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// Copyright 2009 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 (
// defined constants
const (
// G status
// Beyond indicating the general state of a G, the G status
// acts like a lock on the goroutine's stack (and hence its
// ability to execute user code).
// If you add to this list, add to the list
// of "okay during garbage collection" status
// in mgcmark.go too.
// TODO(austin): The _Gscan bit could be much lighter-weight.
// For example, we could choose not to run _Gscanrunnable
// goroutines found in the run queue, rather than CAS-looping
// until they become _Grunnable. And transitions like
// _Gscanwaiting -> _Gscanrunnable are actually okay because
// they don't affect stack ownership.
// _Gidle means this goroutine was just allocated and has not
// yet been initialized.
_Gidle = iota // 0
// _Grunnable means this goroutine is on a run queue. It is
// not currently executing user code. The stack is not owned.
_Grunnable // 1
// _Grunning means this goroutine may execute user code. The
// stack is owned by this goroutine. It is not on a run queue.
// It is assigned an M and a P (g.m and g.m.p are valid).
_Grunning // 2
// _Gsyscall means this goroutine is executing a system call.
// It is not executing user code. The stack is owned by this
// goroutine. It is not on a run queue. It is assigned an M.
_Gsyscall // 3
// _Gwaiting means this goroutine is blocked in the runtime.
// It is not executing user code. It is not on a run queue,
// but should be recorded somewhere (e.g., a channel wait
// queue) so it can be ready()d when necessary. The stack is
// not owned *except* that a channel operation may read or
// write parts of the stack under the appropriate channel
// lock. Otherwise, it is not safe to access the stack after a
// goroutine enters _Gwaiting (e.g., it may get moved).
_Gwaiting // 4
// _Gmoribund_unused is currently unused, but hardcoded in gdb
// scripts.
_Gmoribund_unused // 5
// _Gdead means this goroutine is currently unused. It may be
// just exited, on a free list, or just being initialized. It
// is not executing user code. It may or may not have a stack
// allocated. The G and its stack (if any) are owned by the M
// that is exiting the G or that obtained the G from the free
// list.
_Gdead // 6
// _Genqueue_unused is currently unused.
_Genqueue_unused // 7
// _Gcopystack means this goroutine's stack is being moved. It
// is not executing user code and is not on a run queue. The
// stack is owned by the goroutine that put it in _Gcopystack.
_Gcopystack // 8
// _Gpreempted means this goroutine stopped itself for a
// suspendG preemption. It is like _Gwaiting, but nothing is
// yet responsible for ready()ing it. Some suspendG must CAS
// the status to _Gwaiting to take responsibility for
// ready()ing this G.
_Gpreempted // 9
// _Gexitingsyscall means this goroutine is exiting from a
// system call. This is like _Gsyscall, but the GC should not
// scan its stack. Currently this is only used in exitsyscall0
// as a transient state when it drops the G.
_Gexitingsyscall // 10
// _Gscan combined with one of the above states other than
// _Grunning indicates that GC is scanning the stack. The
// goroutine is not executing user code and the stack is owned
// by the goroutine that set the _Gscan bit.
// _Gscanrunning is different: it is used to briefly block
// state transitions while GC signals the G to scan its own
// stack. This is otherwise like _Grunning.
// atomicstatus&~Gscan gives the state the goroutine will
// return to when the scan completes.
_Gscan = 0x1000
_Gscanrunnable = _Gscan + _Grunnable // 0x1001
_Gscanrunning = _Gscan + _Grunning // 0x1002
_Gscansyscall = _Gscan + _Gsyscall // 0x1003
_Gscanwaiting = _Gscan + _Gwaiting // 0x1004
_Gscanpreempted = _Gscan + _Gpreempted // 0x1009
const (
// P status
// _Pidle means a P is not being used to run user code or the
// scheduler. Typically, it's on the idle P list and available
// to the scheduler, but it may just be transitioning between
// other states.
// The P is owned by the idle list or by whatever is
// transitioning its state. Its run queue is empty.
_Pidle = iota
// _Prunning means a P is owned by an M and is being used to
// run user code or the scheduler. Only the M that owns this P
// is allowed to change the P's status from _Prunning. The M
// may transition the P to _Pidle (if it has no more work to
// do), _Psyscall (when entering a syscall), or _Pgcstop (to
// halt for the GC). The M may also hand ownership of the P
// off directly to another M (e.g., to schedule a locked G).
// _Psyscall means a P is not running user code. It has
// affinity to an M in a syscall but is not owned by it and
// may be stolen by another M. This is similar to _Pidle but
// uses lightweight transitions and maintains M affinity.
// Leaving _Psyscall must be done with a CAS, either to steal
// or retake the P. Note that there's an ABA hazard: even if
// an M successfully CASes its original P back to _Prunning
// after a syscall, it must understand the P may have been
// used by another M in the interim.
// _Pgcstop means a P is halted for STW and owned by the M
// that stopped the world. The M that stopped the world
// continues to use its P, even in _Pgcstop. Transitioning
// from _Prunning to _Pgcstop causes an M to release its P and
// park.
// The P retains its run queue and startTheWorld will restart
// the scheduler on Ps with non-empty run queues.
// _Pdead means a P is no longer used (GOMAXPROCS shrank). We
// reuse Ps if GOMAXPROCS increases. A dead P is mostly
// stripped of its resources, though a few things remain
// (e.g., trace buffers).
// Mutual exclusion locks. In the uncontended case,
// as fast as spin locks (just a few user-level instructions),
// but on the contention path they sleep in the kernel.
// A zeroed Mutex is unlocked (no need to initialize each lock).
// Initialization is helpful for static lock ranking, but not required.
type mutex struct {
// Empty struct if lock ranking is disabled, otherwise includes the lock rank
// Futex-based impl treats it as uint32 key,
// while sema-based impl as M* waitm.
// Used to be a union, but unions break precise GC.
key uintptr
// sleep and wakeup on one-time events.
// before any calls to notesleep or notewakeup,
// must call noteclear to initialize the Note.
// then, exactly one thread can call notesleep
// and exactly one thread can call notewakeup (once).
// once notewakeup has been called, the notesleep
// will return. future notesleep will return immediately.
// subsequent noteclear must be called only after
// previous notesleep has returned, e.g. it's disallowed
// to call noteclear straight after notewakeup.
// notetsleep is like notesleep but wakes up after
// a given number of nanoseconds even if the event
// has not yet happened. if a goroutine uses notetsleep to
// wake up early, it must wait to call noteclear until it
// can be sure that no other goroutine is calling
// notewakeup.
// notesleep/notetsleep are generally called on g0,
// notetsleepg is similar to notetsleep but is called on user g.
type note struct {
// Futex-based impl treats it as uint32 key,
// while sema-based impl as M* waitm.
// Used to be a union, but unions break precise GC.
key uintptr
type funcval struct {
fn uintptr
// variable-size, fn-specific data here
// The representation of a non-empty interface.
// See comment in iface.go for more details on this struct.
type iface struct {
tab unsafe.Pointer
data unsafe.Pointer
// The representation of an empty interface.
// See comment in iface.go for more details on this struct.
type eface struct {
_type *_type
data unsafe.Pointer
func efaceOf(ep *interface{}) *eface {
return (*eface)(unsafe.Pointer(ep))
// The guintptr, muintptr, and puintptr are all used to bypass write barriers.
// It is particularly important to avoid write barriers when the current P has
// been released, because the GC thinks the world is stopped, and an
// unexpected write barrier would not be synchronized with the GC,
// which can lead to a half-executed write barrier that has marked the object
// but not queued it. If the GC skips the object and completes before the
// queuing can occur, it will incorrectly free the object.
// We tried using special assignment functions invoked only when not
// holding a running P, but then some updates to a particular memory
// word went through write barriers and some did not. This breaks the
// write barrier shadow checking mode, and it is also scary: better to have
// a word that is completely ignored by the GC than to have one for which
// only a few updates are ignored.
// Gs and Ps are always reachable via true pointers in the
// allgs and allp lists or (during allocation before they reach those lists)
// from stack variables.
// Ms are always reachable via true pointers either from allm or
// freem. Unlike Gs and Ps we do free Ms, so it's important that
// nothing ever hold an muintptr across a safe point.
// A guintptr holds a goroutine pointer, but typed as a uintptr
// to bypass write barriers. It is used in the Gobuf goroutine state
// and in scheduling lists that are manipulated without a P.
// The Gobuf.g goroutine pointer is almost always updated by assembly code.
// In one of the few places it is updated by Go code - func save - it must be
// treated as a uintptr to avoid a write barrier being emitted at a bad time.
// Instead of figuring out how to emit the write barriers missing in the
// assembly manipulation, we change the type of the field to uintptr,
// so that it does not require write barriers at all.
// Goroutine structs are published in the allg list and never freed.
// That will keep the goroutine structs from being collected.
// There is never a time that Gobuf.g's contain the only references
// to a goroutine: the publishing of the goroutine in allg comes first.
// Goroutine pointers are also kept in non-GC-visible places like TLS,
// so I can't see them ever moving. If we did want to start moving data
// in the GC, we'd need to allocate the goroutine structs from an
// alternate arena. Using guintptr doesn't make that problem any worse.
type guintptr uintptr
func (gp guintptr) ptr() *g { return (*g)(unsafe.Pointer(gp)) }
func (gp *guintptr) set(g *g) { *gp = guintptr(unsafe.Pointer(g)) }
func (gp *guintptr) cas(old, new guintptr) bool {
return atomic.Casuintptr((*uintptr)(unsafe.Pointer(gp)), uintptr(old), uintptr(new))
// setGNoWB performs *gp = new without a write barrier.
// For times when it's impractical to use a guintptr.
func setGNoWB(gp **g, new *g) {
type puintptr uintptr
func (pp puintptr) ptr() *p { return (*p)(unsafe.Pointer(pp)) }
func (pp *puintptr) set(p *p) { *pp = puintptr(unsafe.Pointer(p)) }
// muintptr is a *m that is not tracked by the garbage collector.
// Because we do free Ms, there are some additional constrains on
// muintptrs:
// 1. Never hold an muintptr locally across a safe point.
// 2. Any muintptr in the heap must be owned by the M itself so it can
// ensure it is not in use when the last true *m is released.
type muintptr uintptr
func (mp muintptr) ptr() *m { return (*m)(unsafe.Pointer(mp)) }
func (mp *muintptr) set(m *m) { *mp = muintptr(unsafe.Pointer(m)) }
// setMNoWB performs *mp = new without a write barrier.
// For times when it's impractical to use an muintptr.
func setMNoWB(mp **m, new *m) {
// sudog represents a g in a wait list, such as for sending/receiving
// on a channel.
// sudog is necessary because the g ↔ synchronization object relation
// is many-to-many. A g can be on many wait lists, so there may be
// many sudogs for one g; and many gs may be waiting on the same
// synchronization object, so there may be many sudogs for one object.
// sudogs are allocated from a special pool. Use acquireSudog and
// releaseSudog to allocate and free them.
type sudog struct {
// The following fields are protected by the hchan.lock of the
// channel this sudog is blocking on. shrinkstack depends on
// this for sudogs involved in channel ops.
g *g
next *sudog
prev *sudog
elem unsafe.Pointer // data element (may point to stack)
// The following fields are never accessed concurrently.
// For channels, waitlink is only accessed by g.
// For semaphores, all fields (including the ones above)
// are only accessed when holding a semaRoot lock.
acquiretime int64
releasetime int64
ticket uint32
// isSelect indicates g is participating in a select, so
// g.selectDone must be CAS'd to win the wake-up race.
isSelect bool
parent *sudog // semaRoot binary tree
waitlink *sudog // g.waiting list or semaRoot
waittail *sudog // semaRoot
c *hchan // channel
Not used by gccgo.
type libcall struct {
fn uintptr
n uintptr // number of parameters
args uintptr // parameters
r1 uintptr // return values
r2 uintptr
err uintptr // error number
Not used by gccgo.
// describes how to handle callback
type wincallbackcontext struct {
gobody unsafe.Pointer // go function to call
argsize uintptr // callback arguments size (in bytes)
restorestack uintptr // adjust stack on return by (in bytes) (386 only)
cleanstack bool
Not used by gccgo.
// Stack describes a Go execution stack.
// The bounds of the stack are exactly [lo, hi),
// with no implicit data structures on either side.
type stack struct {
lo uintptr
hi uintptr
// heldLockInfo gives info on a held lock and the rank of that lock
type heldLockInfo struct {
lockAddr uintptr
rank lockRank
type g struct {
// Stack parameters.
// stack describes the actual stack memory: [stack.lo, stack.hi).
// stackguard0 is the stack pointer compared in the Go stack growth prologue.
// It is stack.lo+StackGuard normally, but can be StackPreempt to trigger a preemption.
// stackguard1 is the stack pointer compared in the C stack growth prologue.
// It is stack.lo+StackGuard on g0 and gsignal stacks.
// It is ~0 on other goroutine stacks, to trigger a call to morestackc (and crash).
// Not for gccgo: stack stack // offset known to runtime/cgo
// Not for gccgo: stackguard0 uintptr // offset known to liblink
// Not for gccgo: stackguard1 uintptr // offset known to liblink
_panic *_panic // innermost panic - offset known to liblink
_defer *_defer // innermost defer
m *m // current m; offset known to arm liblink
// Not for gccgo: sched gobuf
syscallsp uintptr // if status==Gsyscall, syscallsp = sched.sp to use during gc
syscallpc uintptr // if status==Gsyscall, syscallpc = sched.pc to use during gc
// Not for gccgo: stktopsp uintptr // expected sp at top of stack, to check in traceback
param unsafe.Pointer // passed parameter on wakeup
atomicstatus uint32
// Not for gccgo: stackLock uint32 // sigprof/scang lock; TODO: fold in to atomicstatus
goid int64
schedlink guintptr
waitsince int64 // approx time when the g become blocked
waitreason waitReason // if status==Gwaiting
preempt bool // preemption signal, duplicates stackguard0 = stackpreempt
preemptStop bool // transition to _Gpreempted on preemption; otherwise, just deschedule
// Not for gccgo: preemptShrink bool // shrink stack at synchronous safe point
// asyncSafePoint is set if g is stopped at an asynchronous
// safe point. This means there are frames on the stack
// without precise pointer information.
asyncSafePoint bool
paniconfault bool // panic (instead of crash) on unexpected fault address
preemptscan bool // preempted g does scan for gc
gcscandone bool // g has scanned stack; protected by _Gscan bit in status
throwsplit bool // must not split stack
gcScannedSyscallStack bool // gccgo specific; see scanSyscallStack
// activeStackChans indicates that there are unlocked channels
// pointing into this goroutine's stack. If true, stack
// copying needs to acquire channel locks to protect these
// areas of the stack.
activeStackChans bool
raceignore int8 // ignore race detection events
sysblocktraced bool // StartTrace has emitted EvGoInSyscall about this goroutine
sysexitticks int64 // cputicks when syscall has returned (for tracing)
traceseq uint64 // trace event sequencer
tracelastp puintptr // last P emitted an event for this goroutine
lockedm muintptr
sig uint32
writebuf []byte
sigcode0 uintptr
sigcode1 uintptr
sigpc uintptr
gopc uintptr // pc of go statement that created this goroutine
ancestors *[]ancestorInfo // ancestor information goroutine(s) that created this goroutine (only used if debug.tracebackancestors)
startpc uintptr // pc of goroutine function
// Not for gccgo: racectx uintptr
waiting *sudog // sudog structures this g is waiting on (that have a valid elem ptr); in lock order
// Not for gccgo: cgoCtxt []uintptr // cgo traceback context
labels unsafe.Pointer // profiler labels
timer *timer // cached timer for time.Sleep
selectDone uint32 // are we participating in a select and did someone win the race?
// Per-G GC state
// gcAssistBytes is this G's GC assist credit in terms of
// bytes allocated. If this is positive, then the G has credit
// to allocate gcAssistBytes bytes without assisting. If this
// is negative, then the G must correct this by performing
// scan work. We track this in bytes to make it fast to update
// and check for debt in the malloc hot path. The assist ratio
// determines how this corresponds to scan work debt.
gcAssistBytes int64
// Remaining fields are specific to gccgo.
exception unsafe.Pointer // current exception being thrown
isforeign bool // whether current exception is not from Go
// When using split-stacks, these fields holds the results of
// __splitstack_find while executing a syscall. These are used
// by the garbage collector to scan the goroutine's stack.
// When not using split-stacks, g0 stacks are allocated by the
// libc and other goroutine stacks are allocated by malg.
// gcstack: unused (sometimes cleared)
// gcstacksize: g0: 0; others: size of stack
// gcnextsegment: unused
// gcnextsp: current SP while executing a syscall
// gcinitialsp: g0: top of stack; others: start of stack memory
// gcnextsp2: current secondary stack pointer (if present)
// gcinitialsp2: start of secondary stack (if present)
gcstack uintptr
gcstacksize uintptr
gcnextsegment uintptr
gcnextsp uintptr
gcinitialsp unsafe.Pointer
gcnextsp2 uintptr
gcinitialsp2 unsafe.Pointer
// gcregs holds the register values while executing a syscall.
// This is set by getcontext and scanned by the garbage collector.
gcregs g_ucontext_t
entry func(unsafe.Pointer) // goroutine function to run
entryfn uintptr // function address passed to __go_go
entrysp uintptr // the stack pointer of the outermost Go frame
fromgogo bool // whether entered from gogo function
scanningself bool // whether goroutine is scanning its own stack
scang uintptr // the g that wants to scan this g's stack (uintptr to avoid write barrier)
scangcw uintptr // gc worker for scanning stack (uintptr to avoid write barrier)
isSystemGoroutine bool // whether goroutine is a "system" goroutine
isFinalizerGoroutine bool // whether goroutine is the finalizer goroutine
deferring bool // whether we are running a deferred function
goexiting bool // whether we are running Goexit
ranCgocallBackDone bool // whether we deferred CgocallBackDone
traceback uintptr // stack traceback buffer
context g_ucontext_t // saved context for setcontext
stackcontext [10]uintptr // split-stack context
type m struct {
g0 *g // goroutine with scheduling stack
// Not for gccgo: morebuf gobuf // gobuf arg to morestack
// Not for gccgo: divmod uint32 // div/mod denominator for arm - known to liblink
// Fields not known to debuggers.
procid uint64 // for debuggers, but offset not hard-coded
gsignal *g // signal-handling g
// Not for gccgo: goSigStack gsignalStack // Go-allocated signal handling stack
sigmask sigset // storage for saved signal mask
// Not for gccgo: tls [6]uintptr // thread-local storage (for x86 extern register)
mstartfn func()
curg *g // current running goroutine
caughtsig guintptr // goroutine running during fatal signal
p puintptr // attached p for executing go code (nil if not executing go code)
nextp puintptr
oldp puintptr // the p that was attached before executing a syscall
id int64
mallocing int32
throwing int32
preemptoff string // if != "", keep curg running on this m
locks int32
softfloat int32
dying int32
profilehz int32
spinning bool // m is out of work and is actively looking for work
blocked bool // m is blocked on a note
newSigstack bool // minit on C thread called sigaltstack
printlock int8
incgo bool // m is executing a cgo call
freeWait uint32 // if == 0, safe to free g0 and delete m (atomic)
fastrand [2]uint32
needextram bool
traceback uint8
ncgocall uint64 // number of cgo calls in total
ncgo int32 // number of cgo calls currently in progress
// Not for gccgo: cgoCallersUse uint32 // if non-zero, cgoCallers in use temporarily
// Not for gccgo: cgoCallers *cgoCallers // cgo traceback if crashing in cgo call
park note
alllink *m // on allm
schedlink muintptr
lockedg guintptr
createstack [32]location // stack that created this thread.
lockedExt uint32 // tracking for external LockOSThread
lockedInt uint32 // tracking for internal lockOSThread
nextwaitm muintptr // next m waiting for lock
waitunlockf func(*g, unsafe.Pointer) bool
waitlock unsafe.Pointer
waittraceev byte
waittraceskip int
startingtrace bool
syscalltick uint32
freelink *m // on sched.freem
// these are here because they are too large to be on the stack
// of low-level NOSPLIT functions.
// Not for gccgo: libcall libcall
// Not for gccgo: libcallpc uintptr // for cpu profiler
// Not for gccgo: libcallsp uintptr
// Not for gccgo: libcallg guintptr
// Not for gccgo: syscall libcall // stores syscall parameters on windows
// preemptGen counts the number of completed preemption
// signals. This is used to detect when a preemption is
// requested, but fails. Accessed atomically.
preemptGen uint32
// Whether this is a pending preemption signal on this M.
// Accessed atomically.
signalPending uint32
// Up to 10 locks held by this m, maintained by the lock ranking code.
locksHeldLen int
locksHeld [10]heldLockInfo
// Remaining fields are specific to gccgo.
gsignalstack unsafe.Pointer // stack for gsignal
gsignalstacksize uintptr
dropextram bool // drop after call is done
exiting bool // thread is exiting
scannote note // synchonization for signal-based stack scanning
type p struct {
id int32
status uint32 // one of pidle/prunning/...
link puintptr
schedtick uint32 // incremented on every scheduler call
syscalltick uint32 // incremented on every system call
sysmontick sysmontick // last tick observed by sysmon
m muintptr // back-link to associated m (nil if idle)
mcache *mcache
pcache pageCache
raceprocctx uintptr
// gccgo has only one size of defer.
deferpool []*_defer
deferpoolbuf [32]*_defer
// Cache of goroutine ids, amortizes accesses to runtime·sched.goidgen.
goidcache uint64
goidcacheend uint64
// Queue of runnable goroutines. Accessed without lock.
runqhead uint32
runqtail uint32
runq [256]guintptr
// runnext, if non-nil, is a runnable G that was ready'd by
// the current G and should be run next instead of what's in
// runq if there's time remaining in the running G's time
// slice. It will inherit the time left in the current time
// slice. If a set of goroutines is locked in a
// communicate-and-wait pattern, this schedules that set as a
// unit and eliminates the (potentially large) scheduling
// latency that otherwise arises from adding the ready'd
// goroutines to the end of the run queue.
runnext guintptr
// Available G's (status == Gdead)
gFree struct {
n int32
sudogcache []*sudog
sudogbuf [128]*sudog
// Cache of mspan objects from the heap.
mspancache struct {
// We need an explicit length here because this field is used
// in allocation codepaths where write barriers are not allowed,
// and eliminating the write barrier/keeping it eliminated from
// slice updates is tricky, moreso than just managing the length
// ourselves.
len int
buf [128]*mspan
tracebuf traceBufPtr
// traceSweep indicates the sweep events should be traced.
// This is used to defer the sweep start event until a span
// has actually been swept.
traceSweep bool
// traceSwept and traceReclaimed track the number of bytes
// swept and reclaimed by sweeping in the current sweep loop.
traceSwept, traceReclaimed uintptr
palloc persistentAlloc // per-P to avoid mutex
_ uint32 // Alignment for atomic fields below
// The when field of the first entry on the timer heap.
// This is updated using atomic functions.
// This is 0 if the timer heap is empty.
timer0When uint64
// Per-P GC state
gcAssistTime int64 // Nanoseconds in assistAlloc
gcFractionalMarkTime int64 // Nanoseconds in fractional mark worker (atomic)
gcBgMarkWorker guintptr // (atomic)
gcMarkWorkerMode gcMarkWorkerMode
// gcMarkWorkerStartTime is the nanotime() at which this mark
// worker started.
gcMarkWorkerStartTime int64
// gcw is this P's GC work buffer cache. The work buffer is
// filled by write barriers, drained by mutator assists, and
// disposed on certain GC state transitions.
gcw gcWork
// wbBuf is this P's GC write barrier buffer.
// TODO: Consider caching this in the running G.
wbBuf wbBuf
runSafePointFn uint32 // if 1, run sched.safePointFn at next safe point
// Lock for timers. We normally access the timers while running
// on this P, but the scheduler can also do it from a different P.
timersLock mutex
// Actions to take at some time. This is used to implement the
// standard library's time package.
// Must hold timersLock to access.
timers []*timer
// Number of timers in P's heap.
// Modified using atomic instructions.
numTimers uint32
// Number of timerModifiedEarlier timers on P's heap.
// This should only be modified while holding timersLock,
// or while the timer status is in a transient state
// such as timerModifying.
adjustTimers uint32
// Number of timerDeleted timers in P's heap.
// Modified using atomic instructions.
deletedTimers uint32
// Race context used while executing timer functions.
// Not for gccgo: timerRaceCtx uintptr
// preempt is set to indicate that this P should be enter the
// scheduler ASAP (regardless of what G is running on it).
preempt bool
pad cpu.CacheLinePad
type schedt struct {
// accessed atomically. keep at top to ensure alignment on 32-bit systems.
goidgen uint64
lastpoll uint64 // time of last network poll, 0 if currently polling
pollUntil uint64 // time to which current poll is sleeping
lock mutex
// When increasing nmidle, nmidlelocked, nmsys, or nmfreed, be
// sure to call checkdead().
midle muintptr // idle m's waiting for work
nmidle int32 // number of idle m's waiting for work
nmidlelocked int32 // number of locked m's waiting for work
mnext int64 // number of m's that have been created and next M ID
maxmcount int32 // maximum number of m's allowed (or die)
nmsys int32 // number of system m's not counted for deadlock
nmfreed int64 // cumulative number of freed m's
ngsys uint32 // number of system goroutines; updated atomically
pidle puintptr // idle p's
npidle uint32
nmspinning uint32 // See "Worker thread parking/unparking" comment in proc.go.
// Global runnable queue.
runq gQueue
runqsize int32
// disable controls selective disabling of the scheduler.
// Use schedEnableUser to control this.
// disable is protected by sched.lock.
disable struct {
// user disables scheduling of user goroutines.
user bool
runnable gQueue // pending runnable Gs
n int32 // length of runnable
// Global cache of dead G's.
gFree struct {
lock mutex
list gList // Gs
n int32
// Central cache of sudog structs.
sudoglock mutex
sudogcache *sudog
// Central pool of available defer structs.
deferlock mutex
deferpool *_defer
// freem is the list of m's waiting to be freed when their
// m.exited is set. Linked through m.freelink.
freem *m
gcwaiting uint32 // gc is waiting to run
stopwait int32
stopnote note
sysmonwait uint32
sysmonnote note
// safepointFn should be called on each P at the next GC
// safepoint if p.runSafePointFn is set.
safePointFn func(*p)
safePointWait int32
safePointNote note
profilehz int32 // cpu profiling rate
procresizetime int64 // nanotime() of last change to gomaxprocs
totaltime int64 // ∫gomaxprocs dt up to procresizetime
// sysmonlock protects sysmon's actions on the runtime.
// Acquire and hold this mutex to block sysmon from interacting
// with the rest of the runtime.
sysmonlock mutex
// Values for the flags field of a sigTabT.
const (
_SigNotify = 1 << iota // let signal.Notify have signal, even if from kernel
_SigKill // if signal.Notify doesn't take it, exit quietly
_SigThrow // if signal.Notify doesn't take it, exit loudly
_SigPanic // if the signal is from the kernel, panic
_SigDefault // if the signal isn't explicitly requested, don't monitor it
_SigGoExit // cause all runtime procs to exit (only used on Plan 9).
_SigSetStack // add SA_ONSTACK to libc handler
_SigUnblock // always unblock; see blockableSig
_SigIgn // _SIG_DFL action is to ignore the signal
// Lock-free stack node.
// Also known to export_test.go.
type lfnode struct {
next uint64
pushcnt uintptr
type forcegcstate struct {
lock mutex
g *g
idle uint32
// startup_random_data holds random bytes initialized at startup. These come from
// the ELF AT_RANDOM auxiliary vector (vdso_linux_amd64.go or os_linux_386.go).
var startupRandomData []byte
// extendRandom extends the random numbers in r[:n] to the whole slice r.
// Treats n<0 as n==0.
func extendRandom(r []byte, n int) {
if n < 0 {
n = 0
for n < len(r) {
// Extend random bits using hash function & time seed
w := n
if w > 16 {
w = 16
h := memhash(unsafe.Pointer(&r[n-w]), uintptr(nanotime()), uintptr(w))
for i := 0; i < sys.PtrSize && n < len(r); i++ {
r[n] = byte(h)
h >>= 8
// A _defer holds an entry on the list of deferred calls.
// If you add a field here, add code to clear it in freedefer.
// This struct must match the code in Defer_statement::defer_struct_type
// in the compiler.
// Some defers will be allocated on the stack and some on the heap.
// All defers are logically part of the stack, so write barriers to
// initialize them are not required. All defers must be manually scanned,
// and for heap defers, marked.
type _defer struct {
// The next entry in the stack.
link *_defer
// The stack variable for the function which called this defer
// statement. This is set to true if we are returning from
// that function, false if we are panicing through it.
frame *bool
// The value of the panic stack when this function is
// deferred. This function can not recover this value from
// the panic stack. This can happen if a deferred function
// has a defer statement itself.
panicStack *_panic
// The panic that caused the defer to run. This is used to
// discard panics that have already been handled.
_panic *_panic
// The function to call.
pfn uintptr
// The argument to pass to the function.
arg unsafe.Pointer
// The return address that a recover thunk matches against.
// This is set by __go_set_defer_retaddr which is called by
// the thunks created by defer statements.
retaddr uintptr
// Set to true if a function created by reflect.MakeFunc is
// permitted to recover. The return address of such a
// function function will be somewhere in libffi, so __retaddr
// is not useful.
makefunccanrecover bool
// Whether the _defer is heap allocated.
heap bool
// panics
// This is the gccgo version.
// This is marked go:notinheap because _panic values must only ever
// live on the stack.
type _panic struct {
// The next entry in the stack.
link *_panic
// The value associated with this panic.
arg interface{}
// Whether this panic has been recovered.
recovered bool
// Whether this panic was pushed on the stack because of an
// exception thrown in some other language.
isforeign bool
// Whether this panic was already seen by a deferred function
// which called panic again.
aborted bool
// Whether this panic was created for goexit.
goexit bool
// ancestorInfo records details of where a goroutine was started.
type ancestorInfo struct {
pcs []uintptr // pcs from the stack of this goroutine
goid int64 // goroutine id of this goroutine; original goroutine possibly dead
gopc uintptr // pc of go statement that created this goroutine
const (
_TraceRuntimeFrames = 1 << iota // include frames for internal runtime functions.
_TraceTrap // the initial PC, SP are from a trap, not a return PC from a call
_TraceJumpStack // if traceback is on a systemstack, resume trace at g that called into it
// The maximum number of frames we print for a traceback
const _TracebackMaxFrames = 100
// A waitReason explains why a goroutine has been stopped.
// See gopark. Do not re-use waitReasons, add new ones.
type waitReason uint8
const (
waitReasonZero waitReason = iota // ""
waitReasonGCAssistMarking // "GC assist marking"
waitReasonIOWait // "IO wait"
waitReasonChanReceiveNilChan // "chan receive (nil chan)"
waitReasonChanSendNilChan // "chan send (nil chan)"
waitReasonDumpingHeap // "dumping heap"
waitReasonGarbageCollection // "garbage collection"
waitReasonGarbageCollectionScan // "garbage collection scan"
waitReasonPanicWait // "panicwait"
waitReasonSelect // "select"
waitReasonSelectNoCases // "select (no cases)"
waitReasonGCAssistWait // "GC assist wait"
waitReasonGCSweepWait // "GC sweep wait"
waitReasonGCScavengeWait // "GC scavenge wait"
waitReasonChanReceive // "chan receive"
waitReasonChanSend // "chan send"
waitReasonFinalizerWait // "finalizer wait"
waitReasonForceGCIdle // "force gc (idle)"
waitReasonSemacquire // "semacquire"
waitReasonSleep // "sleep"
waitReasonSyncCondWait // "sync.Cond.Wait"
waitReasonTimerGoroutineIdle // "timer goroutine (idle)"
waitReasonTraceReaderBlocked // "trace reader (blocked)"
waitReasonWaitForGCCycle // "wait for GC cycle"
waitReasonGCWorkerIdle // "GC worker (idle)"
waitReasonPreempted // "preempted"
waitReasonDebugCall // "debug call"
var waitReasonStrings = [...]string{
waitReasonZero: "",
waitReasonGCAssistMarking: "GC assist marking",
waitReasonIOWait: "IO wait",
waitReasonChanReceiveNilChan: "chan receive (nil chan)",
waitReasonChanSendNilChan: "chan send (nil chan)",
waitReasonDumpingHeap: "dumping heap",
waitReasonGarbageCollection: "garbage collection",
waitReasonGarbageCollectionScan: "garbage collection scan",
waitReasonPanicWait: "panicwait",
waitReasonSelect: "select",
waitReasonSelectNoCases: "select (no cases)",
waitReasonGCAssistWait: "GC assist wait",
waitReasonGCSweepWait: "GC sweep wait",
waitReasonGCScavengeWait: "GC scavenge wait",
waitReasonChanReceive: "chan receive",
waitReasonChanSend: "chan send",
waitReasonFinalizerWait: "finalizer wait",
waitReasonForceGCIdle: "force gc (idle)",
waitReasonSemacquire: "semacquire",
waitReasonSleep: "sleep",
waitReasonSyncCondWait: "sync.Cond.Wait",
waitReasonTimerGoroutineIdle: "timer goroutine (idle)",
waitReasonTraceReaderBlocked: "trace reader (blocked)",
waitReasonWaitForGCCycle: "wait for GC cycle",
waitReasonGCWorkerIdle: "GC worker (idle)",
waitReasonPreempted: "preempted",
waitReasonDebugCall: "debug call",
func (w waitReason) String() string {
if w < 0 || w >= waitReason(len(waitReasonStrings)) {
return "unknown wait reason"
return waitReasonStrings[w]
var (
allglen uintptr
allm *m
allp []*p // len(allp) == gomaxprocs; may change at safe points, otherwise immutable
allpLock mutex // Protects P-less reads of allp and all writes
gomaxprocs int32
ncpu int32
forcegc forcegcstate
sched schedt
newprocs int32
support_aes bool
// Set by the linker so the runtime can determine the buildmode.
var (
islibrary bool // -buildmode=c-shared
isarchive bool // -buildmode=c-archive
// Types that are only used by gccgo.
// g_ucontext_t is a Go version of the C ucontext_t type, used by getcontext.
// _sizeof_ucontext_t is defined by from <ucontext.h>.
// On some systems getcontext and friends require a value that is
// aligned to a 16-byte boundary. We implement this by increasing the
// required size and picking an appropriate offset when we use the
// array.
type g_ucontext_t [(_sizeof_ucontext_t + 15) / unsafe.Sizeof(uintptr(0))]uintptr
// sigset is the Go version of the C type sigset_t.
// _sigset_t is defined by the Makefile from <signal.h>.
type sigset _sigset_t
// getMemstats returns a pointer to the internal memstats variable,
// for C code.
//go:linkname getMemstats
func getMemstats() *mstats {
return &memstats