Source File
proc.go
Belonging Package
runtime
// 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 (
)
// 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
raceFiniLock mutex
)
// This slice records the initializing tasks that need to be
// done to start up the runtime. It is built by the linker.
var runtime_inittasks []*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 ()
// 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 () {
:= getg().m
// Racectx of m0->g0 is used only as the parent of the main goroutine.
// It must not be used for anything else.
.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 != &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_inittasks) // Must be before defer.
// Defer unlock so that runtime.Goexit during init does the unlock too.
:= true
defer func() {
if {
unlockOSThread()
}
}()
gcenable()
main_init_done = make(chan bool)
if iscgo {
if _cgo_pthread_key_created == nil {
throw("_cgo_pthread_key_created missing")
}
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")
}
// Set the x_crosscall2_ptr C function pointer variable point to crosscall2.
if set_crosscall2 == nil {
throw("set_crosscall2 missing")
}
set_crosscall2()
// 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)
}
// Run the initializing tasks. Depending on build mode this
// list can arrive a few different ways, but it will always
// contain the init tasks computed by the linker for all the
// packages in the program (excluding those added at runtime
// by package plugin).
for , := range activeModules() {
doInit(.inittasks)
}
// Disable init tracing after main init done to avoid overhead
// of collecting statistics in malloc and newproc
inittrace.active = false
close(main_init_done)
= false
unlockOSThread()
if isarchive || islibrary {
// A program compiled with -buildmode=c-archive or c-shared
// has a main, but it is not executed.
return
}
:= main_main // make an indirect call, as the linker doesn't know the address of the main package when laying down the runtime
()
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 := 0; < 1000; ++ {
if runningPanicDefers.Load() == 0 {
break
}
Gosched()
}
}
if panicking.Load() != 0 {
gopark(nil, nil, waitReasonPanicWait, traceBlockForever, 1)
}
runExitHooks(0)
exit(0)
for {
var *int32
* = 0
}
}
// os_beforeExit is called from os.Exit(0).
//
//go:linkname os_beforeExit os.runtime_beforeExit
func ( int) {
runExitHooks()
if == 0 && raceenabled {
racefini()
}
}
// start forcegc helper goroutine
func () {
go forcegchelper()
}
func () {
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, traceBlockSystemGoroutine, 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()})
}
}
// Gosched yields the processor, allowing other goroutines to run. It does not
// suspend the current goroutine, so execution resumes automatically.
//
//go:nosplit
func () {
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 () {
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 () {
:= getg()
// Call gosched if gp.preempt is set; we may be in a tight loop that
// doesn't otherwise yield.
if !.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 ( func(*g, unsafe.Pointer) bool, unsafe.Pointer, waitReason, traceBlockReason, int) {
if != waitReasonSleep {
checkTimeouts() // timeouts may expire while two goroutines keep the scheduler busy
}
:= acquirem()
:= .curg
:= readgstatus()
if != _Grunning && != _Gscanrunning {
throw("gopark: bad g status")
}
.waitlock =
.waitunlockf =
.waitreason =
.waitTraceBlockReason =
.waitTraceSkip =
releasem()
// 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 ( *mutex, waitReason, traceBlockReason, int) {
gopark(parkunlock_c, unsafe.Pointer(), , , )
}
func ( *g, int) {
systemstack(func() {
ready(, , true)
})
}
//go:nosplit
func () *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.
:= acquirem()
:= .p.ptr()
if len(.sudogcache) == 0 {
lock(&sched.sudoglock)
// First, try to grab a batch from central cache.
for len(.sudogcache) < cap(.sudogcache)/2 && sched.sudogcache != nil {
:= sched.sudogcache
sched.sudogcache = .next
.next = nil
.sudogcache = append(.sudogcache, )
}
unlock(&sched.sudoglock)
// If the central cache is empty, allocate a new one.
if len(.sudogcache) == 0 {
.sudogcache = append(.sudogcache, new(sudog))
}
}
:= len(.sudogcache)
:= .sudogcache[-1]
.sudogcache[-1] = nil
.sudogcache = .sudogcache[:-1]
if .elem != nil {
throw("acquireSudog: found s.elem != nil in cache")
}
releasem()
return
}
//go:nosplit
func ( *sudog) {
if .elem != nil {
throw("runtime: sudog with non-nil elem")
}
if .isSelect {
throw("runtime: sudog with non-false isSelect")
}
if .next != nil {
throw("runtime: sudog with non-nil next")
}
if .prev != nil {
throw("runtime: sudog with non-nil prev")
}
if .waitlink != nil {
throw("runtime: sudog with non-nil waitlink")
}
if .c != nil {
throw("runtime: sudog with non-nil c")
}
:= getg()
if .param != nil {
throw("runtime: releaseSudog with non-nil gp.param")
}
:= acquirem() // avoid rescheduling to another P
:= .p.ptr()
if len(.sudogcache) == cap(.sudogcache) {
// Transfer half of local cache to the central cache.
var , *sudog
for len(.sudogcache) > cap(.sudogcache)/2 {
:= len(.sudogcache)
:= .sudogcache[-1]
.sudogcache[-1] = nil
.sudogcache = .sudogcache[:-1]
if == nil {
=
} else {
.next =
}
=
}
lock(&sched.sudoglock)
.next = sched.sudogcache
sched.sudogcache =
unlock(&sched.sudoglock)
}
.sudogcache = append(.sudogcache, )
releasem()
}
// called from assembly.
func ( func(*g)) {
throw("runtime: mcall called on m->g0 stack")
}
func ( func(*g)) {
throw("runtime: mcall function returned")
}
func () {
panic(plainError("arg size to reflect.call more than 1GB"))
}
//go:nosplit
//go:nowritebarrierrec
func () {
writeErrStr("fatal: morestack on g0\n")
}
//go:nosplit
//go:nowritebarrierrec
func () {
writeErrStr("fatal: morestack on gsignal\n")
}
//go:nosplit
func () {
throw("ctxt != 0")
}
func () bool {
:= getg()
return .lockedm != 0 && .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 ( *g) {
if readgstatus() == _Gidle {
throw("allgadd: bad status Gidle")
}
lock(&allglock)
allgs = append(allgs, )
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 () []*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 () (**g, uintptr) {
:= atomic.Loaduintptr(&allglen)
:= (**g)(atomic.Loadp(unsafe.Pointer(&allgptr)))
return ,
}
// atomicAllGIndex returns ptr[i] with the allgptr returned from atomicAllG.
func ( **g, uintptr) *g {
return *(**g)(add(unsafe.Pointer(), *goarch.PtrSize))
}
// forEachG calls fn on every G from allgs.
//
// forEachG takes a lock to exclude concurrent addition of new Gs.
func ( func( *g)) {
lock(&allglock)
for , := range allgs {
()
}
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 ( func( *g)) {
, := atomicAllG()
for := uintptr(0); < ; ++ {
:= atomicAllGIndex(, )
()
}
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 ( string) {
switch GOOS {
case "aix", "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd", "illumos", "solaris", "linux":
cpu.DebugOptions = true
}
cpu.Initialize()
// 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 () string {
const = "GODEBUG="
var 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()
:= int32(0)
for argv_index(argv, argc+1+) != nil {
++
}
for := int32(0); < ; ++ {
:= argv_index(argv, argc+1+)
:= unsafe.String(, findnull())
if hasPrefix(, ) {
= gostring()[len():]
break
}
}
}
return
}
// The bootstrap sequence is:
//
// call osinit
// call schedinit
// make & queue new G
// call runtime·mstart
//
// The new G calls runtime·main.
func () {
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(&cpuprof.lock, lockRankCpuprof)
traceLockInit()
// 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.
:= getg()
if raceenabled {
.racectx, raceprocctx0 = raceinit()
}
sched.maxmcount = 10000
// The world starts stopped.
worldStopped()
moduledataverify()
stackinit()
mallocinit()
:= getGodebugEarly()
initPageTrace() // must run after mallocinit but before anything allocates
cpuinit() // must run before alginit
alginit() // maps, hash, fastrand must not be used before this call
fastrandinit() // must run before mcommoninit
mcommoninit(.m, -1)
modulesinit() // provides activeModules
typelinksinit() // uses maps, activeModules
itabsinit() // uses activeModules
stkobjinit() // must run before GC starts
sigsave(&.m.sigmask)
initSigmask = .m.sigmask
goargs()
goenvs()
secure()
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())
:= ncpu
if , := atoi32(gogetenv("GOMAXPROCS")); && > 0 {
=
}
if procresize() != nil {
throw("unknown runnable goroutine during bootstrap")
}
unlock(&sched.lock)
// World is effectively started now, as P's can run.
worldStarted()
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 ( *g) {
:= getg()
print("runtime: gp: gp=", , ", goid=", .goid, ", gp->atomicstatus=", readgstatus(), "\n")
print("runtime: getg: g=", , ", goid=", .goid, ", g->atomicstatus=", readgstatus(), "\n")
}
// sched.lock must be held.
func () {
assertLockHeld(&sched.lock)
// Exclude extra M's, which are used for cgocallback from threads
// created in C.
//
// The purpose of the SetMaxThreads limit is to avoid accidental fork
// bomb from something like millions of goroutines blocking on system
// calls, causing the runtime to create millions of threads. By
// definition, this isn't a problem for threads created in C, so we
// exclude them from the limit. See https://go.dev/issue/60004.
:= mcount() - int32(extraMInUse.Load()) - int32(extraMLength.Load())
if > 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 () int64 {
assertLockHeld(&sched.lock)
if sched.mnext+1 < sched.mnext {
throw("runtime: thread ID overflow")
}
:= sched.mnext
sched.mnext++
checkmcount()
return
}
// Pre-allocated ID may be passed as 'id', or omitted by passing -1.
func ( *m, int64) {
:= getg()
// g0 stack won't make sense for user (and is not necessary unwindable).
if != .m.g0 {
callers(1, .createstack[:])
}
lock(&sched.lock)
if >= 0 {
.id =
} else {
.id = mReserveID()
}
:= uint32(int64Hash(uint64(.id), fastrandseed))
:= uint32(int64Hash(uint64(cputicks()), ^fastrandseed))
if | == 0 {
= 1
}
// Same behavior as for 1.17.
// TODO: Simplify this.
if goarch.BigEndian {
.fastrand = uint64()<<32 | uint64()
} else {
.fastrand = uint64()<<32 | uint64()
}
mpreinit()
if .gsignal != nil {
.gsignal.stackguard1 = .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.
.alllink = allm
// NumCgoCall() iterates over allm w/o schedlock,
// so we need to publish it safely.
atomicstorep(unsafe.Pointer(&allm), unsafe.Pointer())
unlock(&sched.lock)
// Allocate memory to hold a cgo traceback if the cgo call crashes.
if iscgo || GOOS == "solaris" || GOOS == "illumos" || GOOS == "windows" {
.cgoCallers = new(cgoCallers)
}
}
func ( *m) () {
.spinning = true
sched.nmspinning.Add(1)
sched.needspinning.Store(0)
}
func ( *m) () bool {
return .ncgo > 0 || .isextra
}
var fastrandseed uintptr
func () {
:= (*[unsafe.Sizeof(fastrandseed)]byte)(unsafe.Pointer(&fastrandseed))[:]
getRandomData()
}
// Mark gp ready to run.
func ( *g, int, bool) {
if traceEnabled() {
traceGoUnpark(, )
}
:= readgstatus()
// Mark runnable.
:= acquirem() // disable preemption because it can be holding p in a local var
if &^_Gscan != _Gwaiting {
dumpgstatus()
throw("bad g->status in ready")
}
// status is Gwaiting or Gscanwaiting, make Grunnable and put on runq
casgstatus(, _Gwaiting, _Grunnable)
runqput(.p.ptr(), , )
wakep()
releasem()
}
// 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 () {
freezing.Store(true)
if debug.dontfreezetheworld > 0 {
// Don't prempt Ps to stop goroutines. That will perturb
// scheduler state, making debugging more difficult. Instead,
// allow goroutines to continue execution.
//
// fatalpanic will tracebackothers to trace all goroutines. It
// is unsafe to trace a running goroutine, so tracebackothers
// will skip running goroutines. That is OK and expected, we
// expect users of dontfreezetheworld to use core files anyway.
//
// However, allowing the scheduler to continue running free
// introduces a race: a goroutine may be stopped when
// tracebackothers checks its status, and then start running
// later when we are in the middle of traceback, potentially
// causing a crash.
//
// To mitigate this, when an M naturally enters the scheduler,
// schedule checks if freezing is set and if so stops
// execution. This guarantees that while Gs can transition from
// running to stopped, they can never transition from stopped
// to running.
//
// The sleep here allows racing Ms that missed freezing and are
// about to run a G to complete the transition to running
// before we start traceback.
usleep(1000)
return
}
// stopwait and preemption requests can be lost
// due to races with concurrently executing threads,
// so try several times
for := 0; < 5; ++ {
// 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 ( *g) uint32 {
return .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 ( *g, , uint32) {
:= false
// Check that transition is valid.
switch {
default:
print("runtime: casfrom_Gscanstatus bad oldval gp=", , ", oldval=", hex(), ", newval=", hex(), "\n")
dumpgstatus()
throw("casfrom_Gscanstatus:top gp->status is not in scan state")
case _Gscanrunnable,
_Gscanwaiting,
_Gscanrunning,
_Gscansyscall,
_Gscanpreempted:
if == &^_Gscan {
= .atomicstatus.CompareAndSwap(, )
}
}
if ! {
print("runtime: casfrom_Gscanstatus failed gp=", , ", oldval=", hex(), ", newval=", hex(), "\n")
dumpgstatus()
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 ( *g, , uint32) bool {
switch {
case _Grunnable,
_Grunning,
_Gwaiting,
_Gsyscall:
if == |_Gscan {
:= .atomicstatus.CompareAndSwap(, )
if {
acquireLockRank(lockRankGscan)
}
return
}
}
print("runtime: castogscanstatus oldval=", hex(), " newval=", hex(), "\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 ( *g, , uint32) {
if (&_Gscan != 0) || (&_Gscan != 0) || == {
systemstack(func() {
print("runtime: casgstatus: oldval=", hex(), " newval=", hex(), "\n")
throw("casgstatus: bad incoming values")
})
}
acquireLockRank(lockRankGscan)
releaseLockRank(lockRankGscan)
// See https://golang.org/cl/21503 for justification of the yield delay.
const = 5 * 1000
var int64
// loop if gp->atomicstatus is in a scan state giving
// GC time to finish and change the state to oldval.
for := 0; !.atomicstatus.CompareAndSwap(, ); ++ {
if == _Gwaiting && .atomicstatus.Load() == _Grunnable {
throw("casgstatus: waiting for Gwaiting but is Grunnable")
}
if == 0 {
= nanotime() +
}
if nanotime() < {
for := 0; < 10 && .atomicstatus.Load() != ; ++ {
procyield(1)
}
} else {
osyield()
= nanotime() + /2
}
}
if == _Grunning {
// Track every gTrackingPeriod time a goroutine transitions out of running.
if casgstatusAlwaysTrack || .trackingSeq%gTrackingPeriod == 0 {
.tracking = true
}
.trackingSeq++
}
if !.tracking {
return
}
// Handle various kinds of tracking.
//
// Currently:
// - Time spent in runnable.
// - Time spent blocked on a sync.Mutex or sync.RWMutex.
switch {
case _Grunnable:
// We transitioned out of runnable, so measure how much
// time we spent in this state and add it to
// runnableTime.
:= nanotime()
.runnableTime += - .trackingStamp
.trackingStamp = 0
case _Gwaiting:
if !.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.
:= nanotime()
sched.totalMutexWaitTime.Add(( - .trackingStamp) * gTrackingPeriod)
.trackingStamp = 0
}
switch {
case _Gwaiting:
if !.waitreason.isMutexWait() {
// Not blocking on a lock.
break
}
// Blocking on a lock. Write down the timestamp.
:= nanotime()
.trackingStamp =
case _Grunnable:
// We just transitioned into runnable, so record what
// time that happened.
:= nanotime()
.trackingStamp =
case _Grunning:
// We're transitioning into running, so turn off
// tracking and record how much time we spent in
// runnable.
.tracking = false
sched.timeToRun.record(.runnableTime)
.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 ( *g, uint32, waitReason) {
// Set the wait reason before calling casgstatus, because casgstatus will use it.
.waitreason =
casgstatus(, , _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 ( *g) uint32 {
for {
:= readgstatus() &^ _Gscan
if != _Gwaiting && != _Grunnable {
throw("copystack: bad status, not Gwaiting or Grunnable")
}
if .atomicstatus.CompareAndSwap(, _Gcopystack) {
return
}
}
}
// 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 ( *g, , uint32) {
if != _Grunning || != _Gscan|_Gpreempted {
throw("bad g transition")
}
acquireLockRank(lockRankGscan)
for !.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 ( *g, , uint32) bool {
if != _Gpreempted || != _Gwaiting {
throw("bad g transition")
}
.waitreason = waitReasonPreempted
return .atomicstatus.CompareAndSwap(_Gpreempted, _Gwaiting)
}
// stwReason is an enumeration of reasons the world is stopping.
type stwReason uint8
// Reasons to stop-the-world.
//
// Avoid reusing reasons and add new ones instead.
const (
stwUnknown stwReason = iota // "unknown"
stwGCMarkTerm // "GC mark termination"
stwGCSweepTerm // "GC sweep termination"
stwWriteHeapDump // "write heap dump"
stwGoroutineProfile // "goroutine profile"
stwGoroutineProfileCleanup // "goroutine profile cleanup"
stwAllGoroutinesStack // "all goroutines stack trace"
stwReadMemStats // "read mem stats"
stwAllThreadsSyscall // "AllThreadsSyscall"
stwGOMAXPROCS // "GOMAXPROCS"
stwStartTrace // "start trace"
stwStopTrace // "stop trace"
stwForTestCountPagesInUse // "CountPagesInUse (test)"
stwForTestReadMetricsSlow // "ReadMetricsSlow (test)"
stwForTestReadMemStatsSlow // "ReadMemStatsSlow (test)"
stwForTestPageCachePagesLeaked // "PageCachePagesLeaked (test)"
stwForTestResetDebugLog // "ResetDebugLog (test)"
)
func ( stwReason) () string {
return stwReasonStrings[]
}
// If you add to this list, also add it to src/internal/trace/parser.go.
// If you change the values of any of the stw* constants, bump the trace
// version number and make a copy of this.
var stwReasonStrings = [...]string{
stwUnknown: "unknown",
stwGCMarkTerm: "GC mark termination",
stwGCSweepTerm: "GC sweep termination",
stwWriteHeapDump: "write heap dump",
stwGoroutineProfile: "goroutine profile",
stwGoroutineProfileCleanup: "goroutine profile cleanup",
stwAllGoroutinesStack: "all goroutines stack trace",
stwReadMemStats: "read mem stats",
stwAllThreadsSyscall: "AllThreadsSyscall",
stwGOMAXPROCS: "GOMAXPROCS",
stwStartTrace: "start trace",
stwStopTrace: "stop trace",
stwForTestCountPagesInUse: "CountPagesInUse (test)",
stwForTestReadMetricsSlow: "ReadMetricsSlow (test)",
stwForTestReadMemStatsSlow: "ReadMemStatsSlow (test)",
stwForTestPageCachePagesLeaked: "PageCachePagesLeaked (test)",
stwForTestResetDebugLog: "ResetDebugLog (test)",
}
// 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 ( stwReason) {
semacquire(&worldsema)
:= getg()
.m.preemptoff = .String()
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(, _Grunning, waitReasonStoppingTheWorld)
stopTheWorldWithSema()
casgstatus(, _Gwaiting, _Grunning)
})
}
// startTheWorld undoes the effects of stopTheWorld.
func () {
systemstack(func() { startTheWorldWithSema() })
// 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.
:= acquirem()
.preemptoff = ""
semrelease1(&worldsema, true, 0)
releasem()
}
// 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 ( stwReason) {
semacquire(&gcsema)
stopTheWorld()
}
// startTheWorldGC undoes the effects of stopTheWorldGC.
func () {
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 ( stwReason) {
if traceEnabled() {
traceSTWStart()
}
:= 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 .m.locks > 0 {
throw("stopTheWorld: holding locks")
}
lock(&sched.lock)
sched.stopwait = gomaxprocs
sched.gcwaiting.Store(true)
preemptall()
// stop current P
.m.p.ptr().status = _Pgcstop // Pgcstop is only diagnostic.
sched.stopwait--
// try to retake all P's in Psyscall status
for , := range allp {
:= .status
if == _Psyscall && atomic.Cas(&.status, , _Pgcstop) {
if traceEnabled() {
traceGoSysBlock()
traceProcStop()
}
.syscalltick++
sched.stopwait--
}
}
// stop idle P's
:= nanotime()
for {
, := pidleget()
if == nil {
break
}
.status = _Pgcstop
sched.stopwait--
}
:= sched.stopwait > 0
unlock(&sched.lock)
// wait for remaining P's to stop voluntarily
if {
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
:= ""
if sched.stopwait != 0 {
= "stopTheWorld: not stopped (stopwait != 0)"
} else {
for , := range allp {
if .status != _Pgcstop {
= "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 != "" {
throw()
}
worldStopped()
}
func () int64 {
assertWorldStopped()
:= acquirem() // disable preemption because it can be holding p in a local var
if netpollinited() {
:= netpoll(0) // non-blocking
injectglist(&)
}
lock(&sched.lock)
:= gomaxprocs
if newprocs != 0 {
= newprocs
newprocs = 0
}
:= procresize()
sched.gcwaiting.Store(false)
if sched.sysmonwait.Load() {
sched.sysmonwait.Store(false)
notewakeup(&sched.sysmonnote)
}
unlock(&sched.lock)
worldStarted()
for != nil {
:=
= .link.ptr()
if .m != 0 {
:= .m.ptr()
.m = 0
if .nextp != 0 {
throw("startTheWorld: inconsistent mp->nextp")
}
.nextp.set()
notewakeup(&.park)
} else {
// Start M to run P. Do not start another M below.
newm(nil, , -1)
}
}
// Capture start-the-world time before doing clean-up tasks.
:= nanotime()
if traceEnabled() {
traceSTWDone()
}
// 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()
return
}
// usesLibcall indicates whether this runtime performs system calls
// via libcall.
func () 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 () 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 ()
// 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 () {
:= getg()
:= .stack.lo == 0
if {
// 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.
:= .stack.hi
if == 0 {
= 16384 * sys.StackGuardMultiplier
}
.stack.hi = uintptr(noescape(unsafe.Pointer(&)))
.stack.lo = .stack.hi - + 1024
}
// Initialize stack guard so that we can start calling regular
// Go code.
.stackguard0 = .stack.lo + stackGuard
// This is the g0, so we can also call go:systemstack
// functions, which check stackguard1.
.stackguard1 = .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.
= true
}
mexit()
}
// 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 () {
:= getg()
if != .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.
.sched.g = guintptr(unsafe.Pointer())
.sched.pc = getcallerpc()
.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 .m == &m0 {
mstartm0()
}
if := .m.mstartfn; != nil {
()
}
if .m != &m0 {
acquirep(.m.nextp.ptr())
.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 () {
// 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 () {
:= getg()
notesleep(&.m.park)
noteclear(&.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 ( bool) {
:= getg().m
if == &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 .gsignal != nil {
stackfree(.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.
.gsignal = nil
}
// Remove m from allm.
lock(&sched.lock)
for := &allm; * != nil; = &(*).alllink {
if * == {
* = .alllink
goto
}
}
throw("m not found in allm")
:
// 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.
.freeWait.Store(freeMWait)
.freelink = sched.freem
sched.freem =
unlock(&sched.lock)
atomic.Xadd64(&ncgocall, int64(.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 .signalPending.Load() != 0 {
pendingPreemptSignals.Add(-1)
}
}
// Destroy all allocated resources. After this is called, we may no
// longer take any locks.
mdestroy()
if {
// No more uses of mp, so it is safe to drop the reference.
.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(&.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 ( func(*p)) {
:= acquirem()
:= getg().m.p.ptr()
lock(&sched.lock)
if sched.safePointWait != 0 {
throw("forEachP: sched.safePointWait != 0")
}
sched.safePointWait = gomaxprocs - 1
sched.safePointFn =
// Ask all Ps to run the safe point function.
for , := range allp {
if != {
atomic.Store(&.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 := sched.pidle.ptr(); != nil; = .link.ptr() {
if atomic.Cas(&.runSafePointFn, 1, 0) {
()
sched.safePointWait--
}
}
:= sched.safePointWait > 0
unlock(&sched.lock)
// Run fn for the current P.
()
// Force Ps currently in _Psyscall into _Pidle and hand them
// off to induce safe point function execution.
for , := range allp {
:= .status
if == _Psyscall && .runSafePointFn == 1 && atomic.Cas(&.status, , _Pidle) {
if traceEnabled() {
traceGoSysBlock()
traceProcStop()
}
.syscalltick++
handoffp()
}
}
// Wait for remaining Ps to run fn.
if {
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 , := range allp {
if .runSafePointFn != 0 {
throw("forEachP: P did not run fn")
}
}
lock(&sched.lock)
sched.safePointFn = nil
unlock(&sched.lock)
releasem()
}
// 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 () {
:= 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(&.runSafePointFn, 1, 0) {
return
}
sched.safePointFn()
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 ( *p, func(), 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()
:= getg()
if .m.p == 0 {
acquirep() // 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 *m
for := sched.freem; != nil; {
:= .freeWait.Load()
if == freeMWait {
:= .freelink
.freelink =
=
=
continue
}
// Free the stack if needed. For freeMRef, there is
// nothing to do except drop freem from the sched.freem
// list.
if == freeMStack {
// stackfree must be on the system stack, but allocm is
// reachable off the system stack transitively from
// startm.
systemstack(func() {
stackfree(.g0.stack)
})
}
= .freelink
}
sched.freem =
unlock(&sched.lock)
}
:= new(m)
.mstartfn =
mcommoninit(, )
// 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() {
.g0 = malg(-1)
} else {
.g0 = malg(16384 * sys.StackGuardMultiplier)
}
.g0.m =
if == .m.p.ptr() {
releasep()
}
releasem(.m)
allocmLock.runlock()
return
}
// 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.
//
// It calls dropm to put the m back on the list,
// 1. when the callback is done with the m in non-pthread platforms,
// 2. or when the C thread exiting on pthread platforms.
//
// The signal argument indicates whether we're called from a signal
// handler.
//
//go:nosplit
func ( bool) {
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 sigset
sigsave(&)
sigblock(false)
// getExtraM is safe here because of the invariant above,
// that the extra list always contains or will soon contain
// at least one m.
, := getExtraM()
// 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).
.needextram =
// Store the original signal mask for use by minit.
.sigmask =
// Install TLS on some platforms (previously setg
// would do this if necessary).
osSetupTLS()
// Install g (= m->g0) and set the stack bounds
// to match the current stack. If 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.
// If we can get a more accurate stack bound from pthread,
// use that.
setg(.g0)
:= getg()
.stack.hi = getcallersp() + 1024
.stack.lo = getcallersp() - 32*1024
if ! && _cgo_getstackbound != nil {
// Don't adjust if called from the signal handler.
// We are on the signal stack, not the pthread stack.
// (We could get the stack bounds from sigaltstack, but
// we're getting out of the signal handler very soon
// anyway. Not worth it.)
var [2]uintptr
asmcgocall(_cgo_getstackbound, unsafe.Pointer(&))
// getstackbound is an unsupported no-op on Windows.
if [0] != 0 {
.stack.lo = [0]
.stack.hi = [1]
}
}
.stackguard0 = .stack.lo + stackGuard
// Should mark we are already in Go now.
// Otherwise, we may call needm again when we get a signal, before cgocallbackg1,
// which means the extram list may be empty, that will cause a deadlock.
.isExtraInC = false
// Initialize this thread to use the m.
asminit()
minit()
// mp.curg is now a real goroutine.
casgstatus(.curg, _Gdead, _Gsyscall)
sched.ngsys.Add(-1)
}
// Acquire an extra m and bind it to the C thread when a pthread key has been created.
//
//go:nosplit
func () {
needm(false)
if _cgo_pthread_key_created != nil && *(*uintptr)(_cgo_pthread_key_created) != 0 {
cgoBindM()
}
}
// 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 () {
:= extraMWaiters.Swap(0)
if > 0 {
for := uint32(0); < ; ++ {
oneNewExtraM()
}
} else if extraMLength.Load() == 0 {
// Make sure there is at least one extra M.
oneNewExtraM()
}
}
// oneNewExtraM allocates an m and puts it on the extra list.
func () {
// 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.
:= allocm(nil, nil, -1)
:= malg(4096)
.sched.pc = abi.FuncPCABI0(goexit) + sys.PCQuantum
.sched.sp = .stack.hi
.sched.sp -= 4 * goarch.PtrSize // extra space in case of reads slightly beyond frame
.sched.lr = 0
.sched.g = guintptr(unsafe.Pointer())
.syscallpc = .sched.pc
.syscallsp = .sched.sp
.stktopsp = .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(, _Gidle, _Gdead)
.m =
.curg =
.isextra = true
// mark we are in C by default.
.isExtraInC = true
.lockedInt++
.lockedg.set()
.lockedm.set()
.goid = sched.goidgen.Add(1)
if raceenabled {
.racectx = racegostart(abi.FuncPCABIInternal(newextram) + sys.PCQuantum)
}
if traceEnabled() {
traceOneNewExtraM()
}
// put on allg for garbage collector
allgadd()
// 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.
addExtraM()
}
// dropm puts the current m back onto the extra list.
//
// 1. On systems without pthreads, like Windows
// 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.
//
// 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.
//
// 2. On systems with pthreads
// dropm is called while a non-Go thread is exiting.
// We allocate a pthread per-thread variable using pthread_key_create,
// to register a thread-exit-time destructor.
// And store the g into a thread-specific value associated with the pthread key,
// when first return back to C.
// So that the destructor would invoke dropm while the non-Go thread is exiting.
// This is much faster since it avoids expensive signal-related syscalls.
//
// NOTE: this always runs without a P, so, nowritebarrierrec required.
//
//go:nowritebarrierrec
func () {
// 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.
:= getg().m
// Return mp.curg to dead state.
casgstatus(.curg, _Gsyscall, _Gdead)
.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
sigblock(false)
unminit()
setg(nil)
putExtraM()
msigrestore()
}
// bindm store the g0 of the current m into a thread-specific value.
//
// We allocate a pthread per-thread variable using pthread_key_create,
// to register a thread-exit-time destructor.
// We are here setting the thread-specific value of the pthread key, to enable the destructor.
// So that the pthread_key_destructor would dropm while the C thread is exiting.
//
// And the saved g will be used in pthread_key_destructor,
// since the g stored in the TLS by Go might be cleared in some platforms,
// before the destructor invoked, so, we restore g by the stored g, before dropm.
//
// We store g0 instead of m, to make the assembly code simpler,
// since we need to restore g0 in runtime.cgocallback.
//
// On systems without pthreads, like Windows, bindm shouldn't be used.
//
// NOTE: this always runs without a P, so, nowritebarrierrec required.
//
//go:nosplit
//go:nowritebarrierrec
func () {
if GOOS == "windows" || GOOS == "plan9" {
fatal("bindm in unexpected GOOS")
}
:= getg()
if .m.g0 != {
fatal("the current g is not g0")
}
if _cgo_bindm != nil {
asmcgocall(_cgo_bindm, unsafe.Pointer())
}
}
// A helper function for EnsureDropM.
func () uintptr {
return uintptr(unsafe.Pointer(getg().m))
}
var (
// Locking linked list of extra M's, via mp.schedlink. Must be accessed
// only via lockextra/unlockextra.
//
// Can't be atomic.Pointer[m] because we use an invalid pointer as a
// "locked" sentinel value. M's on this list remain visible to the GC
// because their mp.curg is on allgs.
extraM atomic.Uintptr
// Number of M's in the extraM list.
extraMLength atomic.Uint32
// Number of waiters in lockextra.
extraMWaiters atomic.Uint32
// Number of extra M's in use by threads.
extraMInUse 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 ( bool) *m {
const = 1
:= false
for {
:= extraM.Load()
if == {
osyield_no_g()
continue
}
if == 0 && ! {
if ! {
// Add 1 to the number of threads
// waiting for an M.
// This is cleared by newextram.
extraMWaiters.Add(1)
= true
}
usleep_no_g(1)
continue
}
if extraM.CompareAndSwap(, ) {
return (*m)(unsafe.Pointer())
}
osyield_no_g()
continue
}
}
//go:nosplit
func ( *m, int32) {
extraMLength.Add()
extraM.Store(uintptr(unsafe.Pointer()))
}
// Return an M from the extra M list. Returns last == true if the list becomes
// empty because of this call.
//
// Spins waiting for an extra M, so caller must ensure that the list always
// contains or will soon contain at least one M.
//
//go:nosplit
func () ( *m, bool) {
= lockextra(false)
extraMInUse.Add(1)
unlockextra(.schedlink.ptr(), -1)
return , .schedlink.ptr() == nil
}
// Returns an extra M back to the list. mp must be from getExtraM. Newly
// allocated M's should use addExtraM.
//
//go:nosplit
func ( *m) {
extraMInUse.Add(-1)
addExtraM()
}
// Adds a newly allocated M to the extra M list.
//
//go:nosplit
func ( *m) {
:= lockextra(true)
.schedlink.set()
unlockextra(, 1)
}
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 ( func(), *p, 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()
:= allocm(, , )
.nextp.set()
.sigmask = initSigmask
if := getg(); != nil && .m != nil && (.m.lockedExt != 0 || .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")
}
.schedlink = newmHandoff.newm
newmHandoff.newm.set()
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()
releasem(getg().m)
}
func ( *m) {
if iscgo {
var cgothreadstart
if _cgo_thread_start == nil {
throw("_cgo_thread_start missing")
}
.g.set(.g0)
.tls = (*uint64)(unsafe.Pointer(&.tls[0]))
.fn = unsafe.Pointer(abi.FuncPCABI0(mstart))
if msanenabled {
msanwrite(unsafe.Pointer(&), unsafe.Sizeof())
}
if asanenabled {
asanwrite(unsafe.Pointer(&), unsafe.Sizeof())
}
execLock.rlock() // Prevent process clone.
asmcgocall(_cgo_thread_start, unsafe.Pointer(&))
execLock.runlock()
return
}
execLock.rlock() // Prevent process clone.
newosproc()
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 () {
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.
:= acquirem()
if !atomic.Cas(&newmHandoff.haveTemplateThread, 0, 1) {
releasem()
return
}
newm(templateThread, nil, -1)
releasem()
}
// 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 () {
lock(&sched.lock)
sched.nmsys++
checkdead()
unlock(&sched.lock)
for {
lock(&newmHandoff.lock)
for newmHandoff.newm != 0 {
:= newmHandoff.newm.ptr()
newmHandoff.newm = 0
unlock(&newmHandoff.lock)
for != nil {
:= .schedlink.ptr()
.schedlink = 0
newm1()
=
}
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 () {
:= getg()
if .m.locks != 0 {
throw("stopm holding locks")
}
if .m.p != 0 {
throw("stopm holding p")
}
if .m.spinning {
throw("stopm spinning")
}
lock(&sched.lock)
mput(.m)
unlock(&sched.lock)
mPark()
acquirep(.m.nextp.ptr())
.m.nextp = 0
}
func () {
// 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.
//
// Argument lockheld indicates whether the caller already acquired the
// scheduler lock. Callers holding the lock when making the call must pass
// true. The lock might be temporarily dropped, but will be reacquired before
// returning.
//
// Must not have write barriers because this may be called without a P.
//
//go:nowritebarrierrec
func ( *p, , 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.
:= acquirem()
if ! {
lock(&sched.lock)
}
if == nil {
if {
// 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")
}
, _ = pidleget(0)
if == nil {
if ! {
unlock(&sched.lock)
}
releasem()
return
}
}
:= mget()
if == 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.
// This apparent deadlock is possible when startm is called
// from sysmon, which doesn't count as a running M.
//
// 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.
:= mReserveID()
unlock(&sched.lock)
var func()
if {
// The caller incremented nmspinning, so set m.spinning in the new M.
= mspinning
}
newm(, , )
if {
lock(&sched.lock)
}
// Ownership transfer of pp committed by start in newm.
// Preemption is now safe.
releasem()
return
}
if ! {
unlock(&sched.lock)
}
if .spinning {
throw("startm: m is spinning")
}
if .nextp != 0 {
throw("startm: m has p")
}
if && !runqempty() {
throw("startm: p has runnable gs")
}
// The caller incremented nmspinning, so set m.spinning in the new M.
.spinning =
.nextp.set()
notewakeup(&.park)
// Ownership transfer of pp committed by wakeup. Preemption is now
// safe.
releasem()
}
// Hands off P from syscall or locked M.
// Always runs without a P, so write barriers are not allowed.
//
//go:nowritebarrierrec
func ( *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() || sched.runqsize != 0 {
startm(, false, false)
return
}
// if there's trace work to do, start it straight away
if (traceEnabled() || traceShuttingDown()) && traceReaderAvailable() != nil {
startm(, false, false)
return
}
// if it has GC work, start it straight away
if gcBlackenEnabled != 0 && gcMarkWorkAvailable() {
startm(, false, 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(, true, false)
return
}
lock(&sched.lock)
if sched.gcwaiting.Load() {
.status = _Pgcstop
sched.stopwait--
if sched.stopwait == 0 {
notewakeup(&sched.stopnote)
}
unlock(&sched.lock)
return
}
if .runSafePointFn != 0 && atomic.Cas(&.runSafePointFn, 1, 0) {
sched.safePointFn()
sched.safePointWait--
if sched.safePointWait == 0 {
notewakeup(&sched.safePointNote)
}
}
if sched.runqsize != 0 {
unlock(&sched.lock)
startm(, false, 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(, false, false)
return
}
// The scheduler lock cannot be held when calling wakeNetPoller below
// because wakeNetPoller may call wakep which may call startm.
:= nobarrierWakeTime()
pidleput(, 0)
unlock(&sched.lock)
if != 0 {
wakeNetPoller()
}
}
// 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 () {
// 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.
:= acquirem()
var *p
lock(&sched.lock)
, _ = pidlegetSpinning(0)
if == nil {
if sched.nmspinning.Add(-1) < 0 {
throw("wakep: negative nmspinning")
}
unlock(&sched.lock)
releasem()
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(, true, false)
releasem()
}
// Stops execution of the current m that is locked to a g until the g is runnable again.
// Returns with acquired P.
func () {
:= getg()
if .m.lockedg == 0 || .m.lockedg.ptr().lockedm.ptr() != .m {
throw("stoplockedm: inconsistent locking")
}
if .m.p != 0 {
// Schedule another M to run this p.
:= releasep()
handoffp()
}
incidlelocked(1)
// Wait until another thread schedules lockedg again.
mPark()
:= readgstatus(.m.lockedg.ptr())
if &^_Gscan != _Grunnable {
print("runtime:stoplockedm: lockedg (atomicstatus=", , ") is not Grunnable or Gscanrunnable\n")
dumpgstatus(.m.lockedg.ptr())
throw("stoplockedm: not runnable")
}
acquirep(.m.nextp.ptr())
.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 ( *g) {
:= .lockedm.ptr()
if == getg().m {
throw("startlockedm: locked to me")
}
if .nextp != 0 {
throw("startlockedm: m has p")
}
// directly handoff current P to the locked m
incidlelocked(-1)
:= releasep()
.nextp.set()
notewakeup(&.park)
stopm()
}
// Stops the current m for stopTheWorld.
// Returns when the world is restarted.
func () {
:= getg()
if !sched.gcwaiting.Load() {
throw("gcstopm: not waiting for gc")
}
if .m.spinning {
.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")
}
}
:= releasep()
lock(&sched.lock)
.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 ( *g, bool) {
:= 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(, osyield)
}
// Assign gp.m before entering _Grunning so running Gs have an
// M.
.curg =
.m =
casgstatus(, _Grunnable, _Grunning)
.waitsince = 0
.preempt = false
.stackguard0 = .stack.lo + stackGuard
if ! {
.p.ptr().schedtick++
}
// Check whether the profiler needs to be turned on or off.
:= sched.profilehz
if .profilehz != {
setThreadCPUProfiler()
}
if traceEnabled() {
// GoSysExit has to happen when we have a P, but before GoStart.
// So we emit it here.
if .syscallsp != 0 {
traceGoSysExit()
}
traceGoStart()
}
gogo(&.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 () ( *g, , bool) {
:= getg().m
// The conditions here and in handoffp must agree: if
// findrunnable would return a G to run, handoffp must start
// an M.
:
:= .p.ptr()
if sched.gcwaiting.Load() {
gcstopm()
goto
}
if .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.
, , := checkTimers(, 0)
// Try to schedule the trace reader.
if traceEnabled() || traceShuttingDown() {
:= traceReader()
if != nil {
casgstatus(, _Gwaiting, _Grunnable)
traceGoUnpark(, 0)
return , false, true
}
}
// Try to schedule a GC worker.
if gcBlackenEnabled != 0 {
, := gcController.findRunnableGCWorker(, )
if != nil {
return , false, true
}
=
}
// 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 .schedtick%61 == 0 && sched.runqsize > 0 {
lock(&sched.lock)
:= globrunqget(, 1)
unlock(&sched.lock)
if != nil {
return , false, false
}
}
// Wake up the finalizer G.
if fingStatus.Load()&(fingWait|fingWake) == fingWait|fingWake {
if := wakefing(); != nil {
ready(, 0, true)
}
}
if *cgo_yield != nil {
asmcgocall(*cgo_yield, nil)
}
// local runq
if , := runqget(); != nil {
return , , false
}
// global runq
if sched.runqsize != 0 {
lock(&sched.lock)
:= globrunqget(, 0)
unlock(&sched.lock)
if != nil {
return , 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 := netpoll(0); !.empty() { // non-blocking
:= .pop()
injectglist(&)
casgstatus(, _Gwaiting, _Grunnable)
if traceEnabled() {
traceGoUnpark(, 0)
}
return , 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 .spinning || 2*sched.nmspinning.Load() < gomaxprocs-sched.npidle.Load() {
if !.spinning {
.becomeSpinning()
}
, , , , := stealWork()
if != nil {
// Successfully stole.
return , , false
}
if {
// There may be new timer or GC work; restart to
// discover.
goto
}
=
if != 0 && ( == 0 || < ) {
// Earlier timer to wait for.
=
}
}
// 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() && gcController.addIdleMarkWorker() {
:= (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop())
if != nil {
.gcMarkWorkerMode = gcMarkWorkerIdleMode
:= .gp.ptr()
casgstatus(, _Gwaiting, _Grunnable)
if traceEnabled() {
traceGoUnpark(, 0)
}
return , 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.
, := beforeIdle(, )
if != nil {
casgstatus(, _Gwaiting, _Grunnable)
if traceEnabled() {
traceGoUnpark(, 0)
}
return , false, false
}
if {
goto
}
// 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.
:= allp
// Also snapshot masks. Value changes are OK, but we can't allow
// len to change out from under us.
:= idlepMask
:= timerpMask
// return P and block
lock(&sched.lock)
if sched.gcwaiting.Load() || .runSafePointFn != 0 {
unlock(&sched.lock)
goto
}
if sched.runqsize != 0 {
:= globrunqget(, 0)
unlock(&sched.lock)
return , false, false
}
if !.spinning && sched.needspinning.Load() == 1 {
// See "Delicate dance" comment below.
.becomeSpinning()
unlock(&sched.lock)
goto
}
if releasep() != {
throw("findrunnable: wrong p")
}
= pidleput(, )
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.
:= .spinning
if .spinning {
.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.
:= checkRunqsNoP(, )
if != nil {
acquirep()
.becomeSpinning()
goto
}
// Check for idle-priority GC work again.
, := checkIdleGCNoP()
if != nil {
acquirep()
.becomeSpinning()
// Run the idle worker.
.gcMarkWorkerMode = gcMarkWorkerIdleMode
casgstatus(, _Gwaiting, _Grunnable)
if traceEnabled() {
traceGoUnpark(, 0)
}
return , 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.
= checkTimersNoP(, , )
}
// Poll network until next timer.
if netpollinited() && (netpollWaiters.Load() > 0 || != 0) && sched.lastpoll.Swap(0) != 0 {
sched.pollUntil.Store()
if .p != 0 {
throw("findrunnable: netpoll with p")
}
if .spinning {
throw("findrunnable: netpoll with spinning")
}
:= int64(-1)
if != 0 {
if == 0 {
= nanotime()
}
= -
if < 0 {
= 0
}
}
if faketime != 0 {
// When using fake time, just poll.
= 0
}
:= netpoll() // block until new work is available
// Refresh now again, after potentially blocking.
= nanotime()
sched.pollUntil.Store(0)
sched.lastpoll.Store()
if faketime != 0 && .empty() {
// Using fake time and nothing is ready; stop M.
// When all M's stop, checkdead will call timejump.
stopm()
goto
}
lock(&sched.lock)
, := pidleget()
unlock(&sched.lock)
if == nil {
injectglist(&)
} else {
acquirep()
if !.empty() {
:= .pop()
injectglist(&)
casgstatus(, _Gwaiting, _Grunnable)
if traceEnabled() {
traceGoUnpark(, 0)
}
return , false, false
}
if {
.becomeSpinning()
}
goto
}
} else if != 0 && netpollinited() {
:= sched.pollUntil.Load()
if == 0 || > {
netpollBreak()
}
}
stopm()
goto
}
// 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 () bool {
if sched.runqsize != 0 {
return true
}
:= getg().m.p.ptr()
if !runqempty() {
return true
}
if netpollinited() && netpollWaiters.Load() > 0 && sched.lastpoll.Load() != 0 {
if := netpoll(0); !.empty() {
injectglist(&)
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 ( int64) ( *g, bool, , int64, bool) {
:= getg().m.p.ptr()
:= false
const = 4
for := 0; < ; ++ {
:= == -1
for := stealOrder.start(fastrand()); !.done(); .next() {
if sched.gcwaiting.Load() {
// GC work may be available.
return nil, false, , , true
}
:= allp[.position()]
if == {
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 && timerpMask.read(.position()) {
, , := checkTimers(, )
=
if != 0 && ( == 0 || < ) {
=
}
if {
// 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 , := runqget(); != nil {
return , , , ,
}
= true
}
}
// Don't bother to attempt to steal if p2 is idle.
if !idlepMask.read(.position()) {
if := runqsteal(, , ); != nil {
return , false, , ,
}
}
}
}
// 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, , ,
}
// 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 ( []*p, pMask) *p {
for , := range {
if !.read(uint32()) && !runqempty() {
lock(&sched.lock)
, := pidlegetSpinning(0)
if == nil {
// Can't get a P, don't bother checking remaining Ps.
unlock(&sched.lock)
return nil
}
unlock(&sched.lock)
return
}
}
// No work available.
return nil
}
// Check all Ps for a timer expiring sooner than pollUntil.
//
// Returns updated pollUntil value.
func ( []*p, pMask, int64) int64 {
for , := range {
if .read(uint32()) {
:= nobarrierWakeTime()
if != 0 && ( == 0 || < ) {
=
}
}
}
return
}
// 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 () (*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)
, := pidlegetSpinning(0)
if == 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(, )
unlock(&sched.lock)
return nil, nil
}
:= (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop())
if == nil {
pidleput(, )
unlock(&sched.lock)
gcController.removeIdleMarkWorker()
return nil, nil
}
unlock(&sched.lock)
return , .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 ( 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.
:= sched.pollUntil.Load()
if == 0 || > {
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 () {
:= getg()
if !.m.spinning {
throw("resetspinning: not a spinning m")
}
.m.spinning = false
:= sched.nmspinning.Add(-1)
if < 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 ( *gList) {
if .empty() {
return
}
if traceEnabled() {
for := .head.ptr(); != nil; = .schedlink.ptr() {
traceGoUnpark(, 0)
}
}
// Mark all the goroutines as runnable before we put them
// on the run queues.
:= .head.ptr()
var *g
:= 0
for := ; != nil; = .schedlink.ptr() {
=
++
casgstatus(, _Gwaiting, _Grunnable)
}
// Turn the gList into a gQueue.
var gQueue
.head.set()
.tail.set()
* = gList{}
:= func( int) {
for := 0; < ; ++ {
:= acquirem() // See comment in startm.
lock(&sched.lock)
, := pidlegetSpinning(0)
if == nil {
unlock(&sched.lock)
releasem()
break
}
startm(, false, true)
unlock(&sched.lock)
releasem()
}
}
:= getg().m.p.ptr()
if == nil {
lock(&sched.lock)
globrunqputbatch(&, int32())
unlock(&sched.lock)
()
return
}
:= int(sched.npidle.Load())
var gQueue
var int
for = 0; < && !.empty(); ++ {
:= .pop()
.pushBack()
}
if > 0 {
lock(&sched.lock)
globrunqputbatch(&, int32())
unlock(&sched.lock)
()
-=
}
if !.empty() {
runqputbatch(, &, )
}
}
// One round of scheduler: find a runnable goroutine and execute it.
// Never returns.
func () {
:= getg().m
if .locks != 0 {
throw("schedule: holding locks")
}
if .lockedg != 0 {
stoplockedm()
execute(.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 .incgo {
throw("schedule: in cgo")
}
:
:= .p.ptr()
.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 .spinning && (.runnext != 0 || .runqhead != .runqtail) {
throw("schedule: spinning with local work")
}
, , := findRunnable() // blocks until work is available
if debug.dontfreezetheworld > 0 && freezing.Load() {
// See comment in freezetheworld. We don't want to perturb
// scheduler state, so we didn't gcstopm in findRunnable, but
// also don't want to allow new goroutines to run.
//
// Deadlock here rather than in the findRunnable loop so if
// findRunnable is stuck in a loop we don't perturb that
// either.
lock(&deadlock)
lock(&deadlock)
}
// 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 .spinning {
resetspinning()
}
if sched.disable.user && !schedEnabled() {
// 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() {
// Something re-enabled scheduling while we
// were acquiring the lock.
unlock(&sched.lock)
} else {
sched.disable.runnable.pushBack()
sched.disable.n++
unlock(&sched.lock)
goto
}
}
// If about to schedule a not-normal goroutine (a GCworker or tracereader),
// wake a P if there is one.
if {
wakep()
}
if .lockedm != 0 {
// Hands off own p to the locked m,
// then blocks waiting for a new p.
startlockedm()
goto
}
execute(, )
}
// 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 () {
:= getg()
setMNoWB(&.m.curg.m, nil)
setGNoWB(&.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 ( *p, int64) (, int64, bool) {
// If it's not yet time for the first timer, or the first adjusted
// timer, then there is nothing to do.
:= .timer0When.Load()
:= .timerModifiedEarliest.Load()
if == 0 || ( != 0 && < ) {
=
}
if == 0 {
// No timers to run or adjust.
return , 0, false
}
if == 0 {
= nanotime()
}
if < {
// 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 != getg().m.p.ptr() || int(.deletedTimers.Load()) <= int(.numTimers.Load()/4) {
return , , false
}
}
lock(&.timersLock)
if len(.timers) > 0 {
adjusttimers(, )
for len(.timers) > 0 {
// Note that runtimer may temporarily unlock
// pp.timersLock.
if := runtimer(, ); != 0 {
if > 0 {
=
}
break
}
= 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 == getg().m.p.ptr() && int(.deletedTimers.Load()) > len(.timers)/4 {
clearDeletedTimers()
}
unlock(&.timersLock)
return , ,
}
func ( *g, unsafe.Pointer) bool {
unlock((*mutex)())
return true
}
// park continuation on g0.
func ( *g) {
:= getg().m
if traceEnabled() {
traceGoPark(.waitTraceBlockReason, .waitTraceSkip)
}
// N.B. Not using casGToWaiting here because the waitreason is
// set by park_m's caller.
casgstatus(, _Grunning, _Gwaiting)
dropg()
if := .waitunlockf; != nil {
:= (, .waitlock)
.waitunlockf = nil
.waitlock = nil
if ! {
if traceEnabled() {
traceGoUnpark(, 2)
}
casgstatus(, _Gwaiting, _Grunnable)
execute(, true) // Schedule it back, never returns.
}
}
schedule()
}
func ( *g) {
:= readgstatus()
if &^_Gscan != _Grunning {
dumpgstatus()
throw("bad g status")
}
casgstatus(, _Grunning, _Grunnable)
dropg()
lock(&sched.lock)
globrunqput()
unlock(&sched.lock)
schedule()
}
// Gosched continuation on g0.
func ( *g) {
if traceEnabled() {
traceGoSched()
}
goschedImpl()
}
// goschedguarded is a forbidden-states-avoided version of gosched_m.
func ( *g) {
if !canPreemptM(.m) {
gogo(&.sched) // never return
}
if traceEnabled() {
traceGoSched()
}
goschedImpl()
}
func ( *g) {
if traceEnabled() {
traceGoPreempt()
}
goschedImpl()
}
// preemptPark parks gp and puts it in _Gpreempted.
//
//go:systemstack
func ( *g) {
if traceEnabled() {
traceGoPark(traceBlockPreempted, 0)
}
:= readgstatus()
if &^_Gscan != _Grunning {
dumpgstatus()
throw("bad g status")
}
if .asyncSafePoint {
// Double-check that async preemption does not
// happen in SPWRITE assembly functions.
// isAsyncSafePoint must exclude this case.
:= findfunc(.sched.pc)
if !.valid() {
throw("preempt at unknown pc")
}
if .flag&abi.FuncFlagSPWrite != 0 {
println("runtime: unexpected SPWRITE function", funcname(), "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(, _Grunning, _Gscan|_Gpreempted)
dropg()
casfrom_Gscanstatus(, _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 () {
checkTimeouts()
mcall(goyield_m)
}
func ( *g) {
if traceEnabled() {
traceGoPreempt()
}
:= .m.p.ptr()
casgstatus(, _Grunning, _Grunnable)
dropg()
runqput(, , false)
schedule()
}
// Finishes execution of the current goroutine.
func () {
if raceenabled {
racegoend()
}
if traceEnabled() {
traceGoEnd()
}
mcall(goexit0)
}
// goexit continuation on g0.
func ( *g) {
:= getg().m
:= .p.ptr()
casgstatus(, _Grunning, _Gdead)
gcController.addScannableStack(, -int64(.stack.hi-.stack.lo))
if isSystemGoroutine(, false) {
sched.ngsys.Add(-1)
}
.m = nil
:= .lockedm != 0
.lockedm = 0
.lockedg = 0
.preemptStop = false
.paniconfault = false
._defer = nil // should be true already but just in case.
._panic = nil // non-nil for Goexit during panic. points at stack-allocated data.
.writebuf = nil
.waitreason = waitReasonZero
.param = nil
.labels = nil
.timer = nil
if gcBlackenEnabled != 0 && .gcAssistBytes > 0 {
// Flush assist credit to the global pool. This gives
// better information to pacing if the application is
// rapidly creating an exiting goroutines.
:= gcController.assistWorkPerByte.Load()
:= int64( * float64(.gcAssistBytes))
gcController.bgScanCredit.Add()
.gcAssistBytes = 0
}
dropg()
if GOARCH == "wasm" { // no threads yet on wasm
gfput(, )
schedule() // never returns
}
if .lockedInt != 0 {
print("invalid m->lockedInt = ", .lockedInt, "\n")
throw("internal lockOSThread error")
}
gfput(, )
if {
// 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(&.g0.sched)
} else {
// Clear lockedExt on plan9 since we may end up re-using
// this thread.
.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 (, uintptr) {
:= getg()
if == .m.g0 || == .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")
}
.sched.pc =
.sched.sp =
.sched.lr = 0
.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 .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 (, uintptr) {
:= getg()
// Disable preemption because during this function g is in Gsyscall status,
// but can have inconsistent g->sched, do not let GC observe it.
.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.
.stackguard0 = stackPreempt
.throwsplit = true
// Leave SP around for GC and traceback.
save(, )
.syscallsp =
.syscallpc =
casgstatus(, _Grunning, _Gsyscall)
if staticLockRanking {
// When doing static lock ranking casgstatus can call
// systemstack which clobbers g.sched.
save(, )
}
if .syscallsp < .stack.lo || .stack.hi < .syscallsp {
systemstack(func() {
print("entersyscall inconsistent ", hex(.syscallsp), " [", hex(.stack.lo), ",", hex(.stack.hi), "]\n")
throw("entersyscall")
})
}
if traceEnabled() {
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(, )
}
if sched.sysmonwait.Load() {
systemstack(entersyscall_sysmon)
save(, )
}
if .m.p.ptr().runSafePointFn != 0 {
// runSafePointFn may stack split if run on this stack
systemstack(runSafePointFn)
save(, )
}
.m.syscalltick = .m.p.ptr().syscalltick
:= .m.p.ptr()
.m = 0
.m.oldp.set()
.m.p = 0
atomic.Store(&.status, _Psyscall)
if sched.gcwaiting.Load() {
systemstack(entersyscall_gcwait)
save(, )
}
.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 () {
reentersyscall(getcallerpc(), getcallersp())
}
func () {
lock(&sched.lock)
if sched.sysmonwait.Load() {
sched.sysmonwait.Store(false)
notewakeup(&sched.sysmonnote)
}
unlock(&sched.lock)
}
func () {
:= getg()
:= .m.oldp.ptr()
lock(&sched.lock)
if sched.stopwait > 0 && atomic.Cas(&.status, _Psyscall, _Pgcstop) {
if traceEnabled() {
traceGoSysBlock()
traceProcStop()
}
.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 () {
:= getg()
.m.locks++ // see comment in entersyscall
.throwsplit = true
.stackguard0 = stackPreempt // see comment in entersyscall
.m.syscalltick = .m.p.ptr().syscalltick
.m.p.ptr().syscalltick++
// Leave SP around for GC and traceback.
:= getcallerpc()
:= getcallersp()
save(, )
.syscallsp = .sched.sp
.syscallpc = .sched.pc
if .syscallsp < .stack.lo || .stack.hi < .syscallsp {
:=
:= .sched.sp
:= .syscallsp
systemstack(func() {
print("entersyscallblock inconsistent ", hex(), " ", hex(), " ", hex(), " [", hex(.stack.lo), ",", hex(.stack.hi), "]\n")
throw("entersyscallblock")
})
}
casgstatus(, _Grunning, _Gsyscall)
if .syscallsp < .stack.lo || .stack.hi < .syscallsp {
systemstack(func() {
print("entersyscallblock inconsistent ", hex(), " ", hex(.sched.sp), " ", hex(.syscallsp), " [", hex(.stack.lo), ",", hex(.stack.hi), "]\n")
throw("entersyscallblock")
})
}
systemstack(entersyscallblock_handoff)
// Resave for traceback during blocked call.
save(getcallerpc(), getcallersp())
.m.locks--
}
func () {
if traceEnabled() {
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 () {
:= getg()
.m.locks++ // see comment in entersyscall
if getcallersp() > .syscallsp {
throw("exitsyscall: syscall frame is no longer valid")
}
.waitsince = 0
:= .m.oldp.ptr()
.m.oldp = 0
if exitsyscallfast() {
// 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()
})
}
if traceEnabled() {
if != .m.p.ptr() || .m.syscalltick != .m.p.ptr().syscalltick {
systemstack(traceGoStart)
}
}
// There's a cpu for us, so we can run.
.m.p.ptr().syscalltick++
// We need to cas the status and scan before resuming...
casgstatus(, _Gsyscall, _Grunning)
// Garbage collector isn't running (since we are),
// so okay to clear syscallsp.
.syscallsp = 0
.m.locks--
if .preempt {
// restore the preemption request in case we've cleared it in newstack
.stackguard0 = stackPreempt
} else {
// otherwise restore the real stackGuard, we've spoiled it in entersyscall/entersyscallblock
.stackguard0 = .stack.lo + stackGuard
}
.throwsplit = false
if sched.disable.user && !schedEnabled() {
// Scheduling of this goroutine is disabled.
Gosched()
}
return
}
if traceEnabled() {
// Wait till traceGoSysBlock event is emitted.
// This ensures consistency of the trace (the goroutine is started after it is blocked).
for != nil && .syscalltick == .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.
.trace.sysExitTime = traceClockNow()
}
.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.
.syscallsp = 0
.m.p.ptr().syscalltick++
.throwsplit = false
}
//go:nosplit
func ( *p) bool {
:= getg()
// Freezetheworld sets stopwait but does not retake P's.
if sched.stopwait == freezeStopWait {
return false
}
// Try to re-acquire the last P.
if != nil && .status == _Psyscall && atomic.Cas(&.status, _Psyscall, _Pidle) {
// There's a cpu for us, so we can run.
wirep()
exitsyscallfast_reacquired()
return true
}
// Try to get any other idle P.
if sched.pidle != 0 {
var bool
systemstack(func() {
= exitsyscallfast_pidle()
if && traceEnabled() {
if != nil {
// Wait till traceGoSysBlock event is emitted.
// This ensures consistency of the trace (the goroutine is started after it is blocked).
for .syscalltick == .m.syscalltick {
osyield()
}
}
traceGoSysExit()
}
})
if {
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 () {
:= getg()
if .m.syscalltick != .m.p.ptr().syscalltick {
if traceEnabled() {
// 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(.m.p.ptr())
// Denote completion of the current syscall.
traceGoSysExit()
})
}
.m.p.ptr().syscalltick++
}
}
func () bool {
lock(&sched.lock)
, := pidleget(0)
if != nil && sched.sysmonwait.Load() {
sched.sysmonwait.Store(false)
notewakeup(&sched.sysmonnote)
}
unlock(&sched.lock)
if != nil {
acquirep()
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 ( *g) {
casgstatus(, _Gsyscall, _Grunnable)
dropg()
lock(&sched.lock)
var *p
if schedEnabled() {
, _ = pidleget(0)
}
var bool
if == nil {
globrunqput()
// 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.
= .lockedm != 0
} else if sched.sysmonwait.Load() {
sched.sysmonwait.Store(false)
notewakeup(&sched.sysmonnote)
}
unlock(&sched.lock)
if != nil {
acquirep()
execute(, false) // Never returns.
}
if {
// 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(, false) // Never returns.
}
stopm()
schedule() // Never returns.
}
// Called from syscall package before fork.
//
//go:linkname syscall_runtime_BeforeFork syscall.runtime_BeforeFork
//go:nosplit
func () {
:= 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.
.m.locks++
sigsave(&.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.stackguard0 to reliably detect any attempts to grow stack.
// runtime_AfterFork will undo this in parent process, but not in child.
.stackguard0 = stackFork
}
// Called from syscall package after fork in parent.
//
//go:linkname syscall_runtime_AfterFork syscall.runtime_AfterFork
//go:nosplit
func () {
:= getg().m.curg
// See the comments in beforefork.
.stackguard0 = .stack.lo + stackGuard
msigrestore(.m.sigmask)
.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 () {
// 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 () {
// 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 () {
execLock.unlock()
}
// Allocate a new g, with a stack big enough for stacksize bytes.
func ( int32) *g {
:= new(g)
if >= 0 {
= round2(stackSystem + )
systemstack(func() {
.stack = stackalloc(uint32())
})
.stackguard0 = .stack.lo + stackGuard
.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(.stack.lo)) = 0
}
return
}
// 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 ( *funcval) {
:= getg()
:= getcallerpc()
systemstack(func() {
:= newproc1(, , )
:= getg().m.p.ptr()
runqput(, , 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 ( *funcval, *g, uintptr) *g {
if == nil {
fatal("go of nil func value")
}
:= acquirem() // disable preemption because we hold M and P in local vars.
:= .p.ptr()
:= gfget()
if == nil {
= malg(stackMin)
casgstatus(, _Gidle, _Gdead)
allgadd() // publishes with a g->status of Gdead so GC scanner doesn't look at uninitialized stack.
}
if .stack.hi == 0 {
throw("newproc1: newg missing stack")
}
if readgstatus() != _Gdead {
throw("newproc1: new g is not Gdead")
}
:= uintptr(4*goarch.PtrSize + sys.MinFrameSize) // extra space in case of reads slightly beyond frame
= alignUp(, sys.StackAlign)
:= .stack.hi -
:=
if usesLR {
// caller's LR
*(*uintptr)(unsafe.Pointer()) = 0
prepGoExitFrame()
+= sys.MinFrameSize
}
memclrNoHeapPointers(unsafe.Pointer(&.sched), unsafe.Sizeof(.sched))
.sched.sp =
.stktopsp =
.sched.pc = abi.FuncPCABI0(goexit) + sys.PCQuantum // +PCQuantum so that previous instruction is in same function
.sched.g = guintptr(unsafe.Pointer())
gostartcallfn(&.sched, )
.parentGoid = .goid
.gopc =
.ancestors = saveAncestors()
.startpc = .fn
if isSystemGoroutine(, false) {
sched.ngsys.Add(1)
} else {
// Only user goroutines inherit pprof labels.
if .curg != nil {
.labels = .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.
.goroutineProfiled.Store(goroutineProfileSatisfied)
}
}
// Track initial transition?
.trackingSeq = uint8(fastrand())
if .trackingSeq%gTrackingPeriod == 0 {
.tracking = true
}
casgstatus(, _Gdead, _Grunnable)
gcController.addScannableStack(, int64(.stack.hi-.stack.lo))
if .goidcache == .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.
.goidcache = sched.goidgen.Add(_GoidCacheBatch)
.goidcache -= _GoidCacheBatch - 1
.goidcacheend = .goidcache + _GoidCacheBatch
}
.goid = .goidcache
.goidcache++
if raceenabled {
.racectx = racegostart()
.raceignore = 0
if .labels != nil {
// See note in proflabel.go on labelSync's role in synchronizing
// with the reads in the signal handler.
racereleasemergeg(, unsafe.Pointer(&labelSync))
}
}
if traceEnabled() {
traceGoCreate(, .startpc)
}
releasem()
return
}
// saveAncestors copies previous ancestors of the given caller g and
// includes info for the current caller into a new set of tracebacks for
// a g being created.
func ( *g) *[]ancestorInfo {
// Copy all prior info, except for the root goroutine (goid 0).
if debug.tracebackancestors <= 0 || .goid == 0 {
return nil
}
var []ancestorInfo
if .ancestors != nil {
= *.ancestors
}
:= int32(len()) + 1
if > debug.tracebackancestors {
= debug.tracebackancestors
}
:= make([]ancestorInfo, )
copy([1:], )
var [tracebackInnerFrames]uintptr
:= gcallers(, 0, [:])
:= make([]uintptr, )
copy(, [:])
[0] = ancestorInfo{
pcs: ,
goid: .goid,
gopc: .gopc,
}
:= new([]ancestorInfo)
* =
return
}
// Put on gfree list.
// If local list is too long, transfer a batch to the global list.
func ( *p, *g) {
if readgstatus() != _Gdead {
throw("gfput: bad status (not Gdead)")
}
:= .stack.hi - .stack.lo
if != uintptr(startingStackSize) {
// non-standard stack size - free it.
stackfree(.stack)
.stack.lo = 0
.stack.hi = 0
.stackguard0 = 0
}
.gFree.push()
.gFree.n++
if .gFree.n >= 64 {
var (
int32
gQueue
gQueue
)
for .gFree.n >= 32 {
:= .gFree.pop()
.gFree.n--
if .stack.lo == 0 {
.push()
} else {
.push()
}
++
}
lock(&sched.gFree.lock)
sched.gFree.noStack.pushAll()
sched.gFree.stack.pushAll()
sched.gFree.n +=
unlock(&sched.gFree.lock)
}
}
// Get from gfree list.
// If local list is empty, grab a batch from global list.
func ( *p) *g {
:
if .gFree.empty() && (!sched.gFree.stack.empty() || !sched.gFree.noStack.empty()) {
lock(&sched.gFree.lock)
// Move a batch of free Gs to the P.
for .gFree.n < 32 {
// Prefer Gs with stacks.
:= sched.gFree.stack.pop()
if == nil {
= sched.gFree.noStack.pop()
if == nil {
break
}
}
sched.gFree.n--
.gFree.push()
.gFree.n++
}
unlock(&sched.gFree.lock)
goto
}
:= .gFree.pop()
if == nil {
return nil
}
.gFree.n--
if .stack.lo != 0 && .stack.hi-.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(.stack)
.stack.lo = 0
.stack.hi = 0
.stackguard0 = 0
})
}
if .stack.lo == 0 {
// Stack was deallocated in gfput or just above. Allocate a new one.
systemstack(func() {
.stack = stackalloc(startingStackSize)
})
.stackguard0 = .stack.lo + stackGuard
} else {
if raceenabled {
racemalloc(unsafe.Pointer(.stack.lo), .stack.hi-.stack.lo)
}
if msanenabled {
msanmalloc(unsafe.Pointer(.stack.lo), .stack.hi-.stack.lo)
}
if asanenabled {
asanunpoison(unsafe.Pointer(.stack.lo), .stack.hi-.stack.lo)
}
}
return
}
// Purge all cached G's from gfree list to the global list.
func ( *p) {
var (
int32
gQueue
gQueue
)
for !.gFree.empty() {
:= .gFree.pop()
.gFree.n--
if .stack.lo == 0 {
.push()
} else {
.push()
}
++
}
lock(&sched.gFree.lock)
sched.gFree.noStack.pushAll()
sched.gFree.stack.pushAll()
sched.gFree.n +=
unlock(&sched.gFree.lock)
}
// Breakpoint executes a breakpoint trap.
func () {
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 () {
if GOARCH == "wasm" {
return // no threads on wasm yet
}
:= getg()
.m.lockedg.set()
.lockedm.set(.m)
}
// 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.
//
//go:nosplit
func () {
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()
}
:= getg()
.m.lockedExt++
if .m.lockedExt == 0 {
.m.lockedExt--
panic("LockOSThread nesting overflow")
}
dolockOSThread()
}
//go:nosplit
func () {
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 () {
if GOARCH == "wasm" {
return // no threads on wasm yet
}
:= getg()
if .m.lockedInt != 0 || .m.lockedExt != 0 {
return
}
.m.lockedg = 0
.lockedm = 0
}
// 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.
//
//go:nosplit
func () {
:= getg()
if .m.lockedExt == 0 {
return
}
.m.lockedExt--
dounlockOSThread()
}
//go:nosplit
func () {
:= getg()
if .m.lockedInt == 0 {
systemstack(badunlockosthread)
}
.m.lockedInt--
dounlockOSThread()
}
func () {
throw("runtime: internal error: misuse of lockOSThread/unlockOSThread")
}
func () int32 {
:= int32(atomic.Loaduintptr(&allglen)) - sched.gFree.n - sched.ngsys.Load()
for , := range allp {
-= .gFree.n
}
// All these variables can be changed concurrently, so the result can be inconsistent.
// But at least the current goroutine is running.
if < 1 {
= 1
}
return
}
func () 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 () { () }
func () { () }
func () { () }
func () { () }
func () { () }
func () { () }
// Called if we receive a SIGPROF signal.
// Called by the signal handler, may run during STW.
//
//go:nowritebarrierrec
func (, , uintptr, *g, *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 != nil && .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 := findfunc(); .valid() {
if hasPrefix(funcname(), "runtime/internal/atomic") {
cpuprof.lostAtomic++
return
}
}
if GOARCH == "arm" && goarm < 7 && GOOS == "linux" && &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 unwinder
var [maxCPUProfStack]uintptr
:= 0
if .ncgo > 0 && .curg != nil && .curg.syscallpc != 0 && .curg.syscallsp != 0 {
:= 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 .cgoCallersUse.Load() == 0 && .cgoCallers != nil && .cgoCallers[0] != 0 {
for < len(.cgoCallers) && .cgoCallers[] != 0 {
++
}
+= copy([:], .cgoCallers[:])
.cgoCallers[0] = 0
}
// Collect Go stack that leads to the cgo call.
.initAt(.curg.syscallpc, .curg.syscallsp, 0, .curg, unwindSilentErrors)
} else if usesLibcall() && .libcallg != 0 && .libcallpc != 0 && .libcallsp != 0 {
// Libcall, i.e. runtime syscall on windows.
// Collect Go stack that leads to the call.
.initAt(.libcallpc, .libcallsp, 0, .libcallg.ptr(), unwindSilentErrors)
} else if != nil && .vdsoSP != 0 {
// VDSO call, e.g. nanotime1 on Linux.
// Collect Go stack that leads to the call.
.initAt(.vdsoPC, .vdsoSP, 0, , unwindSilentErrors|unwindJumpStack)
} else {
.initAt(, , , , unwindSilentErrors|unwindTrap|unwindJumpStack)
}
+= tracebackPCs(&, 0, [:])
if <= 0 {
// Normal traceback is impossible or has failed.
// Account it against abstract "System" or "GC".
= 2
if inVDSOPage() {
= abi.FuncPCABIInternal(_VDSO) + sys.PCQuantum
} else if > firstmoduledata.etext {
// "ExternalCode" is better than "etext".
= abi.FuncPCABIInternal(_ExternalCode) + sys.PCQuantum
}
[0] =
if .preemptoff != "" {
[1] = abi.FuncPCABIInternal(_GC) + sys.PCQuantum
} else {
[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 *unsafe.Pointer
if != nil && .m != nil && .m.curg != nil {
= &.m.curg.labels
}
cpuprof.add(, [:])
:=
var *p
if != nil && .m != nil {
if .m.curg != nil {
= .m.curg
}
= .m.p.ptr()
}
traceCPUSample(, , [:])
}
getg().m.mallocing--
}
// setcpuprofilerate sets the CPU profiling rate to hz times per second.
// If hz <= 0, setcpuprofilerate turns off CPU profiling.
func ( int32) {
// Force sane arguments.
if < 0 {
= 0
}
// Disable preemption, otherwise we can be rescheduled to another thread
// that has profiling enabled.
:= getg()
.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() != {
setProcessCPUProfiler()
prof.hz.Store()
}
prof.signalLock.Store(0)
lock(&sched.lock)
sched.profilehz =
unlock(&sched.lock)
if != 0 {
setThreadCPUProfiler()
}
.m.locks--
}
// init initializes pp, which may be a freshly allocated p or a
// previously destroyed p, and transitions it to status _Pgcstop.
func ( *p) ( int32) {
.id =
.status = _Pgcstop
.sudogcache = .sudogbuf[:0]
.deferpool = .deferpoolbuf[:0]
.wbBuf.reset()
if .mcache == nil {
if == 0 {
if mcache0 == nil {
throw("missing mcache?")
}
// Use the bootstrap mcache0. Only one P will get
// mcache0: the one with ID 0.
.mcache = mcache0
} else {
.mcache = allocmcache()
}
}
if raceenabled && .raceprocctx == 0 {
if == 0 {
.raceprocctx = raceprocctx0
raceprocctx0 = 0 // bootstrap
} else {
.raceprocctx = raceproccreate()
}
}
lockInit(&.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()
// Similarly, we may not go through pidleget before this P starts
// running if it is P 0 on startup.
idlepMask.clear()
}
// 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 ( *p) () {
assertLockHeld(&sched.lock)
assertWorldStopped()
// Move all runnable goroutines to the global queue
for .runqhead != .runqtail {
// Pop from tail of local queue
.runqtail--
:= .runq[.runqtail%uint32(len(.runq))].ptr()
// Push onto head of global queue
globrunqputhead()
}
if .runnext != 0 {
globrunqputhead(.runnext.ptr())
.runnext = 0
}
if len(.timers) > 0 {
:= 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(&.timersLock)
lock(&.timersLock)
moveTimers(, .timers)
.timers = nil
.numTimers.Store(0)
.deletedTimers.Store(0)
.timer0When.Store(0)
unlock(&.timersLock)
unlock(&.timersLock)
}
// Flush p's write barrier buffer.
if gcphase != _GCoff {
wbBufFlush1()
.gcw.dispose()
}
for := range .sudogbuf {
.sudogbuf[] = nil
}
.sudogcache = .sudogbuf[:0]
.pinnerCache = nil
for := range .deferpoolbuf {
.deferpoolbuf[] = nil
}
.deferpool = .deferpoolbuf[:0]
systemstack(func() {
for := 0; < .mspancache.len; ++ {
// Safe to call since the world is stopped.
mheap_.spanalloc.free(unsafe.Pointer(.mspancache.buf[]))
}
.mspancache.len = 0
lock(&mheap_.lock)
.pcache.flush(&mheap_.pages)
unlock(&mheap_.lock)
})
freemcache(.mcache)
.mcache = nil
gfpurge()
traceProcFree()
if raceenabled {
if .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.
:= getg().m
:= .p.ptr()
.p.set()
racectxend(.timerRaceCtx)
.timerRaceCtx = 0
.p.set()
}
raceprocdestroy(.raceprocctx)
.raceprocctx = 0
}
.gcAssistTime = 0
.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 ( int32) *p {
assertLockHeld(&sched.lock)
assertWorldStopped()
:= gomaxprocs
if < 0 || <= 0 {
throw("procresize: invalid arg")
}
if traceEnabled() {
traceGomaxprocs()
}
// update statistics
:= nanotime()
if sched.procresizetime != 0 {
sched.totaltime += int64() * ( - sched.procresizetime)
}
sched.procresizetime =
:= ( + 31) / 32
// Grow allp if necessary.
if > int32(len(allp)) {
// Synchronize with retake, which could be running
// concurrently since it doesn't run on a P.
lock(&allpLock)
if <= int32(cap(allp)) {
allp = allp[:]
} else {
:= make([]*p, )
// Copy everything up to allp's cap so we
// never lose old allocated Ps.
copy(, allp[:cap(allp)])
allp =
}
if <= int32(cap(idlepMask)) {
idlepMask = idlepMask[:]
timerpMask = timerpMask[:]
} else {
:= make([]uint32, )
// No need to copy beyond len, old Ps are irrelevant.
copy(, idlepMask)
idlepMask =
:= make([]uint32, )
copy(, timerpMask)
timerpMask =
}
unlock(&allpLock)
}
// initialize new P's
for := ; < ; ++ {
:= allp[]
if == nil {
= new(p)
}
.init()
atomicstorep(unsafe.Pointer(&allp[]), unsafe.Pointer())
}
:= getg()
if .m.p != 0 && .m.p.ptr().id < {
// continue to use the current P
.m.p.ptr().status = _Prunning
.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 .m.p != 0 {
if traceEnabled() {
// Pretend that we were descheduled
// and then scheduled again to keep
// the trace sane.
traceGoSched()
traceProcStop(.m.p.ptr())
}
.m.p.ptr().m = 0
}
.m.p = 0
:= allp[0]
.m = 0
.status = _Pidle
acquirep()
if traceEnabled() {
traceGoStart()
}
}
// g.m.p is now set, so we no longer need mcache0 for bootstrapping.
mcache0 = nil
// release resources from unused P's
for := ; < ; ++ {
:= allp[]
.destroy()
// can't free P itself because it can be referenced by an M in syscall
}
// Trim allp.
if int32(len(allp)) != {
lock(&allpLock)
allp = allp[:]
idlepMask = idlepMask[:]
timerpMask = timerpMask[:]
unlock(&allpLock)
}
var *p
for := - 1; >= 0; -- {
:= allp[]
if .m.p.ptr() == {
continue
}
.status = _Pidle
if runqempty() {
pidleput(, )
} else {
.m.set(mget())
.link.set()
=
}
}
stealOrder.reset(uint32())
var *int32 = &gomaxprocs // make compiler check that gomaxprocs is an int32
atomic.Store((*uint32)(unsafe.Pointer()), uint32())
if != {
// Notify the limiter that the amount of procs has changed.
gcCPULimiter.resetCapacity(, )
}
return
}
// 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 ( *p) {
// Do the part that isn't allowed to have write barriers.
wirep()
// Have p; write barriers now allowed.
// Perform deferred mcache flush before this P can allocate
// from a potentially stale mcache.
.mcache.prepareForSweep()
if traceEnabled() {
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 ( *p) {
:= getg()
if .m.p != 0 {
throw("wirep: already in go")
}
if .m != 0 || .status != _Pidle {
:= int64(0)
if .m != 0 {
= .m.ptr().id
}
print("wirep: p->m=", .m, "(", , ") p->status=", .status, "\n")
throw("wirep: invalid p state")
}
.m.p.set()
.m.set(.m)
.status = _Prunning
}
// Disassociate p and the current m.
func () *p {
:= getg()
if .m.p == 0 {
throw("releasep: invalid arg")
}
:= .m.p.ptr()
if .m.ptr() != .m || .status != _Prunning {
print("releasep: m=", .m, " m->p=", .m.p.ptr(), " p->m=", hex(.m), " p->status=", .status, "\n")
throw("releasep: invalid p state")
}
if traceEnabled() {
traceProcStop(.m.p.ptr())
}
.m.p = 0
.m = 0
.status = _Pidle
return
}
func ( int32) {
lock(&sched.lock)
sched.nmidlelocked +=
if > 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 () {
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 int32
if !iscgo && cgoHasExtraM && extraMLength.Load() > 0 {
= 1
}
:= mcount() - sched.nmidle - sched.nmidlelocked - sched.nmsys
if > {
return
}
if < 0 {
print("runtime: checkdead: nmidle=", sched.nmidle, " nmidlelocked=", sched.nmidlelocked, " mcount=", mcount(), " nmsys=", sched.nmsys, "\n")
unlock(&sched.lock)
throw("checkdead: inconsistent counts")
}
:= 0
forEachG(func( *g) {
if isSystemGoroutine(, false) {
return
}
:= readgstatus()
switch &^ _Gscan {
case _Gwaiting,
_Gpreempted:
++
case _Grunnable,
_Grunning,
_Gsyscall:
print("runtime: checkdead: find g ", .goid, " in status ", , "\n")
unlock(&sched.lock)
throw("checkdead: runnable g")
}
})
if == 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 := timeSleepUntil(); < maxWhen {
faketime =
// Start an M to steal the timer.
, := pidleget(faketime)
if == nil {
// There should always be a free P since
// nothing is running.
unlock(&sched.lock)
throw("checkdead: no p for timer")
}
:= mget()
if == nil {
// There should always be a free M since
// nothing is running.
unlock(&sched.lock)
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)
.spinning = true
.nextp.set()
notewakeup(&.park)
return
}
}
// There are no goroutines running, so we can look at the P's.
for , := range allp {
if len(.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 () {
lock(&sched.lock)
sched.nmsys++
checkdead()
unlock(&sched.lock)
:= int64(0)
:= 0 // how many cycles in succession we had not wokeup somebody
:= uint32(0)
for {
if == 0 { // start with 20us sleep...
= 20
} else if > 50 { // start doubling the sleep after 1ms...
*= 2
}
if > 10*1000 { // up to 10ms
= 10 * 1000
}
usleep()
// 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.
:= nanotime()
if debug.schedtrace <= 0 && (sched.gcwaiting.Load() || sched.npidle.Load() == gomaxprocs) {
lock(&sched.lock)
if sched.gcwaiting.Load() || sched.npidle.Load() == gomaxprocs {
:= false
:= timeSleepUntil()
if > {
sched.sysmonwait.Store(true)
unlock(&sched.lock)
// Make wake-up period small enough
// for the sampling to be correct.
:= forcegcperiod / 2
if - < {
= -
}
:= >= osRelaxMinNS
if {
osRelax(true)
}
= notetsleep(&sched.sysmonnote, )
if {
osRelax(false)
}
lock(&sched.lock)
sched.sysmonwait.Store(false)
noteclear(&sched.sysmonnote)
}
if {
= 0
= 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.
= nanotime()
// trigger libc interceptors if needed
if *cgo_yield != nil {
asmcgocall(*cgo_yield, nil)
}
// poll network if not polled for more than 10ms
:= sched.lastpoll.Load()
if netpollinited() && != 0 && +10*1000*1000 < {
sched.lastpoll.CompareAndSwap(, )
:= netpoll(0) // non-blocking - returns list of goroutines
if !.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(&)
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 := timeSleepUntil(); < {
startm(nil, false, 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() != 0 {
= 0
} else {
++
}
// check if we need to force a GC
if := (gcTrigger{kind: gcTriggerTime, now: }); .test() && forcegc.idle.Load() {
lock(&forcegc.lock)
forcegc.idle.Store(false)
var gList
.push(forcegc.g)
injectglist(&)
unlock(&forcegc.lock)
}
if debug.schedtrace > 0 && +int64(debug.schedtrace)*1000000 <= {
=
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 ( int64) uint32 {
:= 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 := 0; < len(allp); ++ {
:= allp[]
if == nil {
// This can happen if procresize has grown
// allp but not yet created new Ps.
continue
}
:= &.sysmontick
:= .status
:= false
if == _Prunning || == _Psyscall {
// Preempt G if it's running for too long.
:= int64(.schedtick)
if int64(.schedtick) != {
.schedtick = uint32()
.schedwhen =
} else if .schedwhen+forcePreemptNS <= {
preemptone()
// In case of syscall, preemptone() doesn't
// work, because there is no M wired to P.
= true
}
}
if == _Psyscall {
// Retake P from syscall if it's there for more than 1 sysmon tick (at least 20us).
:= int64(.syscalltick)
if ! && int64(.syscalltick) != {
.syscalltick = uint32()
.syscallwhen =
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() && sched.nmspinning.Load()+sched.npidle.Load() > 0 && .syscallwhen+10*1000*1000 > {
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(&.status, , _Pidle) {
if traceEnabled() {
traceGoSysBlock()
traceProcStop()
}
++
.syscalltick++
handoffp()
}
incidlelocked(1)
lock(&allpLock)
}
}
unlock(&allpLock)
return uint32()
}
// 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 () bool {
:= false
for , := range allp {
if .status != _Prunning {
continue
}
if preemptone() {
= true
}
}
return
}