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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.
// _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.
_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
// _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
const (
// P status
_Pidle = iota
_Prunning // Only this P is allowed to change from _Prunning.
// 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).
type mutex 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
// 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
type iface struct {
tab *itab
data unsafe.Pointer
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, Ms, and Ps are always reachable via true pointers in the
// allgs, allm, and allp lists or (during allocation before they reach those lists)
// from stack variables.
// 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))
type puintptr uintptr
func (pp puintptr) ptr() *p { return (*p)(unsafe.Pointer(pp)) }
func (pp *puintptr) set(p *p) { *pp = puintptr(unsafe.Pointer(p)) }
type muintptr uintptr
func (mp muintptr) ptr() *m { return (*m)(unsafe.Pointer(mp)) }
func (mp *muintptr) set(m *m) { *mp = muintptr(unsafe.Pointer(m)) }
type gobuf struct {
// The offsets of sp, pc, and g are known to (hard-coded in) libmach.
sp uintptr
pc uintptr
g guintptr
ctxt unsafe.Pointer // this has to be a pointer so that gc scans it
ret sys.Uintreg
lr uintptr
bp uintptr // for GOEXPERIMENT=framepointer
// 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.
g *g
selectdone *uint32 // CAS to 1 to win select race (may point to stack)
next *sudog
prev *sudog
elem unsafe.Pointer // data element (may point to stack)
// The following fields are never accessed concurrently.
// waitlink is only accessed by g.
releasetime int64
ticket uint32
waitlink *sudog // g.waiting list
c *hchan // channel
type gcstats struct {
// the struct must consist of only uint64's,
// because it is casted to uint64[].
nhandoff uint64
nhandoffcnt uint64
nprocyield uint64
nosyield uint64
nsleep uint64
type libcall struct {
fn uintptr
n uintptr // number of parameters
args uintptr // parameters
r1 uintptr // return values
r2 uintptr
err uintptr // error number
// 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
// 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
// stkbar records the state of a G's stack barrier.
type stkbar struct {
savedLRPtr uintptr // location overwritten by stack barrier PC
savedLRVal uintptr // value overwritten at savedLRPtr
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).
stack stack // offset known to runtime/cgo
stackguard0 uintptr // offset known to liblink
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
stackAlloc uintptr // stack allocation is [stack.lo,stack.lo+stackAlloc)
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
stkbar []stkbar // stack barriers, from low to high (see top of mstkbar.go)
stkbarPos uintptr // index of lowest stack barrier not hit
stktopsp uintptr // expected sp at top of stack, to check in traceback
param unsafe.Pointer // passed parameter on wakeup
atomicstatus uint32
stackLock uint32 // sigprof/scang lock; TODO: fold in to atomicstatus
goid int64
waitsince int64 // approx time when the g become blocked
waitreason string // if status==Gwaiting
schedlink guintptr
preempt bool // preemption signal, duplicates stackguard0 = stackpreempt
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
gcscanvalid bool // false at start of gc cycle, true if G has not run since last scan; transition from true to false by calling queueRescan and false to true by calling dequeueRescan
throwsplit bool // must not split stack
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 *m
sig uint32
writebuf []byte
sigcode0 uintptr
sigcode1 uintptr
sigpc uintptr
gopc uintptr // pc of go statement that created this goroutine
startpc uintptr // pc of goroutine function
racectx uintptr
waiting *sudog // sudog structures this g is waiting on (that have a valid elem ptr); in lock order
cgoCtxt []uintptr // cgo traceback context
// Per-G GC state
// gcRescan is this G's index in work.rescan.list. If this is
// -1, this G is not on the rescan list.
// If gcphase != _GCoff and this G is visible to the garbage
// collector, writes to this are protected by work.rescan.lock.
gcRescan int32
// 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
type m struct {
g0 *g // goroutine with scheduling stack
morebuf gobuf // gobuf arg to morestack
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
sigmask sigset // storage for saved signal mask
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
id int32
mallocing int32
throwing int32
preemptoff string // if != "", keep curg running on this m
locks int32
softfloat int32
dying int32
profilehz int32
helpgc int32
spinning bool // m is out of work and is actively looking for work
blocked bool // m is blocked on a note
inwb bool // m is executing a write barrier
newSigstack bool // minit on C thread called sigaltstack
printlock int8
fastrand uint32
ncgocall uint64 // number of cgo calls in total
ncgo int32 // number of cgo calls currently in progress
cgoCallersUse uint32 // if non-zero, cgoCallers in use temporarily
cgoCallers *cgoCallers // cgo traceback if crashing in cgo call
park note
alllink *m // on allm
schedlink muintptr
mcache *mcache
lockedg *g
createstack [32]uintptr // stack that created this thread.
freglo [16]uint32 // d[i] lsb and f[i]
freghi [16]uint32 // d[i] msb and f[i+16]
fflag uint32 // floating point compare flags
locked uint32 // tracking for lockosthread
nextwaitm uintptr // next m waiting for lock
gcstats gcstats
needextram bool
traceback uint8
waitunlockf unsafe.Pointer // todo go func(*g, unsafe.pointer) bool
waitlock unsafe.Pointer
waittraceev byte
waittraceskip int
startingtrace bool
syscalltick uint32
thread uintptr // thread handle
// these are here because they are too large to be on the stack
// of low-level NOSPLIT functions.
libcall libcall
libcallpc uintptr // for cpu profiler
libcallsp uintptr
libcallg guintptr
syscall libcall // stores syscall parameters on windows
type p struct {
lock mutex
id int32
status uint32 // one of pidle/prunning/...
link puintptr
schedtick uint32 // incremented on every scheduler call
syscalltick uint32 // incremented on every system call
m muintptr // back-link to associated m (nil if idle)
mcache *mcache
racectx uintptr
deferpool [5][]*_defer // pool of available defer structs of different sizes (see panic.go)
deferpoolbuf [5][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 *g
gfreecnt int32
sudogcache []*sudog
sudogbuf [128]*sudog
tracebuf traceBufPtr
palloc persistentAlloc // per-P to avoid mutex
// Per-P GC state
gcAssistTime int64 // Nanoseconds in assistAlloc
gcBgMarkWorker guintptr
gcMarkWorkerMode gcMarkWorkerMode
// 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
runSafePointFn uint32 // if 1, run sched.safePointFn at next safe point
pad [64]byte
const (
// The max value of GOMAXPROCS.
// There are no fundamental restrictions on the value.
_MaxGomaxprocs = 1 << 8
type schedt struct {
// accessed atomically. keep at top to ensure alignment on 32-bit systems.
goidgen uint64
lastpoll uint64
lock mutex
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
mcount int32 // number of m's that have been created
maxmcount int32 // maximum number of m's allowed (or die)
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.
runqhead guintptr
runqtail guintptr
runqsize int32
// Global cache of dead G's.
gflock mutex
gfreeStack *g
gfreeNoStack *g
ngfree int32
// Central cache of sudog structs.
sudoglock mutex
sudogcache *sudog
// Central pool of available defer structs of different sizes.
deferlock mutex
deferpool [5]*_defer
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
// The m.locked word holds two pieces of state counting active calls to LockOSThread/lockOSThread.
// The low bit (LockExternal) is a boolean reporting whether any LockOSThread call is active.
// External locks are not recursive; a second lock is silently ignored.
// The upper bits of m.locked record the nesting depth of calls to lockOSThread
// (counting up by LockInternal), popped by unlockOSThread (counting down by LockInternal).
// Internal locks can be recursive. For instance, a lock for cgo can occur while the main
// goroutine is holding the lock during the initialization phase.
const (
_LockExternal = 1
_LockInternal = 2
type sigtabtt struct {
flags int32
name *int8
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
_SigHandling // our signal handler is registered
_SigGoExit // cause all runtime procs to exit (only used on Plan 9).
_SigSetStack // add SA_ONSTACK to libc handler
_SigUnblock // unblocked in minit
// Layout of in-memory per-function information prepared by linker
// See
// Keep in sync with linker
// and with package debug/gosym and with symtab.go in package runtime.
type _func struct {
entry uintptr // start pc
nameoff int32 // function name
args int32 // in/out args size
_ int32 // previously legacy frame size; kept for layout compatibility
pcsp int32
pcfile int32
pcln int32
npcdata int32
nfuncdata int32
// layout of Itab known to compilers
// allocated in non-garbage-collected memory
// Needs to be in sync with
// ../cmd/compile/internal/gc/reflect.go:/^func.dumptypestructs.
type itab struct {
inter *interfacetype
_type *_type
link *itab
bad int32
unused int32
fun [1]uintptr // variable sized
// 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
// deferred subroutine calls
type _defer struct {
siz int32
started bool
sp uintptr // sp at time of defer
pc uintptr
fn *funcval
_panic *_panic // panic that is running defer
link *_defer
// panics
type _panic struct {
argp unsafe.Pointer // pointer to arguments of deferred call run during panic; cannot move - known to liblink
arg interface{} // argument to panic
link *_panic // link to earlier panic
recovered bool // whether this panic is over
aborted bool // the panic was aborted
// stack traces
type stkframe struct {
fn *_func // function being run
pc uintptr // program counter within fn
continpc uintptr // program counter where execution can continue, or 0 if not
lr uintptr // program counter at caller aka link register
sp uintptr // stack pointer at pc
fp uintptr // stack pointer at caller aka frame pointer
varp uintptr // top of local variables
argp uintptr // pointer to function arguments
arglen uintptr // number of bytes at argp
argmap *bitvector // force use of this argmap
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
var (
emptystring string
allglen uintptr
allm *m
allp [_MaxGomaxprocs + 1]*p
gomaxprocs int32
panicking uint32
ncpu int32
forcegc forcegcstate
sched schedt
newprocs int32
// Information about what cpu features are available.
// Set on startup in asm_{x86,amd64}.s.
cpuid_ecx uint32
cpuid_edx uint32
cpuid_ebx7 uint32
lfenceBeforeRdtsc bool
support_avx bool
support_avx2 bool
goarm uint8 // set by cmd/link on arm systems
framepointer_enabled bool // set by cmd/link
// Set by the linker so the runtime can determine the buildmode.
var (
islibrary bool // -buildmode=c-shared
isarchive bool // -buildmode=c-archive