can reuse the current frame.
// And goexit0 does a gogo that needs to return from mstart1
// and let mstart0 exit the thread.
gp.sched.g = guintptr(unsafe.Pointer(gp))
gp.sched.pc = getcallerpc()
gp.sched.sp = getcallersp()
asminit()
minit()
// Install signal handlers; after minit so that minit can
// prepare the thread to be able to handle the signals.
if gp.m == &m0 {
mstartm0()
}
if fn := gp.m.mstartfn; fn != nil {
fn()
}
if gp.m != &m0 {
acquirep(gp.m.nextp.ptr())
gp.m.nextp = 0
}
schedule()
}
// mstartm0 implements part of mstart1 that only runs on the m0.
//
// Write barriers are allowed here because we know the GC can't be
// running yet, so they'll be no-ops.
//
//go:yeswritebarrierrec
func mstartm0() {
// Create an extra M for callbacks on threads not created by Go.
// An extra M is also needed on Windows for callbacks created by
// syscall.NewCallback. See issue #6751 for details.
if (iscgo || GOOS == "windows") && !cgoHasExtraM {
cgoHasExtraM = true
newextram()
}
initsig(false)
}
// mPark causes a thread to park itself, returning once woken.
//
//go:nosplit
func mPark() {
gp := getg()
notesleep(&gp.m.park)
noteclear(&gp.m.park)
}
// mexit tears down and exits the current thread.
//
// Don't call this directly to exit the thread, since it must run at
// the top of the thread stack. Instead, use gogo(&gp.m.g0.sched) to
// unwind the stack to the point that exits the thread.
//
// It is entered with m.p != nil, so write barriers are allowed. It
// will release the P before exiting.
//
//go:yeswritebarrierrec
func mexit(osStack bool) {
mp := getg().m
if mp == &m0 {
// This is the main thread. Just wedge it.
//
// On Linux, exiting the main thread puts the process
// into a non-waitable zombie state. On Plan 9,
// exiting the main thread unblocks wait even though
// other threads are still running. On Solaris we can
// neither exitThread nor return from mstart. Other
// bad things probably happen on other platforms.
//
// We could try to clean up this M more before wedging
// it, but that complicates signal handling.
handoffp(releasep())
lock(&sched.lock)
sched.nmfreed++
checkdead()
unlock(&sched.lock)
mPark()
throw("locked m0 woke up")
}
sigblock(true)
unminit()
// Free the gsignal stack.
if mp.gsignal != nil {
stackfree(mp.gsignal.stack)
// On some platforms, when calling into VDSO (e.g. nanotime)
// we store our g on the gsignal stack, if there is one.
// Now the stack is freed, unlink it from the m, so we
// won't write to it when calling VDSO code.
mp.gsignal = nil
}
// Remove m from allm.
lock(&sched.lock)
for pprev := &allm; *pprev != nil; pprev = &(*pprev).alllink {
if *pprev == mp {
*pprev = mp.alllink
goto found
}
}
throw("m not found in allm")
found:
// Delay reaping m until it's done with the stack.
//
// Put mp on the free list, though it will not be reaped while freeWait
// is freeMWait. mp is no longer reachable via allm, so even if it is
// on an OS stack, we must keep a reference to mp alive so that the GC
// doesn't free mp while we are still using it.
//
// Note that the free list must not be linked through alllink because
// some functions walk allm without locking, so may be using alllink.
mp.freeWait.Store(freeMWait)
mp.freelink = sched.freem
sched.freem = mp
unlock(&sched.lock)
atomic.Xadd64(&ncgocall, int64(mp.ncgocall))
// Release the P.
handoffp(releasep())
// After this point we must not have write barriers.
// Invoke the deadlock detector. This must happen after
// handoffp because it may have started a new M to take our
// P's work.
lock(&sched.lock)
sched.nmfreed++
checkdead()
unlock(&sched.lock)
if GOOS == "darwin" || GOOS == "ios" {
// Make sure pendingPreemptSignals is correct when an M exits.
// For #41702.
if mp.signalPending.Load() != 0 {
pendingPreemptSignals.Add(-1)
}
}
// Destroy all allocated resources. After this is called, we may no
// longer take any locks.
mdestroy(mp)
if osStack {
// No more uses of mp, so it is safe to drop the reference.
mp.freeWait.Store(freeMRef)
// Return from mstart and let the system thread
// library free the g0 stack and terminate the thread.
return
}
// mstart is the thread's entry point, so there's nothing to
// return to. Exit the thread directly. exitThread will clear
// m.freeWait when it's done with the stack and the m can be
// reaped.
exitThread(&mp.freeWait)
}
// forEachP calls fn(p) for every P p when p reaches a GC safe point.
// If a P is currently executing code, this will bring the P to a GC
// safe point and execute fn on that P. If the P is not executing code
// (it is idle or in a syscall), this will call fn(p) directly while
// preventing the P from exiting its state. This does not ensure that
// fn will run on every CPU executing Go code, but it acts as a global
// memory barrier. GC uses this as a "ragged barrier."
//
// The caller must hold worldsema.
//
//go:systemstack
func forEachP(fn func(*p)) {
mp := acquirem()
pp := getg().m.p.ptr()
lock(&sched.lock)
if sched.safePointWait != 0 {
throw("forEachP: sched.safePointWait != 0")
}
sched.safePointWait = gomaxprocs - 1
sched.safePointFn = fn
// Ask all Ps to run the safe point function.
for _, p2 := range allp {
if p2 != pp {
atomic.Store(&p2.runSafePointFn, 1)
}
}
preemptall()
// Any P entering _Pidle or _Psyscall from now on will observe
// p.runSafePointFn == 1 and will call runSafePointFn when
// changing its status to _Pidle/_Psyscall.
// Run safe point function for all idle Ps. sched.pidle will
// not change because we hold sched.lock.
for p := sched.pidle.ptr(); p != nil; p = p.link.ptr() {
if atomic.Cas(&p.runSafePointFn, 1, 0) {
fn(p)
sched.safePointWait--
}
}
wait := sched.safePointWait > 0
unlock(&sched.lock)
// Run fn for the current P.
fn(pp)
// Force Ps currently in _Psyscall into _Pidle and hand them
// off to induce safe point function execution.
for _, p2 := range allp {
s := p2.status
if s == _Psyscall && p2.runSafePointFn == 1 && atomic.Cas(&p2.status, s, _Pidle) {
if trace.enabled {
traceGoSysBlock(p2)
traceProcStop(p2)
}
p2.syscalltick++
handoffp(p2)
}
}
// Wait for remaining Ps to run fn.
if wait {
for {
// Wait for 100us, then try to re-preempt in
// case of any races.
//
// Requires system stack.
if notetsleep(&sched.safePointNote, 100*1000) {
noteclear(&sched.safePointNote)
break
}
preemptall()
}
}
if sched.safePointWait != 0 {
throw("forEachP: not done")
}
for _, p2 := range allp {
if p2.runSafePointFn != 0 {
throw("forEachP: P did not run fn")
}
}
lock(&sched.lock)
sched.safePointFn = nil
unlock(&sched.lock)
releasem(mp)
}
// runSafePointFn runs the safe point function, if any, for this P.
// This should be called like
//
// if getg().m.p.runSafePointFn != 0 {
// runSafePointFn()
// }
//
// runSafePointFn must be checked on any transition in to _Pidle or
// _Psyscall to avoid a race where forEachP sees that the P is running
// just before the P goes into _Pidle/_Psyscall and neither forEachP
// nor the P run the safe-point function.
func runSafePointFn() {
p := getg().m.p.ptr()
// Resolve the race between forEachP running the safe-point
// function on this P's behalf and this P running the
// safe-point function directly.
if !atomic.Cas(&p.runSafePointFn, 1, 0) {
return
}
sched.safePointFn(p)
lock(&sched.lock)
sched.safePointWait--
if sched.safePointWait == 0 {
notewakeup(&sched.safePointNote)
}
unlock(&sched.lock)
}
// When running with cgo, we call _cgo_thread_start
// to start threads for us so that we can play nicely with
// foreign code.
var cgoThreadStart unsafe.Pointer
type cgothreadstart struct {
g guintptr
tls *uint64
fn unsafe.Pointer
}
// Allocate a new m unassociated with any thread.
// Can use p for allocation context if needed.
// fn is recorded as the new m's m.mstartfn.
// id is optional pre-allocated m ID. Omit by passing -1.
//
// This function is allowed to have write barriers even if the caller
// isn't because it borrows pp.
//
//go:yeswritebarrierrec
func allocm(pp *p, fn func(), id int64) *m {
allocmLock.rlock()
// The caller owns pp, but we may borrow (i.e., acquirep) it. We must
// disable preemption to ensure it is not stolen, which would make the
// caller lose ownership.
acquirem()
gp := getg()
if gp.m.p == 0 {
acquirep(pp) // temporarily borrow p for mallocs in this function
}
// Release the free M list. We need to do this somewhere and
// this may free up a stack we can use.
if sched.freem != nil {
lock(&sched.lock)
var newList *m
for freem := sched.freem; freem != nil; {
wait := freem.freeWait.Load()
if wait == freeMWait {
next := freem.freelink
freem.freelink = newList
newList = freem
freem = next
continue
}
// Free the stack if needed. For freeMRef, there is
// nothing to do except drop freem from the sched.freem
// list.
if wait == freeMStack {
// stackfree must be on the system stack, but allocm is
// reachable off the system stack transitively from
// startm.
systemstack(func() {
stackfree(freem.g0.stack)
})
}
freem = freem.freelink
}
sched.freem = newList
unlock(&sched.lock)
}
mp := new(m)
mp.mstartfn = fn
mcommoninit(mp, id)
// In case of cgo or Solaris or illumos or Darwin, pthread_create will make us a stack.
// Windows and Plan 9 will layout sched stack on OS stack.
if iscgo || mStackIsSystemAllocated() {
mp.g0 = malg(-1)
} else {
mp.g0 = malg(8192 * sys.StackGuardMultiplier)
}
mp.g0.m = mp
if pp == gp.m.p.ptr() {
releasep()
}
releasem(gp.m)
allocmLock.runlock()
return mp
}
// needm is called when a cgo callback happens on a
// thread without an m (a thread not created by Go).
// In this case, needm is expected to find an m to use
// and return with m, g initialized correctly.
// Since m and g are not set now (likely nil, but see below)
// needm is limited in what routines it can call. In particular
// it can only call nosplit functions (textflag 7) and cannot
// do any scheduling that requires an m.
//
// In order to avoid needing heavy lifting here, we adopt
// the following strategy: there is a stack of available m's
// that can be stolen. Using compare-and-swap
// to pop from the stack has ABA races, so we simulate
// a lock by doing an exchange (via Casuintptr) to steal the stack
// head and replace the top pointer with MLOCKED (1).
// This serves as a simple spin lock that we can use even
// without an m. The thread that locks the stack in this way
// unlocks the stack by storing a valid stack head pointer.
//
// In order to make sure that there is always an m structure
// available to be stolen, we maintain the invariant that there
// is always one more than needed. At the beginning of the
// program (if cgo is in use) the list is seeded with a single m.
// If needm finds that it has taken the last m off the list, its job
// is - once it has installed its own m so that it can do things like
// allocate memory - to create a spare m and put it on the list.
//
// Each of these extra m's also has a g0 and a curg that are
// pressed into service as the scheduling stack and current
// goroutine for the duration of the cgo callback.
//
// When the callback is done with the m, it calls dropm to
// put the m back on the list.
//
//go:nosplit
func needm() {
if (iscgo || GOOS == "windows") && !cgoHasExtraM {
// Can happen if C/C++ code calls Go from a global ctor.
// Can also happen on Windows if a global ctor uses a
// callback created by syscall.NewCallback. See issue #6751
// for details.
//
// Can not throw, because scheduler is not initialized yet.
writeErrStr("fatal error: cgo callback before cgo call\n")
exit(1)
}
// Save and block signals before getting an M.
// The signal handler may call needm itself,
// and we must avoid a deadlock. Also, once g is installed,
// any incoming signals will try to execute,
// but we won't have the sigaltstack settings and other data
// set up appropriately until the end of minit, which will
// unblock the signals. This is the same dance as when
// starting a new m to run Go code via newosproc.
var sigmask sigset
sigsave(&sigmask)
sigblock(false)
// Lock extra list, take head, unlock popped list.
// nilokay=false is safe here because of the invariant above,
// that the extra list always contains or will soon contain
// at least one m.
mp := lockextra(false)
// Set needextram when we've just emptied the list,
// so that the eventual call into cgocallbackg will
// allocate a new m for the extra list. We delay the
// allocation until then so that it can be done
// after exitsyscall makes sure it is okay to be
// running at all (that is, there's no garbage collection
// running right now).
mp.needextram = mp.schedlink == 0
extraMCount--
unlockextra(mp.schedlink.ptr())
// Store the original signal mask for use by minit.
mp.sigmask = sigmask
// Install TLS on some platforms (previously setg
// would do this if necessary).
osSetupTLS(mp)
// Install g (= m->g0) and set the stack bounds
// to match the current stack. We don't actually know
// how big the stack is, like we don't know how big any
// scheduling stack is, but we assume there's at least 32 kB,
// which is more than enough for us.
setg(mp.g0)
gp := getg()
gp.stack.hi = getcallersp() + 1024
gp.stack.lo = getcallersp() - 32*1024
gp.stackguard0 = gp.stack.lo + _StackGuard
// Initialize this thread to use the m.
asminit()
minit()
// mp.curg is now a real goroutine.
casgstatus(mp.curg, _Gdead, _Gsyscall)
sched.ngsys.Add(-1)
}
// newextram allocates m's and puts them on the extra list.
// It is called with a working local m, so that it can do things
// like call schedlock and allocate.
func newextram() {
c := extraMWaiters.Swap(0)
if c > 0 {
for i := uint32(0); i < c; i++ {
oneNewExtraM()
}
} else {
// Make sure there is at least one extra M.
mp := lockextra(true)
unlockextra(mp)
if mp == nil {
oneNewExtraM()
}
}
}
// oneNewExtraM allocates an m and puts it on the extra list.
func oneNewExtraM() {
// Create extra goroutine locked to extra m.
// The goroutine is the context in which the cgo callback will run.
// The sched.pc will never be returned to, but setting it to
// goexit makes clear to the traceback routines where
// the goroutine stack ends.
mp := allocm(nil, nil, -1)
gp := malg(4096)
gp.sched.pc = abi.FuncPCABI0(goexit) + sys.PCQuantum
gp.sched.sp = gp.stack.hi
gp.sched.sp -= 4 * goarch.PtrSize // extra space in case of reads slightly beyond frame
gp.sched.lr = 0
gp.sched.g = guintptr(unsafe.Pointer(gp))
gp.syscallpc = gp.sched.pc
gp.syscallsp = gp.sched.sp
gp.stktopsp = gp.sched.sp
// malg returns status as _Gidle. Change to _Gdead before
// adding to allg where GC can see it. We use _Gdead to hide
// this from tracebacks and stack scans since it isn't a
// "real" goroutine until needm grabs it.
casgstatus(gp, _Gidle, _Gdead)
gp.m = mp
mp.curg = gp
mp.isextra = true
mp.lockedInt++
mp.lockedg.set(gp)
gp.lockedm.set(mp)
gp.goid = sched.goidgen.Add(1)
gp.sysblocktraced = true
if raceenabled {
gp.racectx = racegostart(abi.FuncPCABIInternal(newextram) + sys.PCQuantum)
}
if trace.enabled {
// Trigger two trace events for the locked g in the extra m,
// since the next event of the g will be traceEvGoSysExit in exitsyscall,
// while calling from C thread to Go.
traceGoCreate(gp, 0) // no start pc
gp.traceseq++
traceEvent(traceEvGoInSyscall, -1, gp.goid)
}
// put on allg for garbage collector
allgadd(gp)
// gp is now on the allg list, but we don't want it to be
// counted by gcount. It would be more "proper" to increment
// sched.ngfree, but that requires locking. Incrementing ngsys
// has the same effect.
sched.ngsys.Add(1)
// Add m to the extra list.
mnext := lockextra(true)
mp.schedlink.set(mnext)
extraMCount++
unlockextra(mp)
}
// dropm is called when a cgo callback has called needm but is now
// done with the callback and returning back into the non-Go thread.
// It puts the current m back onto the extra list.
//
// The main expense here is the call to signalstack to release the
// m's signal stack, and then the call to needm on the next callback
// from this thread. It is tempting to try to save the m for next time,
// which would eliminate both these costs, but there might not be
// a next time: the current thread (which Go does not control) might exit.
// If we saved the m for that thread, there would be an m leak each time
// such a thread exited. Instead, we acquire and release an m on each
// call. These should typically not be scheduling operations, just a few
// atomics, so the cost should be small.
//
// TODO(rsc): An alternative would be to allocate a dummy pthread per-thread
// variable using pthread_key_create. Unlike the pthread keys we already use
// on OS X, this dummy key would never be read by Go code. It would exist
// only so that we could register at thread-exit-time destructor.
// That destructor would put the m back onto the extra list.
// This is purely a performance optimization. The current version,
// in which dropm happens on each cgo call, is still correct too.
// We may have to keep the current version on systems with cgo
// but without pthreads, like Windows.
func dropm() {
// Clear m and g, and return m to the extra list.
// After the call to setg we can only call nosplit functions
// with no pointer manipulation.
mp := getg().m
// Return mp.curg to dead state.
casgstatus(mp.curg, _Gsyscall, _Gdead)
mp.curg.preemptStop = false
sched.ngsys.Add(1)
// Block signals before unminit.
// Unminit unregisters the signal handling stack (but needs g on some systems).
// Setg(nil) clears g, which is the signal handler's cue not to run Go handlers.
// It's important not to try to handle a signal between those two steps.
sigmask := mp.sigmask
sigblock(false)
unminit()
mnext := lockextra(true)
extraMCount++
mp.schedlink.set(mnext)
setg(nil)
// Commit the release of mp.
unlockextra(mp)
msigrestore(sigmask)
}
// A helper function for EnsureDropM.
func getm() uintptr {
return uintptr(unsafe.Pointer(getg().m))
}
var extram atomic.Uintptr
var extraMCount uint32 // Protected by lockextra
var extraMWaiters atomic.Uint32
// lockextra locks the extra list and returns the list head.
// The caller must unlock the list by storing a new list head
// to extram. If nilokay is true, then lockextra will
// return a nil list head if that's what it finds. If nilokay is false,
// lockextra will keep waiting until the list head is no longer nil.
//
//go:nosplit
func lockextra(nilokay bool) *m {
const locked = 1
incr := false
for {
old := extram.Load()
if old == locked {
osyield_no_g()
continue
}
if old == 0 && !nilokay {
if !incr {
// Add 1 to the number of threads
// waiting for an M.
// This is cleared by newextram.
extraMWaiters.Add(1)
incr = true
}
usleep_no_g(1)
continue
}
if extram.CompareAndSwap(old, locked) {
return (*m)(unsafe.Pointer(old))
}
osyield_no_g()
continue
}
}
//go:nosplit
func unlockextra(mp *m) {
extram.Store(uintptr(unsafe.Pointer(mp)))
}
var (
// allocmLock is locked for read when creating new Ms in allocm and their
// addition to allm. Thus acquiring this lock for write blocks the
// creation of new Ms.
allocmLock rwmutex
// execLock serializes exec and clone to avoid bugs or unspecified
// behaviour around exec'ing while creating/destroying threads. See
// issue #19546.
execLock rwmutex
)
// These errors are reported (via writeErrStr) by some OS-specific
// versions of newosproc and newosproc0.
const (
failthreadcreate = "runtime: failed to create new OS thread\n"
failallocatestack = "runtime: failed to allocate stack for the new OS thread\n"
)
// newmHandoff contains a list of m structures that need new OS threads.
// This is used by newm in situations where newm itself can't safely
// start an OS thread.
var newmHandoff struct {
lock mutex
// newm points to a list of M structures that need new OS
// threads. The list is linked through m.schedlink.
newm muintptr
// waiting indicates that wake needs to be notified when an m
// is put on the list.
waiting bool
wake note
// haveTemplateThread indicates that the templateThread has
// been started. This is not protected by lock. Use cas to set
// to 1.
haveTemplateThread uint32
}
// Create a new m. It will start off with a call to fn, or else the scheduler.
// fn needs to be static and not a heap allocated closure.
// May run with m.p==nil, so write barriers are not allowed.
//
// id is optional pre-allocated m ID. Omit by passing -1.
//
//go:nowritebarrierrec
func newm(fn func(), pp *p, id int64) {
// allocm adds a new M to allm, but they do not start until created by
// the OS in newm1 or the template thread.
//
// doAllThreadsSyscall requires that every M in allm will eventually
// start and be signal-able, even with a STW.
//
// Disable preemption here until we start the thread to ensure that
// newm is not preempted between allocm and starting the new thread,
// ensuring that anything added to allm is guaranteed to eventually
// start.
acquirem()
mp := allocm(pp, fn, id)
mp.nextp.set(pp)
mp.sigmask = initSigmask
if gp := getg(); gp != nil && gp.m != nil && (gp.m.lockedExt != 0 || gp.m.incgo) && GOOS != "plan9" {
// We're on a locked M or a thread that may have been
// started by C. The kernel state of this thread may
// be strange (the user may have locked it for that
// purpose). We don't want to clone that into another
// thread. Instead, ask a known-good thread to create
// the thread for us.
//
// This is disabled on Plan 9. See golang.org/issue/22227.
//
// TODO: This may be unnecessary on Windows, which
// doesn't model thread creation off fork.
lock(&newmHandoff.lock)
if newmHandoff.haveTemplateThread == 0 {
throw("on a locked thread with no template thread")
}
mp.schedlink = newmHandoff.newm
newmHandoff.newm.set(mp)
if newmHandoff.waiting {
newmHandoff.waiting = false
notewakeup(&newmHandoff.wake)
}
unlock(&newmHandoff.lock)
// The M has not started yet, but the template thread does not
// participate in STW, so it will always process queued Ms and
// it is safe to releasem.
releasem(getg().m)
return
}
newm1(mp)
releasem(getg().m)
}
func newm1(mp *m) {
if iscgo {
var ts cgothreadstart
if _cgo_thread_start == nil {
throw("_cgo_thread_start missing")
}
ts.g.set(mp.g0)
ts.tls = (*uint64)(unsafe.Pointer(&mp.tls[0]))
ts.fn = unsafe.Pointer(abi.FuncPCABI0(mstart))
if msanenabled {
msanwrite(unsafe.Pointer(&ts), unsafe.Sizeof(ts))
}
if asanenabled {
asanwrite(unsafe.Pointer(&ts), unsafe.Sizeof(ts))
}
execLock.rlock() // Prevent process clone.
asmcgocall(_cgo_thread_start, unsafe.Pointer(&ts))
execLock.runlock()
return
}
execLock.rlock() // Prevent process clone.
newosproc(mp)
execLock.runlock()
}
// startTemplateThread starts the template thread if it is not already
// running.
//
// The calling thread must itself be in a known-good state.
func startTemplateThread() {
if GOARCH == "wasm" { // no threads on wasm yet
return
}
// Disable preemption to guarantee that the template thread will be
// created before a park once haveTemplateThread is set.
mp := acquirem()
if !atomic.Cas(&newmHandoff.haveTemplateThread, 0, 1) {
releasem(mp)
return
}
newm(templateThread, nil, -1)
releasem(mp)
}
// templateThread is a thread in a known-good state that exists solely
// to start new threads in known-good states when the calling thread
// may not be in a good state.
//
// Many programs never need this, so templateThread is started lazily
// when we first enter a state that might lead to running on a thread
// in an unknown state.
//
// templateThread runs on an M without a P, so it must not have write
// barriers.
//
//go:nowritebarrierrec
func templateThread() {
lock(&sched.lock)
sched.nmsys++
checkdead()
unlock(&sched.lock)
for {
lock(&newmHandoff.lock)
for newmHandoff.newm != 0 {
newm := newmHandoff.newm.ptr()
newmHandoff.newm = 0
unlock(&newmHandoff.lock)
for newm != nil {
next := newm.schedlink.ptr()
newm.schedlink = 0
newm1(newm)
newm = next
}
lock(&newmHandoff.lock)
}
newmHandoff.waiting = true
noteclear(&newmHandoff.wake)
unlock(&newmHandoff.lock)
notesleep(&newmHandoff.wake)
}
}
// Stops execution of the current m until new work is available.
// Returns with acquired P.
func stopm() {
gp := getg()
if gp.m.locks != 0 {
throw("stopm holding locks")
}
if gp.m.p != 0 {
throw("stopm holding p")
}
if gp.m.spinning {
throw("stopm spinning")
}
lock(&sched.lock)
mput(gp.m)
unlock(&sched.lock)
mPark()
acquirep(gp.m.nextp.ptr())
gp.m.nextp = 0
}
func mspinning() {
// startm's caller incremented nmspinning. Set the new M's spinning.
getg().m.spinning = true
}
// Schedules some M to run the p (creates an M if necessary).
// If p==nil, tries to get an idle P, if no idle P's does nothing.
// May run with m.p==nil, so write barriers are not allowed.
// If spinning is set, the caller has incremented nmspinning and must provide a
// P. startm will set m.spinning in the newly started M.
//
// Callers passing a non-nil P must call from a non-preemptible context. See
// comment on acquirem below.
//
// Must not have write barriers because this may be called without a P.
//
//go:nowritebarrierrec
func startm(pp *p, spinning bool) {
// Disable preemption.
//
// Every owned P must have an owner that will eventually stop it in the
// event of a GC stop request. startm takes transient ownership of a P
// (either from argument or pidleget below) and transfers ownership to
// a started M, which will be responsible for performing the stop.
//
// Preemption must be disabled during this transient ownership,
// otherwise the P this is running on may enter GC stop while still
// holding the transient P, leaving that P in limbo and deadlocking the
// STW.
//
// Callers passing a non-nil P must already be in non-preemptible
// context, otherwise such preemption could occur on function entry to
// startm. Callers passing a nil P may be preemptible, so we must
// disable preemption before acquiring a P from pidleget below.
mp := acquirem()
lock(&sched.lock)
if pp == nil {
if spinning {
// TODO(prattmic): All remaining calls to this function
// with _p_ == nil could be cleaned up to find a P
// before calling startm.
throw("startm: P required for spinning=true")
}
pp, _ = pidleget(0)
if pp == nil {
unlock(&sched.lock)
releasem(mp)
return
}
}
nmp := mget()
if nmp == nil {
// No M is available, we must drop sched.lock and call newm.
// However, we already own a P to assign to the M.
//
// Once sched.lock is released, another G (e.g., in a syscall),
// could find no idle P while checkdead finds a runnable G but
// no running M's because this new M hasn't started yet, thus
// throwing in an apparent deadlock.
//
// Avoid this situation by pre-allocating the ID for the new M,
// thus marking it as 'running' before we drop sched.lock. This
// new M will eventually run the scheduler to execute any
// queued G's.
id := mReserveID()
unlock(&sched.lock)
var fn func()
if spinning {
// The caller incremented nmspinning, so set m.spinning in the new M.
fn = mspinning
}
newm(fn, pp, id)
// Ownership transfer of pp committed by start in newm.
// Preemption is now safe.
releasem(mp)
return
}
unlock(&sched.lock)
if nmp.spinning {
throw("startm: m is spinning")
}
if nmp.nextp != 0 {
throw("startm: m has p")
}
if spinning && !runqempty(pp) {
throw("startm: p has runnable gs")
}
// The caller incremented nmspinning, so set m.spinning in the new M.
nmp.spinning = spinning
nmp.nextp.set(pp)
notewakeup(&nmp.park)
// Ownership transfer of pp committed by wakeup. Preemption is now
// safe.
releasem(mp)
}
// Hands off P from syscall or locked M.
// Always runs without a P, so write barriers are not allowed.
//
//go:nowritebarrierrec
func handoffp(pp *p) {
// handoffp must start an M in any situation where
// findrunnable would return a G to run on pp.
// if it has local work, start it straight away
if !runqempty(pp) || sched.runqsize != 0 {
startm(pp, false)
return
}
// if there's trace work to do, start it straight away
if (trace.enabled || trace.shutdown) && traceReaderAvailable() != nil {
startm(pp, false)
return
}
// if it has GC work, start it straight away
if gcBlackenEnabled != 0 && gcMarkWorkAvailable(pp) {
startm(pp, false)
return
}
// no local work, check that there are no spinning/idle M's,
// otherwise our help is not required
if sched.nmspinning.Load()+sched.npidle.Load() == 0 && sched.nmspinning.CompareAndSwap(0, 1) { // TODO: fast atomic
sched.needspinning.Store(0)
startm(pp, true)
return
}
lock(&sched.lock)
if sched.gcwaiting.Load() {
pp.status = _Pgcstop
sched.stopwait--
if sched.stopwait == 0 {
notewakeup(&sched.stopnote)
}
unlock(&sched.lock)
return
}
if pp.runSafePointFn != 0 && atomic.Cas(&pp.runSafePointFn, 1, 0) {
sched.safePointFn(pp)
sched.safePointWait--
if sched.safePointWait == 0 {
notewakeup(&sched.safePointNote)
}
}
if sched.runqsize != 0 {
unlock(&sched.lock)
startm(pp, false)
return
}
// If this is the last running P and nobody is polling network,
// need to wakeup another M to poll network.
if sched.npidle.Load() == gomaxprocs-1 && sched.lastpoll.Load() != 0 {
unlock(&sched.lock)
startm(pp, false)
return
}
// The scheduler lock cannot be held when calling wakeNetPoller below
// because wakeNetPoller may call wakep which may call startm.
when := nobarrierWakeTime(pp)
pidleput(pp, 0)
unlock(&sched.lock)
if when != 0 {
wakeNetPoller(when)
}
}
// Tries to add one more P to execute G's.
// Called when a G is made runnable (newproc, ready).
// Must be called with a P.
func wakep() {
// Be conservative about spinning threads, only start one if none exist
// already.
if sched.nmspinning.Load() != 0 || !sched.nmspinning.CompareAndSwap(0, 1) {
return
}
// Disable preemption until ownership of pp transfers to the next M in
// startm. Otherwise preemption here would leave pp stuck waiting to
// enter _Pgcstop.
//
// See preemption comment on acquirem in startm for more details.
mp := acquirem()
var pp *p
lock(&sched.lock)
pp, _ = pidlegetSpinning(0)
if pp == nil {
if sched.nmspinning.Add(-1) < 0 {
throw("wakep: negative nmspinning")
}
unlock(&sched.lock)
releasem(mp)
return
}
// Since we always have a P, the race in the "No M is available"
// comment in startm doesn't apply during the small window between the
// unlock here and lock in startm. A checkdead in between will always
// see at least one running M (ours).
unlock(&sched.lock)
startm(pp, true)
releasem(mp)
}
// Stops execution of the current m that is locked to a g until the g is runnable again.
// Returns with acquired P.
func stoplockedm() {
gp := getg()
if gp.m.lockedg == 0 || gp.m.lockedg.ptr().lockedm.ptr() != gp.m {
throw("stoplockedm: inconsistent locking")
}
if gp.m.p != 0 {
// Schedule another M to run this p.
pp := releasep()
handoffp(pp)
}
incidlelocked(1)
// Wait until another thread schedules lockedg again.
mPark()
status := readgstatus(gp.m.lockedg.ptr())
if status&^_Gscan != _Grunnable {
print("runtime:stoplockedm: lockedg (atomicstatus=", status, ") is not Grunnable or Gscanrunnable\n")
dumpgstatus(gp.m.lockedg.ptr())
throw("stoplockedm: not runnable")
}
acquirep(gp.m.nextp.ptr())
gp.m.nextp = 0
}
// Schedules the locked m to run the locked gp.
// May run during STW, so write barriers are not allowed.
//
//go:nowritebarrierrec
func startlockedm(gp *g) {
mp := gp.lockedm.ptr()
if mp == getg().m {
throw("startlockedm: locked to me")
}
if mp.nextp != 0 {
throw("startlockedm: m has p")
}
// directly handoff current P to the locked m
incidlelocked(-1)
pp := releasep()
mp.nextp.set(pp)
notewakeup(&mp.park)
stopm()
}
// Stops the current m for stopTheWorld.
// Returns when the world is restarted.
func gcstopm() {
gp := getg()
if !sched.gcwaiting.Load() {
throw("gcstopm: not waiting for gc")
}
if gp.m.spinning {
gp.m.spinning = false
// OK to just drop nmspinning here,
// startTheWorld will unpark threads as necessary.
if sched.nmspinning.Add(-1) < 0 {
throw("gcstopm: negative nmspinning")
}
}
pp := releasep()
lock(&sched.lock)
pp.status = _Pgcstop
sched.stopwait--
if sched.stopwait == 0 {
notewakeup(&sched.stopnote)
}
unlock(&sched.lock)
stopm()
}
// Schedules gp to run on the current M.
// If inheritTime is true, gp inherits the remaining time in the
// current time slice. Otherwise, it starts a new time slice.
// Never returns.
//
// Write barriers are allowed because this is called immediately after
// acquiring a P in several places.
//
//go:yeswritebarrierrec
func execute(gp *g, inheritTime bool) {
mp := getg().m
if goroutineProfile.active {
// Make sure that gp has had its stack written out to the goroutine
// profile, exactly as it was when the goroutine profiler first stopped
// the world.
tryRecordGoroutineProfile(gp, osyield)
}
// Assign gp.m before entering _Grunning so running Gs have an
// M.
mp.curg = gp
gp.m = mp
casgstatus(gp, _Grunnable, _Grunning)
gp.waitsince = 0
gp.preempt = false
gp.stackguard0 = gp.stack.lo + _StackGuard
if !inheritTime {
mp.p.ptr().schedtick++
}
// Check whether the profiler needs to be turned on or off.
hz := sched.profilehz
if mp.profilehz != hz {
setThreadCPUProfiler(hz)
}
if trace.enabled {
// GoSysExit has to happen when we have a P, but before GoStart.
// So we emit it here.
if gp.syscallsp != 0 && gp.sysblocktraced {
traceGoSysExit(gp.sysexitticks)
}
traceGoStart()
}
gogo(&gp.sched)
}
// Finds a runnable goroutine to execute.
// Tries to steal from other P's, get g from local or global queue, poll network.
// tryWakeP indicates that the returned goroutine is not normal (GC worker, trace
// reader) so the caller should try to wake a P.
func findRunnable() (gp *g, inheritTime, tryWakeP bool) {
mp := getg().m
// The conditions here and in handoffp must agree: if
// findrunnable would return a G to run, handoffp must start
// an M.
top:
pp := mp.p.ptr()
if sched.gcwaiting.Load() {
gcstopm()
goto top
}
if pp.runSafePointFn != 0 {
runSafePointFn()
}
// now and pollUntil are saved for work stealing later,
// which may steal timers. It's important that between now
// and then, nothing blocks, so these numbers remain mostly
// relevant.
now, pollUntil, _ := checkTimers(pp, 0)
// Try to schedule the trace reader.
if trace.enabled || trace.shutdown {
gp := traceReader()
if gp != nil {
casgstatus(gp, _Gwaiting, _Grunnable)
traceGoUnpark(gp, 0)
return gp, false, true
}
}
// Try to schedule a GC worker.
if gcBlackenEnabled != 0 {
gp, tnow := gcController.findRunnableGCWorker(pp, now)
if gp != nil {
return gp, false, true
}
now = tnow
}
// Check the global runnable queue once in a while to ensure fairness.
// Otherwise two goroutines can completely occupy the local runqueue
// by constantly respawning each other.
if pp.schedtick%61 == 0 && sched.runqsize > 0 {
lock(&sched.lock)
gp := globrunqget(pp, 1)
unlock(&sched.lock)
if gp != nil {
return gp, false, false
}
}
// Wake up the finalizer G.
if fingStatus.Load()&(fingWait|fingWake) == fingWait|fingWake {
if gp := wakefing(); gp != nil {
ready(gp, 0, true)
}
}
if *cgo_yield != nil {
asmcgocall(*cgo_yield, nil)
}
// local runq
if gp, inheritTime := runqget(pp); gp != nil {
return gp, inheritTime, false
}
// global runq
if sched.runqsize != 0 {
lock(&sched.lock)
gp := globrunqget(pp, 0)
unlock(&sched.lock)
if gp != nil {
return gp, false, false
}
}
// Poll network.
// This netpoll is only an optimization before we resort to stealing.
// We can safely skip it if there are no waiters or a thread is blocked
// in netpoll already. If there is any kind of logical race with that
// blocked thread (e.g. it has already returned from netpoll, but does
// not set lastpoll yet), this thread will do blocking netpoll below
// anyway.
if netpollinited() && netpollWaiters.Load() > 0 && sched.lastpoll.Load() != 0 {
if list := netpoll(0); !list.empty() { // non-blocking
gp := list.pop()
injectglist(&list)
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.enabled {
traceGoUnpark(gp, 0)
}
return gp, false, false
}
}
// Spinning Ms: steal work from other Ps.
//
// Limit the number of spinning Ms to half the number of busy Ps.
// This is necessary to prevent excessive CPU consumption when
// GOMAXPROCS>>1 but the program parallelism is low.
if mp.spinning || 2*sched.nmspinning.Load() < gomaxprocs-sched.npidle.Load() {
if !mp.spinning {
mp.becomeSpinning()
}
gp, inheritTime, tnow, w, newWork := stealWork(now)
if gp != nil {
// Successfully stole.
return gp, inheritTime, false
}
if newWork {
// There may be new timer or GC work; restart to
// discover.
goto top
}
now = tnow
if w != 0 && (pollUntil == 0 || w < pollUntil) {
// Earlier timer to wait for.
pollUntil = w
}
}
// We have nothing to do.
//
// If we're in the GC mark phase, can safely scan and blacken objects,
// and have work to do, run idle-time marking rather than give up the P.
if gcBlackenEnabled != 0 && gcMarkWorkAvailable(pp) && gcController.addIdleMarkWorker() {
node := (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop())
if node != nil {
pp.gcMarkWorkerMode = gcMarkWorkerIdleMode
gp := node.gp.ptr()
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.enabled {
traceGoUnpark(gp, 0)
}
return gp, false, false
}
gcController.removeIdleMarkWorker()
}
// wasm only:
// If a callback returned and no other goroutine is awake,
// then wake event handler goroutine which pauses execution
// until a callback was triggered.
gp, otherReady := beforeIdle(now, pollUntil)
if gp != nil {
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.enabled {
traceGoUnpark(gp, 0)
}
return gp, false, false
}
if otherReady {
goto top
}
// Before we drop our P, make a snapshot of the allp slice,
// which can change underfoot once we no longer block
// safe-points. We don't need to snapshot the contents because
// everything up to cap(allp) is immutable.
allpSnapshot := allp
// Also snapshot masks. Value changes are OK, but we can't allow
// len to change out from under us.
idlepMaskSnapshot := idlepMask
timerpMaskSnapshot := timerpMask
// return P and block
lock(&sched.lock)
if sched.gcwaiting.Load() || pp.runSafePointFn != 0 {
unlock(&sched.lock)
goto top
}
if sched.runqsize != 0 {
gp := globrunqget(pp, 0)
unlock(&sched.lock)
return gp, false, false
}
if !mp.spinning && sched.needspinning.Load() == 1 {
// See "Delicate dance" comment below.
mp.becomeSpinning()
unlock(&sched.lock)
goto top
}
if releasep() != pp {
throw("findrunnable: wrong p")
}
now = pidleput(pp, now)
unlock(&sched.lock)
// Delicate dance: thread transitions from spinning to non-spinning
// state, potentially concurrently with submission of new work. We must
// drop nmspinning first and then check all sources again (with
// #StoreLoad memory barrier in between). If we do it the other way
// around, another thread can submit work after we've checked all
// sources but before we drop nmspinning; as a result nobody will
// unpark a thread to run the work.
//
// This applies to the following sources of work:
//
// * Goroutines added to a per-P run queue.
// * New/modified-earlier timers on a per-P timer heap.
// * Idle-priority GC work (barring golang.org/issue/19112).
//
// If we discover new work below, we need to restore m.spinning as a
// signal for resetspinning to unpark a new worker thread (because
// there can be more than one starving goroutine).
//
// However, if after discovering new work we also observe no idle Ps
// (either here or in resetspinning), we have a problem. We may be
// racing with a non-spinning M in the block above, having found no
// work and preparing to release its P and park. Allowing that P to go
// idle will result in loss of work conservation (idle P while there is
// runnable work). This could result in complete deadlock in the
// unlikely event that we discover new work (from netpoll) right as we
// are racing with _all_ other Ps going idle.
//
// We use sched.needspinning to synchronize with non-spinning Ms going
// idle. If needspinning is set when they are about to drop their P,
// they abort the drop and instead become a new spinning M on our
// behalf. If we are not racing and the system is truly fully loaded
// then no spinning threads are required, and the next thread to
// naturally become spinning will clear the flag.
//
// Also see "Worker thread parking/unparking" comment at the top of the
// file.
wasSpinning := mp.spinning
if mp.spinning {
mp.spinning = false
if sched.nmspinning.Add(-1) < 0 {
throw("findrunnable: negative nmspinning")
}
// Note the for correctness, only the last M transitioning from
// spinning to non-spinning must perform these rechecks to
// ensure no missed work. However, the runtime has some cases
// of transient increments of nmspinning that are decremented
// without going through this path, so we must be conservative
// and perform the check on all spinning Ms.
//
// See https://go.dev/issue/43997.
// Check all runqueues once again.
pp := checkRunqsNoP(allpSnapshot, idlepMaskSnapshot)
if pp != nil {
acquirep(pp)
mp.becomeSpinning()
goto top
}
// Check for idle-priority GC work again.
pp, gp := checkIdleGCNoP()
if pp != nil {
acquirep(pp)
mp.becomeSpinning()
// Run the idle worker.
pp.gcMarkWorkerMode = gcMarkWorkerIdleMode
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.enabled {
traceGoUnpark(gp, 0)
}
return gp, false, false
}
// Finally, check for timer creation or expiry concurrently with
// transitioning from spinning to non-spinning.
//
// Note that we cannot use checkTimers here because it calls
// adjusttimers which may need to allocate memory, and that isn't
// allowed when we don't have an active P.
pollUntil = checkTimersNoP(allpSnapshot, timerpMaskSnapshot, pollUntil)
}
// Poll network until next timer.
if netpollinited() && (netpollWaiters.Load() > 0 || pollUntil != 0) && sched.lastpoll.Swap(0) != 0 {
sched.pollUntil.Store(pollUntil)
if mp.p != 0 {
throw("findrunnable: netpoll with p")
}
if mp.spinning {
throw("findrunnable: netpoll with spinning")
}
// Refresh now.
now = nanotime()
delay := int64(-1)
if pollUntil != 0 {
delay = pollUntil - now
if delay < 0 {
delay = 0
}
}
if faketime != 0 {
// When using fake time, just poll.
delay = 0
}
list := netpoll(delay) // block until new work is available
sched.pollUntil.Store(0)
sched.lastpoll.Store(now)
if faketime != 0 && list.empty() {
// Using fake time and nothing is ready; stop M.
// When all M's stop, checkdead will call timejump.
stopm()
goto top
}
lock(&sched.lock)
pp, _ := pidleget(now)
unlock(&sched.lock)
if pp == nil {
injectglist(&list)
} else {
acquirep(pp)
if !list.empty() {
gp := list.pop()
injectglist(&list)
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.enabled {
traceGoUnpark(gp, 0)
}
return gp, false, false
}
if wasSpinning {
mp.becomeSpinning()
}
goto top
}
} else if pollUntil != 0 && netpollinited() {
pollerPollUntil := sched.pollUntil.Load()
if pollerPollUntil == 0 || pollerPollUntil > pollUntil {
netpollBreak()
}
}
stopm()
goto top
}
// pollWork reports whether there is non-background work this P could
// be doing. This is a fairly lightweight check to be used for
// background work loops, like idle GC. It checks a subset of the
// conditions checked by the actual scheduler.
func pollWork() bool {
if sched.runqsize != 0 {
return true
}
p := getg().m.p.ptr()
if !runqempty(p) {
return true
}
if netpollinited() && netpollWaiters.Load() > 0 && sched.lastpoll.Load() != 0 {
if list := netpoll(0); !list.empty() {
injectglist(&list)
return true
}
}
return false
}
// stealWork attempts to steal a runnable goroutine or timer from any P.
//
// If newWork is true, new work may have been readied.
//
// If now is not 0 it is the current time. stealWork returns the passed time or
// the current time if now was passed as 0.
func stealWork(now int64) (gp *g, inheritTime bool, rnow, pollUntil int64, newWork bool) {
pp := getg().m.p.ptr()
ranTimer := false
const stealTries = 4
for i := 0; i < stealTries; i++ {
stealTimersOrRunNextG := i == stealTries-1
for enum := stealOrder.start(fastrand()); !enum.done(); enum.next() {
if sched.gcwaiting.Load() {
// GC work may be available.
return nil, false, now, pollUntil, true
}
p2 := allp[enum.position()]
if pp == p2 {
continue
}
// Steal timers from p2. This call to checkTimers is the only place
// where we might hold a lock on a different P's timers. We do this
// once on the last pass before checking runnext because stealing
// from the other P's runnext should be the last resort, so if there
// are timers to steal do that first.
//
// We only check timers on one of the stealing iterations because
// the time stored in now doesn't change in this loop and checking
// the timers for each P more than once with the same value of now
// is probably a waste of time.
//
// timerpMask tells us whether the P may have timers at all. If it
// can't, no need to check at all.
if stealTimersOrRunNextG && timerpMask.read(enum.position()) {
tnow, w, ran := checkTimers(p2, now)
now = tnow
if w != 0 && (pollUntil == 0 || w < pollUntil) {
pollUntil = w
}
if ran {
// Running the timers may have
// made an arbitrary number of G's
// ready and added them to this P's
// local run queue. That invalidates
// the assumption of runqsteal
// that it always has room to add
// stolen G's. So check now if there
// is a local G to run.
if gp, inheritTime := runqget(pp); gp != nil {
return gp, inheritTime, now, pollUntil, ranTimer
}
ranTimer = true
}
}
// Don't bother to attempt to steal if p2 is idle.
if !idlepMask.read(enum.position()) {
if gp := runqsteal(pp, p2, stealTimersOrRunNextG); gp != nil {
return gp, false, now, pollUntil, ranTimer
}
}
}
}
// No goroutines found to steal. Regardless, running a timer may have
// made some goroutine ready that we missed. Indicate the next timer to
// wait for.
return nil, false, now, pollUntil, ranTimer
}
// Check all Ps for a runnable G to steal.
//
// On entry we have no P. If a G is available to steal and a P is available,
// the P is returned which the caller should acquire and attempt to steal the
// work to.
func checkRunqsNoP(allpSnapshot []*p, idlepMaskSnapshot pMask) *p {
for id, p2 := range allpSnapshot {
if !idlepMaskSnapshot.read(uint32(id)) && !runqempty(p2) {
lock(&sched.lock)
pp, _ := pidlegetSpinning(0)
if pp == nil {
// Can't get a P, don't bother checking remaining Ps.
unlock(&sched.lock)
return nil
}
unlock(&sched.lock)
return pp
}
}
// No work available.
return nil
}
// Check all Ps for a timer expiring sooner than pollUntil.
//
// Returns updated pollUntil value.
func checkTimersNoP(allpSnapshot []*p, timerpMaskSnapshot pMask, pollUntil int64) int64 {
for id, p2 := range allpSnapshot {
if timerpMaskSnapshot.read(uint32(id)) {
w := nobarrierWakeTime(p2)
if w != 0 && (pollUntil == 0 || w < pollUntil) {
pollUntil = w
}
}
}
return pollUntil
}
// Check for idle-priority GC, without a P on entry.
//
// If some GC work, a P, and a worker G are all available, the P and G will be
// returned. The returned P has not been wired yet.
func checkIdleGCNoP() (*p, *g) {
// N.B. Since we have no P, gcBlackenEnabled may change at any time; we
// must check again after acquiring a P. As an optimization, we also check
// if an idle mark worker is needed at all. This is OK here, because if we
// observe that one isn't needed, at least one is currently running. Even if
// it stops running, its own journey into the scheduler should schedule it
// again, if need be (at which point, this check will pass, if relevant).
if atomic.Load(&gcBlackenEnabled) == 0 || !gcController.needIdleMarkWorker() {
return nil, nil
}
if !gcMarkWorkAvailable(nil) {
return nil, nil
}
// Work is available; we can start an idle GC worker only if there is
// an available P and available worker G.
//
// We can attempt to acquire these in either order, though both have
// synchronization concerns (see below). Workers are almost always
// available (see comment in findRunnableGCWorker for the one case
// there may be none). Since we're slightly less likely to find a P,
// check for that first.
//
// Synchronization: note that we must hold sched.lock until we are
// committed to keeping it. Otherwise we cannot put the unnecessary P
// back in sched.pidle without performing the full set of idle
// transition checks.
//
// If we were to check gcBgMarkWorkerPool first, we must somehow handle
// the assumption in gcControllerState.findRunnableGCWorker that an
// empty gcBgMarkWorkerPool is only possible if gcMarkDone is running.
lock(&sched.lock)
pp, now := pidlegetSpinning(0)
if pp == nil {
unlock(&sched.lock)
return nil, nil
}
// Now that we own a P, gcBlackenEnabled can't change (as it requires STW).
if gcBlackenEnabled == 0 || !gcController.addIdleMarkWorker() {
pidleput(pp, now)
unlock(&sched.lock)
return nil, nil
}
node := (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop())
if node == nil {
pidleput(pp, now)
unlock(&sched.lock)
gcController.removeIdleMarkWorker()
return nil, nil
}
unlock(&sched.lock)
return pp, node.gp.ptr()
}
// wakeNetPoller wakes up the thread sleeping in the network poller if it isn't
// going to wake up before the when argument; or it wakes an idle P to service
// timers and the network poller if there isn't one already.
func wakeNetPoller(when int64) {
if sched.lastpoll.Load() == 0 {
// In findrunnable we ensure that when polling the pollUntil
// field is either zero or the time to which the current
// poll is expected to run. This can have a spurious wakeup
// but should never miss a wakeup.
pollerPollUntil := sched.pollUntil.Load()
if pollerPollUntil == 0 || pollerPollUntil > when {
netpollBreak()
}
} else {
// There are no threads in the network poller, try to get
// one there so it can handle new timers.
if GOOS != "plan9" { // Temporary workaround - see issue #42303.
wakep()
}
}
}
func resetspinning() {
gp := getg()
if !gp.m.spinning {
throw("resetspinning: not a spinning m")
}
gp.m.spinning = false
nmspinning := sched.nmspinning.Add(-1)
if nmspinning < 0 {
throw("findrunnable: negative nmspinning")
}
// M wakeup policy is deliberately somewhat conservative, so check if we
// need to wakeup another P here. See "Worker thread parking/unparking"
// comment at the top of the file for details.
wakep()
}
// injectglist adds each runnable G on the list to some run queue,
// and clears glist. If there is no current P, they are added to the
// global queue, and up to npidle M's are started to run them.
// Otherwise, for each idle P, this adds a G to the global queue
// and starts an M. Any remaining G's are added to the current P's
// local run queue.
// This may temporarily acquire sched.lock.
// Can run concurrently with GC.
func injectglist(glist *gList) {
if glist.empty() {
return
}
if trace.enabled {
for gp := glist.head.ptr(); gp != nil; gp = gp.schedlink.ptr() {
traceGoUnpark(gp, 0)
}
}
// Mark all the goroutines as runnable before we put them
// on the run queues.
head := glist.head.ptr()
var tail *g
qsize := 0
for gp := head; gp != nil; gp = gp.schedlink.ptr() {
tail = gp
qsize++
casgstatus(gp, _Gwaiting, _Grunnable)
}
// Turn the gList into a gQueue.
var q gQueue
q.head.set(head)
q.tail.set(tail)
*glist = gList{}
startIdle := func(n int) {
for i := 0; i < n; i++ {
mp := acquirem() // See comment in startm.
lock(&sched.lock)
pp, _ := pidlegetSpinning(0)
if pp == nil {
unlock(&sched.lock)
releasem(mp)
break
}
unlock(&sched.lock)
startm(pp, false)
releasem(mp)
}
}
pp := getg().m.p.ptr()
if pp == nil {
lock(&sched.lock)
globrunqputbatch(&q, int32(qsize))
unlock(&sched.lock)
startIdle(qsize)
return
}
npidle := int(sched.npidle.Load())
var globq gQueue
var n int
for n = 0; n < npidle && !q.empty(); n++ {
g := q.pop()
globq.pushBack(g)
}
if n > 0 {
lock(&sched.lock)
globrunqputbatch(&globq, int32(n))
unlock(&sched.lock)
startIdle(n)
qsize -= n
}
if !q.empty() {
runqputbatch(pp, &q, qsize)
}
}
// One round of scheduler: find a runnable goroutine and execute it.
// Never returns.
func schedule() {
mp := getg().m
if mp.locks != 0 {
throw("schedule: holding locks")
}
if mp.lockedg != 0 {
stoplockedm()
execute(mp.lockedg.ptr(), false) // Never returns.
}
// We should not schedule away from a g that is executing a cgo call,
// since the cgo call is using the m's g0 stack.
if mp.incgo {
throw("schedule: in cgo")
}
top:
pp := mp.p.ptr()
pp.preempt = false
// Safety check: if we are spinning, the run queue should be empty.
// Check this before calling checkTimers, as that might call
// goready to put a ready goroutine on the local run queue.
if mp.spinning && (pp.runnext != 0 || pp.runqhead != pp.runqtail) {
throw("schedule: spinning with local work")
}
gp, inheritTime, tryWakeP := findRunnable() // blocks until work is available
// This thread is going to run a goroutine and is not spinning anymore,
// so if it was marked as spinning we need to reset it now and potentially
// start a new spinning M.
if mp.spinning {
resetspinning()
}
if sched.disable.user && !schedEnabled(gp) {
// Scheduling of this goroutine is disabled. Put it on
// the list of pending runnable goroutines for when we
// re-enable user scheduling and look again.
lock(&sched.lock)
if schedEnabled(gp) {
// Something re-enabled scheduling while we
// were acquiring the lock.
unlock(&sched.lock)
} else {
sched.disable.runnable.pushBack(gp)
sched.disable.n++
unlock(&sched.lock)
goto top
}
}
// If about to schedule a not-normal goroutine (a GCworker or tracereader),
// wake a P if there is one.
if tryWakeP {
wakep()
}
if gp.lockedm != 0 {
// Hands off own p to the locked m,
// then blocks waiting for a new p.
startlockedm(gp)
goto top
}
execute(gp, inheritTime)
}
// dropg removes the association between m and the current goroutine m->curg (gp for short).
// Typically a caller sets gp's status away from Grunning and then
// immediately calls dropg to finish the job. The caller is also responsible
// for arranging that gp will be restarted using ready at an
// appropriate time. After calling dropg and arranging for gp to be
// readied later, the caller can do other work but eventually should
// call schedule to restart the scheduling of goroutines on this m.
func dropg() {
gp := getg()
setMNoWB(&gp.m.curg.m, nil)
setGNoWB(&gp.m.curg, nil)
}
// checkTimers runs any timers for the P that are ready.
// If now is not 0 it is the current time.
// It returns the passed time or the current time if now was passed as 0.
// and the time when the next timer should run or 0 if there is no next timer,
// and reports whether it ran any timers.
// If the time when the next timer should run is not 0,
// it is always larger than the returned time.
// We pass now in and out to avoid extra calls of nanotime.
//
//go:yeswritebarrierrec
func checkTimers(pp *p, now int64) (rnow, pollUntil int64, ran bool) {
// If it's not yet time for the first timer, or the first adjusted
// timer, then there is nothing to do.
next := pp.timer0When.Load()
nextAdj := pp.timerModifiedEarliest.Load()
if next == 0 || (nextAdj != 0 && nextAdj < next) {
next = nextAdj
}
if next == 0 {
// No timers to run or adjust.
return now, 0, false
}
if now == 0 {
now = nanotime()
}
if now < next {
// Next timer is not ready to run, but keep going
// if we would clear deleted timers.
// This corresponds to the condition below where
// we decide whether to call clearDeletedTimers.
if pp != getg().m.p.ptr() || int(pp.deletedTimers.Load()) <= int(pp.numTimers.Load()/4) {
return now, next, false
}
}
lock(&pp.timersLock)
if len(pp.timers) > 0 {
adjusttimers(pp, now)
for len(pp.timers) > 0 {
// Note that runtimer may temporarily unlock
// pp.timersLock.
if tw := runtimer(pp, now); tw != 0 {
if tw > 0 {
pollUntil = tw
}
break
}
ran = true
}
}
// If this is the local P, and there are a lot of deleted timers,
// clear them out. We only do this for the local P to reduce
// lock contention on timersLock.
if pp == getg().m.p.ptr() && int(pp.deletedTimers.Load()) > len(pp.timers)/4 {
clearDeletedTimers(pp)
}
unlock(&pp.timersLock)
return now, pollUntil, ran
}
func parkunlock_c(gp *g, lock unsafe.Pointer) bool {
unlock((*mutex)(lock))
return true
}
// park continuation on g0.
func park_m(gp *g) {
mp := getg().m
if trace.enabled {
traceGoPark(mp.waittraceev, mp.waittraceskip)
}
// N.B. Not using casGToWaiting here because the waitreason is
// set by park_m's caller.
casgstatus(gp, _Grunning, _Gwaiting)
dropg()
if fn := mp.waitunlockf; fn != nil {
ok := fn(gp, mp.waitlock)
mp.waitunlockf = nil
mp.waitlock = nil
if !ok {
if trace.enabled {
traceGoUnpark(gp, 2)
}
casgstatus(gp, _Gwaiting, _Grunnable)
execute(gp, true) // Schedule it back, never returns.
}
}
schedule()
}
func goschedImpl(gp *g) {
status := readgstatus(gp)
if status&^_Gscan != _Grunning {
dumpgstatus(gp)
throw("bad g status")
}
casgstatus(gp, _Grunning, _Grunnable)
dropg()
lock(&sched.lock)
globrunqput(gp)
unlock(&sched.lock)
schedule()
}
// Gosched continuation on g0.
func gosched_m(gp *g) {
if trace.enabled {
traceGoSched()
}
goschedImpl(gp)
}
// goschedguarded is a forbidden-states-avoided version of gosched_m.
func goschedguarded_m(gp *g) {
if !canPreemptM(gp.m) {
gogo(&gp.sched) // never return
}
if trace.enabled {
traceGoSched()
}
goschedImpl(gp)
}
func gopreempt_m(gp *g) {
if trace.enabled {
traceGoPreempt()
}
goschedImpl(gp)
}
// preemptPark parks gp and puts it in _Gpreempted.
//
//go:systemstack
func preemptPark(gp *g) {
if trace.enabled {
traceGoPark(traceEvGoBlock, 0)
}
status := readgstatus(gp)
if status&^_Gscan != _Grunning {
dumpgstatus(gp)
throw("bad g status")
}
if gp.asyncSafePoint {
// Double-check that async preemption does not
// happen in SPWRITE assembly functions.
// isAsyncSafePoint must exclude this case.
f := findfunc(gp.sched.pc)
if !f.valid() {
throw("preempt at unknown pc")
}
if f.flag&funcFlag_SPWRITE != 0 {
println("runtime: unexpected SPWRITE function", funcname(f), "in async preempt")
throw("preempt SPWRITE")
}
}
// Transition from _Grunning to _Gscan|_Gpreempted. We can't
// be in _Grunning when we dropg because then we'd be running
// without an M, but the moment we're in _Gpreempted,
// something could claim this G before we've fully cleaned it
// up. Hence, we set the scan bit to lock down further
// transitions until we can dropg.
casGToPreemptScan(gp, _Grunning, _Gscan|_Gpreempted)
dropg()
casfrom_Gscanstatus(gp, _Gscan|_Gpreempted, _Gpreempted)
schedule()
}
// goyield is like Gosched, but it:
// - emits a GoPreempt trace event instead of a GoSched trace event
// - puts the current G on the runq of the current P instead of the globrunq
func goyield() {
checkTimeouts()
mcall(goyield_m)
}
func goyield_m(gp *g) {
if trace.enabled {
traceGoPreempt()
}
pp := gp.m.p.ptr()
casgstatus(gp, _Grunning, _Grunnable)
dropg()
runqput(pp, gp, false)
schedule()
}
// Finishes execution of the current goroutine.
func goexit1() {
if raceenabled {
racegoend()
}
if trace.enabled {
traceGoEnd()
}
mcall(goexit0)
}
// goexit continuation on g0.
func goexit0(gp *g) {
mp := getg().m
pp := mp.p.ptr()
casgstatus(gp, _Grunning, _Gdead)
gcController.addScannableStack(pp, -int64(gp.stack.hi-gp.stack.lo))
if isSystemGoroutine(gp, false) {
sched.ngsys.Add(-1)
}
gp.m = nil
locked := gp.lockedm != 0
gp.lockedm = 0
mp.lockedg = 0
gp.preemptStop = false
gp.paniconfault = false
gp._defer = nil // should be true already but just in case.
gp._panic = nil // non-nil for Goexit during panic. points at stack-allocated data.
gp.writebuf = nil
gp.waitreason = waitReasonZero
gp.param = nil
gp.labels = nil
gp.timer = nil
if gcBlackenEnabled != 0 && gp.gcAssistBytes > 0 {
// Flush assist credit to the global pool. This gives
// better information to pacing if the application is
// rapidly creating an exiting goroutines.
assistWorkPerByte := gcController.assistWorkPerByte.Load()
scanCredit := int64(assistWorkPerByte * float64(gp.gcAssistBytes))
gcController.bgScanCredit.Add(scanCredit)
gp.gcAssistBytes = 0
}
dropg()
if GOARCH == "wasm" { // no threads yet on wasm
gfput(pp, gp)
schedule() // never returns
}
if mp.lockedInt != 0 {
print("invalid m->lockedInt = ", mp.lockedInt, "\n")
throw("internal lockOSThread error")
}
gfput(pp, gp)
if locked {
// The goroutine may have locked this thread because
// it put it in an unusual kernel state. Kill it
// rather than returning it to the thread pool.
// Return to mstart, which will release the P and exit
// the thread.
if GOOS != "plan9" { // See golang.org/issue/22227.
gogo(&mp.g0.sched)
} else {
// Clear lockedExt on plan9 since we may end up re-using
// this thread.
mp.lockedExt = 0
}
}
schedule()
}
// save updates getg().sched to refer to pc and sp so that a following
// gogo will restore pc and sp.
//
// save must not have write barriers because invoking a write barrier
// can clobber getg().sched.
//
//go:nosplit
//go:nowritebarrierrec
func save(pc, sp uintptr) {
gp := getg()
if gp == gp.m.g0 || gp == gp.m.gsignal {
// m.g0.sched is special and must describe the context
// for exiting the thread. mstart1 writes to it directly.
// m.gsignal.sched should not be used at all.
// This check makes sure save calls do not accidentally
// run in contexts where they'd write to system g's.
throw("save on system g not allowed")
}
gp.sched.pc = pc
gp.sched.sp = sp
gp.sched.lr = 0
gp.sched.ret = 0
// We need to ensure ctxt is zero, but can't have a write
// barrier here. However, it should always already be zero.
// Assert that.
if gp.sched.ctxt != nil {
badctxt()
}
}
// The goroutine g is about to enter a system call.
// Record that it's not using the cpu anymore.
// This is called only from the go syscall library and cgocall,
// not from the low-level system calls used by the runtime.
//
// Entersyscall cannot split the stack: the save must
// make g->sched refer to the caller's stack segment, because
// entersyscall is going to return immediately after.
//
// Nothing entersyscall calls can split the stack either.
// We cannot safely move the stack during an active call to syscall,
// because we do not know which of the uintptr arguments are
// really pointers (back into the stack).
// In practice, this means that we make the fast path run through
// entersyscall doing no-split things, and the slow path has to use systemstack
// to run bigger things on the system stack.
//
// reentersyscall is the entry point used by cgo callbacks, where explicitly
// saved SP and PC are restored. This is needed when exitsyscall will be called
// from a function further up in the call stack than the parent, as g->syscallsp
// must always point to a valid stack frame. entersyscall below is the normal
// entry point for syscalls, which obtains the SP and PC from the caller.
//
// Syscall tracing:
// At the start of a syscall we emit traceGoSysCall to capture the stack trace.
// If the syscall does not block, that is it, we do not emit any other events.
// If the syscall blocks (that is, P is retaken), retaker emits traceGoSysBlock;
// when syscall returns we emit traceGoSysExit and when the goroutine starts running
// (potentially instantly, if exitsyscallfast returns true) we emit traceGoStart.
// To ensure that traceGoSysExit is emitted strictly after traceGoSysBlock,
// we remember current value of syscalltick in m (gp.m.syscalltick = gp.m.p.ptr().syscalltick),
// whoever emits traceGoSysBlock increments p.syscalltick afterwards;
// and we wait for the increment before emitting traceGoSysExit.
// Note that the increment is done even if tracing is not enabled,
// because tracing can be enabled in the middle of syscall. We don't want the wait to hang.
//
//go:nosplit
func reentersyscall(pc, sp uintptr) {
gp := getg()
// Disable preemption because during this function g is in Gsyscall status,
// but can have inconsistent g->sched, do not let GC observe it.
gp.m.locks++
// Entersyscall must not call any function that might split/grow the stack.
// (See details in comment above.)
// Catch calls that might, by replacing the stack guard with something that
// will trip any stack check and leaving a flag to tell newstack to die.
gp.stackguard0 = stackPreempt
gp.throwsplit = true
// Leave SP around for GC and traceback.
save(pc, sp)
gp.syscallsp = sp
gp.syscallpc = pc
casgstatus(gp, _Grunning, _Gsyscall)
if gp.syscallsp < gp.stack.lo || gp.stack.hi < gp.syscallsp {
systemstack(func() {
print("entersyscall inconsistent ", hex(gp.syscallsp), " [", hex(gp.stack.lo), ",", hex(gp.stack.hi), "]\n")
throw("entersyscall")
})
}
if trace.enabled {
systemstack(traceGoSysCall)
// systemstack itself clobbers g.sched.{pc,sp} and we might
// need them later when the G is genuinely blocked in a
// syscall
save(pc, sp)
}
if sched.sysmonwait.Load() {
systemstack(entersyscall_sysmon)
save(pc, sp)
}
if gp.m.p.ptr().runSafePointFn != 0 {
// runSafePointFn may stack split if run on this stack
systemstack(runSafePointFn)
save(pc, sp)
}
gp.m.syscalltick = gp.m.p.ptr().syscalltick
gp.sysblocktraced = true
pp := gp.m.p.ptr()
pp.m = 0
gp.m.oldp.set(pp)
gp.m.p = 0
atomic.Store(&pp.status, _Psyscall)
if sched.gcwaiting.Load() {
systemstack(entersyscall_gcwait)
save(pc, sp)
}
gp.m.locks--
}
// Standard syscall entry used by the go syscall library and normal cgo calls.
//
// This is exported via linkname to assembly in the syscall package and x/sys.
//
//go:nosplit
//go:linkname entersyscall
func entersyscall() {
reentersyscall(getcallerpc(), getcallersp())
}
func entersyscall_sysmon() {
lock(&sched.lock)
if sched.sysmonwait.Load() {
sched.sysmonwait.Store(false)
notewakeup(&sched.sysmonnote)
}
unlock(&sched.lock)
}
func entersyscall_gcwait() {
gp := getg()
pp := gp.m.oldp.ptr()
lock(&sched.lock)
if sched.stopwait > 0 && atomic.Cas(&pp.status, _Psyscall, _Pgcstop) {
if trace.enabled {
traceGoSysBlock(pp)
traceProcStop(pp)
}
pp.syscalltick++
if sched.stopwait--; sched.stopwait == 0 {
notewakeup(&sched.stopnote)
}
}
unlock(&sched.lock)
}
// The same as entersyscall(), but with a hint that the syscall is blocking.
//
//go:nosplit
func entersyscallblock() {
gp := getg()
gp.m.locks++ // see comment in entersyscall
gp.throwsplit = true
gp.stackguard0 = stackPreempt // see comment in entersyscall
gp.m.syscalltick = gp.m.p.ptr().syscalltick
gp.sysblocktraced = true
gp.m.p.ptr().syscalltick++
// Leave SP around for GC and traceback.
pc := getcallerpc()
sp := getcallersp()
save(pc, sp)
gp.syscallsp = gp.sched.sp
gp.syscallpc = gp.sched.pc
if gp.syscallsp < gp.stack.lo || gp.stack.hi < gp.syscallsp {
sp1 := sp
sp2 := gp.sched.sp
sp3 := gp.syscallsp
systemstack(func() {
print("entersyscallblock inconsistent ", hex(sp1), " ", hex(sp2), " ", hex(sp3), " [", hex(gp.stack.lo), ",", hex(gp.stack.hi), "]\n")
throw("entersyscallblock")
})
}
casgstatus(gp, _Grunning, _Gsyscall)
if gp.syscallsp < gp.stack.lo || gp.stack.hi < gp.syscallsp {
systemstack(func() {
print("entersyscallblock inconsistent ", hex(sp), " ", hex(gp.sched.sp), " ", hex(gp.syscallsp), " [", hex(gp.stack.lo), ",", hex(gp.stack.hi), "]\n")
throw("entersyscallblock")
})
}
systemstack(entersyscallblock_handoff)
// Resave for traceback during blocked call.
save(getcallerpc(), getcallersp())
gp.m.locks--
}
func entersyscallblock_handoff() {
if trace.enabled {
traceGoSysCall()
traceGoSysBlock(getg().m.p.ptr())
}
handoffp(releasep())
}
// The goroutine g exited its system call.
// Arrange for it to run on a cpu again.
// This is called only from the go syscall library, not
// from the low-level system calls used by the runtime.
//
// Write barriers are not allowed because our P may have been stolen.
//
// This is exported via linkname to assembly in the syscall package.
//
//go:nosplit
//go:nowritebarrierrec
//go:linkname exitsyscall
func exitsyscall() {
gp := getg()
gp.m.locks++ // see comment in entersyscall
if getcallersp() > gp.syscallsp {
throw("exitsyscall: syscall frame is no longer valid")
}
gp.waitsince = 0
oldp := gp.m.oldp.ptr()
gp.m.oldp = 0
if exitsyscallfast(oldp) {
// When exitsyscallfast returns success, we have a P so can now use
// write barriers
if goroutineProfile.active {
// Make sure that gp has had its stack written out to the goroutine
// profile, exactly as it was when the goroutine profiler first
// stopped the world.
systemstack(func() {
tryRecordGoroutineProfileWB(gp)
})
}
if trace.enabled {
if oldp != gp.m.p.ptr() || gp.m.syscalltick != gp.m.p.ptr().syscalltick {
systemstack(traceGoStart)
}
}
// There's a cpu for us, so we can run.
gp.m.p.ptr().syscalltick++
// We need to cas the status and scan before resuming...
casgstatus(gp, _Gsyscall, _Grunning)
// Garbage collector isn't running (since we are),
// so okay to clear syscallsp.
gp.syscallsp = 0
gp.m.locks--
if gp.preempt {
// restore the preemption request in case we've cleared it in newstack
gp.stackguard0 = stackPreempt
} else {
// otherwise restore the real _StackGuard, we've spoiled it in entersyscall/entersyscallblock
gp.stackguard0 = gp.stack.lo + _StackGuard
}
gp.throwsplit = false
if sched.disable.user && !schedEnabled(gp) {
// Scheduling of this goroutine is disabled.
Gosched()
}
return
}
gp.sysexitticks = 0
if trace.enabled {
// Wait till traceGoSysBlock event is emitted.
// This ensures consistency of the trace (the goroutine is started after it is blocked).
for oldp != nil && oldp.syscalltick == gp.m.syscalltick {
osyield()
}
// We can't trace syscall exit right now because we don't have a P.
// Tracing code can invoke write barriers that cannot run without a P.
// So instead we remember the syscall exit time and emit the event
// in execute when we have a P.
gp.sysexitticks = cputicks()
}
gp.m.locks--
// Call the scheduler.
mcall(exitsyscall0)
// Scheduler returned, so we're allowed to run now.
// Delete the syscallsp information that we left for
// the garbage collector during the system call.
// Must wait until now because until gosched returns
// we don't know for sure that the garbage collector
// is not running.
gp.syscallsp = 0
gp.m.p.ptr().syscalltick++
gp.throwsplit = false
}
//go:nosplit
func exitsyscallfast(oldp *p) bool {
gp := getg()
// Freezetheworld sets stopwait but does not retake P's.
if sched.stopwait == freezeStopWait {
return false
}
// Try to re-acquire the last P.
if oldp != nil && oldp.status == _Psyscall && atomic.Cas(&oldp.status, _Psyscall, _Pidle) {
// There's a cpu for us, so we can run.
wirep(oldp)
exitsyscallfast_reacquired()
return true
}
// Try to get any other idle P.
if sched.pidle != 0 {
var ok bool
systemstack(func() {
ok = exitsyscallfast_pidle()
if ok && trace.enabled {
if oldp != nil {
// Wait till traceGoSysBlock event is emitted.
// This ensures consistency of the trace (the goroutine is started after it is blocked).
for oldp.syscalltick == gp.m.syscalltick {
osyield()
}
}
traceGoSysExit(0)
}
})
if ok {
return true
}
}
return false
}
// exitsyscallfast_reacquired is the exitsyscall path on which this G
// has successfully reacquired the P it was running on before the
// syscall.
//
//go:nosplit
func exitsyscallfast_reacquired() {
gp := getg()
if gp.m.syscalltick != gp.m.p.ptr().syscalltick {
if trace.enabled {
// The p was retaken and then enter into syscall again (since gp.m.syscalltick has changed).
// traceGoSysBlock for this syscall was already emitted,
// but here we effectively retake the p from the new syscall running on the same p.
systemstack(func() {
// Denote blocking of the new syscall.
traceGoSysBlock(gp.m.p.ptr())
// Denote completion of the current syscall.
traceGoSysExit(0)
})
}
gp.m.p.ptr().syscalltick++
}
}
func exitsyscallfast_pidle() bool {
lock(&sched.lock)
pp, _ := pidleget(0)
if pp != nil && sched.sysmonwait.Load() {
sched.sysmonwait.Store(false)
notewakeup(&sched.sysmonnote)
}
unlock(&sched.lock)
if pp != nil {
acquirep(pp)
return true
}
return false
}
// exitsyscall slow path on g0.
// Failed to acquire P, enqueue gp as runnable.
//
// Called via mcall, so gp is the calling g from this M.
//
//go:nowritebarrierrec
func exitsyscall0(gp *g) {
casgstatus(gp, _Gsyscall, _Grunnable)
dropg()
lock(&sched.lock)
var pp *p
if schedEnabled(gp) {
pp, _ = pidleget(0)
}
var locked bool
if pp == nil {
globrunqput(gp)
// Below, we stoplockedm if gp is locked. globrunqput releases
// ownership of gp, so we must check if gp is locked prior to
// committing the release by unlocking sched.lock, otherwise we
// could race with another M transitioning gp from unlocked to
// locked.
locked = gp.lockedm != 0
} else if sched.sysmonwait.Load() {
sched.sysmonwait.Store(false)
notewakeup(&sched.sysmonnote)
}
unlock(&sched.lock)
if pp != nil {
acquirep(pp)
execute(gp, false) // Never returns.
}
if locked {
// Wait until another thread schedules gp and so m again.
//
// N.B. lockedm must be this M, as this g was running on this M
// before entersyscall.
stoplockedm()
execute(gp, false) // Never returns.
}
stopm()
schedule() // Never returns.
}
// Called from syscall package before fork.
//
//go:linkname syscall_runtime_BeforeFork syscall.runtime_BeforeFork
//go:nosplit
func syscall_runtime_BeforeFork() {
gp := getg().m.curg
// Block signals during a fork, so that the child does not run
// a signal handler before exec if a signal is sent to the process
// group. See issue #18600.
gp.m.locks++
sigsave(&gp.m.sigmask)
sigblock(false)
// This function is called before fork in syscall package.
// Code between fork and exec must not allocate memory nor even try to grow stack.
// Here we spoil g->_StackGuard to reliably detect any attempts to grow stack.
// runtime_AfterFork will undo this in parent process, but not in child.
gp.stackguard0 = stackFork
}
// Called from syscall package after fork in parent.
//
//go:linkname syscall_runtime_AfterFork syscall.runtime_AfterFork
//go:nosplit
func syscall_runtime_AfterFork() {
gp := getg().m.curg
// See the comments in beforefork.
gp.stackguard0 = gp.stack.lo + _StackGuard
msigrestore(gp.m.sigmask)
gp.m.locks--
}
// inForkedChild is true while manipulating signals in the child process.
// This is used to avoid calling libc functions in case we are using vfork.
var inForkedChild bool
// Called from syscall package after fork in child.
// It resets non-sigignored signals to the default handler, and
// restores the signal mask in preparation for the exec.
//
// Because this might be called during a vfork, and therefore may be
// temporarily sharing address space with the parent process, this must
// not change any global variables or calling into C code that may do so.
//
//go:linkname syscall_runtime_AfterForkInChild syscall.runtime_AfterForkInChild
//go:nosplit
//go:nowritebarrierrec
func syscall_runtime_AfterForkInChild() {
// It's OK to change the global variable inForkedChild here
// because we are going to change it back. There is no race here,
// because if we are sharing address space with the parent process,
// then the parent process can not be running concurrently.
inForkedChild = true
clearSignalHandlers()
// When we are the child we are the only thread running,
// so we know that nothing else has changed gp.m.sigmask.
msigrestore(getg().m.sigmask)
inForkedChild = false
}
// pendingPreemptSignals is the number of preemption signals
// that have been sent but not received. This is only used on Darwin.
// For #41702.
var pendingPreemptSignals atomic.Int32
// Called from syscall package before Exec.
//
//go:linkname syscall_runtime_BeforeExec syscall.runtime_BeforeExec
func syscall_runtime_BeforeExec() {
// Prevent thread creation during exec.
execLock.lock()
// On Darwin, wait for all pending preemption signals to
// be received. See issue #41702.
if GOOS == "darwin" || GOOS == "ios" {
for pendingPreemptSignals.Load() > 0 {
osyield()
}
}
}
// Called from syscall package after Exec.
//
//go:linkname syscall_runtime_AfterExec syscall.runtime_AfterExec
func syscall_runtime_AfterExec() {
execLock.unlock()
}
// Allocate a new g, with a stack big enough for stacksize bytes.
func malg(stacksize int32) *g {
newg := new(g)
if stacksize >= 0 {
stacksize = round2(_StackSystem + stacksize)
systemstack(func() {
newg.stack = stackalloc(uint32(stacksize))
})
newg.stackguard0 = newg.stack.lo + _StackGuard
newg.stackguard1 = ^uintptr(0)
// Clear the bottom word of the stack. We record g
// there on gsignal stack during VDSO on ARM and ARM64.
*(*uintptr)(unsafe.Pointer(newg.stack.lo)) = 0
}
return newg
}
// Create a new g running fn.
// Put it on the queue of g's waiting to run.
// The compiler turns a go statement into a call to this.
func newproc(fn *funcval) {
gp := getg()
pc := getcallerpc()
systemstack(func() {
newg := newproc1(fn, gp, pc)
pp := getg().m.p.ptr()
runqput(pp, newg, true)
if mainStarted {
wakep()
}
})
}
// Create a new g in state _Grunnable, starting at fn. callerpc is the
// address of the go statement that created this. The caller is responsible
// for adding the new g to the scheduler.
func newproc1(fn *funcval, callergp *g, callerpc uintptr) *g {
if fn == nil {
fatal("go of nil func value")
}
mp := acquirem() // disable preemption because we hold M and P in local vars.
pp := mp.p.ptr()
newg := gfget(pp)
if newg == nil {
newg = malg(_StackMin)
casgstatus(newg, _Gidle, _Gdead)
allgadd(newg) // publishes with a g->status of Gdead so GC scanner doesn't look at uninitialized stack.
}
if newg.stack.hi == 0 {
throw("newproc1: newg missing stack")
}
if readgstatus(newg) != _Gdead {
throw("newproc1: new g is not Gdead")
}
totalSize := uintptr(4*goarch.PtrSize + sys.MinFrameSize) // extra space in case of reads slightly beyond frame
totalSize = alignUp(totalSize, sys.StackAlign)
sp := newg.stack.hi - totalSize
spArg := sp
if usesLR {
// caller's LR
*(*uintptr)(unsafe.Pointer(sp)) = 0
prepGoExitFrame(sp)
spArg += sys.MinFrameSize
}
memclrNoHeapPointers(unsafe.Pointer(&newg.sched), unsafe.Sizeof(newg.sched))
newg.sched.sp = sp
newg.stktopsp = sp
newg.sched.pc = abi.FuncPCABI0(goexit) + sys.PCQuantum // +PCQuantum so that previous instruction is in same function
newg.sched.g = guintptr(unsafe.Pointer(newg))
gostartcallfn(&newg.sched, fn)
newg.gopc = callerpc
newg.ancestors = saveAncestors(callergp)
newg.startpc = fn.fn
if isSystemGoroutine(newg, false) {
sched.ngsys.Add(1)
} else {
// Only user goroutines inherit pprof labels.
if mp.curg != nil {
newg.labels = mp.curg.labels
}
if goroutineProfile.active {
// A concurrent goroutine profile is running. It should include
// exactly the set of goroutines that were alive when the goroutine
// profiler first stopped the world. That does not include newg, so
// mark it as not needing a profile before transitioning it from
// _Gdead.
newg.goroutineProfiled.Store(goroutineProfileSatisfied)
}
}
// Track initial transition?
newg.trackingSeq = uint8(fastrand())
if newg.trackingSeq%gTrackingPeriod == 0 {
newg.tracking = true
}
casgstatus(newg, _Gdead, _Grunnable)
gcController.addScannableStack(pp, int64(newg.stack.hi-newg.stack.lo))
if pp.goidcache == pp.goidcacheend {
// Sched.goidgen is the last allocated id,
// this batch must be [sched.goidgen+1, sched.goidgen+GoidCacheBatch].
// At startup sched.goidgen=0, so main goroutine receives goid=1.
pp.goidcache = sched.goidgen.Add(_GoidCacheBatch)
pp.goidcache -= _GoidCacheBatch - 1
pp.goidcacheend = pp.goidcache + _GoidCacheBatch
}
newg.goid = pp.goidcache
pp.goidcache++
if raceenabled {
newg.racectx = racegostart(callerpc)
if newg.labels != nil {
// See note in proflabel.go on labelSync's role in synchronizing
// with the reads in the signal handler.
racereleasemergeg(newg, unsafe.Pointer(&labelSync))
}
}
if trace.enabled {
traceGoCreate(newg, newg.startpc)
}
releasem(mp)
return newg
}
// saveAncestors copies previous ancestors of the given caller g and
// includes infor for the current caller into a new set of tracebacks for
// a g being created.
func saveAncestors(callergp *g) *[]ancestorInfo {
// Copy all prior info, except for the root goroutine (goid 0).
if debug.tracebackancestors <= 0 || callergp.goid == 0 {
return nil
}
var callerAncestors []ancestorInfo
if callergp.ancestors != nil {
callerAncestors = *callergp.ancestors
}
n := int32(len(callerAncestors)) + 1
if n > debug.tracebackancestors {
n = debug.tracebackancestors
}
ancestors := make([]ancestorInfo, n)
copy(ancestors[1:], callerAncestors)
var pcs [_TracebackMaxFrames]uintptr
npcs := gcallers(callergp, 0, pcs[:])
ipcs := make([]uintptr, npcs)
copy(ipcs, pcs[:])
ancestors[0] = ancestorInfo{
pcs: ipcs,
goid: callergp.goid,
gopc: callergp.gopc,
}
ancestorsp := new([]ancestorInfo)
*ancestorsp = ancestors
return ancestorsp
}
// Put on gfree list.
// If local list is too long, transfer a batch to the global list.
func gfput(pp *p, gp *g) {
if readgstatus(gp) != _Gdead {
throw("gfput: bad status (not Gdead)")
}
stksize := gp.stack.hi - gp.stack.lo
if stksize != uintptr(startingStackSize) {
// non-standard stack size - free it.
stackfree(gp.stack)
gp.stack.lo = 0
gp.stack.hi = 0
gp.stackguard0 = 0
}
pp.gFree.push(gp)
pp.gFree.n++
if pp.gFree.n >= 64 {
var (
inc int32
stackQ gQueue
noStackQ gQueue
)
for pp.gFree.n >= 32 {
gp := pp.gFree.pop()
pp.gFree.n--
if gp.stack.lo == 0 {
noStackQ.push(gp)
} else {
stackQ.push(gp)
}
inc++
}
lock(&sched.gFree.lock)
sched.gFree.noStack.pushAll(noStackQ)
sched.gFree.stack.pushAll(stackQ)
sched.gFree.n += inc
unlock(&sched.gFree.lock)
}
}
// Get from gfree list.
// If local list is empty, grab a batch from global list.
func gfget(pp *p) *g {
retry:
if pp.gFree.empty() && (!sched.gFree.stack.empty() || !sched.gFree.noStack.empty()) {
lock(&sched.gFree.lock)
// Move a batch of free Gs to the P.
for pp.gFree.n < 32 {
// Prefer Gs with stacks.
gp := sched.gFree.stack.pop()
if gp == nil {
gp = sched.gFree.noStack.pop()
if gp == nil {
break
}
}
sched.gFree.n--
pp.gFree.push(gp)
pp.gFree.n++
}
unlock(&sched.gFree.lock)
goto retry
}
gp := pp.gFree.pop()
if gp == nil {
return nil
}
pp.gFree.n--
if gp.stack.lo != 0 && gp.stack.hi-gp.stack.lo != uintptr(startingStackSize) {
// Deallocate old stack. We kept it in gfput because it was the
// right size when the goroutine was put on the free list, but
// the right size has changed since then.
systemstack(func() {
stackfree(gp.stack)
gp.stack.lo = 0
gp.stack.hi = 0
gp.stackguard0 = 0
})
}
if gp.stack.lo == 0 {
// Stack was deallocated in gfput or just above. Allocate a new one.
systemstack(func() {
gp.stack = stackalloc(startingStackSize)
})
gp.stackguard0 = gp.stack.lo + _StackGuard
} else {
if raceenabled {
racemalloc(unsafe.Pointer(gp.stack.lo), gp.stack.hi-gp.stack.lo)
}
if msanenabled {
msanmalloc(unsafe.Pointer(gp.stack.lo), gp.stack.hi-gp.stack.lo)
}
if asanenabled {
asanunpoison(unsafe.Pointer(gp.stack.lo), gp.stack.hi-gp.stack.lo)
}
}
return gp
}
// Purge all cached G's from gfree list to the global list.
func gfpurge(pp *p) {
var (
inc int32
stackQ gQueue
noStackQ gQueue
)
for !pp.gFree.empty() {
gp := pp.gFree.pop()
pp.gFree.n--
if gp.stack.lo == 0 {
noStackQ.push(gp)
} else {
stackQ.push(gp)
}
inc++
}
lock(&sched.gFree.lock)
sched.gFree.noStack.pushAll(noStackQ)
sched.gFree.stack.pushAll(stackQ)
sched.gFree.n += inc
unlock(&sched.gFree.lock)
}
// Breakpoint executes a breakpoint trap.
func Breakpoint() {
breakpoint()
}
// dolockOSThread is called by LockOSThread and lockOSThread below
// after they modify m.locked. Do not allow preemption during this call,
// or else the m might be different in this function than in the caller.
//
//go:nosplit
func dolockOSThread() {
if GOARCH == "wasm" {
return // no threads on wasm yet
}
gp := getg()
gp.m.lockedg.set(gp)
gp.lockedm.set(gp.m)
}
//go:nosplit
// LockOSThread wires the calling goroutine to its current operating system thread.
// The calling goroutine will always execute in that thread,
// and no other goroutine will execute in it,
// until the calling goroutine has made as many calls to
// UnlockOSThread as to LockOSThread.
// If the calling goroutine exits without unlocking the thread,
// the thread will be terminated.
//
// All init functions are run on the startup thread. Calling LockOSThread
// from an init function will cause the main function to be invoked on
// that thread.
//
// A goroutine should call LockOSThread before calling OS services or
// non-Go library functions that depend on per-thread state.
func LockOSThread() {
if atomic.Load(&newmHandoff.haveTemplateThread) == 0 && GOOS != "plan9" {
// If we need to start a new thread from the locked
// thread, we need the template thread. Start it now
// while we're in a known-good state.
startTemplateThread()
}
gp := getg()
gp.m.lockedExt++
if gp.m.lockedExt == 0 {
gp.m.lockedExt--
panic("LockOSThread nesting overflow")
}
dolockOSThread()
}
//go:nosplit
func lockOSThread() {
getg().m.lockedInt++
dolockOSThread()
}
// dounlockOSThread is called by UnlockOSThread and unlockOSThread below
// after they update m->locked. Do not allow preemption during this call,
// or else the m might be in different in this function than in the caller.
//
//go:nosplit
func dounlockOSThread() {
if GOARCH == "wasm" {
return // no threads on wasm yet
}
gp := getg()
if gp.m.lockedInt != 0 || gp.m.lockedExt != 0 {
return
}
gp.m.lockedg = 0
gp.lockedm = 0
}
//go:nosplit
// UnlockOSThread undoes an earlier call to LockOSThread.
// If this drops the number of active LockOSThread calls on the
// calling goroutine to zero, it unwires the calling goroutine from
// its fixed operating system thread.
// If there are no active LockOSThread calls, this is a no-op.
//
// Before calling UnlockOSThread, the caller must ensure that the OS
// thread is suitable for running other goroutines. If the caller made
// any permanent changes to the state of the thread that would affect
// other goroutines, it should not call this function and thus leave
// the goroutine locked to the OS thread until the goroutine (and
// hence the thread) exits.
func UnlockOSThread() {
gp := getg()
if gp.m.lockedExt == 0 {
return
}
gp.m.lockedExt--
dounlockOSThread()
}
//go:nosplit
func unlockOSThread() {
gp := getg()
if gp.m.lockedInt == 0 {
systemstack(badunlockosthread)
}
gp.m.lockedInt--
dounlockOSThread()
}
func badunlockosthread() {
throw("runtime: internal error: misuse of lockOSThread/unlockOSThread")
}
func gcount() int32 {
n := int32(atomic.Loaduintptr(&allglen)) - sched.gFree.n - sched.ngsys.Load()
for _, pp := range allp {
n -= pp.gFree.n
}
// All these variables can be changed concurrently, so the result can be inconsistent.
// But at least the current goroutine is running.
if n < 1 {
n = 1
}
return n
}
func mcount() int32 {
return int32(sched.mnext - sched.nmfreed)
}
var prof struct {
signalLock atomic.Uint32
// Must hold signalLock to write. Reads may be lock-free, but
// signalLock should be taken to synchronize with changes.
hz atomic.Int32
}
func _System() { _System() }
func _ExternalCode() { _ExternalCode() }
func _LostExternalCode() { _LostExternalCode() }
func _GC() { _GC() }
func _LostSIGPROFDuringAtomic64() { _LostSIGPROFDuringAtomic64() }
func _VDSO() { _VDSO() }
// Called if we receive a SIGPROF signal.
// Called by the signal handler, may run during STW.
//
//go:nowritebarrierrec
func sigprof(pc, sp, lr uintptr, gp *g, mp *m) {
if prof.hz.Load() == 0 {
return
}
// If mp.profilehz is 0, then profiling is not enabled for this thread.
// We must check this to avoid a deadlock between setcpuprofilerate
// and the call to cpuprof.add, below.
if mp != nil && mp.profilehz == 0 {
return
}
// On mips{,le}/arm, 64bit atomics are emulated with spinlocks, in
// runtime/internal/atomic. If SIGPROF arrives while the program is inside
// the critical section, it creates a deadlock (when writing the sample).
// As a workaround, create a counter of SIGPROFs while in critical section
// to store the count, and pass it to sigprof.add() later when SIGPROF is
// received from somewhere else (with _LostSIGPROFDuringAtomic64 as pc).
if GOARCH == "mips" || GOARCH == "mipsle" || GOARCH == "arm" {
if f := findfunc(pc); f.valid() {
if hasPrefix(funcname(f), "runtime/internal/atomic") {
cpuprof.lostAtomic++
return
}
}
if GOARCH == "arm" && goarm < 7 && GOOS == "linux" && pc&0xffff0000 == 0xffff0000 {
// runtime/internal/atomic functions call into kernel
// helpers on arm < 7. See
// runtime/internal/atomic/sys_linux_arm.s.
cpuprof.lostAtomic++
return
}
}
// Profiling runs concurrently with GC, so it must not allocate.
// Set a trap in case the code does allocate.
// Note that on windows, one thread takes profiles of all the
// other threads, so mp is usually not getg().m.
// In fact mp may not even be stopped.
// See golang.org/issue/17165.
getg().m.mallocing++
var stk [maxCPUProfStack]uintptr
n := 0
if mp.ncgo > 0 && mp.curg != nil && mp.curg.syscallpc != 0 && mp.curg.syscallsp != 0 {
cgoOff := 0
// Check cgoCallersUse to make sure that we are not
// interrupting other code that is fiddling with
// cgoCallers. We are running in a signal handler
// with all signals blocked, so we don't have to worry
// about any other code interrupting us.
if mp.cgoCallersUse.Load() == 0 && mp.cgoCallers != nil && mp.cgoCallers[0] != 0 {
for cgoOff < len(mp.cgoCallers) && mp.cgoCallers[cgoOff] != 0 {
cgoOff++
}
copy(stk[:], mp.cgoCallers[:cgoOff])
mp.cgoCallers[0] = 0
}
// Collect Go stack that leads to the cgo call.
n = gentraceback(mp.curg.syscallpc, mp.curg.syscallsp, 0, mp.curg, 0, &stk[cgoOff], len(stk)-cgoOff, nil, nil, 0)
if n > 0 {
n += cgoOff
}
} else if usesLibcall() && mp.libcallg != 0 && mp.libcallpc != 0 && mp.libcallsp != 0 {
// Libcall, i.e. runtime syscall on windows.
// Collect Go stack that leads to the call.
n = gentraceback(mp.libcallpc, mp.libcallsp, 0, mp.libcallg.ptr(), 0, &stk[n], len(stk[n:]), nil, nil, 0)
} else if mp != nil && mp.vdsoSP != 0 {
// VDSO call, e.g. nanotime1 on Linux.
// Collect Go stack that leads to the call.
n = gentraceback(mp.vdsoPC, mp.vdsoSP, 0, gp, 0, &stk[n], len(stk[n:]), nil, nil, _TraceJumpStack)
} else {
n = gentraceback(pc, sp, lr, gp, 0, &stk[0], len(stk), nil, nil, _TraceTrap|_TraceJumpStack)
}
if n <= 0 {
// Normal traceback is impossible or has failed.
// Account it against abstract "System" or "GC".
n = 2
if inVDSOPage(pc) {
pc = abi.FuncPCABIInternal(_VDSO) + sys.PCQuantum
} else if pc > firstmoduledata.etext {
// "ExternalCode" is better than "etext".
pc = abi.FuncPCABIInternal(_ExternalCode) + sys.PCQuantum
}
stk[0] = pc
if mp.preemptoff != "" {
stk[1] = abi.FuncPCABIInternal(_GC) + sys.PCQuantum
} else {
stk[1] = abi.FuncPCABIInternal(_System) + sys.PCQuantum
}
}
if prof.hz.Load() != 0 {
// Note: it can happen on Windows that we interrupted a system thread
// with no g, so gp could nil. The other nil checks are done out of
// caution, but not expected to be nil in practice.
var tagPtr *unsafe.Pointer
if gp != nil && gp.m != nil && gp.m.curg != nil {
tagPtr = &gp.m.curg.labels
}
cpuprof.add(tagPtr, stk[:n])
gprof := gp
var pp *p
if gp != nil && gp.m != nil {
if gp.m.curg != nil {
gprof = gp.m.curg
}
pp = gp.m.p.ptr()
}
traceCPUSample(gprof, pp, stk[:n])
}
getg().m.mallocing--
}
// setcpuprofilerate sets the CPU profiling rate to hz times per second.
// If hz <= 0, setcpuprofilerate turns off CPU profiling.
func setcpuprofilerate(hz int32) {
// Force sane arguments.
if hz < 0 {
hz = 0
}
// Disable preemption, otherwise we can be rescheduled to another thread
// that has profiling enabled.
gp := getg()
gp.m.locks++
// Stop profiler on this thread so that it is safe to lock prof.
// if a profiling signal came in while we had prof locked,
// it would deadlock.
setThreadCPUProfiler(0)
for !prof.signalLock.CompareAndSwap(0, 1) {
osyield()
}
if prof.hz.Load() != hz {
setProcessCPUProfiler(hz)
prof.hz.Store(hz)
}
prof.signalLock.Store(0)
lock(&sched.lock)
sched.profilehz = hz
unlock(&sched.lock)
if hz != 0 {
setThreadCPUProfiler(hz)
}
gp.m.locks--
}
// init initializes pp, which may be a freshly allocated p or a
// previously destroyed p, and transitions it to status _Pgcstop.
func (pp *p) init(id int32) {
pp.id = id
pp.status = _Pgcstop
pp.sudogcache = pp.sudogbuf[:0]
pp.deferpool = pp.deferpoolbuf[:0]
pp.wbBuf.reset()
if pp.mcache == nil {
if id == 0 {
if mcache0 == nil {
throw("missing mcache?")
}
// Use the bootstrap mcache0. Only one P will get
// mcache0: the one with ID 0.
pp.mcache = mcache0
} else {
pp.mcache = allocmcache()
}
}
if raceenabled && pp.raceprocctx == 0 {
if id == 0 {
pp.raceprocctx = raceprocctx0
raceprocctx0 = 0 // bootstrap
} else {
pp.raceprocctx = raceproccreate()
}
}
lockInit(&pp.timersLock, lockRankTimers)
// This P may get timers when it starts running. Set the mask here
// since the P may not go through pidleget (notably P 0 on startup).
timerpMask.set(id)
// Similarly, we may not go through pidleget before this P starts
// running if it is P 0 on startup.
idlepMask.clear(id)
}
// destroy releases all of the resources associated with pp and
// transitions it to status _Pdead.
//
// sched.lock must be held and the world must be stopped.
func (pp *p) destroy() {
assertLockHeld(&sched.lock)
assertWorldStopped()
// Move all runnable goroutines to the global queue
for pp.runqhead != pp.runqtail {
// Pop from tail of local queue
pp.runqtail--
gp := pp.runq[pp.runqtail%uint32(len(pp.runq))].ptr()
// Push onto head of global queue
globrunqputhead(gp)
}
if pp.runnext != 0 {
globrunqputhead(pp.runnext.ptr())
pp.runnext = 0
}
if len(pp.timers) > 0 {
plocal := getg().m.p.ptr()
// The world is stopped, but we acquire timersLock to
// protect against sysmon calling timeSleepUntil.
// This is the only case where we hold the timersLock of
// more than one P, so there are no deadlock concerns.
lock(&plocal.timersLock)
lock(&pp.timersLock)
moveTimers(plocal, pp.timers)
pp.timers = nil
pp.numTimers.Store(0)
pp.deletedTimers.Store(0)
pp.timer0When.Store(0)
unlock(&pp.timersLock)
unlock(&plocal.timersLock)
}
// Flush p's write barrier buffer.
if gcphase != _GCoff {
wbBufFlush1(pp)
pp.gcw.dispose()
}
for i := range pp.sudogbuf {
pp.sudogbuf[i] = nil
}
pp.sudogcache = pp.sudogbuf[:0]
for j := range pp.deferpoolbuf {
pp.deferpoolbuf[j] = nil
}
pp.deferpool = pp.deferpoolbuf[:0]
systemstack(func() {
for i := 0; i < pp.mspancache.len; i++ {
// Safe to call since the world is stopped.
mheap_.spanalloc.free(unsafe.Pointer(pp.mspancache.buf[i]))
}
pp.mspancache.len = 0
lock(&mheap_.lock)
pp.pcache.flush(&mheap_.pages)
unlock(&mheap_.lock)
})
freemcache(pp.mcache)
pp.mcache = nil
gfpurge(pp)
traceProcFree(pp)
if raceenabled {
if pp.timerRaceCtx != 0 {
// The race detector code uses a callback to fetch
// the proc context, so arrange for that callback
// to see the right thing.
// This hack only works because we are the only
// thread running.
mp := getg().m
phold := mp.p.ptr()
mp.p.set(pp)
racectxend(pp.timerRaceCtx)
pp.timerRaceCtx = 0
mp.p.set(phold)
}
raceprocdestroy(pp.raceprocctx)
pp.raceprocctx = 0
}
pp.gcAssistTime = 0
pp.status = _Pdead
}
// Change number of processors.
//
// sched.lock must be held, and the world must be stopped.
//
// gcworkbufs must not be being modified by either the GC or the write barrier
// code, so the GC must not be running if the number of Ps actually changes.
//
// Returns list of Ps with local work, they need to be scheduled by the caller.
func procresize(nprocs int32) *p {
assertLockHeld(&sched.lock)
assertWorldStopped()
old := gomaxprocs
if old < 0 || nprocs <= 0 {
throw("procresize: invalid arg")
}
if trace.enabled {
traceGomaxprocs(nprocs)
}
// update statistics
now := nanotime()
if sched.procresizetime != 0 {
sched.totaltime += int64(old) * (now - sched.procresizetime)
}
sched.procresizetime = now
maskWords := (nprocs + 31) / 32
// Grow allp if necessary.
if nprocs > int32(len(allp)) {
// Synchronize with retake, which could be running
// concurrently since it doesn't run on a P.
lock(&allpLock)
if nprocs <= int32(cap(allp)) {
allp = allp[:nprocs]
} else {
nallp := make([]*p, nprocs)
// Copy everything up to allp's cap so we
// never lose old allocated Ps.
copy(nallp, allp[:cap(allp)])
allp = nallp
}
if maskWords <= int32(cap(idlepMask)) {
idlepMask = idlepMask[:maskWords]
timerpMask = timerpMask[:maskWords]
} else {
nidlepMask := make([]uint32, maskWords)
// No need to copy beyond len, old Ps are irrelevant.
copy(nidlepMask, idlepMask)
idlepMask = nidlepMask
ntimerpMask := make([]uint32, maskWords)
copy(ntimerpMask, timerpMask)
timerpMask = ntimerpMask
}
unlock(&allpLock)
}
// initialize new P's
for i := old; i < nprocs; i++ {
pp := allp[i]
if pp == nil {
pp = new(p)
}
pp.init(i)
atomicstorep(unsafe.Pointer(&allp[i]), unsafe.Pointer(pp))
}
gp := getg()
if gp.m.p != 0 && gp.m.p.ptr().id < nprocs {
// continue to use the current P
gp.m.p.ptr().status = _Prunning
gp.m.p.ptr().mcache.prepareForSweep()
} else {
// release the current P and acquire allp[0].
//
// We must do this before destroying our current P
// because p.destroy itself has write barriers, so we
// need to do that from a valid P.
if gp.m.p != 0 {
if trace.enabled {
// Pretend that we were descheduled
// and then scheduled again to keep
// the trace sane.
traceGoSched()
traceProcStop(gp.m.p.ptr())
}
gp.m.p.ptr().m = 0
}
gp.m.p = 0
pp := allp[0]
pp.m = 0
pp.status = _Pidle
acquirep(pp)
if trace.enabled {
traceGoStart()
}
}
// g.m.p is now set, so we no longer need mcache0 for bootstrapping.
mcache0 = nil
// release resources from unused P's
for i := nprocs; i < old; i++ {
pp := allp[i]
pp.destroy()
// can't free P itself because it can be referenced by an M in syscall
}
// Trim allp.
if int32(len(allp)) != nprocs {
lock(&allpLock)
allp = allp[:nprocs]
idlepMask = idlepMask[:maskWords]
timerpMask = timerpMask[:maskWords]
unlock(&allpLock)
}
var runnablePs *p
for i := nprocs - 1; i >= 0; i-- {
pp := allp[i]
if gp.m.p.ptr() == pp {
continue
}
pp.status = _Pidle
if runqempty(pp) {
pidleput(pp, now)
} else {
pp.m.set(mget())
pp.link.set(runnablePs)
runnablePs = pp
}
}
stealOrder.reset(uint32(nprocs))
var int32p *int32 = &gomaxprocs // make compiler check that gomaxprocs is an int32
atomic.Store((*uint32)(unsafe.Pointer(int32p)), uint32(nprocs))
if old != nprocs {
// Notify the limiter that the amount of procs has changed.
gcCPULimiter.resetCapacity(now, nprocs)
}
return runnablePs
}
// Associate p and the current m.
//
// This function is allowed to have write barriers even if the caller
// isn't because it immediately acquires pp.
//
//go:yeswritebarrierrec
func acquirep(pp *p) {
// Do the part that isn't allowed to have write barriers.
wirep(pp)
// Have p; write barriers now allowed.
// Perform deferred mcache flush before this P can allocate
// from a potentially stale mcache.
pp.mcache.prepareForSweep()
if trace.enabled {
traceProcStart()
}
}
// wirep is the first step of acquirep, which actually associates the
// current M to pp. This is broken out so we can disallow write
// barriers for this part, since we don't yet have a P.
//
//go:nowritebarrierrec
//go:nosplit
func wirep(pp *p) {
gp := getg()
if gp.m.p != 0 {
throw("wirep: already in go")
}
if pp.m != 0 || pp.status != _Pidle {
id := int64(0)
if pp.m != 0 {
id = pp.m.ptr().id
}
print("wirep: p->m=", pp.m, "(", id, ") p->status=", pp.status, "\n")
throw("wirep: invalid p state")
}
gp.m.p.set(pp)
pp.m.set(gp.m)
pp.status = _Prunning
}
// Disassociate p and the current m.
func releasep() *p {
gp := getg()
if gp.m.p == 0 {
throw("releasep: invalid arg")
}
pp := gp.m.p.ptr()
if pp.m.ptr() != gp.m || pp.status != _Prunning {
print("releasep: m=", gp.m, " m->p=", gp.m.p.ptr(), " p->m=", hex(pp.m), " p->status=", pp.status, "\n")
throw("releasep: invalid p state")
}
if trace.enabled {
traceProcStop(gp.m.p.ptr())
}
gp.m.p = 0
pp.m = 0
pp.status = _Pidle
return pp
}
func incidlelocked(v int32) {
lock(&sched.lock)
sched.nmidlelocked += v
if v > 0 {
checkdead()
}
unlock(&sched.lock)
}
// Check for deadlock situation.
// The check is based on number of running M's, if 0 -> deadlock.
// sched.lock must be held.
func checkdead() {
assertLockHeld(&sched.lock)
// For -buildmode=c-shared or -buildmode=c-archive it's OK if
// there are no running goroutines. The calling program is
// assumed to be running.
if islibrary || isarchive {
return
}
// If we are dying because of a signal caught on an already idle thread,
// freezetheworld will cause all running threads to block.
// And runtime will essentially enter into deadlock state,
// except that there is a thread that will call exit soon.
if panicking.Load() > 0 {
return
}
// If we are not running under cgo, but we have an extra M then account
// for it. (It is possible to have an extra M on Windows without cgo to
// accommodate callbacks created by syscall.NewCallback. See issue #6751
// for details.)
var run0 int32
if !iscgo && cgoHasExtraM {
mp := lockextra(true)
haveExtraM := extraMCount > 0
unlockextra(mp)
if haveExtraM {
run0 = 1
}
}
run := mcount() - sched.nmidle - sched.nmidlelocked - sched.nmsys
if run > run0 {
return
}
if run < 0 {
print("runtime: checkdead: nmidle=", sched.nmidle, " nmidlelocked=", sched.nmidlelocked, " mcount=", mcount(), " nmsys=", sched.nmsys, "\n")
throw("checkdead: inconsistent counts")
}
grunning := 0
forEachG(func(gp *g) {
if isSystemGoroutine(gp, false) {
return
}
s := readgstatus(gp)
switch s &^ _Gscan {
case _Gwaiting,
_Gpreempted:
grunning++
case _Grunnable,
_Grunning,
_Gsyscall:
print("runtime: checkdead: find g ", gp.goid, " in status ", s, "\n")
throw("checkdead: runnable g")
}
})
if grunning == 0 { // possible if main goroutine calls runtime·Goexit()
unlock(&sched.lock) // unlock so that GODEBUG=scheddetail=1 doesn't hang
fatal("no goroutines (main called runtime.Goexit) - deadlock!")
}
// Maybe jump time forward for playground.
if faketime != 0 {
if when := timeSleepUntil(); when < maxWhen {
faketime = when
// Start an M to steal the timer.
pp, _ := pidleget(faketime)
if pp == nil {
// There should always be a free P since
// nothing is running.
throw("checkdead: no p for timer")
}
mp := mget()
if mp == nil {
// There should always be a free M since
// nothing is running.
throw("checkdead: no m for timer")
}
// M must be spinning to steal. We set this to be
// explicit, but since this is the only M it would
// become spinning on its own anyways.
sched.nmspinning.Add(1)
mp.spinning = true
mp.nextp.set(pp)
notewakeup(&mp.park)
return
}
}
// There are no goroutines running, so we can look at the P's.
for _, pp := range allp {
if len(pp.timers) > 0 {
return
}
}
unlock(&sched.lock) // unlock so that GODEBUG=scheddetail=1 doesn't hang
fatal("all goroutines are asleep - deadlock!")
}
// forcegcperiod is the maximum time in nanoseconds between garbage
// collections. If we go this long without a garbage collection, one
// is forced to run.
//
// This is a variable for testing purposes. It normally doesn't change.
var forcegcperiod int64 = 2 * 60 * 1e9
// needSysmonWorkaround is true if the workaround for
// golang.org/issue/42515 is needed on NetBSD.
var needSysmonWorkaround bool = false
// Always runs without a P, so write barriers are not allowed.
//
//go:nowritebarrierrec
func sysmon() {
lock(&sched.lock)
sched.nmsys++
checkdead()
unlock(&sched.lock)
lasttrace := int64(0)
idle := 0 // how many cycles in succession we had not wokeup somebody
delay := uint32(0)
for {
if idle == 0 { // start with 20us sleep...
delay = 20
} else if idle > 50 { // start doubling the sleep after 1ms...
delay *= 2
}
if delay > 10*1000 { // up to 10ms
delay = 10 * 1000
}
usleep(delay)
// sysmon should not enter deep sleep if schedtrace is enabled so that
// it can print that information at the right time.
//
// It should also not enter deep sleep if there are any active P's so
// that it can retake P's from syscalls, preempt long running G's, and
// poll the network if all P's are busy for long stretches.
//
// It should wakeup from deep sleep if any P's become active either due
// to exiting a syscall or waking up due to a timer expiring so that it
// can resume performing those duties. If it wakes from a syscall it
// resets idle and delay as a bet that since it had retaken a P from a
// syscall before, it may need to do it again shortly after the
// application starts work again. It does not reset idle when waking
// from a timer to avoid adding system load to applications that spend
// most of their time sleeping.
now := nanotime()
if debug.schedtrace <= 0 && (sched.gcwaiting.Load() || sched.npidle.Load() == gomaxprocs) {
lock(&sched.lock)
if sched.gcwaiting.Load() || sched.npidle.Load() == gomaxprocs {
syscallWake := false
next := timeSleepUntil()
if next > now {
sched.sysmonwait.Store(true)
unlock(&sched.lock)
// Make wake-up period small enough
// for the sampling to be correct.
sleep := forcegcperiod / 2
if next-now < sleep {
sleep = next - now
}
shouldRelax := sleep >= osRelaxMinNS
if shouldRelax {
osRelax(true)
}
syscallWake = notetsleep(&sched.sysmonnote, sleep)
if shouldRelax {
osRelax(false)
}
lock(&sched.lock)
sched.sysmonwait.Store(false)
noteclear(&sched.sysmonnote)
}
if syscallWake {
idle = 0
delay = 20
}
}
unlock(&sched.lock)
}
lock(&sched.sysmonlock)
// Update now in case we blocked on sysmonnote or spent a long time
// blocked on schedlock or sysmonlock above.
now = nanotime()
// trigger libc interceptors if needed
if *cgo_yield != nil {
asmcgocall(*cgo_yield, nil)
}
// poll network if not polled for more than 10ms
lastpoll := sched.lastpoll.Load()
if netpollinited() && lastpoll != 0 && lastpoll+10*1000*1000 < now {
sched.lastpoll.CompareAndSwap(lastpoll, now)
list := netpoll(0) // non-blocking - returns list of goroutines
if !list.empty() {
// Need to decrement number of idle locked M's
// (pretending that one more is running) before injectglist.
// Otherwise it can lead to the following situation:
// injectglist grabs all P's but before it starts M's to run the P's,
// another M returns from syscall, finishes running its G,
// observes that there is no work to do and no other running M's
// and reports deadlock.
incidlelocked(-1)
injectglist(&list)
incidlelocked(1)
}
}
if GOOS == "netbsd" && needSysmonWorkaround {
// netpoll is responsible for waiting for timer
// expiration, so we typically don't have to worry
// about starting an M to service timers. (Note that
// sleep for timeSleepUntil above simply ensures sysmon
// starts running again when that timer expiration may
// cause Go code to run again).
//
// However, netbsd has a kernel bug that sometimes
// misses netpollBreak wake-ups, which can lead to
// unbounded delays servicing timers. If we detect this
// overrun, then startm to get something to handle the
// timer.
//
// See issue 42515 and
// https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=50094.
if next := timeSleepUntil(); next < now {
startm(nil, false)
}
}
if scavenger.sysmonWake.Load() != 0 {
// Kick the scavenger awake if someone requested it.
scavenger.wake()
}
// retake P's blocked in syscalls
// and preempt long running G's
if retake(now) != 0 {
idle = 0
} else {
idle++
}
// check if we need to force a GC
if t := (gcTrigger{kind: gcTriggerTime, now: now}); t.test() && forcegc.idle.Load() {
lock(&forcegc.lock)
forcegc.idle.Store(false)
var list gList
list.push(forcegc.g)
injectglist(&list)
unlock(&forcegc.lock)
}
if debug.schedtrace > 0 && lasttrace+int64(debug.schedtrace)*1000000 <= now {
lasttrace = now
schedtrace(debug.scheddetail > 0)
}
unlock(&sched.sysmonlock)
}
}
type sysmontick struct {
schedtick uint32
schedwhen int64
syscalltick uint32
syscallwhen int64
}
// forcePreemptNS is the time slice given to a G before it is
// preempted.
const forcePreemptNS = 10 * 1000 * 1000 // 10ms
func retake(now int64) uint32 {
n := 0
// Prevent allp slice changes. This lock will be completely
// uncontended unless we're already stopping the world.
lock(&allpLock)
// We can't use a range loop over allp because we may
// temporarily drop the allpLock. Hence, we need to re-fetch
// allp each time around the loop.
for i := 0; i < len(allp); i++ {
pp := allp[i]
if pp == nil {
// This can happen if procresize has grown
// allp but not yet created new Ps.
continue
}
pd := &pp.sysmontick
s := pp.status
sysretake := false
if s == _Prunning || s == _Psyscall {
// Preempt G if it's running for too long.
t := int64(pp.schedtick)
if int64(pd.schedtick) != t {
pd.schedtick = uint32(t)
pd.schedwhen = now
} else if pd.schedwhen+forcePreemptNS <= now {
preemptone(pp)
// In case of syscall, preemptone() doesn't
// work, because there is no M wired to P.
sysretake = true
}
}
if s == _Psyscall {
// Retake P from syscall if it's there for more than 1 sysmon tick (at least 20us).
t := int64(pp.syscalltick)
if !sysretake && int64(pd.syscalltick) != t {
pd.syscalltick = uint32(t)
pd.syscallwhen = now
continue
}
// On the one hand we don't want to retake Ps if there is no other work to do,
// but on the other hand we want to retake them eventually
// because they can prevent the sysmon thread from deep sleep.
if runqempty(pp) && sched.nmspinning.Load()+sched.npidle.Load() > 0 && pd.syscallwhen+10*1000*1000 > now {
continue
}
// Drop allpLock so we can take sched.lock.
unlock(&allpLock)
// Need to decrement number of idle locked M's
// (pretending that one more is running) before the CAS.
// Otherwise the M from which we retake can exit the syscall,
// increment nmidle and report deadlock.
incidlelocked(-1)
if atomic.Cas(&pp.status, s, _Pidle) {
if trace.enabled {
traceGoSysBlock(pp)
traceProcStop(pp)
}
n++
pp.syscalltick++
handoffp(pp)
}
incidlelocked(1)
lock(&allpLock)
}
}
unlock(&allpLock)
return uint32(n)
}
// Tell all goroutines that they have been preempted and they should stop.
// This function is purely best-effort. It can fail to inform a goroutine if a
// processor just started running it.
// No locks need to be held.
// Returns true if preemption request was issued to at least one goroutine.
func preemptall() bool {
res := false
for _, pp := range allp {
if pp.status != _Prunning {
continue
}
if preemptone(pp) {
res = true
}
}
return res
}
// Tell the goroutine running on processor P to stop.
// This function is purely best-effort. It can incorrectly fail to inform the
// goroutine. It can inform the wrong goroutine. Even if it informs the
// correct goroutine, that goroutine might ignore the request if it is
// simultaneously executing newstack.
// No lock needs to be held.
// Returns true if preemption request was issued.
// The actual preemption will happen at some point in the future
// and will be indicated by the gp->status no longer being
// Grunning
func preemptone(pp *p) bool {
mp := pp.m.ptr()
if mp == nil || mp == getg().m {
return false
}
gp := mp.curg
if gp == nil || gp == mp.g0 {
return false
}
gp.preempt = true
// Every call in a goroutine checks for stack overflow by
// comparing the current stack pointer to gp->stackguard0.
// Setting gp->stackguard0 to StackPreempt folds
// preemption into the normal stack overflow check.
gp.stackguard0 = stackPreempt
// Request an async preemption of this P.
if preemptMSupported && debug.asyncpreemptoff == 0 {
pp.preempt = true
preemptM(mp)
}
return true
}
var starttime int64
func schedtrace(detailed bool) {
now := nanotime()
if starttime == 0 {
starttime = now
}
lock(&sched.lock)
print("SCHED ", (now-starttime)/1e6, "ms: gomaxprocs=", gomaxprocs, " idleprocs=", sched.npidle.Load(), " threads=", mcount(), " spinningthreads=", sched.nmspinning.Load(), " needspinning=", sched.needspinning.Load(), " idlethreads=", sched.nmidle, " runqueue=", sched.runqsize)
if detailed {
print(" gcwaiting=", sched.gcwaiting.Load(), " nmidlelocked=", sched.nmidlelocked, " stopwait=", sched.stopwait, " sysmonwait=", sched.sysmonwait.Load(), "\n")
}
// We must be careful while reading data from P's, M's and G's.
// Even if we hold schedlock, most data can be changed concurrently.
// E.g. (p->m ? p->m->id : -1) can crash if p->m changes from non-nil to nil.
for i, pp := range allp {
mp := pp.m.ptr()
h := atomic.Load(&pp.runqhead)
t := atomic.Load(&pp.runqtail)
if detailed {
print(" P", i, ": status=", pp.status, " schedtick=", pp.schedtick, " syscalltick=", pp.syscalltick, " m=")
if mp != nil {
print(mp.id)
} else {
print("nil")
}
print(" runqsize=", t-h, " gfreecnt=", pp.gFree.n, " timerslen=", len(pp.timers), "\n")
} else {
// In non-detailed mode format lengths of per-P run queues as:
// [len1 len2 len3 len4]
print(" ")
if i == 0 {
print("[")
}
print(t - h)
if i == len(allp)-1 {
print("]\n")
}
}
}
if !detailed {
unlock(&sched.lock)
return
}
for mp := allm; mp != nil; mp = mp.alllink {
pp := mp.p.ptr()
print(" M", mp.id, ": p=")
if pp != nil {
print(pp.id)
} else {
print("nil")
}
print(" curg=")
if mp.curg != nil {
print(mp.curg.goid)
} else {
print("nil")
}
print(" mallocing=", mp.mallocing, " throwing=", mp.throwing, " preemptoff=", mp.preemptoff, " locks=", mp.locks, " dying=", mp.dying, " spinning=", mp.spinning, " blocked=", mp.blocked, " lockedg=")
if lockedg := mp.lockedg.ptr(); lockedg != nil {
print(lockedg.goid)
} else {
print("nil")
}
print("\n")
}
forEachG(func(gp *g) {
print(" G", gp.goid, ": status=", readgstatus(gp), "(", gp.waitreason.String(), ") m=")
if gp.m != nil {
print(gp.m.id)
} else {
print("nil")
}
print(" lockedm=")
if lockedm := gp.lockedm.ptr(); lockedm != nil {
print(lockedm.id)
} else {
print("nil")
}
print("\n")
})
unlock(&sched.lock)
}
// schedEnableUser enables or disables the scheduling of user
// goroutines.
//
// This does not stop already running user goroutines, so the caller
// should first stop the world when disabling user goroutines.
func schedEnableUser(enable bool) {
lock(&sched.lock)
if sched.disable.user == !enable {
unlock(&sched.lock)
return
}
sched.disable.user = !enable
if enable {
n := sched.disable.n
sched.disable.n = 0
globrunqputbatch(&sched.disable.runnable, n)
unlock(&sched.lock)
for ; n != 0 && sched.npidle.Load() != 0; n-- {
startm(nil, false)
}
} else {
unlock(&sched.lock)
}
}
// schedEnabled reports whether gp should be scheduled. It returns
// false is scheduling of gp is disabled.
//
// sched.lock must be held.
func schedEnabled(gp *g) bool {
assertLockHeld(&sched.lock)
if sched.disable.user {
return isSystemGoroutine(gp, true)
}
return true
}
// Put mp on midle list.
// sched.lock must be held.
// May run during STW, so write barriers are not allowed.
//
//go:nowritebarrierrec
func mput(mp *m) {
assertLockHeld(&sched.lock)
mp.schedlink = sched.midle
sched.midle.set(mp)
sched.nmidle++
checkdead()
}
// Try to get an m from midle list.
// sched.lock must be held.
// May run during STW, so write barriers are not allowed.
//
//go:nowritebarrierrec
func mget() *m {
assertLockHeld(&sched.lock)
mp := sched.midle.ptr()
if mp != nil {
sched.midle = mp.schedlink
sched.nmidle--
}
return mp
}
// Put gp on the global runnable queue.
// sched.lock must be held.
// May run during STW, so write barriers are not allowed.
//
//go:nowritebarrierrec
func globrunqput(gp *g) {
assertLockHeld(&sched.lock)
sched.runq.pushBack(gp)
sched.runqsize++
}
// Put gp at the head of the global runnable queue.
// sched.lock must be held.
// May run during STW, so write barriers are not allowed.
//
//go:nowritebarrierrec
func globrunqputhead(gp *g) {
assertLockHeld(&sched.lock)
sched.runq.push(gp)
sched.runqsize++
}
// Put a batch of runnable goroutines on the global runnable queue.
// This clears *batch.
// sched.lock must be held.
// May run during STW, so write barriers are not allowed.
//
//go:nowritebarrierrec
func globrunqputbatch(batch *gQueue, n int32) {
assertLockHeld(&sched.lock)
sched.runq.pushBackAll(*batch)
sched.runqsize += n
*batch = gQueue{}
}
// Try get a batch of G's from the global runnable queue.
// sched.lock must be held.
func globrunqget(pp *p, max int32) *g {
assertLockHeld(&sched.lock)
if sched.runqsize == 0 {
return nil
}
n := sched.runqsize/gomaxprocs + 1
if n > sched.runqsize {
n = sched.runqsize
}
if max > 0 && n > max {
n = max
}
if n > int32(len(pp.runq))/2 {
n = int32(len(pp.runq)) / 2
}
sched.runqsize -= n
gp := sched.runq.pop()
n--
for ; n > 0; n-- {
gp1 := sched.runq.pop()
runqput(pp, gp1, false)
}
return gp
}
// pMask is an atomic bitstring with one bit per P.
type pMask []uint32
// read returns true if P id's bit is set.
func (p pMask) read(id uint32) bool {
word := id / 32
mask := uint32(1) << (id % 32)
return (atomic.Load(&p[word]) & mask) != 0
}
// set sets P id's bit.
func (p pMask) set(id int32) {
word := id / 32
mask := uint32(1) << (id % 32)
atomic.Or(&p[word], mask)
}
// clear clears P id's bit.
func (p pMask) clear(id int32) {
word := id / 32
mask := uint32(1) << (id % 32)
atomic.And(&p[word], ^mask)
}
// updateTimerPMask clears pp's timer mask if it has no timers on its heap.
//
// Ideally, the timer mask would be kept immediately consistent on any timer
// operations. Unfortunately, updating a shared global data structure in the
// timer hot path adds too much overhead in applications frequently switching
// between no timers and some timers.
//
// As a compromise, the timer mask is updated only on pidleget / pidleput. A
// running P (returned by pidleget) may add a timer at any time, so its mask
// must be set. An idle P (passed to pidleput) cannot add new timers while
// idle, so if it has no timers at that time, its mask may be cleared.
//
// Thus, we get the following effects on timer-stealing in findrunnable:
//
// - Idle Ps with no timers when they go idle are never checked in findrunnable
// (for work- or timer-stealing; this is the ideal case).
// - Running Ps must always be checked.
// - Idle Ps whose timers are stolen must continue to be checked until they run
// again, even after timer expiration.
//
// When the P starts running again, the mask should be set, as a timer may be
// added at any time.
//
// TODO(prattmic): Additional targeted updates may improve the above cases.
// e.g., updating the mask when stealing a timer.
func updateTimerPMask(pp *p) {
if pp.numTimers.Load() > 0 {
return
}
// Looks like there are no timers, however another P may transiently
// decrement numTimers when handling a timerModified timer in
// checkTimers. We must take timersLock to serialize with these changes.
lock(&pp.timersLock)
if pp.numTimers.Load() == 0 {
timerpMask.clear(pp.id)
}
unlock(&pp.timersLock)
}
// pidleput puts p on the _Pidle list. now must be a relatively recent call
// to nanotime or zero. Returns now or the current time if now was zero.
//
// This releases ownership of p. Once sched.lock is released it is no longer
// safe to use p.
//
// sched.lock must be held.
//
// May run during STW, so write barriers are not allowed.
//
//go:nowritebarrierrec
func pidleput(pp *p, now int64) int64 {
assertLockHeld(&sched.lock)
if !runqempty(pp) {
throw("pidleput: P has non-empty run queue")
}
if now == 0 {
now = nanotime()
}
updateTimerPMask(pp) // clear if there are no timers.
idlepMask.set(pp.id)
pp.link = sched.pidle
sched.pidle.set(pp)
sched.npidle.Add(1)
if !pp.limiterEvent.start(limiterEventIdle, now) {
throw("must be able to track idle limiter event")
}
return now
}
// pidleget tries to get a p from the _Pidle list, acquiring ownership.
//
// sched.lock must be held.
//
// May run during STW, so write barriers are not allowed.
//
//go:nowritebarrierrec
func pidleget(now int64) (*p, int64) {
assertLockHeld(&sched.lock)
pp := sched.pidle.ptr()
if pp != nil {
// Timer may get added at any time now.
if now == 0 {
now = nanotime()
}
timerpMask.set(pp.id)
idlepMask.clear(pp.id)
sched.pidle = pp.link
sched.npidle.Add(-1)
pp.limiterEvent.stop(limiterEventIdle, now)
}
return pp, now
}
// pidlegetSpinning tries to get a p from the _Pidle list, acquiring ownership.
// This is called by spinning Ms (or callers than need a spinning M) that have
// found work. If no P is available, this must synchronized with non-spinning
// Ms that may be preparing to drop their P without discovering this work.
//
// sched.lock must be held.
//
// May run during STW, so write barriers are not allowed.
//
//go:nowritebarrierrec
func pidlegetSpinning(now int64) (*p, int64) {
assertLockHeld(&sched.lock)
pp, now := pidleget(now)
if pp == nil {
// See "Delicate dance" comment in findrunnable. We found work
// that we cannot take, we must synchronize with non-spinning
// Ms that may be preparing to drop their P.
sched.needspinning.Store(1)
return nil, now
}
return pp, now
}
// runqempty reports whether pp has no Gs on its local run queue.
// It never returns true spuriously.
func runqempty(pp *p) bool {
// Defend against a race where 1) pp has G1 in runqnext but runqhead == runqtail,
// 2) runqput on pp kicks G1 to the runq, 3) runqget on pp empties runqnext.
// Simply observing that runqhead == runqtail and then observing that runqnext == nil
// does not mean the queue is empty.
for {
head := atomic.Load(&pp.runqhead)
tail := atomic.Load(&pp.runqtail)
runnext := atomic.Loaduintptr((*uintptr)(unsafe.Pointer(&pp.runnext)))
if tail == atomic.Load(&pp.runqtail) {
return head == tail && runnext == 0
}
}
}
// To shake out latent assumptions about scheduling order,
// we introduce some randomness into scheduling decisions
// when running with the race detector.
// The need for this was made obvious by changing the
// (deterministic) scheduling order in Go 1.5 and breaking
// many poorly-written tests.
// With the randomness here, as long as the tests pass
// consistently with -race, they shouldn't have latent scheduling
// assumptions.
const randomizeScheduler = raceenabled
// runqput tries to put g on the local runnable queue.
// If next is false, runqput adds g to the tail of the runnable queue.
// If next is true, runqput puts g in the pp.runnext slot.
// If the run queue is full, runnext puts g on the global queue.
// Executed only by the owner P.
func runqput(pp *p, gp *g, next bool) {
if randomizeScheduler && next && fastrandn(2) == 0 {
next = false
}
if next {
retryNext:
oldnext := pp.runnext
if !pp.runnext.cas(oldnext, guintptr(unsafe.Pointer(gp))) {
goto retryNext
}
if oldnext == 0 {
return
}
// Kick the old runnext out to the regular run queue.
gp = oldnext.ptr()
}
retry:
h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with consumers
t := pp.runqtail
if t-h < uint32(len(pp.runq)) {
pp.runq[t%uint32(len(pp.runq))].set(gp)
atomic.StoreRel(&pp.runqtail, t+1) // store-release, makes the item available for consumption
return
}
if runqputslow(pp, gp, h, t) {
return
}
// the queue is not full, now the put above must succeed
goto retry
}
// Put g and a batch of work from local runnable queue on global queue.
// Executed only by the owner P.
func runqputslow(pp *p, gp *g, h, t uint32) bool {
var batch [len(pp.runq)/2 + 1]*g
// First, grab a batch from local queue.
n := t - h
n = n / 2
if n != uint32(len(pp.runq)/2) {
throw("runqputslow: queue is not full")
}
for i := uint32(0); i < n; i++ {
batch[i] = pp.runq[(h+i)%uint32(len(pp.runq))].ptr()
}
if !atomic.CasRel(&pp.runqhead, h, h+n) { // cas-release, commits consume
return false
}
batch[n] = gp
if randomizeScheduler {
for i := uint32(1); i <= n; i++ {
j := fastrandn(i + 1)
batch[i], batch[j] = batch[j], batch[i]
}
}
// Link the goroutines.
for i := uint32(0); i < n; i++ {
batch[i].schedlink.set(batch[i+1])
}
var q gQueue
q.head.set(batch[0])
q.tail.set(batch[n])
// Now put the batch on global queue.
lock(&sched.lock)
globrunqputbatch(&q, int32(n+1))
unlock(&sched.lock)
return true
}
// runqputbatch tries to put all the G's on q on the local runnable queue.
// If the queue is full, they are put on the global queue; in that case
// this will temporarily acquire the scheduler lock.
// Executed only by the owner P.
func runqputbatch(pp *p, q *gQueue, qsize int) {
h := atomic.LoadAcq(&pp.runqhead)
t := pp.runqtail
n := uint32(0)
for !q.empty() && t-h < uint32(len(pp.runq)) {
gp := q.pop()
pp.runq[t%uint32(len(pp.runq))].set(gp)
t++
n++
}
qsize -= int(n)
if randomizeScheduler {
off := func(o uint32) uint32 {
return (pp.runqtail + o) % uint32(len(pp.runq))
}
for i := uint32(1); i < n; i++ {
j := fastrandn(i + 1)
pp.runq[off(i)], pp.runq[off(j)] = pp.runq[off(j)], pp.runq[off(i)]
}
}
atomic.StoreRel(&pp.runqtail, t)
if !q.empty() {
lock(&sched.lock)
globrunqputbatch(q, int32(qsize))
unlock(&sched.lock)
}
}
// Get g from local runnable queue.
// If inheritTime is true, gp should inherit the remaining time in the
// current time slice. Otherwise, it should start a new time slice.
// Executed only by the owner P.
func runqget(pp *p) (gp *g, inheritTime bool) {
// If there's a runnext, it's the next G to run.
next := pp.runnext
// If the runnext is non-0 and the CAS fails, it could only have been stolen by another P,
// because other Ps can race to set runnext to 0, but only the current P can set it to non-0.
// Hence, there's no need to retry this CAS if it fails.
if next != 0 && pp.runnext.cas(next, 0) {
return next.ptr(), true
}
for {
h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with other consumers
t := pp.runqtail
if t == h {
return nil, false
}
gp := pp.runq[h%uint32(len(pp.runq))].ptr()
if atomic.CasRel(&pp.runqhead, h, h+1) { // cas-release, commits consume
return gp, false
}
}
}
// runqdrain drains the local runnable queue of pp and returns all goroutines in it.
// Executed only by the owner P.
func runqdrain(pp *p) (drainQ gQueue, n uint32) {
oldNext := pp.runnext
if oldNext != 0 && pp.runnext.cas(oldNext, 0) {
drainQ.pushBack(oldNext.ptr())
n++
}
retry:
h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with other consumers
t := pp.runqtail
qn := t - h
if qn == 0 {
return
}
if qn > uint32(len(pp.runq)) { // read inconsistent h and t
goto retry
}
if !atomic.CasRel(&pp.runqhead, h, h+qn) { // cas-release, commits consume
goto retry
}
// We've inverted the order in which it gets G's from the local P's runnable queue
// and then advances the head pointer because we don't want to mess up the statuses of G's
// while runqdrain() and runqsteal() are running in parallel.
// Thus we should advance the head pointer before draining the local P into a gQueue,
// so that we can update any gp.schedlink only after we take the full ownership of G,
// meanwhile, other P's can't access to all G's in local P's runnable queue and steal them.
// See https://groups.google.com/g/golang-dev/c/0pTKxEKhHSc/m/6Q85QjdVBQAJ for more details.
for i := uint32(0); i < qn; i++ {
gp := pp.runq[(h+i)%uint32(len(pp.runq))].ptr()
drainQ.pushBack(gp)
n++
}
return
}
// Grabs a batch of goroutines from pp's runnable queue into batch.
// Batch is a ring buffer starting at batchHead.
// Returns number of grabbed goroutines.
// Can be executed by any P.
func runqgrab(pp *p, batch *[256]guintptr, batchHead uint32, stealRunNextG bool) uint32 {
for {
h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with other consumers
t := atomic.LoadAcq(&pp.runqtail) // load-acquire, synchronize with the producer
n := t - h
n = n - n/2
if n == 0 {
if stealRunNextG {
// Try to steal from pp.runnext.
if next := pp.runnext; next != 0 {
if pp.status == _Prunning {
// Sleep to ensure that pp isn't about to run the g
// we are about to steal.
// The important use case here is when the g running
// on pp ready()s another g and then almost
// immediately blocks. Instead of stealing runnext
// in this window, back off to give pp a chance to
// schedule runnext. This will avoid thrashing gs
// between different Ps.
// A sync chan send/recv takes ~50ns as of time of
// writing, so 3us gives ~50x overshoot.
if GOOS != "windows" && GOOS != "openbsd" && GOOS != "netbsd" {
usleep(3)
} else {
// On some platforms system timer granularity is
// 1-15ms, which is way too much for this
// optimization. So just yield.
osyield()
}
}
if !pp.runnext.cas(next, 0) {
continue
}
batch[batchHead%uint32(len(batch))] = next
return 1
}
}
return 0
}
if n > uint32(len(pp.runq)/2) { // read inconsistent h and t
continue
}
for i := uint32(0); i < n; i++ {
g := pp.runq[(h+i)%uint32(len(pp.runq))]
batch[(batchHead+i)%uint32(len(batch))] = g
}
if atomic.CasRel(&pp.runqhead, h, h+n) { // cas-release, commits consume
return n
}
}
}
// Steal half of elements from local runnable queue of p2
// and put onto local runnable queue of p.
// Returns one of the stolen elements (or nil if failed).
func runqsteal(pp, p2 *p, stealRunNextG bool) *g {
t := pp.runqtail
n := runqgrab(p2, &pp.runq, t, stealRunNextG)
if n == 0 {
return nil
}
n--
gp := pp.runq[(t+n)%uint32(len(pp.runq))].ptr()
if n == 0 {
return gp
}
h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with consumers
if t-h+n >= uint32(len(pp.runq)) {
throw("runqsteal: runq overflow")
}
atomic.StoreRel(&pp.runqtail, t+n) // store-release, makes the item available for consumption
return gp
}
// A gQueue is a dequeue of Gs linked through g.schedlink. A G can only
// be on one gQueue or gList at a time.
type gQueue struct {
head guintptr
tail guintptr
}
// empty reports whether q is empty.
func (q *gQueue) empty() bool {
return q.head == 0
}
// push adds gp to the head of q.
func (q *gQueue) push(gp *g) {
gp.schedlink = q.head
q.head.set(gp)
if q.tail == 0 {
q.tail.set(gp)
}
}
// pushBack adds gp to the tail of q.
func (q *gQueue) pushBack(gp *g) {
gp.schedlink = 0
if q.tail != 0 {
q.tail.ptr().schedlink.set(gp)
} else {
q.head.set(gp)
}
q.tail.set(gp)
}
// pushBackAll adds all Gs in q2 to the tail of q. After this q2 must
// not be used.
func (q *gQueue) pushBackAll(q2 gQueue) {
if q2.tail == 0 {
return
}
q2.tail.ptr().schedlink = 0
if q.tail != 0 {
q.tail.ptr().schedlink = q2.head
} else {
q.head = q2.head
}
q.tail = q2.tail
}
// pop removes and returns the head of queue q. It returns nil if
// q is empty.
func (q *gQueue) pop() *g {
gp := q.head.ptr()
if gp != nil {
q.head = gp.schedlink
if q.head == 0 {
q.tail = 0
}
}
return gp
}
// popList takes all Gs in q and returns them as a gList.
func (q *gQueue) popList() gList {
stack := gList{q.head}
*q = gQueue{}
return stack
}
// A gList is a list of Gs linked through g.schedlink. A G can only be
// on one gQueue or gList at a time.
type gList struct {
head guintptr
}
// empty reports whether l is empty.
func (l *gList) empty() bool {
return l.head == 0
}
// push adds gp to the head of l.
func (l *gList) push(gp *g) {
gp.schedlink = l.head
l.head.set(gp)
}
// pushAll prepends all Gs in q to l.
func (l *gList) pushAll(q gQueue) {
if !q.empty() {
q.tail.ptr().schedlink = l.head
l.head = q.head
}
}
// pop removes and returns the head of l. If l is empty, it returns nil.
func (l *gList) pop() *g {
gp := l.head.ptr()
if gp != nil {
l.head = gp.schedlink
}
return gp
}
//go:linkname setMaxThreads runtime/debug.setMaxThreads
func setMaxThreads(in int) (out int) {
lock(&sched.lock)
out = int(sched.maxmcount)
if in > 0x7fffffff { // MaxInt32
sched.maxmcount = 0x7fffffff
} else {
sched.maxmcount = int32(in)
}
checkmcount()
unlock(&sched.lock)
return
}
//go:nosplit
func procPin() int {
gp := getg()
mp := gp.m
mp.locks++
return int(mp.p.ptr().id)
}
//go:nosplit
func procUnpin() {
gp := getg()
gp.m.locks--
}
//go:linkname sync_runtime_procPin sync.runtime_procPin
//go:nosplit
func sync_runtime_procPin() int {
return procPin()
}
//go:linkname sync_runtime_procUnpin sync.runtime_procUnpin
//go:nosplit
func sync_runtime_procUnpin() {
procUnpin()
}
//go:linkname sync_atomic_runtime_procPin sync/atomic.runtime_procPin
//go:nosplit
func sync_atomic_runtime_procPin() int {
return procPin()
}
//go:linkname sync_atomic_runtime_procUnpin sync/atomic.runtime_procUnpin
//go:nosplit
func sync_atomic_runtime_procUnpin() {
procUnpin()
}
// Active spinning for sync.Mutex.
//
//go:linkname sync_runtime_canSpin sync.runtime_canSpin
//go:nosplit
func sync_runtime_canSpin(i int) bool {
// sync.Mutex is cooperative, so we are conservative with spinning.
// Spin only few times and only if running on a multicore machine and
// GOMAXPROCS>1 and there is at least one other running P and local runq is empty.
// As opposed to runtime mutex we don't do passive spinning here,
// because there can be work on global runq or on other Ps.
if i >= active_spin || ncpu <= 1 || gomaxprocs <= sched.npidle.Load()+sched.nmspinning.Load()+1 {
return false
}
if p := getg().m.p.ptr(); !runqempty(p) {
return false
}
return true
}
//go:linkname sync_runtime_doSpin sync.runtime_doSpin
//go:nosplit
func sync_runtime_doSpin() {
procyield(active_spin_cnt)
}
var stealOrder randomOrder
// randomOrder/randomEnum are helper types for randomized work stealing.
// They allow to enumerate all Ps in different pseudo-random orders without repetitions.
// The algorithm is based on the fact that if we have X such that X and GOMAXPROCS
// are coprime, then a sequences of (i + X) % GOMAXPROCS gives the required enumeration.
type randomOrder struct {
count uint32
coprimes []uint32
}
type randomEnum struct {
i uint32
count uint32
pos uint32
inc uint32
}
func (ord *randomOrder) reset(count uint32) {
ord.count = count
ord.coprimes = ord.coprimes[:0]
for i := uint32(1); i <= count; i++ {
if gcd(i, count) == 1 {
ord.coprimes = append(ord.coprimes, i)
}
}
}
func (ord *randomOrder) start(i uint32) randomEnum {
return randomEnum{
count: ord.count,
pos: i % ord.count,
inc: ord.coprimes[i/ord.count%uint32(len(ord.coprimes))],
}
}
func (enum *randomEnum) done() bool {
return enum.i == enum.count
}
func (enum *randomEnum) next() {
enum.i++
enum.pos = (enum.pos + enum.inc) % enum.count
}
func (enum *randomEnum) position() uint32 {
return enum.pos
}
func gcd(a, b uint32) uint32 {
for b != 0 {
a, b = b, a%b
}
return a
}
// An initTask represents the set of initializations that need to be done for a package.
// Keep in sync with ../../test/initempty.go:initTask
type initTask struct {
// TODO: pack the first 3 fields more tightly?
state uintptr // 0 = uninitialized, 1 = in progress, 2 = done
ndeps uintptr
nfns uintptr
// followed by ndeps instances of an *initTask, one per package depended on
// followed by nfns pcs, one per init function to run
}
// inittrace stores statistics for init functions which are
// updated by malloc and newproc when active is true.
var inittrace tracestat
type tracestat struct {
active bool // init tracing activation status
id uint64 // init goroutine id
allocs uint64 // heap allocations
bytes uint64 // heap allocated bytes
}
func doInit(t *initTask) {
switch t.state {
case 2: // fully initialized
return
case 1: // initialization in progress
throw("recursive call during initialization - linker skew")
default: // not initialized yet
t.state = 1 // initialization in progress
for i := uintptr(0); i < t.ndeps; i++ {
p := add(unsafe.Pointer(t), (3+i)*goarch.PtrSize)
t2 := *(**initTask)(p)
doInit(t2)
}
if t.nfns == 0 {
t.state = 2 // initialization done
return
}
var (
start int64
before tracestat
)
if inittrace.active {
start = nanotime()
// Load stats non-atomically since tracinit is updated only by this init goroutine.
before = inittrace
}
firstFunc := add(unsafe.Pointer(t), (3+t.ndeps)*goarch.PtrSize)
for i := uintptr(0); i < t.nfns; i++ {
p := add(firstFunc, i*goarch.PtrSize)
f := *(*func())(unsafe.Pointer(&p))
f()
}
if inittrace.active {
end := nanotime()
// Load stats non-atomically since tracinit is updated only by this init goroutine.
after := inittrace
f := *(*func())(unsafe.Pointer(&firstFunc))
pkg := funcpkgpath(findfunc(abi.FuncPCABIInternal(f)))
var sbuf [24]byte
print("init ", pkg, " @")
print(string(fmtNSAsMS(sbuf[:], uint64(start-runtimeInitTime))), " ms, ")
print(string(fmtNSAsMS(sbuf[:], uint64(end-start))), " ms clock, ")
print(string(itoa(sbuf[:], after.bytes-before.bytes)), " bytes, ")
print(string(itoa(sbuf[:], after.allocs-before.allocs)), " allocs")
print("\n")
}
t.state = 2 // initialization done
}
}