1 // Copyright 2014 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
11 "runtime/internal/atomic"
12 "runtime/internal/sys"
16 // set using cmd/go/internal/modload.ModInfoProg
19 // Goroutine scheduler
20 // The scheduler's job is to distribute ready-to-run goroutines over worker threads.
22 // The main concepts are:
24 // M - worker thread, or machine.
25 // P - processor, a resource that is required to execute Go code.
26 // M must have an associated P to execute Go code, however it can be
27 // blocked or in a syscall w/o an associated P.
29 // Design doc at https://golang.org/s/go11sched.
31 // Worker thread parking/unparking.
32 // We need to balance between keeping enough running worker threads to utilize
33 // available hardware parallelism and parking excessive running worker threads
34 // to conserve CPU resources and power. This is not simple for two reasons:
35 // (1) scheduler state is intentionally distributed (in particular, per-P work
36 // queues), so it is not possible to compute global predicates on fast paths;
37 // (2) for optimal thread management we would need to know the future (don't park
38 // a worker thread when a new goroutine will be readied in near future).
40 // Three rejected approaches that would work badly:
41 // 1. Centralize all scheduler state (would inhibit scalability).
42 // 2. Direct goroutine handoff. That is, when we ready a new goroutine and there
43 // is a spare P, unpark a thread and handoff it the thread and the goroutine.
44 // This would lead to thread state thrashing, as the thread that readied the
45 // goroutine can be out of work the very next moment, we will need to park it.
46 // Also, it would destroy locality of computation as we want to preserve
47 // dependent goroutines on the same thread; and introduce additional latency.
48 // 3. Unpark an additional thread whenever we ready a goroutine and there is an
49 // idle P, but don't do handoff. This would lead to excessive thread parking/
50 // unparking as the additional threads will instantly park without discovering
53 // The current approach:
55 // This approach applies to three primary sources of potential work: readying a
56 // goroutine, new/modified-earlier timers, and idle-priority GC. See below for
57 // additional details.
59 // We unpark an additional thread when we submit work if (this is wakep()):
60 // 1. There is an idle P, and
61 // 2. There are no "spinning" worker threads.
63 // A worker thread is considered spinning if it is out of local work and did
64 // not find work in the global run queue or netpoller; the spinning state is
65 // denoted in m.spinning and in sched.nmspinning. Threads unparked this way are
66 // also considered spinning; we don't do goroutine handoff so such threads are
67 // out of work initially. Spinning threads spin on looking for work in per-P
68 // run queues and timer heaps or from the GC before parking. If a spinning
69 // thread finds work it takes itself out of the spinning state and proceeds to
70 // execution. If it does not find work it takes itself out of the spinning
71 // state and then parks.
73 // If there is at least one spinning thread (sched.nmspinning>1), we don't
74 // unpark new threads when submitting work. To compensate for that, if the last
75 // spinning thread finds work and stops spinning, it must unpark a new spinning
76 // thread. This approach smooths out unjustified spikes of thread unparking,
77 // but at the same time guarantees eventual maximal CPU parallelism
80 // The main implementation complication is that we need to be very careful
81 // during spinning->non-spinning thread transition. This transition can race
82 // with submission of new work, and either one part or another needs to unpark
83 // another worker thread. If they both fail to do that, we can end up with
84 // semi-persistent CPU underutilization.
86 // The general pattern for submission is:
87 // 1. Submit work to the local run queue, timer heap, or GC state.
88 // 2. #StoreLoad-style memory barrier.
89 // 3. Check sched.nmspinning.
91 // The general pattern for spinning->non-spinning transition is:
92 // 1. Decrement nmspinning.
93 // 2. #StoreLoad-style memory barrier.
94 // 3. Check all per-P work queues and GC for new work.
96 // Note that all this complexity does not apply to global run queue as we are
97 // not sloppy about thread unparking when submitting to global queue. Also see
98 // comments for nmspinning manipulation.
100 // How these different sources of work behave varies, though it doesn't affect
101 // the synchronization approach:
102 // * Ready goroutine: this is an obvious source of work; the goroutine is
103 // immediately ready and must run on some thread eventually.
104 // * New/modified-earlier timer: The current timer implementation (see time.go)
105 // uses netpoll in a thread with no work available to wait for the soonest
106 // timer. If there is no thread waiting, we want a new spinning thread to go
108 // * Idle-priority GC: The GC wakes a stopped idle thread to contribute to
109 // background GC work (note: currently disabled per golang.org/issue/19112).
110 // Also see golang.org/issue/44313, as this should be extended to all GC
121 // This slice records the initializing tasks that need to be
122 // done to start up the runtime. It is built by the linker.
123 var runtime_inittasks []*initTask
125 // main_init_done is a signal used by cgocallbackg that initialization
126 // has been completed. It is made before _cgo_notify_runtime_init_done,
127 // so all cgo calls can rely on it existing. When main_init is complete,
128 // it is closed, meaning cgocallbackg can reliably receive from it.
129 var main_init_done chan bool
131 //go:linkname main_main main.main
134 // mainStarted indicates that the main M has started.
137 // runtimeInitTime is the nanotime() at which the runtime started.
138 var runtimeInitTime int64
140 // Value to use for signal mask for newly created M's.
141 var initSigmask sigset
143 // The main goroutine.
147 // Racectx of m0->g0 is used only as the parent of the main goroutine.
148 // It must not be used for anything else.
151 // Max stack size is 1 GB on 64-bit, 250 MB on 32-bit.
152 // Using decimal instead of binary GB and MB because
153 // they look nicer in the stack overflow failure message.
154 if goarch.PtrSize == 8 {
155 maxstacksize = 1000000000
157 maxstacksize = 250000000
160 // An upper limit for max stack size. Used to avoid random crashes
161 // after calling SetMaxStack and trying to allocate a stack that is too big,
162 // since stackalloc works with 32-bit sizes.
163 maxstackceiling = 2 * maxstacksize
165 // Allow newproc to start new Ms.
168 if GOARCH != "wasm" { // no threads on wasm yet, so no sysmon
170 newm(sysmon, nil, -1)
174 // Lock the main goroutine onto this, the main OS thread,
175 // during initialization. Most programs won't care, but a few
176 // do require certain calls to be made by the main thread.
177 // Those can arrange for main.main to run in the main thread
178 // by calling runtime.LockOSThread during initialization
179 // to preserve the lock.
183 throw("runtime.main not on m0")
186 // Record when the world started.
187 // Must be before doInit for tracing init.
188 runtimeInitTime = nanotime()
189 if runtimeInitTime == 0 {
190 throw("nanotime returning zero")
193 if debug.inittrace != 0 {
194 inittrace.id = getg().goid
195 inittrace.active = true
198 doInit(runtime_inittasks) // Must be before defer.
200 // Defer unlock so that runtime.Goexit during init does the unlock too.
210 main_init_done = make(chan bool)
212 if _cgo_pthread_key_created == nil {
213 throw("_cgo_pthread_key_created missing")
216 if _cgo_thread_start == nil {
217 throw("_cgo_thread_start missing")
219 if GOOS != "windows" {
220 if _cgo_setenv == nil {
221 throw("_cgo_setenv missing")
223 if _cgo_unsetenv == nil {
224 throw("_cgo_unsetenv missing")
227 if _cgo_notify_runtime_init_done == nil {
228 throw("_cgo_notify_runtime_init_done missing")
231 // Set the x_crosscall2_ptr C function pointer variable point to crosscall2.
232 if set_crosscall2 == nil {
233 throw("set_crosscall2 missing")
237 // Start the template thread in case we enter Go from
238 // a C-created thread and need to create a new thread.
239 startTemplateThread()
240 cgocall(_cgo_notify_runtime_init_done, nil)
243 // Run the initializing tasks. Depending on build mode this
244 // list can arrive a few different ways, but it will always
245 // contain the init tasks computed by the linker for all the
246 // packages in the program (excluding those added at runtime
247 // by package plugin).
248 for _, m := range activeModules() {
252 // Disable init tracing after main init done to avoid overhead
253 // of collecting statistics in malloc and newproc
254 inittrace.active = false
256 close(main_init_done)
261 if isarchive || islibrary {
262 // A program compiled with -buildmode=c-archive or c-shared
263 // has a main, but it is not executed.
266 fn := main_main // make an indirect call, as the linker doesn't know the address of the main package when laying down the runtime
269 runExitHooks(0) // run hooks now, since racefini does not return
273 // Make racy client program work: if panicking on
274 // another goroutine at the same time as main returns,
275 // let the other goroutine finish printing the panic trace.
276 // Once it does, it will exit. See issues 3934 and 20018.
277 if runningPanicDefers.Load() != 0 {
278 // Running deferred functions should not take long.
279 for c := 0; c < 1000; c++ {
280 if runningPanicDefers.Load() == 0 {
286 if panicking.Load() != 0 {
287 gopark(nil, nil, waitReasonPanicWait, traceBlockForever, 1)
298 // os_beforeExit is called from os.Exit(0).
300 //go:linkname os_beforeExit os.runtime_beforeExit
301 func os_beforeExit(exitCode int) {
302 runExitHooks(exitCode)
303 if exitCode == 0 && raceenabled {
308 // start forcegc helper goroutine
313 func forcegchelper() {
315 lockInit(&forcegc.lock, lockRankForcegc)
318 if forcegc.idle.Load() {
319 throw("forcegc: phase error")
321 forcegc.idle.Store(true)
322 goparkunlock(&forcegc.lock, waitReasonForceGCIdle, traceBlockSystemGoroutine, 1)
323 // this goroutine is explicitly resumed by sysmon
324 if debug.gctrace > 0 {
327 // Time-triggered, fully concurrent.
328 gcStart(gcTrigger{kind: gcTriggerTime, now: nanotime()})
332 // Gosched yields the processor, allowing other goroutines to run. It does not
333 // suspend the current goroutine, so execution resumes automatically.
341 // goschedguarded yields the processor like gosched, but also checks
342 // for forbidden states and opts out of the yield in those cases.
345 func goschedguarded() {
346 mcall(goschedguarded_m)
349 // goschedIfBusy yields the processor like gosched, but only does so if
350 // there are no idle Ps or if we're on the only P and there's nothing in
351 // the run queue. In both cases, there is freely available idle time.
354 func goschedIfBusy() {
356 // Call gosched if gp.preempt is set; we may be in a tight loop that
357 // doesn't otherwise yield.
358 if !gp.preempt && sched.npidle.Load() > 0 {
364 // Puts the current goroutine into a waiting state and calls unlockf on the
367 // If unlockf returns false, the goroutine is resumed.
369 // unlockf must not access this G's stack, as it may be moved between
370 // the call to gopark and the call to unlockf.
372 // Note that because unlockf is called after putting the G into a waiting
373 // state, the G may have already been readied by the time unlockf is called
374 // unless there is external synchronization preventing the G from being
375 // readied. If unlockf returns false, it must guarantee that the G cannot be
376 // externally readied.
378 // Reason explains why the goroutine has been parked. It is displayed in stack
379 // traces and heap dumps. Reasons should be unique and descriptive. Do not
380 // re-use reasons, add new ones.
381 func gopark(unlockf func(*g, unsafe.Pointer) bool, lock unsafe.Pointer, reason waitReason, traceReason traceBlockReason, traceskip int) {
382 if reason != waitReasonSleep {
383 checkTimeouts() // timeouts may expire while two goroutines keep the scheduler busy
387 status := readgstatus(gp)
388 if status != _Grunning && status != _Gscanrunning {
389 throw("gopark: bad g status")
392 mp.waitunlockf = unlockf
393 gp.waitreason = reason
394 mp.waitTraceBlockReason = traceReason
395 mp.waitTraceSkip = traceskip
397 // can't do anything that might move the G between Ms here.
401 // Puts the current goroutine into a waiting state and unlocks the lock.
402 // The goroutine can be made runnable again by calling goready(gp).
403 func goparkunlock(lock *mutex, reason waitReason, traceReason traceBlockReason, traceskip int) {
404 gopark(parkunlock_c, unsafe.Pointer(lock), reason, traceReason, traceskip)
407 func goready(gp *g, traceskip int) {
409 ready(gp, traceskip, true)
414 func acquireSudog() *sudog {
415 // Delicate dance: the semaphore implementation calls
416 // acquireSudog, acquireSudog calls new(sudog),
417 // new calls malloc, malloc can call the garbage collector,
418 // and the garbage collector calls the semaphore implementation
420 // Break the cycle by doing acquirem/releasem around new(sudog).
421 // The acquirem/releasem increments m.locks during new(sudog),
422 // which keeps the garbage collector from being invoked.
425 if len(pp.sudogcache) == 0 {
426 lock(&sched.sudoglock)
427 // First, try to grab a batch from central cache.
428 for len(pp.sudogcache) < cap(pp.sudogcache)/2 && sched.sudogcache != nil {
429 s := sched.sudogcache
430 sched.sudogcache = s.next
432 pp.sudogcache = append(pp.sudogcache, s)
434 unlock(&sched.sudoglock)
435 // If the central cache is empty, allocate a new one.
436 if len(pp.sudogcache) == 0 {
437 pp.sudogcache = append(pp.sudogcache, new(sudog))
440 n := len(pp.sudogcache)
441 s := pp.sudogcache[n-1]
442 pp.sudogcache[n-1] = nil
443 pp.sudogcache = pp.sudogcache[:n-1]
445 throw("acquireSudog: found s.elem != nil in cache")
452 func releaseSudog(s *sudog) {
454 throw("runtime: sudog with non-nil elem")
457 throw("runtime: sudog with non-false isSelect")
460 throw("runtime: sudog with non-nil next")
463 throw("runtime: sudog with non-nil prev")
465 if s.waitlink != nil {
466 throw("runtime: sudog with non-nil waitlink")
469 throw("runtime: sudog with non-nil c")
473 throw("runtime: releaseSudog with non-nil gp.param")
475 mp := acquirem() // avoid rescheduling to another P
477 if len(pp.sudogcache) == cap(pp.sudogcache) {
478 // Transfer half of local cache to the central cache.
479 var first, last *sudog
480 for len(pp.sudogcache) > cap(pp.sudogcache)/2 {
481 n := len(pp.sudogcache)
482 p := pp.sudogcache[n-1]
483 pp.sudogcache[n-1] = nil
484 pp.sudogcache = pp.sudogcache[:n-1]
492 lock(&sched.sudoglock)
493 last.next = sched.sudogcache
494 sched.sudogcache = first
495 unlock(&sched.sudoglock)
497 pp.sudogcache = append(pp.sudogcache, s)
501 // called from assembly.
502 func badmcall(fn func(*g)) {
503 throw("runtime: mcall called on m->g0 stack")
506 func badmcall2(fn func(*g)) {
507 throw("runtime: mcall function returned")
510 func badreflectcall() {
511 panic(plainError("arg size to reflect.call more than 1GB"))
515 //go:nowritebarrierrec
516 func badmorestackg0() {
517 writeErrStr("fatal: morestack on g0\n")
521 //go:nowritebarrierrec
522 func badmorestackgsignal() {
523 writeErrStr("fatal: morestack on gsignal\n")
531 func lockedOSThread() bool {
533 return gp.lockedm != 0 && gp.m.lockedg != 0
537 // allgs contains all Gs ever created (including dead Gs), and thus
540 // Access via the slice is protected by allglock or stop-the-world.
541 // Readers that cannot take the lock may (carefully!) use the atomic
546 // allglen and allgptr are atomic variables that contain len(allgs) and
547 // &allgs[0] respectively. Proper ordering depends on totally-ordered
548 // loads and stores. Writes are protected by allglock.
550 // allgptr is updated before allglen. Readers should read allglen
551 // before allgptr to ensure that allglen is always <= len(allgptr). New
552 // Gs appended during the race can be missed. For a consistent view of
553 // all Gs, allglock must be held.
555 // allgptr copies should always be stored as a concrete type or
556 // unsafe.Pointer, not uintptr, to ensure that GC can still reach it
557 // even if it points to a stale array.
562 func allgadd(gp *g) {
563 if readgstatus(gp) == _Gidle {
564 throw("allgadd: bad status Gidle")
568 allgs = append(allgs, gp)
569 if &allgs[0] != allgptr {
570 atomicstorep(unsafe.Pointer(&allgptr), unsafe.Pointer(&allgs[0]))
572 atomic.Storeuintptr(&allglen, uintptr(len(allgs)))
576 // allGsSnapshot returns a snapshot of the slice of all Gs.
578 // The world must be stopped or allglock must be held.
579 func allGsSnapshot() []*g {
580 assertWorldStoppedOrLockHeld(&allglock)
582 // Because the world is stopped or allglock is held, allgadd
583 // cannot happen concurrently with this. allgs grows
584 // monotonically and existing entries never change, so we can
585 // simply return a copy of the slice header. For added safety,
586 // we trim everything past len because that can still change.
587 return allgs[:len(allgs):len(allgs)]
590 // atomicAllG returns &allgs[0] and len(allgs) for use with atomicAllGIndex.
591 func atomicAllG() (**g, uintptr) {
592 length := atomic.Loaduintptr(&allglen)
593 ptr := (**g)(atomic.Loadp(unsafe.Pointer(&allgptr)))
597 // atomicAllGIndex returns ptr[i] with the allgptr returned from atomicAllG.
598 func atomicAllGIndex(ptr **g, i uintptr) *g {
599 return *(**g)(add(unsafe.Pointer(ptr), i*goarch.PtrSize))
602 // forEachG calls fn on every G from allgs.
604 // forEachG takes a lock to exclude concurrent addition of new Gs.
605 func forEachG(fn func(gp *g)) {
607 for _, gp := range allgs {
613 // forEachGRace calls fn on every G from allgs.
615 // forEachGRace avoids locking, but does not exclude addition of new Gs during
616 // execution, which may be missed.
617 func forEachGRace(fn func(gp *g)) {
618 ptr, length := atomicAllG()
619 for i := uintptr(0); i < length; i++ {
620 gp := atomicAllGIndex(ptr, i)
627 // Number of goroutine ids to grab from sched.goidgen to local per-P cache at once.
628 // 16 seems to provide enough amortization, but other than that it's mostly arbitrary number.
632 // cpuinit sets up CPU feature flags and calls internal/cpu.Initialize. env should be the complete
633 // value of the GODEBUG environment variable.
634 func cpuinit(env string) {
636 case "aix", "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd", "illumos", "solaris", "linux":
637 cpu.DebugOptions = true
641 // Support cpu feature variables are used in code generated by the compiler
642 // to guard execution of instructions that can not be assumed to be always supported.
645 x86HasPOPCNT = cpu.X86.HasPOPCNT
646 x86HasSSE41 = cpu.X86.HasSSE41
647 x86HasFMA = cpu.X86.HasFMA
650 armHasVFPv4 = cpu.ARM.HasVFPv4
653 arm64HasATOMICS = cpu.ARM64.HasATOMICS
657 // getGodebugEarly extracts the environment variable GODEBUG from the environment on
658 // Unix-like operating systems and returns it. This function exists to extract GODEBUG
659 // early before much of the runtime is initialized.
660 func getGodebugEarly() string {
661 const prefix = "GODEBUG="
664 case "aix", "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd", "illumos", "solaris", "linux":
665 // Similar to goenv_unix but extracts the environment value for
667 // TODO(moehrmann): remove when general goenvs() can be called before cpuinit()
669 for argv_index(argv, argc+1+n) != nil {
673 for i := int32(0); i < n; i++ {
674 p := argv_index(argv, argc+1+i)
675 s := unsafe.String(p, findnull(p))
677 if hasPrefix(s, prefix) {
678 env = gostring(p)[len(prefix):]
686 // The bootstrap sequence is:
690 // make & queue new G
691 // call runtime·mstart
693 // The new G calls runtime·main.
695 lockInit(&sched.lock, lockRankSched)
696 lockInit(&sched.sysmonlock, lockRankSysmon)
697 lockInit(&sched.deferlock, lockRankDefer)
698 lockInit(&sched.sudoglock, lockRankSudog)
699 lockInit(&deadlock, lockRankDeadlock)
700 lockInit(&paniclk, lockRankPanic)
701 lockInit(&allglock, lockRankAllg)
702 lockInit(&allpLock, lockRankAllp)
703 lockInit(&reflectOffs.lock, lockRankReflectOffs)
704 lockInit(&finlock, lockRankFin)
705 lockInit(&cpuprof.lock, lockRankCpuprof)
707 // Enforce that this lock is always a leaf lock.
708 // All of this lock's critical sections should be
710 lockInit(&memstats.heapStats.noPLock, lockRankLeafRank)
712 // raceinit must be the first call to race detector.
713 // In particular, it must be done before mallocinit below calls racemapshadow.
716 gp.racectx, raceprocctx0 = raceinit()
719 sched.maxmcount = 10000
721 // The world starts stopped.
727 godebug := getGodebugEarly()
728 initPageTrace(godebug) // must run after mallocinit but before anything allocates
729 cpuinit(godebug) // must run before alginit
730 alginit() // maps, hash, fastrand must not be used before this call
731 fastrandinit() // must run before mcommoninit
732 mcommoninit(gp.m, -1)
733 modulesinit() // provides activeModules
734 typelinksinit() // uses maps, activeModules
735 itabsinit() // uses activeModules
736 stkobjinit() // must run before GC starts
738 sigsave(&gp.m.sigmask)
739 initSigmask = gp.m.sigmask
747 // if disableMemoryProfiling is set, update MemProfileRate to 0 to turn off memprofile.
748 // Note: parsedebugvars may update MemProfileRate, but when disableMemoryProfiling is
749 // set to true by the linker, it means that nothing is consuming the profile, it is
750 // safe to set MemProfileRate to 0.
751 if disableMemoryProfiling {
756 sched.lastpoll.Store(nanotime())
758 if n, ok := atoi32(gogetenv("GOMAXPROCS")); ok && n > 0 {
761 if procresize(procs) != nil {
762 throw("unknown runnable goroutine during bootstrap")
766 // World is effectively started now, as P's can run.
769 if buildVersion == "" {
770 // Condition should never trigger. This code just serves
771 // to ensure runtime·buildVersion is kept in the resulting binary.
772 buildVersion = "unknown"
774 if len(modinfo) == 1 {
775 // Condition should never trigger. This code just serves
776 // to ensure runtime·modinfo is kept in the resulting binary.
781 func dumpgstatus(gp *g) {
783 print("runtime: gp: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n")
784 print("runtime: getg: g=", thisg, ", goid=", thisg.goid, ", g->atomicstatus=", readgstatus(thisg), "\n")
787 // sched.lock must be held.
789 assertLockHeld(&sched.lock)
791 // Exclude extra M's, which are used for cgocallback from threads
794 // The purpose of the SetMaxThreads limit is to avoid accidental fork
795 // bomb from something like millions of goroutines blocking on system
796 // calls, causing the runtime to create millions of threads. By
797 // definition, this isn't a problem for threads created in C, so we
798 // exclude them from the limit. See https://go.dev/issue/60004.
799 count := mcount() - int32(extraMInUse.Load()) - int32(extraMLength.Load())
800 if count > sched.maxmcount {
801 print("runtime: program exceeds ", sched.maxmcount, "-thread limit\n")
802 throw("thread exhaustion")
806 // mReserveID returns the next ID to use for a new m. This new m is immediately
807 // considered 'running' by checkdead.
809 // sched.lock must be held.
810 func mReserveID() int64 {
811 assertLockHeld(&sched.lock)
813 if sched.mnext+1 < sched.mnext {
814 throw("runtime: thread ID overflow")
822 // Pre-allocated ID may be passed as 'id', or omitted by passing -1.
823 func mcommoninit(mp *m, id int64) {
826 // g0 stack won't make sense for user (and is not necessary unwindable).
828 callers(1, mp.createstack[:])
839 lo := uint32(int64Hash(uint64(mp.id), fastrandseed))
840 hi := uint32(int64Hash(uint64(cputicks()), ^fastrandseed))
844 // Same behavior as for 1.17.
845 // TODO: Simplify this.
846 if goarch.BigEndian {
847 mp.fastrand = uint64(lo)<<32 | uint64(hi)
849 mp.fastrand = uint64(hi)<<32 | uint64(lo)
853 if mp.gsignal != nil {
854 mp.gsignal.stackguard1 = mp.gsignal.stack.lo + stackGuard
857 // Add to allm so garbage collector doesn't free g->m
858 // when it is just in a register or thread-local storage.
861 // NumCgoCall() iterates over allm w/o schedlock,
862 // so we need to publish it safely.
863 atomicstorep(unsafe.Pointer(&allm), unsafe.Pointer(mp))
866 // Allocate memory to hold a cgo traceback if the cgo call crashes.
867 if iscgo || GOOS == "solaris" || GOOS == "illumos" || GOOS == "windows" {
868 mp.cgoCallers = new(cgoCallers)
872 func (mp *m) becomeSpinning() {
874 sched.nmspinning.Add(1)
875 sched.needspinning.Store(0)
878 func (mp *m) hasCgoOnStack() bool {
879 return mp.ncgo > 0 || mp.isextra
882 var fastrandseed uintptr
884 func fastrandinit() {
885 s := (*[unsafe.Sizeof(fastrandseed)]byte)(unsafe.Pointer(&fastrandseed))[:]
889 // Mark gp ready to run.
890 func ready(gp *g, traceskip int, next bool) {
892 traceGoUnpark(gp, traceskip)
895 status := readgstatus(gp)
898 mp := acquirem() // disable preemption because it can be holding p in a local var
899 if status&^_Gscan != _Gwaiting {
901 throw("bad g->status in ready")
904 // status is Gwaiting or Gscanwaiting, make Grunnable and put on runq
905 casgstatus(gp, _Gwaiting, _Grunnable)
906 runqput(mp.p.ptr(), gp, next)
911 // freezeStopWait is a large value that freezetheworld sets
912 // sched.stopwait to in order to request that all Gs permanently stop.
913 const freezeStopWait = 0x7fffffff
915 // freezing is set to non-zero if the runtime is trying to freeze the
917 var freezing atomic.Bool
919 // Similar to stopTheWorld but best-effort and can be called several times.
920 // There is no reverse operation, used during crashing.
921 // This function must not lock any mutexes.
922 func freezetheworld() {
924 if debug.dontfreezetheworld > 0 {
925 // Don't prempt Ps to stop goroutines. That will perturb
926 // scheduler state, making debugging more difficult. Instead,
927 // allow goroutines to continue execution.
929 // fatalpanic will tracebackothers to trace all goroutines. It
930 // is unsafe to trace a running goroutine, so tracebackothers
931 // will skip running goroutines. That is OK and expected, we
932 // expect users of dontfreezetheworld to use core files anyway.
934 // However, allowing the scheduler to continue running free
935 // introduces a race: a goroutine may be stopped when
936 // tracebackothers checks its status, and then start running
937 // later when we are in the middle of traceback, potentially
940 // To mitigate this, when an M naturally enters the scheduler,
941 // schedule checks if freezing is set and if so stops
942 // execution. This guarantees that while Gs can transition from
943 // running to stopped, they can never transition from stopped
946 // The sleep here allows racing Ms that missed freezing and are
947 // about to run a G to complete the transition to running
948 // before we start traceback.
953 // stopwait and preemption requests can be lost
954 // due to races with concurrently executing threads,
955 // so try several times
956 for i := 0; i < 5; i++ {
957 // this should tell the scheduler to not start any new goroutines
958 sched.stopwait = freezeStopWait
959 sched.gcwaiting.Store(true)
960 // this should stop running goroutines
962 break // no running goroutines
972 // All reads and writes of g's status go through readgstatus, casgstatus
973 // castogscanstatus, casfrom_Gscanstatus.
976 func readgstatus(gp *g) uint32 {
977 return gp.atomicstatus.Load()
980 // The Gscanstatuses are acting like locks and this releases them.
981 // If it proves to be a performance hit we should be able to make these
982 // simple atomic stores but for now we are going to throw if
983 // we see an inconsistent state.
984 func casfrom_Gscanstatus(gp *g, oldval, newval uint32) {
987 // Check that transition is valid.
990 print("runtime: casfrom_Gscanstatus bad oldval gp=", gp, ", oldval=", hex(oldval), ", newval=", hex(newval), "\n")
992 throw("casfrom_Gscanstatus:top gp->status is not in scan state")
998 if newval == oldval&^_Gscan {
999 success = gp.atomicstatus.CompareAndSwap(oldval, newval)
1003 print("runtime: casfrom_Gscanstatus failed gp=", gp, ", oldval=", hex(oldval), ", newval=", hex(newval), "\n")
1005 throw("casfrom_Gscanstatus: gp->status is not in scan state")
1007 releaseLockRank(lockRankGscan)
1010 // This will return false if the gp is not in the expected status and the cas fails.
1011 // This acts like a lock acquire while the casfromgstatus acts like a lock release.
1012 func castogscanstatus(gp *g, oldval, newval uint32) bool {
1018 if newval == oldval|_Gscan {
1019 r := gp.atomicstatus.CompareAndSwap(oldval, newval)
1021 acquireLockRank(lockRankGscan)
1027 print("runtime: castogscanstatus oldval=", hex(oldval), " newval=", hex(newval), "\n")
1028 throw("castogscanstatus")
1029 panic("not reached")
1032 // casgstatusAlwaysTrack is a debug flag that causes casgstatus to always track
1033 // various latencies on every transition instead of sampling them.
1034 var casgstatusAlwaysTrack = false
1036 // If asked to move to or from a Gscanstatus this will throw. Use the castogscanstatus
1037 // and casfrom_Gscanstatus instead.
1038 // casgstatus will loop if the g->atomicstatus is in a Gscan status until the routine that
1039 // put it in the Gscan state is finished.
1042 func casgstatus(gp *g, oldval, newval uint32) {
1043 if (oldval&_Gscan != 0) || (newval&_Gscan != 0) || oldval == newval {
1044 systemstack(func() {
1045 print("runtime: casgstatus: oldval=", hex(oldval), " newval=", hex(newval), "\n")
1046 throw("casgstatus: bad incoming values")
1050 acquireLockRank(lockRankGscan)
1051 releaseLockRank(lockRankGscan)
1053 // See https://golang.org/cl/21503 for justification of the yield delay.
1054 const yieldDelay = 5 * 1000
1057 // loop if gp->atomicstatus is in a scan state giving
1058 // GC time to finish and change the state to oldval.
1059 for i := 0; !gp.atomicstatus.CompareAndSwap(oldval, newval); i++ {
1060 if oldval == _Gwaiting && gp.atomicstatus.Load() == _Grunnable {
1061 throw("casgstatus: waiting for Gwaiting but is Grunnable")
1064 nextYield = nanotime() + yieldDelay
1066 if nanotime() < nextYield {
1067 for x := 0; x < 10 && gp.atomicstatus.Load() != oldval; x++ {
1072 nextYield = nanotime() + yieldDelay/2
1076 if oldval == _Grunning {
1077 // Track every gTrackingPeriod time a goroutine transitions out of running.
1078 if casgstatusAlwaysTrack || gp.trackingSeq%gTrackingPeriod == 0 {
1087 // Handle various kinds of tracking.
1090 // - Time spent in runnable.
1091 // - Time spent blocked on a sync.Mutex or sync.RWMutex.
1094 // We transitioned out of runnable, so measure how much
1095 // time we spent in this state and add it to
1098 gp.runnableTime += now - gp.trackingStamp
1099 gp.trackingStamp = 0
1101 if !gp.waitreason.isMutexWait() {
1102 // Not blocking on a lock.
1105 // Blocking on a lock, measure it. Note that because we're
1106 // sampling, we have to multiply by our sampling period to get
1107 // a more representative estimate of the absolute value.
1108 // gTrackingPeriod also represents an accurate sampling period
1109 // because we can only enter this state from _Grunning.
1111 sched.totalMutexWaitTime.Add((now - gp.trackingStamp) * gTrackingPeriod)
1112 gp.trackingStamp = 0
1116 if !gp.waitreason.isMutexWait() {
1117 // Not blocking on a lock.
1120 // Blocking on a lock. Write down the timestamp.
1122 gp.trackingStamp = now
1124 // We just transitioned into runnable, so record what
1125 // time that happened.
1127 gp.trackingStamp = now
1129 // We're transitioning into running, so turn off
1130 // tracking and record how much time we spent in
1133 sched.timeToRun.record(gp.runnableTime)
1138 // casGToWaiting transitions gp from old to _Gwaiting, and sets the wait reason.
1140 // Use this over casgstatus when possible to ensure that a waitreason is set.
1141 func casGToWaiting(gp *g, old uint32, reason waitReason) {
1142 // Set the wait reason before calling casgstatus, because casgstatus will use it.
1143 gp.waitreason = reason
1144 casgstatus(gp, old, _Gwaiting)
1147 // casgstatus(gp, oldstatus, Gcopystack), assuming oldstatus is Gwaiting or Grunnable.
1148 // Returns old status. Cannot call casgstatus directly, because we are racing with an
1149 // async wakeup that might come in from netpoll. If we see Gwaiting from the readgstatus,
1150 // it might have become Grunnable by the time we get to the cas. If we called casgstatus,
1151 // it would loop waiting for the status to go back to Gwaiting, which it never will.
1154 func casgcopystack(gp *g) uint32 {
1156 oldstatus := readgstatus(gp) &^ _Gscan
1157 if oldstatus != _Gwaiting && oldstatus != _Grunnable {
1158 throw("copystack: bad status, not Gwaiting or Grunnable")
1160 if gp.atomicstatus.CompareAndSwap(oldstatus, _Gcopystack) {
1166 // casGToPreemptScan transitions gp from _Grunning to _Gscan|_Gpreempted.
1168 // TODO(austin): This is the only status operation that both changes
1169 // the status and locks the _Gscan bit. Rethink this.
1170 func casGToPreemptScan(gp *g, old, new uint32) {
1171 if old != _Grunning || new != _Gscan|_Gpreempted {
1172 throw("bad g transition")
1174 acquireLockRank(lockRankGscan)
1175 for !gp.atomicstatus.CompareAndSwap(_Grunning, _Gscan|_Gpreempted) {
1179 // casGFromPreempted attempts to transition gp from _Gpreempted to
1180 // _Gwaiting. If successful, the caller is responsible for
1181 // re-scheduling gp.
1182 func casGFromPreempted(gp *g, old, new uint32) bool {
1183 if old != _Gpreempted || new != _Gwaiting {
1184 throw("bad g transition")
1186 gp.waitreason = waitReasonPreempted
1187 return gp.atomicstatus.CompareAndSwap(_Gpreempted, _Gwaiting)
1190 // stwReason is an enumeration of reasons the world is stopping.
1191 type stwReason uint8
1193 // Reasons to stop-the-world.
1195 // Avoid reusing reasons and add new ones instead.
1197 stwUnknown stwReason = iota // "unknown"
1198 stwGCMarkTerm // "GC mark termination"
1199 stwGCSweepTerm // "GC sweep termination"
1200 stwWriteHeapDump // "write heap dump"
1201 stwGoroutineProfile // "goroutine profile"
1202 stwGoroutineProfileCleanup // "goroutine profile cleanup"
1203 stwAllGoroutinesStack // "all goroutines stack trace"
1204 stwReadMemStats // "read mem stats"
1205 stwAllThreadsSyscall // "AllThreadsSyscall"
1206 stwGOMAXPROCS // "GOMAXPROCS"
1207 stwStartTrace // "start trace"
1208 stwStopTrace // "stop trace"
1209 stwForTestCountPagesInUse // "CountPagesInUse (test)"
1210 stwForTestReadMetricsSlow // "ReadMetricsSlow (test)"
1211 stwForTestReadMemStatsSlow // "ReadMemStatsSlow (test)"
1212 stwForTestPageCachePagesLeaked // "PageCachePagesLeaked (test)"
1213 stwForTestResetDebugLog // "ResetDebugLog (test)"
1216 func (r stwReason) String() string {
1217 return stwReasonStrings[r]
1220 // If you add to this list, also add it to src/internal/trace/parser.go.
1221 // If you change the values of any of the stw* constants, bump the trace
1222 // version number and make a copy of this.
1223 var stwReasonStrings = [...]string{
1224 stwUnknown: "unknown",
1225 stwGCMarkTerm: "GC mark termination",
1226 stwGCSweepTerm: "GC sweep termination",
1227 stwWriteHeapDump: "write heap dump",
1228 stwGoroutineProfile: "goroutine profile",
1229 stwGoroutineProfileCleanup: "goroutine profile cleanup",
1230 stwAllGoroutinesStack: "all goroutines stack trace",
1231 stwReadMemStats: "read mem stats",
1232 stwAllThreadsSyscall: "AllThreadsSyscall",
1233 stwGOMAXPROCS: "GOMAXPROCS",
1234 stwStartTrace: "start trace",
1235 stwStopTrace: "stop trace",
1236 stwForTestCountPagesInUse: "CountPagesInUse (test)",
1237 stwForTestReadMetricsSlow: "ReadMetricsSlow (test)",
1238 stwForTestReadMemStatsSlow: "ReadMemStatsSlow (test)",
1239 stwForTestPageCachePagesLeaked: "PageCachePagesLeaked (test)",
1240 stwForTestResetDebugLog: "ResetDebugLog (test)",
1243 // stopTheWorld stops all P's from executing goroutines, interrupting
1244 // all goroutines at GC safe points and records reason as the reason
1245 // for the stop. On return, only the current goroutine's P is running.
1246 // stopTheWorld must not be called from a system stack and the caller
1247 // must not hold worldsema. The caller must call startTheWorld when
1248 // other P's should resume execution.
1250 // stopTheWorld is safe for multiple goroutines to call at the
1251 // same time. Each will execute its own stop, and the stops will
1254 // This is also used by routines that do stack dumps. If the system is
1255 // in panic or being exited, this may not reliably stop all
1257 func stopTheWorld(reason stwReason) {
1258 semacquire(&worldsema)
1260 gp.m.preemptoff = reason.String()
1261 systemstack(func() {
1262 // Mark the goroutine which called stopTheWorld preemptible so its
1263 // stack may be scanned.
1264 // This lets a mark worker scan us while we try to stop the world
1265 // since otherwise we could get in a mutual preemption deadlock.
1266 // We must not modify anything on the G stack because a stack shrink
1267 // may occur. A stack shrink is otherwise OK though because in order
1268 // to return from this function (and to leave the system stack) we
1269 // must have preempted all goroutines, including any attempting
1270 // to scan our stack, in which case, any stack shrinking will
1271 // have already completed by the time we exit.
1272 // Don't provide a wait reason because we're still executing.
1273 casGToWaiting(gp, _Grunning, waitReasonStoppingTheWorld)
1274 stopTheWorldWithSema(reason)
1275 casgstatus(gp, _Gwaiting, _Grunning)
1279 // startTheWorld undoes the effects of stopTheWorld.
1280 func startTheWorld() {
1281 systemstack(func() { startTheWorldWithSema() })
1283 // worldsema must be held over startTheWorldWithSema to ensure
1284 // gomaxprocs cannot change while worldsema is held.
1286 // Release worldsema with direct handoff to the next waiter, but
1287 // acquirem so that semrelease1 doesn't try to yield our time.
1289 // Otherwise if e.g. ReadMemStats is being called in a loop,
1290 // it might stomp on other attempts to stop the world, such as
1291 // for starting or ending GC. The operation this blocks is
1292 // so heavy-weight that we should just try to be as fair as
1295 // We don't want to just allow us to get preempted between now
1296 // and releasing the semaphore because then we keep everyone
1297 // (including, for example, GCs) waiting longer.
1300 semrelease1(&worldsema, true, 0)
1304 // stopTheWorldGC has the same effect as stopTheWorld, but blocks
1305 // until the GC is not running. It also blocks a GC from starting
1306 // until startTheWorldGC is called.
1307 func stopTheWorldGC(reason stwReason) {
1309 stopTheWorld(reason)
1312 // startTheWorldGC undoes the effects of stopTheWorldGC.
1313 func startTheWorldGC() {
1318 // Holding worldsema grants an M the right to try to stop the world.
1319 var worldsema uint32 = 1
1321 // Holding gcsema grants the M the right to block a GC, and blocks
1322 // until the current GC is done. In particular, it prevents gomaxprocs
1323 // from changing concurrently.
1325 // TODO(mknyszek): Once gomaxprocs and the execution tracer can handle
1326 // being changed/enabled during a GC, remove this.
1327 var gcsema uint32 = 1
1329 // stopTheWorldWithSema is the core implementation of stopTheWorld.
1330 // The caller is responsible for acquiring worldsema and disabling
1331 // preemption first and then should stopTheWorldWithSema on the system
1334 // semacquire(&worldsema, 0)
1335 // m.preemptoff = "reason"
1336 // systemstack(stopTheWorldWithSema)
1338 // When finished, the caller must either call startTheWorld or undo
1339 // these three operations separately:
1341 // m.preemptoff = ""
1342 // systemstack(startTheWorldWithSema)
1343 // semrelease(&worldsema)
1345 // It is allowed to acquire worldsema once and then execute multiple
1346 // startTheWorldWithSema/stopTheWorldWithSema pairs.
1347 // Other P's are able to execute between successive calls to
1348 // startTheWorldWithSema and stopTheWorldWithSema.
1349 // Holding worldsema causes any other goroutines invoking
1350 // stopTheWorld to block.
1351 func stopTheWorldWithSema(reason stwReason) {
1353 traceSTWStart(reason)
1357 // If we hold a lock, then we won't be able to stop another M
1358 // that is blocked trying to acquire the lock.
1360 throw("stopTheWorld: holding locks")
1364 sched.stopwait = gomaxprocs
1365 sched.gcwaiting.Store(true)
1368 gp.m.p.ptr().status = _Pgcstop // Pgcstop is only diagnostic.
1370 // try to retake all P's in Psyscall status
1371 for _, pp := range allp {
1373 if s == _Psyscall && atomic.Cas(&pp.status, s, _Pgcstop) {
1385 pp, _ := pidleget(now)
1389 pp.status = _Pgcstop
1392 wait := sched.stopwait > 0
1395 // wait for remaining P's to stop voluntarily
1398 // wait for 100us, then try to re-preempt in case of any races
1399 if notetsleep(&sched.stopnote, 100*1000) {
1400 noteclear(&sched.stopnote)
1409 if sched.stopwait != 0 {
1410 bad = "stopTheWorld: not stopped (stopwait != 0)"
1412 for _, pp := range allp {
1413 if pp.status != _Pgcstop {
1414 bad = "stopTheWorld: not stopped (status != _Pgcstop)"
1418 if freezing.Load() {
1419 // Some other thread is panicking. This can cause the
1420 // sanity checks above to fail if the panic happens in
1421 // the signal handler on a stopped thread. Either way,
1422 // we should halt this thread.
1433 func startTheWorldWithSema() int64 {
1434 assertWorldStopped()
1436 mp := acquirem() // disable preemption because it can be holding p in a local var
1437 if netpollinited() {
1438 list, delta := netpoll(0) // non-blocking
1440 netpollAdjustWaiters(delta)
1449 p1 := procresize(procs)
1450 sched.gcwaiting.Store(false)
1451 if sched.sysmonwait.Load() {
1452 sched.sysmonwait.Store(false)
1453 notewakeup(&sched.sysmonnote)
1466 throw("startTheWorld: inconsistent mp->nextp")
1469 notewakeup(&mp.park)
1471 // Start M to run P. Do not start another M below.
1476 // Capture start-the-world time before doing clean-up tasks.
1477 startTime := nanotime()
1482 // Wakeup an additional proc in case we have excessive runnable goroutines
1483 // in local queues or in the global queue. If we don't, the proc will park itself.
1484 // If we have lots of excessive work, resetspinning will unpark additional procs as necessary.
1492 // usesLibcall indicates whether this runtime performs system calls
1494 func usesLibcall() bool {
1496 case "aix", "darwin", "illumos", "ios", "solaris", "windows":
1499 return GOARCH == "386" || GOARCH == "amd64" || GOARCH == "arm" || GOARCH == "arm64"
1504 // mStackIsSystemAllocated indicates whether this runtime starts on a
1505 // system-allocated stack.
1506 func mStackIsSystemAllocated() bool {
1508 case "aix", "darwin", "plan9", "illumos", "ios", "solaris", "windows":
1512 case "386", "amd64", "arm", "arm64":
1519 // mstart is the entry-point for new Ms.
1520 // It is written in assembly, uses ABI0, is marked TOPFRAME, and calls mstart0.
1523 // mstart0 is the Go entry-point for new Ms.
1524 // This must not split the stack because we may not even have stack
1525 // bounds set up yet.
1527 // May run during STW (because it doesn't have a P yet), so write
1528 // barriers are not allowed.
1531 //go:nowritebarrierrec
1535 osStack := gp.stack.lo == 0
1537 // Initialize stack bounds from system stack.
1538 // Cgo may have left stack size in stack.hi.
1539 // minit may update the stack bounds.
1541 // Note: these bounds may not be very accurate.
1542 // We set hi to &size, but there are things above
1543 // it. The 1024 is supposed to compensate this,
1544 // but is somewhat arbitrary.
1547 size = 8192 * sys.StackGuardMultiplier
1549 gp.stack.hi = uintptr(noescape(unsafe.Pointer(&size)))
1550 gp.stack.lo = gp.stack.hi - size + 1024
1552 // Initialize stack guard so that we can start calling regular
1554 gp.stackguard0 = gp.stack.lo + stackGuard
1555 // This is the g0, so we can also call go:systemstack
1556 // functions, which check stackguard1.
1557 gp.stackguard1 = gp.stackguard0
1560 // Exit this thread.
1561 if mStackIsSystemAllocated() {
1562 // Windows, Solaris, illumos, Darwin, AIX and Plan 9 always system-allocate
1563 // the stack, but put it in gp.stack before mstart,
1564 // so the logic above hasn't set osStack yet.
1570 // The go:noinline is to guarantee the getcallerpc/getcallersp below are safe,
1571 // so that we can set up g0.sched to return to the call of mstart1 above.
1578 throw("bad runtime·mstart")
1581 // Set up m.g0.sched as a label returning to just
1582 // after the mstart1 call in mstart0 above, for use by goexit0 and mcall.
1583 // We're never coming back to mstart1 after we call schedule,
1584 // so other calls can reuse the current frame.
1585 // And goexit0 does a gogo that needs to return from mstart1
1586 // and let mstart0 exit the thread.
1587 gp.sched.g = guintptr(unsafe.Pointer(gp))
1588 gp.sched.pc = getcallerpc()
1589 gp.sched.sp = getcallersp()
1594 // Install signal handlers; after minit so that minit can
1595 // prepare the thread to be able to handle the signals.
1600 if fn := gp.m.mstartfn; fn != nil {
1605 acquirep(gp.m.nextp.ptr())
1611 // mstartm0 implements part of mstart1 that only runs on the m0.
1613 // Write barriers are allowed here because we know the GC can't be
1614 // running yet, so they'll be no-ops.
1616 //go:yeswritebarrierrec
1618 // Create an extra M for callbacks on threads not created by Go.
1619 // An extra M is also needed on Windows for callbacks created by
1620 // syscall.NewCallback. See issue #6751 for details.
1621 if (iscgo || GOOS == "windows") && !cgoHasExtraM {
1628 // mPark causes a thread to park itself, returning once woken.
1633 notesleep(&gp.m.park)
1634 noteclear(&gp.m.park)
1637 // mexit tears down and exits the current thread.
1639 // Don't call this directly to exit the thread, since it must run at
1640 // the top of the thread stack. Instead, use gogo(&gp.m.g0.sched) to
1641 // unwind the stack to the point that exits the thread.
1643 // It is entered with m.p != nil, so write barriers are allowed. It
1644 // will release the P before exiting.
1646 //go:yeswritebarrierrec
1647 func mexit(osStack bool) {
1651 // This is the main thread. Just wedge it.
1653 // On Linux, exiting the main thread puts the process
1654 // into a non-waitable zombie state. On Plan 9,
1655 // exiting the main thread unblocks wait even though
1656 // other threads are still running. On Solaris we can
1657 // neither exitThread nor return from mstart. Other
1658 // bad things probably happen on other platforms.
1660 // We could try to clean up this M more before wedging
1661 // it, but that complicates signal handling.
1662 handoffp(releasep())
1668 throw("locked m0 woke up")
1674 // Free the gsignal stack.
1675 if mp.gsignal != nil {
1676 stackfree(mp.gsignal.stack)
1677 // On some platforms, when calling into VDSO (e.g. nanotime)
1678 // we store our g on the gsignal stack, if there is one.
1679 // Now the stack is freed, unlink it from the m, so we
1680 // won't write to it when calling VDSO code.
1684 // Remove m from allm.
1686 for pprev := &allm; *pprev != nil; pprev = &(*pprev).alllink {
1692 throw("m not found in allm")
1694 // Delay reaping m until it's done with the stack.
1696 // Put mp on the free list, though it will not be reaped while freeWait
1697 // is freeMWait. mp is no longer reachable via allm, so even if it is
1698 // on an OS stack, we must keep a reference to mp alive so that the GC
1699 // doesn't free mp while we are still using it.
1701 // Note that the free list must not be linked through alllink because
1702 // some functions walk allm without locking, so may be using alllink.
1703 mp.freeWait.Store(freeMWait)
1704 mp.freelink = sched.freem
1708 atomic.Xadd64(&ncgocall, int64(mp.ncgocall))
1711 handoffp(releasep())
1712 // After this point we must not have write barriers.
1714 // Invoke the deadlock detector. This must happen after
1715 // handoffp because it may have started a new M to take our
1722 if GOOS == "darwin" || GOOS == "ios" {
1723 // Make sure pendingPreemptSignals is correct when an M exits.
1725 if mp.signalPending.Load() != 0 {
1726 pendingPreemptSignals.Add(-1)
1730 // Destroy all allocated resources. After this is called, we may no
1731 // longer take any locks.
1735 // No more uses of mp, so it is safe to drop the reference.
1736 mp.freeWait.Store(freeMRef)
1738 // Return from mstart and let the system thread
1739 // library free the g0 stack and terminate the thread.
1743 // mstart is the thread's entry point, so there's nothing to
1744 // return to. Exit the thread directly. exitThread will clear
1745 // m.freeWait when it's done with the stack and the m can be
1747 exitThread(&mp.freeWait)
1750 // forEachP calls fn(p) for every P p when p reaches a GC safe point.
1751 // If a P is currently executing code, this will bring the P to a GC
1752 // safe point and execute fn on that P. If the P is not executing code
1753 // (it is idle or in a syscall), this will call fn(p) directly while
1754 // preventing the P from exiting its state. This does not ensure that
1755 // fn will run on every CPU executing Go code, but it acts as a global
1756 // memory barrier. GC uses this as a "ragged barrier."
1758 // The caller must hold worldsema.
1761 func forEachP(fn func(*p)) {
1763 pp := getg().m.p.ptr()
1766 if sched.safePointWait != 0 {
1767 throw("forEachP: sched.safePointWait != 0")
1769 sched.safePointWait = gomaxprocs - 1
1770 sched.safePointFn = fn
1772 // Ask all Ps to run the safe point function.
1773 for _, p2 := range allp {
1775 atomic.Store(&p2.runSafePointFn, 1)
1780 // Any P entering _Pidle or _Psyscall from now on will observe
1781 // p.runSafePointFn == 1 and will call runSafePointFn when
1782 // changing its status to _Pidle/_Psyscall.
1784 // Run safe point function for all idle Ps. sched.pidle will
1785 // not change because we hold sched.lock.
1786 for p := sched.pidle.ptr(); p != nil; p = p.link.ptr() {
1787 if atomic.Cas(&p.runSafePointFn, 1, 0) {
1789 sched.safePointWait--
1793 wait := sched.safePointWait > 0
1796 // Run fn for the current P.
1799 // Force Ps currently in _Psyscall into _Pidle and hand them
1800 // off to induce safe point function execution.
1801 for _, p2 := range allp {
1803 if s == _Psyscall && p2.runSafePointFn == 1 && atomic.Cas(&p2.status, s, _Pidle) {
1813 // Wait for remaining Ps to run fn.
1816 // Wait for 100us, then try to re-preempt in
1817 // case of any races.
1819 // Requires system stack.
1820 if notetsleep(&sched.safePointNote, 100*1000) {
1821 noteclear(&sched.safePointNote)
1827 if sched.safePointWait != 0 {
1828 throw("forEachP: not done")
1830 for _, p2 := range allp {
1831 if p2.runSafePointFn != 0 {
1832 throw("forEachP: P did not run fn")
1837 sched.safePointFn = nil
1842 // runSafePointFn runs the safe point function, if any, for this P.
1843 // This should be called like
1845 // if getg().m.p.runSafePointFn != 0 {
1849 // runSafePointFn must be checked on any transition in to _Pidle or
1850 // _Psyscall to avoid a race where forEachP sees that the P is running
1851 // just before the P goes into _Pidle/_Psyscall and neither forEachP
1852 // nor the P run the safe-point function.
1853 func runSafePointFn() {
1854 p := getg().m.p.ptr()
1855 // Resolve the race between forEachP running the safe-point
1856 // function on this P's behalf and this P running the
1857 // safe-point function directly.
1858 if !atomic.Cas(&p.runSafePointFn, 1, 0) {
1861 sched.safePointFn(p)
1863 sched.safePointWait--
1864 if sched.safePointWait == 0 {
1865 notewakeup(&sched.safePointNote)
1870 // When running with cgo, we call _cgo_thread_start
1871 // to start threads for us so that we can play nicely with
1873 var cgoThreadStart unsafe.Pointer
1875 type cgothreadstart struct {
1881 // Allocate a new m unassociated with any thread.
1882 // Can use p for allocation context if needed.
1883 // fn is recorded as the new m's m.mstartfn.
1884 // id is optional pre-allocated m ID. Omit by passing -1.
1886 // This function is allowed to have write barriers even if the caller
1887 // isn't because it borrows pp.
1889 //go:yeswritebarrierrec
1890 func allocm(pp *p, fn func(), id int64) *m {
1893 // The caller owns pp, but we may borrow (i.e., acquirep) it. We must
1894 // disable preemption to ensure it is not stolen, which would make the
1895 // caller lose ownership.
1900 acquirep(pp) // temporarily borrow p for mallocs in this function
1903 // Release the free M list. We need to do this somewhere and
1904 // this may free up a stack we can use.
1905 if sched.freem != nil {
1908 for freem := sched.freem; freem != nil; {
1909 wait := freem.freeWait.Load()
1910 if wait == freeMWait {
1911 next := freem.freelink
1912 freem.freelink = newList
1917 // Free the stack if needed. For freeMRef, there is
1918 // nothing to do except drop freem from the sched.freem
1920 if wait == freeMStack {
1921 // stackfree must be on the system stack, but allocm is
1922 // reachable off the system stack transitively from
1924 systemstack(func() {
1925 stackfree(freem.g0.stack)
1928 freem = freem.freelink
1930 sched.freem = newList
1938 // In case of cgo or Solaris or illumos or Darwin, pthread_create will make us a stack.
1939 // Windows and Plan 9 will layout sched stack on OS stack.
1940 if iscgo || mStackIsSystemAllocated() {
1943 mp.g0 = malg(8192 * sys.StackGuardMultiplier)
1947 if pp == gp.m.p.ptr() {
1952 allocmLock.runlock()
1956 // needm is called when a cgo callback happens on a
1957 // thread without an m (a thread not created by Go).
1958 // In this case, needm is expected to find an m to use
1959 // and return with m, g initialized correctly.
1960 // Since m and g are not set now (likely nil, but see below)
1961 // needm is limited in what routines it can call. In particular
1962 // it can only call nosplit functions (textflag 7) and cannot
1963 // do any scheduling that requires an m.
1965 // In order to avoid needing heavy lifting here, we adopt
1966 // the following strategy: there is a stack of available m's
1967 // that can be stolen. Using compare-and-swap
1968 // to pop from the stack has ABA races, so we simulate
1969 // a lock by doing an exchange (via Casuintptr) to steal the stack
1970 // head and replace the top pointer with MLOCKED (1).
1971 // This serves as a simple spin lock that we can use even
1972 // without an m. The thread that locks the stack in this way
1973 // unlocks the stack by storing a valid stack head pointer.
1975 // In order to make sure that there is always an m structure
1976 // available to be stolen, we maintain the invariant that there
1977 // is always one more than needed. At the beginning of the
1978 // program (if cgo is in use) the list is seeded with a single m.
1979 // If needm finds that it has taken the last m off the list, its job
1980 // is - once it has installed its own m so that it can do things like
1981 // allocate memory - to create a spare m and put it on the list.
1983 // Each of these extra m's also has a g0 and a curg that are
1984 // pressed into service as the scheduling stack and current
1985 // goroutine for the duration of the cgo callback.
1987 // It calls dropm to put the m back on the list,
1988 // 1. when the callback is done with the m in non-pthread platforms,
1989 // 2. or when the C thread exiting on pthread platforms.
1991 // The signal argument indicates whether we're called from a signal
1995 func needm(signal bool) {
1996 if (iscgo || GOOS == "windows") && !cgoHasExtraM {
1997 // Can happen if C/C++ code calls Go from a global ctor.
1998 // Can also happen on Windows if a global ctor uses a
1999 // callback created by syscall.NewCallback. See issue #6751
2002 // Can not throw, because scheduler is not initialized yet.
2003 writeErrStr("fatal error: cgo callback before cgo call\n")
2007 // Save and block signals before getting an M.
2008 // The signal handler may call needm itself,
2009 // and we must avoid a deadlock. Also, once g is installed,
2010 // any incoming signals will try to execute,
2011 // but we won't have the sigaltstack settings and other data
2012 // set up appropriately until the end of minit, which will
2013 // unblock the signals. This is the same dance as when
2014 // starting a new m to run Go code via newosproc.
2019 // getExtraM is safe here because of the invariant above,
2020 // that the extra list always contains or will soon contain
2022 mp, last := getExtraM()
2024 // Set needextram when we've just emptied the list,
2025 // so that the eventual call into cgocallbackg will
2026 // allocate a new m for the extra list. We delay the
2027 // allocation until then so that it can be done
2028 // after exitsyscall makes sure it is okay to be
2029 // running at all (that is, there's no garbage collection
2030 // running right now).
2031 mp.needextram = last
2033 // Store the original signal mask for use by minit.
2034 mp.sigmask = sigmask
2036 // Install TLS on some platforms (previously setg
2037 // would do this if necessary).
2040 // Install g (= m->g0) and set the stack bounds
2041 // to match the current stack. If we don't actually know
2042 // how big the stack is, like we don't know how big any
2043 // scheduling stack is, but we assume there's at least 32 kB.
2044 // If we can get a more accurate stack bound from pthread,
2048 gp.stack.hi = getcallersp() + 1024
2049 gp.stack.lo = getcallersp() - 32*1024
2050 if !signal && _cgo_getstackbound != nil {
2051 // Don't adjust if called from the signal handler.
2052 // We are on the signal stack, not the pthread stack.
2053 // (We could get the stack bounds from sigaltstack, but
2054 // we're getting out of the signal handler very soon
2055 // anyway. Not worth it.)
2056 var bounds [2]uintptr
2057 asmcgocall(_cgo_getstackbound, unsafe.Pointer(&bounds))
2058 // getstackbound is an unsupported no-op on Windows.
2060 gp.stack.lo = bounds[0]
2061 gp.stack.hi = bounds[1]
2064 gp.stackguard0 = gp.stack.lo + stackGuard
2066 // Should mark we are already in Go now.
2067 // Otherwise, we may call needm again when we get a signal, before cgocallbackg1,
2068 // which means the extram list may be empty, that will cause a deadlock.
2069 mp.isExtraInC = false
2071 // Initialize this thread to use the m.
2075 // mp.curg is now a real goroutine.
2076 casgstatus(mp.curg, _Gdead, _Gsyscall)
2080 // Acquire an extra m and bind it to the C thread when a pthread key has been created.
2083 func needAndBindM() {
2086 if _cgo_pthread_key_created != nil && *(*uintptr)(_cgo_pthread_key_created) != 0 {
2091 // newextram allocates m's and puts them on the extra list.
2092 // It is called with a working local m, so that it can do things
2093 // like call schedlock and allocate.
2095 c := extraMWaiters.Swap(0)
2097 for i := uint32(0); i < c; i++ {
2100 } else if extraMLength.Load() == 0 {
2101 // Make sure there is at least one extra M.
2106 // oneNewExtraM allocates an m and puts it on the extra list.
2107 func oneNewExtraM() {
2108 // Create extra goroutine locked to extra m.
2109 // The goroutine is the context in which the cgo callback will run.
2110 // The sched.pc will never be returned to, but setting it to
2111 // goexit makes clear to the traceback routines where
2112 // the goroutine stack ends.
2113 mp := allocm(nil, nil, -1)
2115 gp.sched.pc = abi.FuncPCABI0(goexit) + sys.PCQuantum
2116 gp.sched.sp = gp.stack.hi
2117 gp.sched.sp -= 4 * goarch.PtrSize // extra space in case of reads slightly beyond frame
2119 gp.sched.g = guintptr(unsafe.Pointer(gp))
2120 gp.syscallpc = gp.sched.pc
2121 gp.syscallsp = gp.sched.sp
2122 gp.stktopsp = gp.sched.sp
2123 // malg returns status as _Gidle. Change to _Gdead before
2124 // adding to allg where GC can see it. We use _Gdead to hide
2125 // this from tracebacks and stack scans since it isn't a
2126 // "real" goroutine until needm grabs it.
2127 casgstatus(gp, _Gidle, _Gdead)
2131 // mark we are in C by default.
2132 mp.isExtraInC = true
2136 gp.goid = sched.goidgen.Add(1)
2138 gp.racectx = racegostart(abi.FuncPCABIInternal(newextram) + sys.PCQuantum)
2141 traceOneNewExtraM(gp)
2143 // put on allg for garbage collector
2146 // gp is now on the allg list, but we don't want it to be
2147 // counted by gcount. It would be more "proper" to increment
2148 // sched.ngfree, but that requires locking. Incrementing ngsys
2149 // has the same effect.
2152 // Add m to the extra list.
2156 // dropm puts the current m back onto the extra list.
2158 // 1. On systems without pthreads, like Windows
2159 // dropm is called when a cgo callback has called needm but is now
2160 // done with the callback and returning back into the non-Go thread.
2162 // The main expense here is the call to signalstack to release the
2163 // m's signal stack, and then the call to needm on the next callback
2164 // from this thread. It is tempting to try to save the m for next time,
2165 // which would eliminate both these costs, but there might not be
2166 // a next time: the current thread (which Go does not control) might exit.
2167 // If we saved the m for that thread, there would be an m leak each time
2168 // such a thread exited. Instead, we acquire and release an m on each
2169 // call. These should typically not be scheduling operations, just a few
2170 // atomics, so the cost should be small.
2172 // 2. On systems with pthreads
2173 // dropm is called while a non-Go thread is exiting.
2174 // We allocate a pthread per-thread variable using pthread_key_create,
2175 // to register a thread-exit-time destructor.
2176 // And store the g into a thread-specific value associated with the pthread key,
2177 // when first return back to C.
2178 // So that the destructor would invoke dropm while the non-Go thread is exiting.
2179 // This is much faster since it avoids expensive signal-related syscalls.
2181 // NOTE: this always runs without a P, so, nowritebarrierrec required.
2183 //go:nowritebarrierrec
2185 // Clear m and g, and return m to the extra list.
2186 // After the call to setg we can only call nosplit functions
2187 // with no pointer manipulation.
2190 // Return mp.curg to dead state.
2191 casgstatus(mp.curg, _Gsyscall, _Gdead)
2192 mp.curg.preemptStop = false
2195 // Block signals before unminit.
2196 // Unminit unregisters the signal handling stack (but needs g on some systems).
2197 // Setg(nil) clears g, which is the signal handler's cue not to run Go handlers.
2198 // It's important not to try to handle a signal between those two steps.
2199 sigmask := mp.sigmask
2207 msigrestore(sigmask)
2210 // bindm store the g0 of the current m into a thread-specific value.
2212 // We allocate a pthread per-thread variable using pthread_key_create,
2213 // to register a thread-exit-time destructor.
2214 // We are here setting the thread-specific value of the pthread key, to enable the destructor.
2215 // So that the pthread_key_destructor would dropm while the C thread is exiting.
2217 // And the saved g will be used in pthread_key_destructor,
2218 // since the g stored in the TLS by Go might be cleared in some platforms,
2219 // before the destructor invoked, so, we restore g by the stored g, before dropm.
2221 // We store g0 instead of m, to make the assembly code simpler,
2222 // since we need to restore g0 in runtime.cgocallback.
2224 // On systems without pthreads, like Windows, bindm shouldn't be used.
2226 // NOTE: this always runs without a P, so, nowritebarrierrec required.
2229 //go:nowritebarrierrec
2231 if GOOS == "windows" || GOOS == "plan9" {
2232 fatal("bindm in unexpected GOOS")
2236 fatal("the current g is not g0")
2238 if _cgo_bindm != nil {
2239 asmcgocall(_cgo_bindm, unsafe.Pointer(g))
2243 // A helper function for EnsureDropM.
2244 func getm() uintptr {
2245 return uintptr(unsafe.Pointer(getg().m))
2249 // Locking linked list of extra M's, via mp.schedlink. Must be accessed
2250 // only via lockextra/unlockextra.
2252 // Can't be atomic.Pointer[m] because we use an invalid pointer as a
2253 // "locked" sentinel value. M's on this list remain visible to the GC
2254 // because their mp.curg is on allgs.
2255 extraM atomic.Uintptr
2256 // Number of M's in the extraM list.
2257 extraMLength atomic.Uint32
2258 // Number of waiters in lockextra.
2259 extraMWaiters atomic.Uint32
2261 // Number of extra M's in use by threads.
2262 extraMInUse atomic.Uint32
2265 // lockextra locks the extra list and returns the list head.
2266 // The caller must unlock the list by storing a new list head
2267 // to extram. If nilokay is true, then lockextra will
2268 // return a nil list head if that's what it finds. If nilokay is false,
2269 // lockextra will keep waiting until the list head is no longer nil.
2272 func lockextra(nilokay bool) *m {
2277 old := extraM.Load()
2282 if old == 0 && !nilokay {
2284 // Add 1 to the number of threads
2285 // waiting for an M.
2286 // This is cleared by newextram.
2287 extraMWaiters.Add(1)
2293 if extraM.CompareAndSwap(old, locked) {
2294 return (*m)(unsafe.Pointer(old))
2302 func unlockextra(mp *m, delta int32) {
2303 extraMLength.Add(delta)
2304 extraM.Store(uintptr(unsafe.Pointer(mp)))
2307 // Return an M from the extra M list. Returns last == true if the list becomes
2308 // empty because of this call.
2310 // Spins waiting for an extra M, so caller must ensure that the list always
2311 // contains or will soon contain at least one M.
2314 func getExtraM() (mp *m, last bool) {
2315 mp = lockextra(false)
2317 unlockextra(mp.schedlink.ptr(), -1)
2318 return mp, mp.schedlink.ptr() == nil
2321 // Returns an extra M back to the list. mp must be from getExtraM. Newly
2322 // allocated M's should use addExtraM.
2325 func putExtraM(mp *m) {
2330 // Adds a newly allocated M to the extra M list.
2333 func addExtraM(mp *m) {
2334 mnext := lockextra(true)
2335 mp.schedlink.set(mnext)
2340 // allocmLock is locked for read when creating new Ms in allocm and their
2341 // addition to allm. Thus acquiring this lock for write blocks the
2342 // creation of new Ms.
2345 // execLock serializes exec and clone to avoid bugs or unspecified
2346 // behaviour around exec'ing while creating/destroying threads. See
2351 // These errors are reported (via writeErrStr) by some OS-specific
2352 // versions of newosproc and newosproc0.
2354 failthreadcreate = "runtime: failed to create new OS thread\n"
2355 failallocatestack = "runtime: failed to allocate stack for the new OS thread\n"
2358 // newmHandoff contains a list of m structures that need new OS threads.
2359 // This is used by newm in situations where newm itself can't safely
2360 // start an OS thread.
2361 var newmHandoff struct {
2364 // newm points to a list of M structures that need new OS
2365 // threads. The list is linked through m.schedlink.
2368 // waiting indicates that wake needs to be notified when an m
2369 // is put on the list.
2373 // haveTemplateThread indicates that the templateThread has
2374 // been started. This is not protected by lock. Use cas to set
2376 haveTemplateThread uint32
2379 // Create a new m. It will start off with a call to fn, or else the scheduler.
2380 // fn needs to be static and not a heap allocated closure.
2381 // May run with m.p==nil, so write barriers are not allowed.
2383 // id is optional pre-allocated m ID. Omit by passing -1.
2385 //go:nowritebarrierrec
2386 func newm(fn func(), pp *p, id int64) {
2387 // allocm adds a new M to allm, but they do not start until created by
2388 // the OS in newm1 or the template thread.
2390 // doAllThreadsSyscall requires that every M in allm will eventually
2391 // start and be signal-able, even with a STW.
2393 // Disable preemption here until we start the thread to ensure that
2394 // newm is not preempted between allocm and starting the new thread,
2395 // ensuring that anything added to allm is guaranteed to eventually
2399 mp := allocm(pp, fn, id)
2401 mp.sigmask = initSigmask
2402 if gp := getg(); gp != nil && gp.m != nil && (gp.m.lockedExt != 0 || gp.m.incgo) && GOOS != "plan9" {
2403 // We're on a locked M or a thread that may have been
2404 // started by C. The kernel state of this thread may
2405 // be strange (the user may have locked it for that
2406 // purpose). We don't want to clone that into another
2407 // thread. Instead, ask a known-good thread to create
2408 // the thread for us.
2410 // This is disabled on Plan 9. See golang.org/issue/22227.
2412 // TODO: This may be unnecessary on Windows, which
2413 // doesn't model thread creation off fork.
2414 lock(&newmHandoff.lock)
2415 if newmHandoff.haveTemplateThread == 0 {
2416 throw("on a locked thread with no template thread")
2418 mp.schedlink = newmHandoff.newm
2419 newmHandoff.newm.set(mp)
2420 if newmHandoff.waiting {
2421 newmHandoff.waiting = false
2422 notewakeup(&newmHandoff.wake)
2424 unlock(&newmHandoff.lock)
2425 // The M has not started yet, but the template thread does not
2426 // participate in STW, so it will always process queued Ms and
2427 // it is safe to releasem.
2437 var ts cgothreadstart
2438 if _cgo_thread_start == nil {
2439 throw("_cgo_thread_start missing")
2442 ts.tls = (*uint64)(unsafe.Pointer(&mp.tls[0]))
2443 ts.fn = unsafe.Pointer(abi.FuncPCABI0(mstart))
2445 msanwrite(unsafe.Pointer(&ts), unsafe.Sizeof(ts))
2448 asanwrite(unsafe.Pointer(&ts), unsafe.Sizeof(ts))
2450 execLock.rlock() // Prevent process clone.
2451 asmcgocall(_cgo_thread_start, unsafe.Pointer(&ts))
2455 execLock.rlock() // Prevent process clone.
2460 // startTemplateThread starts the template thread if it is not already
2463 // The calling thread must itself be in a known-good state.
2464 func startTemplateThread() {
2465 if GOARCH == "wasm" { // no threads on wasm yet
2469 // Disable preemption to guarantee that the template thread will be
2470 // created before a park once haveTemplateThread is set.
2472 if !atomic.Cas(&newmHandoff.haveTemplateThread, 0, 1) {
2476 newm(templateThread, nil, -1)
2480 // templateThread is a thread in a known-good state that exists solely
2481 // to start new threads in known-good states when the calling thread
2482 // may not be in a good state.
2484 // Many programs never need this, so templateThread is started lazily
2485 // when we first enter a state that might lead to running on a thread
2486 // in an unknown state.
2488 // templateThread runs on an M without a P, so it must not have write
2491 //go:nowritebarrierrec
2492 func templateThread() {
2499 lock(&newmHandoff.lock)
2500 for newmHandoff.newm != 0 {
2501 newm := newmHandoff.newm.ptr()
2502 newmHandoff.newm = 0
2503 unlock(&newmHandoff.lock)
2505 next := newm.schedlink.ptr()
2510 lock(&newmHandoff.lock)
2512 newmHandoff.waiting = true
2513 noteclear(&newmHandoff.wake)
2514 unlock(&newmHandoff.lock)
2515 notesleep(&newmHandoff.wake)
2519 // Stops execution of the current m until new work is available.
2520 // Returns with acquired P.
2524 if gp.m.locks != 0 {
2525 throw("stopm holding locks")
2528 throw("stopm holding p")
2531 throw("stopm spinning")
2538 acquirep(gp.m.nextp.ptr())
2543 // startm's caller incremented nmspinning. Set the new M's spinning.
2544 getg().m.spinning = true
2547 // Schedules some M to run the p (creates an M if necessary).
2548 // If p==nil, tries to get an idle P, if no idle P's does nothing.
2549 // May run with m.p==nil, so write barriers are not allowed.
2550 // If spinning is set, the caller has incremented nmspinning and must provide a
2551 // P. startm will set m.spinning in the newly started M.
2553 // Callers passing a non-nil P must call from a non-preemptible context. See
2554 // comment on acquirem below.
2556 // Argument lockheld indicates whether the caller already acquired the
2557 // scheduler lock. Callers holding the lock when making the call must pass
2558 // true. The lock might be temporarily dropped, but will be reacquired before
2561 // Must not have write barriers because this may be called without a P.
2563 //go:nowritebarrierrec
2564 func startm(pp *p, spinning, lockheld bool) {
2565 // Disable preemption.
2567 // Every owned P must have an owner that will eventually stop it in the
2568 // event of a GC stop request. startm takes transient ownership of a P
2569 // (either from argument or pidleget below) and transfers ownership to
2570 // a started M, which will be responsible for performing the stop.
2572 // Preemption must be disabled during this transient ownership,
2573 // otherwise the P this is running on may enter GC stop while still
2574 // holding the transient P, leaving that P in limbo and deadlocking the
2577 // Callers passing a non-nil P must already be in non-preemptible
2578 // context, otherwise such preemption could occur on function entry to
2579 // startm. Callers passing a nil P may be preemptible, so we must
2580 // disable preemption before acquiring a P from pidleget below.
2587 // TODO(prattmic): All remaining calls to this function
2588 // with _p_ == nil could be cleaned up to find a P
2589 // before calling startm.
2590 throw("startm: P required for spinning=true")
2603 // No M is available, we must drop sched.lock and call newm.
2604 // However, we already own a P to assign to the M.
2606 // Once sched.lock is released, another G (e.g., in a syscall),
2607 // could find no idle P while checkdead finds a runnable G but
2608 // no running M's because this new M hasn't started yet, thus
2609 // throwing in an apparent deadlock.
2610 // This apparent deadlock is possible when startm is called
2611 // from sysmon, which doesn't count as a running M.
2613 // Avoid this situation by pre-allocating the ID for the new M,
2614 // thus marking it as 'running' before we drop sched.lock. This
2615 // new M will eventually run the scheduler to execute any
2622 // The caller incremented nmspinning, so set m.spinning in the new M.
2630 // Ownership transfer of pp committed by start in newm.
2631 // Preemption is now safe.
2639 throw("startm: m is spinning")
2642 throw("startm: m has p")
2644 if spinning && !runqempty(pp) {
2645 throw("startm: p has runnable gs")
2647 // The caller incremented nmspinning, so set m.spinning in the new M.
2648 nmp.spinning = spinning
2650 notewakeup(&nmp.park)
2651 // Ownership transfer of pp committed by wakeup. Preemption is now
2656 // Hands off P from syscall or locked M.
2657 // Always runs without a P, so write barriers are not allowed.
2659 //go:nowritebarrierrec
2660 func handoffp(pp *p) {
2661 // handoffp must start an M in any situation where
2662 // findrunnable would return a G to run on pp.
2664 // if it has local work, start it straight away
2665 if !runqempty(pp) || sched.runqsize != 0 {
2666 startm(pp, false, false)
2669 // if there's trace work to do, start it straight away
2670 if (traceEnabled() || traceShuttingDown()) && traceReaderAvailable() != nil {
2671 startm(pp, false, false)
2674 // if it has GC work, start it straight away
2675 if gcBlackenEnabled != 0 && gcMarkWorkAvailable(pp) {
2676 startm(pp, false, false)
2679 // no local work, check that there are no spinning/idle M's,
2680 // otherwise our help is not required
2681 if sched.nmspinning.Load()+sched.npidle.Load() == 0 && sched.nmspinning.CompareAndSwap(0, 1) { // TODO: fast atomic
2682 sched.needspinning.Store(0)
2683 startm(pp, true, false)
2687 if sched.gcwaiting.Load() {
2688 pp.status = _Pgcstop
2690 if sched.stopwait == 0 {
2691 notewakeup(&sched.stopnote)
2696 if pp.runSafePointFn != 0 && atomic.Cas(&pp.runSafePointFn, 1, 0) {
2697 sched.safePointFn(pp)
2698 sched.safePointWait--
2699 if sched.safePointWait == 0 {
2700 notewakeup(&sched.safePointNote)
2703 if sched.runqsize != 0 {
2705 startm(pp, false, false)
2708 // If this is the last running P and nobody is polling network,
2709 // need to wakeup another M to poll network.
2710 if sched.npidle.Load() == gomaxprocs-1 && sched.lastpoll.Load() != 0 {
2712 startm(pp, false, false)
2716 // The scheduler lock cannot be held when calling wakeNetPoller below
2717 // because wakeNetPoller may call wakep which may call startm.
2718 when := nobarrierWakeTime(pp)
2727 // Tries to add one more P to execute G's.
2728 // Called when a G is made runnable (newproc, ready).
2729 // Must be called with a P.
2731 // Be conservative about spinning threads, only start one if none exist
2733 if sched.nmspinning.Load() != 0 || !sched.nmspinning.CompareAndSwap(0, 1) {
2737 // Disable preemption until ownership of pp transfers to the next M in
2738 // startm. Otherwise preemption here would leave pp stuck waiting to
2741 // See preemption comment on acquirem in startm for more details.
2746 pp, _ = pidlegetSpinning(0)
2748 if sched.nmspinning.Add(-1) < 0 {
2749 throw("wakep: negative nmspinning")
2755 // Since we always have a P, the race in the "No M is available"
2756 // comment in startm doesn't apply during the small window between the
2757 // unlock here and lock in startm. A checkdead in between will always
2758 // see at least one running M (ours).
2761 startm(pp, true, false)
2766 // Stops execution of the current m that is locked to a g until the g is runnable again.
2767 // Returns with acquired P.
2768 func stoplockedm() {
2771 if gp.m.lockedg == 0 || gp.m.lockedg.ptr().lockedm.ptr() != gp.m {
2772 throw("stoplockedm: inconsistent locking")
2775 // Schedule another M to run this p.
2780 // Wait until another thread schedules lockedg again.
2782 status := readgstatus(gp.m.lockedg.ptr())
2783 if status&^_Gscan != _Grunnable {
2784 print("runtime:stoplockedm: lockedg (atomicstatus=", status, ") is not Grunnable or Gscanrunnable\n")
2785 dumpgstatus(gp.m.lockedg.ptr())
2786 throw("stoplockedm: not runnable")
2788 acquirep(gp.m.nextp.ptr())
2792 // Schedules the locked m to run the locked gp.
2793 // May run during STW, so write barriers are not allowed.
2795 //go:nowritebarrierrec
2796 func startlockedm(gp *g) {
2797 mp := gp.lockedm.ptr()
2799 throw("startlockedm: locked to me")
2802 throw("startlockedm: m has p")
2804 // directly handoff current P to the locked m
2808 notewakeup(&mp.park)
2812 // Stops the current m for stopTheWorld.
2813 // Returns when the world is restarted.
2817 if !sched.gcwaiting.Load() {
2818 throw("gcstopm: not waiting for gc")
2821 gp.m.spinning = false
2822 // OK to just drop nmspinning here,
2823 // startTheWorld will unpark threads as necessary.
2824 if sched.nmspinning.Add(-1) < 0 {
2825 throw("gcstopm: negative nmspinning")
2830 pp.status = _Pgcstop
2832 if sched.stopwait == 0 {
2833 notewakeup(&sched.stopnote)
2839 // Schedules gp to run on the current M.
2840 // If inheritTime is true, gp inherits the remaining time in the
2841 // current time slice. Otherwise, it starts a new time slice.
2844 // Write barriers are allowed because this is called immediately after
2845 // acquiring a P in several places.
2847 //go:yeswritebarrierrec
2848 func execute(gp *g, inheritTime bool) {
2851 if goroutineProfile.active {
2852 // Make sure that gp has had its stack written out to the goroutine
2853 // profile, exactly as it was when the goroutine profiler first stopped
2855 tryRecordGoroutineProfile(gp, osyield)
2858 // Assign gp.m before entering _Grunning so running Gs have an
2862 casgstatus(gp, _Grunnable, _Grunning)
2865 gp.stackguard0 = gp.stack.lo + stackGuard
2867 mp.p.ptr().schedtick++
2870 // Check whether the profiler needs to be turned on or off.
2871 hz := sched.profilehz
2872 if mp.profilehz != hz {
2873 setThreadCPUProfiler(hz)
2877 // GoSysExit has to happen when we have a P, but before GoStart.
2878 // So we emit it here.
2879 if gp.syscallsp != 0 {
2888 // Finds a runnable goroutine to execute.
2889 // Tries to steal from other P's, get g from local or global queue, poll network.
2890 // tryWakeP indicates that the returned goroutine is not normal (GC worker, trace
2891 // reader) so the caller should try to wake a P.
2892 func findRunnable() (gp *g, inheritTime, tryWakeP bool) {
2895 // The conditions here and in handoffp must agree: if
2896 // findrunnable would return a G to run, handoffp must start
2901 if sched.gcwaiting.Load() {
2905 if pp.runSafePointFn != 0 {
2909 // now and pollUntil are saved for work stealing later,
2910 // which may steal timers. It's important that between now
2911 // and then, nothing blocks, so these numbers remain mostly
2913 now, pollUntil, _ := checkTimers(pp, 0)
2915 // Try to schedule the trace reader.
2916 if traceEnabled() || traceShuttingDown() {
2919 casgstatus(gp, _Gwaiting, _Grunnable)
2920 traceGoUnpark(gp, 0)
2921 return gp, false, true
2925 // Try to schedule a GC worker.
2926 if gcBlackenEnabled != 0 {
2927 gp, tnow := gcController.findRunnableGCWorker(pp, now)
2929 return gp, false, true
2934 // Check the global runnable queue once in a while to ensure fairness.
2935 // Otherwise two goroutines can completely occupy the local runqueue
2936 // by constantly respawning each other.
2937 if pp.schedtick%61 == 0 && sched.runqsize > 0 {
2939 gp := globrunqget(pp, 1)
2942 return gp, false, false
2946 // Wake up the finalizer G.
2947 if fingStatus.Load()&(fingWait|fingWake) == fingWait|fingWake {
2948 if gp := wakefing(); gp != nil {
2952 if *cgo_yield != nil {
2953 asmcgocall(*cgo_yield, nil)
2957 if gp, inheritTime := runqget(pp); gp != nil {
2958 return gp, inheritTime, false
2962 if sched.runqsize != 0 {
2964 gp := globrunqget(pp, 0)
2967 return gp, false, false
2972 // This netpoll is only an optimization before we resort to stealing.
2973 // We can safely skip it if there are no waiters or a thread is blocked
2974 // in netpoll already. If there is any kind of logical race with that
2975 // blocked thread (e.g. it has already returned from netpoll, but does
2976 // not set lastpoll yet), this thread will do blocking netpoll below
2978 if netpollinited() && netpollAnyWaiters() && sched.lastpoll.Load() != 0 {
2979 if list, delta := netpoll(0); !list.empty() { // non-blocking
2982 netpollAdjustWaiters(delta)
2983 casgstatus(gp, _Gwaiting, _Grunnable)
2985 traceGoUnpark(gp, 0)
2987 return gp, false, false
2991 // Spinning Ms: steal work from other Ps.
2993 // Limit the number of spinning Ms to half the number of busy Ps.
2994 // This is necessary to prevent excessive CPU consumption when
2995 // GOMAXPROCS>>1 but the program parallelism is low.
2996 if mp.spinning || 2*sched.nmspinning.Load() < gomaxprocs-sched.npidle.Load() {
3001 gp, inheritTime, tnow, w, newWork := stealWork(now)
3003 // Successfully stole.
3004 return gp, inheritTime, false
3007 // There may be new timer or GC work; restart to
3013 if w != 0 && (pollUntil == 0 || w < pollUntil) {
3014 // Earlier timer to wait for.
3019 // We have nothing to do.
3021 // If we're in the GC mark phase, can safely scan and blacken objects,
3022 // and have work to do, run idle-time marking rather than give up the P.
3023 if gcBlackenEnabled != 0 && gcMarkWorkAvailable(pp) && gcController.addIdleMarkWorker() {
3024 node := (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop())
3026 pp.gcMarkWorkerMode = gcMarkWorkerIdleMode
3028 casgstatus(gp, _Gwaiting, _Grunnable)
3030 traceGoUnpark(gp, 0)
3032 return gp, false, false
3034 gcController.removeIdleMarkWorker()
3038 // If a callback returned and no other goroutine is awake,
3039 // then wake event handler goroutine which pauses execution
3040 // until a callback was triggered.
3041 gp, otherReady := beforeIdle(now, pollUntil)
3043 casgstatus(gp, _Gwaiting, _Grunnable)
3045 traceGoUnpark(gp, 0)
3047 return gp, false, false
3053 // Before we drop our P, make a snapshot of the allp slice,
3054 // which can change underfoot once we no longer block
3055 // safe-points. We don't need to snapshot the contents because
3056 // everything up to cap(allp) is immutable.
3057 allpSnapshot := allp
3058 // Also snapshot masks. Value changes are OK, but we can't allow
3059 // len to change out from under us.
3060 idlepMaskSnapshot := idlepMask
3061 timerpMaskSnapshot := timerpMask
3063 // return P and block
3065 if sched.gcwaiting.Load() || pp.runSafePointFn != 0 {
3069 if sched.runqsize != 0 {
3070 gp := globrunqget(pp, 0)
3072 return gp, false, false
3074 if !mp.spinning && sched.needspinning.Load() == 1 {
3075 // See "Delicate dance" comment below.
3080 if releasep() != pp {
3081 throw("findrunnable: wrong p")
3083 now = pidleput(pp, now)
3086 // Delicate dance: thread transitions from spinning to non-spinning
3087 // state, potentially concurrently with submission of new work. We must
3088 // drop nmspinning first and then check all sources again (with
3089 // #StoreLoad memory barrier in between). If we do it the other way
3090 // around, another thread can submit work after we've checked all
3091 // sources but before we drop nmspinning; as a result nobody will
3092 // unpark a thread to run the work.
3094 // This applies to the following sources of work:
3096 // * Goroutines added to a per-P run queue.
3097 // * New/modified-earlier timers on a per-P timer heap.
3098 // * Idle-priority GC work (barring golang.org/issue/19112).
3100 // If we discover new work below, we need to restore m.spinning as a
3101 // signal for resetspinning to unpark a new worker thread (because
3102 // there can be more than one starving goroutine).
3104 // However, if after discovering new work we also observe no idle Ps
3105 // (either here or in resetspinning), we have a problem. We may be
3106 // racing with a non-spinning M in the block above, having found no
3107 // work and preparing to release its P and park. Allowing that P to go
3108 // idle will result in loss of work conservation (idle P while there is
3109 // runnable work). This could result in complete deadlock in the
3110 // unlikely event that we discover new work (from netpoll) right as we
3111 // are racing with _all_ other Ps going idle.
3113 // We use sched.needspinning to synchronize with non-spinning Ms going
3114 // idle. If needspinning is set when they are about to drop their P,
3115 // they abort the drop and instead become a new spinning M on our
3116 // behalf. If we are not racing and the system is truly fully loaded
3117 // then no spinning threads are required, and the next thread to
3118 // naturally become spinning will clear the flag.
3120 // Also see "Worker thread parking/unparking" comment at the top of the
3122 wasSpinning := mp.spinning
3125 if sched.nmspinning.Add(-1) < 0 {
3126 throw("findrunnable: negative nmspinning")
3129 // Note the for correctness, only the last M transitioning from
3130 // spinning to non-spinning must perform these rechecks to
3131 // ensure no missed work. However, the runtime has some cases
3132 // of transient increments of nmspinning that are decremented
3133 // without going through this path, so we must be conservative
3134 // and perform the check on all spinning Ms.
3136 // See https://go.dev/issue/43997.
3138 // Check all runqueues once again.
3139 pp := checkRunqsNoP(allpSnapshot, idlepMaskSnapshot)
3146 // Check for idle-priority GC work again.
3147 pp, gp := checkIdleGCNoP()
3152 // Run the idle worker.
3153 pp.gcMarkWorkerMode = gcMarkWorkerIdleMode
3154 casgstatus(gp, _Gwaiting, _Grunnable)
3156 traceGoUnpark(gp, 0)
3158 return gp, false, false
3161 // Finally, check for timer creation or expiry concurrently with
3162 // transitioning from spinning to non-spinning.
3164 // Note that we cannot use checkTimers here because it calls
3165 // adjusttimers which may need to allocate memory, and that isn't
3166 // allowed when we don't have an active P.
3167 pollUntil = checkTimersNoP(allpSnapshot, timerpMaskSnapshot, pollUntil)
3170 // Poll network until next timer.
3171 if netpollinited() && (netpollAnyWaiters() || pollUntil != 0) && sched.lastpoll.Swap(0) != 0 {
3172 sched.pollUntil.Store(pollUntil)
3174 throw("findrunnable: netpoll with p")
3177 throw("findrunnable: netpoll with spinning")
3184 delay = pollUntil - now
3190 // When using fake time, just poll.
3193 list, delta := netpoll(delay) // block until new work is available
3194 // Refresh now again, after potentially blocking.
3196 sched.pollUntil.Store(0)
3197 sched.lastpoll.Store(now)
3198 if faketime != 0 && list.empty() {
3199 // Using fake time and nothing is ready; stop M.
3200 // When all M's stop, checkdead will call timejump.
3205 pp, _ := pidleget(now)
3209 netpollAdjustWaiters(delta)
3215 netpollAdjustWaiters(delta)
3216 casgstatus(gp, _Gwaiting, _Grunnable)
3218 traceGoUnpark(gp, 0)
3220 return gp, false, false
3227 } else if pollUntil != 0 && netpollinited() {
3228 pollerPollUntil := sched.pollUntil.Load()
3229 if pollerPollUntil == 0 || pollerPollUntil > pollUntil {
3237 // pollWork reports whether there is non-background work this P could
3238 // be doing. This is a fairly lightweight check to be used for
3239 // background work loops, like idle GC. It checks a subset of the
3240 // conditions checked by the actual scheduler.
3241 func pollWork() bool {
3242 if sched.runqsize != 0 {
3245 p := getg().m.p.ptr()
3249 if netpollinited() && netpollAnyWaiters() && sched.lastpoll.Load() != 0 {
3250 if list, delta := netpoll(0); !list.empty() {
3252 netpollAdjustWaiters(delta)
3259 // stealWork attempts to steal a runnable goroutine or timer from any P.
3261 // If newWork is true, new work may have been readied.
3263 // If now is not 0 it is the current time. stealWork returns the passed time or
3264 // the current time if now was passed as 0.
3265 func stealWork(now int64) (gp *g, inheritTime bool, rnow, pollUntil int64, newWork bool) {
3266 pp := getg().m.p.ptr()
3270 const stealTries = 4
3271 for i := 0; i < stealTries; i++ {
3272 stealTimersOrRunNextG := i == stealTries-1
3274 for enum := stealOrder.start(fastrand()); !enum.done(); enum.next() {
3275 if sched.gcwaiting.Load() {
3276 // GC work may be available.
3277 return nil, false, now, pollUntil, true
3279 p2 := allp[enum.position()]
3284 // Steal timers from p2. This call to checkTimers is the only place
3285 // where we might hold a lock on a different P's timers. We do this
3286 // once on the last pass before checking runnext because stealing
3287 // from the other P's runnext should be the last resort, so if there
3288 // are timers to steal do that first.
3290 // We only check timers on one of the stealing iterations because
3291 // the time stored in now doesn't change in this loop and checking
3292 // the timers for each P more than once with the same value of now
3293 // is probably a waste of time.
3295 // timerpMask tells us whether the P may have timers at all. If it
3296 // can't, no need to check at all.
3297 if stealTimersOrRunNextG && timerpMask.read(enum.position()) {
3298 tnow, w, ran := checkTimers(p2, now)
3300 if w != 0 && (pollUntil == 0 || w < pollUntil) {
3304 // Running the timers may have
3305 // made an arbitrary number of G's
3306 // ready and added them to this P's
3307 // local run queue. That invalidates
3308 // the assumption of runqsteal
3309 // that it always has room to add
3310 // stolen G's. So check now if there
3311 // is a local G to run.
3312 if gp, inheritTime := runqget(pp); gp != nil {
3313 return gp, inheritTime, now, pollUntil, ranTimer
3319 // Don't bother to attempt to steal if p2 is idle.
3320 if !idlepMask.read(enum.position()) {
3321 if gp := runqsteal(pp, p2, stealTimersOrRunNextG); gp != nil {
3322 return gp, false, now, pollUntil, ranTimer
3328 // No goroutines found to steal. Regardless, running a timer may have
3329 // made some goroutine ready that we missed. Indicate the next timer to
3331 return nil, false, now, pollUntil, ranTimer
3334 // Check all Ps for a runnable G to steal.
3336 // On entry we have no P. If a G is available to steal and a P is available,
3337 // the P is returned which the caller should acquire and attempt to steal the
3339 func checkRunqsNoP(allpSnapshot []*p, idlepMaskSnapshot pMask) *p {
3340 for id, p2 := range allpSnapshot {
3341 if !idlepMaskSnapshot.read(uint32(id)) && !runqempty(p2) {
3343 pp, _ := pidlegetSpinning(0)
3345 // Can't get a P, don't bother checking remaining Ps.
3354 // No work available.
3358 // Check all Ps for a timer expiring sooner than pollUntil.
3360 // Returns updated pollUntil value.
3361 func checkTimersNoP(allpSnapshot []*p, timerpMaskSnapshot pMask, pollUntil int64) int64 {
3362 for id, p2 := range allpSnapshot {
3363 if timerpMaskSnapshot.read(uint32(id)) {
3364 w := nobarrierWakeTime(p2)
3365 if w != 0 && (pollUntil == 0 || w < pollUntil) {
3374 // Check for idle-priority GC, without a P on entry.
3376 // If some GC work, a P, and a worker G are all available, the P and G will be
3377 // returned. The returned P has not been wired yet.
3378 func checkIdleGCNoP() (*p, *g) {
3379 // N.B. Since we have no P, gcBlackenEnabled may change at any time; we
3380 // must check again after acquiring a P. As an optimization, we also check
3381 // if an idle mark worker is needed at all. This is OK here, because if we
3382 // observe that one isn't needed, at least one is currently running. Even if
3383 // it stops running, its own journey into the scheduler should schedule it
3384 // again, if need be (at which point, this check will pass, if relevant).
3385 if atomic.Load(&gcBlackenEnabled) == 0 || !gcController.needIdleMarkWorker() {
3388 if !gcMarkWorkAvailable(nil) {
3392 // Work is available; we can start an idle GC worker only if there is
3393 // an available P and available worker G.
3395 // We can attempt to acquire these in either order, though both have
3396 // synchronization concerns (see below). Workers are almost always
3397 // available (see comment in findRunnableGCWorker for the one case
3398 // there may be none). Since we're slightly less likely to find a P,
3399 // check for that first.
3401 // Synchronization: note that we must hold sched.lock until we are
3402 // committed to keeping it. Otherwise we cannot put the unnecessary P
3403 // back in sched.pidle without performing the full set of idle
3404 // transition checks.
3406 // If we were to check gcBgMarkWorkerPool first, we must somehow handle
3407 // the assumption in gcControllerState.findRunnableGCWorker that an
3408 // empty gcBgMarkWorkerPool is only possible if gcMarkDone is running.
3410 pp, now := pidlegetSpinning(0)
3416 // Now that we own a P, gcBlackenEnabled can't change (as it requires STW).
3417 if gcBlackenEnabled == 0 || !gcController.addIdleMarkWorker() {
3423 node := (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop())
3427 gcController.removeIdleMarkWorker()
3433 return pp, node.gp.ptr()
3436 // wakeNetPoller wakes up the thread sleeping in the network poller if it isn't
3437 // going to wake up before the when argument; or it wakes an idle P to service
3438 // timers and the network poller if there isn't one already.
3439 func wakeNetPoller(when int64) {
3440 if sched.lastpoll.Load() == 0 {
3441 // In findrunnable we ensure that when polling the pollUntil
3442 // field is either zero or the time to which the current
3443 // poll is expected to run. This can have a spurious wakeup
3444 // but should never miss a wakeup.
3445 pollerPollUntil := sched.pollUntil.Load()
3446 if pollerPollUntil == 0 || pollerPollUntil > when {
3450 // There are no threads in the network poller, try to get
3451 // one there so it can handle new timers.
3452 if GOOS != "plan9" { // Temporary workaround - see issue #42303.
3458 func resetspinning() {
3461 throw("resetspinning: not a spinning m")
3463 gp.m.spinning = false
3464 nmspinning := sched.nmspinning.Add(-1)
3466 throw("findrunnable: negative nmspinning")
3468 // M wakeup policy is deliberately somewhat conservative, so check if we
3469 // need to wakeup another P here. See "Worker thread parking/unparking"
3470 // comment at the top of the file for details.
3474 // injectglist adds each runnable G on the list to some run queue,
3475 // and clears glist. If there is no current P, they are added to the
3476 // global queue, and up to npidle M's are started to run them.
3477 // Otherwise, for each idle P, this adds a G to the global queue
3478 // and starts an M. Any remaining G's are added to the current P's
3480 // This may temporarily acquire sched.lock.
3481 // Can run concurrently with GC.
3482 func injectglist(glist *gList) {
3487 for gp := glist.head.ptr(); gp != nil; gp = gp.schedlink.ptr() {
3488 traceGoUnpark(gp, 0)
3492 // Mark all the goroutines as runnable before we put them
3493 // on the run queues.
3494 head := glist.head.ptr()
3497 for gp := head; gp != nil; gp = gp.schedlink.ptr() {
3500 casgstatus(gp, _Gwaiting, _Grunnable)
3503 // Turn the gList into a gQueue.
3509 startIdle := func(n int) {
3510 for i := 0; i < n; i++ {
3511 mp := acquirem() // See comment in startm.
3514 pp, _ := pidlegetSpinning(0)
3521 startm(pp, false, true)
3527 pp := getg().m.p.ptr()
3530 globrunqputbatch(&q, int32(qsize))
3536 npidle := int(sched.npidle.Load())
3539 for n = 0; n < npidle && !q.empty(); n++ {
3545 globrunqputbatch(&globq, int32(n))
3552 runqputbatch(pp, &q, qsize)
3556 // One round of scheduler: find a runnable goroutine and execute it.
3562 throw("schedule: holding locks")
3565 if mp.lockedg != 0 {
3567 execute(mp.lockedg.ptr(), false) // Never returns.
3570 // We should not schedule away from a g that is executing a cgo call,
3571 // since the cgo call is using the m's g0 stack.
3573 throw("schedule: in cgo")
3580 // Safety check: if we are spinning, the run queue should be empty.
3581 // Check this before calling checkTimers, as that might call
3582 // goready to put a ready goroutine on the local run queue.
3583 if mp.spinning && (pp.runnext != 0 || pp.runqhead != pp.runqtail) {
3584 throw("schedule: spinning with local work")
3587 gp, inheritTime, tryWakeP := findRunnable() // blocks until work is available
3589 if debug.dontfreezetheworld > 0 && freezing.Load() {
3590 // See comment in freezetheworld. We don't want to perturb
3591 // scheduler state, so we didn't gcstopm in findRunnable, but
3592 // also don't want to allow new goroutines to run.
3594 // Deadlock here rather than in the findRunnable loop so if
3595 // findRunnable is stuck in a loop we don't perturb that
3601 // This thread is going to run a goroutine and is not spinning anymore,
3602 // so if it was marked as spinning we need to reset it now and potentially
3603 // start a new spinning M.
3608 if sched.disable.user && !schedEnabled(gp) {
3609 // Scheduling of this goroutine is disabled. Put it on
3610 // the list of pending runnable goroutines for when we
3611 // re-enable user scheduling and look again.
3613 if schedEnabled(gp) {
3614 // Something re-enabled scheduling while we
3615 // were acquiring the lock.
3618 sched.disable.runnable.pushBack(gp)
3625 // If about to schedule a not-normal goroutine (a GCworker or tracereader),
3626 // wake a P if there is one.
3630 if gp.lockedm != 0 {
3631 // Hands off own p to the locked m,
3632 // then blocks waiting for a new p.
3637 execute(gp, inheritTime)
3640 // dropg removes the association between m and the current goroutine m->curg (gp for short).
3641 // Typically a caller sets gp's status away from Grunning and then
3642 // immediately calls dropg to finish the job. The caller is also responsible
3643 // for arranging that gp will be restarted using ready at an
3644 // appropriate time. After calling dropg and arranging for gp to be
3645 // readied later, the caller can do other work but eventually should
3646 // call schedule to restart the scheduling of goroutines on this m.
3650 setMNoWB(&gp.m.curg.m, nil)
3651 setGNoWB(&gp.m.curg, nil)
3654 // checkTimers runs any timers for the P that are ready.
3655 // If now is not 0 it is the current time.
3656 // It returns the passed time or the current time if now was passed as 0.
3657 // and the time when the next timer should run or 0 if there is no next timer,
3658 // and reports whether it ran any timers.
3659 // If the time when the next timer should run is not 0,
3660 // it is always larger than the returned time.
3661 // We pass now in and out to avoid extra calls of nanotime.
3663 //go:yeswritebarrierrec
3664 func checkTimers(pp *p, now int64) (rnow, pollUntil int64, ran bool) {
3665 // If it's not yet time for the first timer, or the first adjusted
3666 // timer, then there is nothing to do.
3667 next := pp.timer0When.Load()
3668 nextAdj := pp.timerModifiedEarliest.Load()
3669 if next == 0 || (nextAdj != 0 && nextAdj < next) {
3674 // No timers to run or adjust.
3675 return now, 0, false
3682 // Next timer is not ready to run, but keep going
3683 // if we would clear deleted timers.
3684 // This corresponds to the condition below where
3685 // we decide whether to call clearDeletedTimers.
3686 if pp != getg().m.p.ptr() || int(pp.deletedTimers.Load()) <= int(pp.numTimers.Load()/4) {
3687 return now, next, false
3691 lock(&pp.timersLock)
3693 if len(pp.timers) > 0 {
3694 adjusttimers(pp, now)
3695 for len(pp.timers) > 0 {
3696 // Note that runtimer may temporarily unlock
3698 if tw := runtimer(pp, now); tw != 0 {
3708 // If this is the local P, and there are a lot of deleted timers,
3709 // clear them out. We only do this for the local P to reduce
3710 // lock contention on timersLock.
3711 if pp == getg().m.p.ptr() && int(pp.deletedTimers.Load()) > len(pp.timers)/4 {
3712 clearDeletedTimers(pp)
3715 unlock(&pp.timersLock)
3717 return now, pollUntil, ran
3720 func parkunlock_c(gp *g, lock unsafe.Pointer) bool {
3721 unlock((*mutex)(lock))
3725 // park continuation on g0.
3726 func park_m(gp *g) {
3730 traceGoPark(mp.waitTraceBlockReason, mp.waitTraceSkip)
3733 // N.B. Not using casGToWaiting here because the waitreason is
3734 // set by park_m's caller.
3735 casgstatus(gp, _Grunning, _Gwaiting)
3738 if fn := mp.waitunlockf; fn != nil {
3739 ok := fn(gp, mp.waitlock)
3740 mp.waitunlockf = nil
3744 traceGoUnpark(gp, 2)
3746 casgstatus(gp, _Gwaiting, _Grunnable)
3747 execute(gp, true) // Schedule it back, never returns.
3753 func goschedImpl(gp *g) {
3754 status := readgstatus(gp)
3755 if status&^_Gscan != _Grunning {
3757 throw("bad g status")
3759 casgstatus(gp, _Grunning, _Grunnable)
3768 // Gosched continuation on g0.
3769 func gosched_m(gp *g) {
3776 // goschedguarded is a forbidden-states-avoided version of gosched_m.
3777 func goschedguarded_m(gp *g) {
3779 if !canPreemptM(gp.m) {
3780 gogo(&gp.sched) // never return
3789 func gopreempt_m(gp *g) {
3796 // preemptPark parks gp and puts it in _Gpreempted.
3799 func preemptPark(gp *g) {
3801 traceGoPark(traceBlockPreempted, 0)
3803 status := readgstatus(gp)
3804 if status&^_Gscan != _Grunning {
3806 throw("bad g status")
3809 if gp.asyncSafePoint {
3810 // Double-check that async preemption does not
3811 // happen in SPWRITE assembly functions.
3812 // isAsyncSafePoint must exclude this case.
3813 f := findfunc(gp.sched.pc)
3815 throw("preempt at unknown pc")
3817 if f.flag&abi.FuncFlagSPWrite != 0 {
3818 println("runtime: unexpected SPWRITE function", funcname(f), "in async preempt")
3819 throw("preempt SPWRITE")
3823 // Transition from _Grunning to _Gscan|_Gpreempted. We can't
3824 // be in _Grunning when we dropg because then we'd be running
3825 // without an M, but the moment we're in _Gpreempted,
3826 // something could claim this G before we've fully cleaned it
3827 // up. Hence, we set the scan bit to lock down further
3828 // transitions until we can dropg.
3829 casGToPreemptScan(gp, _Grunning, _Gscan|_Gpreempted)
3831 casfrom_Gscanstatus(gp, _Gscan|_Gpreempted, _Gpreempted)
3835 // goyield is like Gosched, but it:
3836 // - emits a GoPreempt trace event instead of a GoSched trace event
3837 // - puts the current G on the runq of the current P instead of the globrunq
3843 func goyield_m(gp *g) {
3848 casgstatus(gp, _Grunning, _Grunnable)
3850 runqput(pp, gp, false)
3854 // Finishes execution of the current goroutine.
3865 // goexit continuation on g0.
3866 func goexit0(gp *g) {
3870 casgstatus(gp, _Grunning, _Gdead)
3871 gcController.addScannableStack(pp, -int64(gp.stack.hi-gp.stack.lo))
3872 if isSystemGoroutine(gp, false) {
3876 locked := gp.lockedm != 0
3879 gp.preemptStop = false
3880 gp.paniconfault = false
3881 gp._defer = nil // should be true already but just in case.
3882 gp._panic = nil // non-nil for Goexit during panic. points at stack-allocated data.
3884 gp.waitreason = waitReasonZero
3889 if gcBlackenEnabled != 0 && gp.gcAssistBytes > 0 {
3890 // Flush assist credit to the global pool. This gives
3891 // better information to pacing if the application is
3892 // rapidly creating an exiting goroutines.
3893 assistWorkPerByte := gcController.assistWorkPerByte.Load()
3894 scanCredit := int64(assistWorkPerByte * float64(gp.gcAssistBytes))
3895 gcController.bgScanCredit.Add(scanCredit)
3896 gp.gcAssistBytes = 0
3901 if GOARCH == "wasm" { // no threads yet on wasm
3903 schedule() // never returns
3906 if mp.lockedInt != 0 {
3907 print("invalid m->lockedInt = ", mp.lockedInt, "\n")
3908 throw("internal lockOSThread error")
3912 // The goroutine may have locked this thread because
3913 // it put it in an unusual kernel state. Kill it
3914 // rather than returning it to the thread pool.
3916 // Return to mstart, which will release the P and exit
3918 if GOOS != "plan9" { // See golang.org/issue/22227.
3921 // Clear lockedExt on plan9 since we may end up re-using
3929 // save updates getg().sched to refer to pc and sp so that a following
3930 // gogo will restore pc and sp.
3932 // save must not have write barriers because invoking a write barrier
3933 // can clobber getg().sched.
3936 //go:nowritebarrierrec
3937 func save(pc, sp uintptr) {
3940 if gp == gp.m.g0 || gp == gp.m.gsignal {
3941 // m.g0.sched is special and must describe the context
3942 // for exiting the thread. mstart1 writes to it directly.
3943 // m.gsignal.sched should not be used at all.
3944 // This check makes sure save calls do not accidentally
3945 // run in contexts where they'd write to system g's.
3946 throw("save on system g not allowed")
3953 // We need to ensure ctxt is zero, but can't have a write
3954 // barrier here. However, it should always already be zero.
3956 if gp.sched.ctxt != nil {
3961 // The goroutine g is about to enter a system call.
3962 // Record that it's not using the cpu anymore.
3963 // This is called only from the go syscall library and cgocall,
3964 // not from the low-level system calls used by the runtime.
3966 // Entersyscall cannot split the stack: the save must
3967 // make g->sched refer to the caller's stack segment, because
3968 // entersyscall is going to return immediately after.
3970 // Nothing entersyscall calls can split the stack either.
3971 // We cannot safely move the stack during an active call to syscall,
3972 // because we do not know which of the uintptr arguments are
3973 // really pointers (back into the stack).
3974 // In practice, this means that we make the fast path run through
3975 // entersyscall doing no-split things, and the slow path has to use systemstack
3976 // to run bigger things on the system stack.
3978 // reentersyscall is the entry point used by cgo callbacks, where explicitly
3979 // saved SP and PC are restored. This is needed when exitsyscall will be called
3980 // from a function further up in the call stack than the parent, as g->syscallsp
3981 // must always point to a valid stack frame. entersyscall below is the normal
3982 // entry point for syscalls, which obtains the SP and PC from the caller.
3985 // At the start of a syscall we emit traceGoSysCall to capture the stack trace.
3986 // If the syscall does not block, that is it, we do not emit any other events.
3987 // If the syscall blocks (that is, P is retaken), retaker emits traceGoSysBlock;
3988 // when syscall returns we emit traceGoSysExit and when the goroutine starts running
3989 // (potentially instantly, if exitsyscallfast returns true) we emit traceGoStart.
3990 // To ensure that traceGoSysExit is emitted strictly after traceGoSysBlock,
3991 // we remember current value of syscalltick in m (gp.m.syscalltick = gp.m.p.ptr().syscalltick),
3992 // whoever emits traceGoSysBlock increments p.syscalltick afterwards;
3993 // and we wait for the increment before emitting traceGoSysExit.
3994 // Note that the increment is done even if tracing is not enabled,
3995 // because tracing can be enabled in the middle of syscall. We don't want the wait to hang.
3998 func reentersyscall(pc, sp uintptr) {
4001 // Disable preemption because during this function g is in Gsyscall status,
4002 // but can have inconsistent g->sched, do not let GC observe it.
4005 // Entersyscall must not call any function that might split/grow the stack.
4006 // (See details in comment above.)
4007 // Catch calls that might, by replacing the stack guard with something that
4008 // will trip any stack check and leaving a flag to tell newstack to die.
4009 gp.stackguard0 = stackPreempt
4010 gp.throwsplit = true
4012 // Leave SP around for GC and traceback.
4016 casgstatus(gp, _Grunning, _Gsyscall)
4017 if staticLockRanking {
4018 // When doing static lock ranking casgstatus can call
4019 // systemstack which clobbers g.sched.
4022 if gp.syscallsp < gp.stack.lo || gp.stack.hi < gp.syscallsp {
4023 systemstack(func() {
4024 print("entersyscall inconsistent ", hex(gp.syscallsp), " [", hex(gp.stack.lo), ",", hex(gp.stack.hi), "]\n")
4025 throw("entersyscall")
4030 systemstack(traceGoSysCall)
4031 // systemstack itself clobbers g.sched.{pc,sp} and we might
4032 // need them later when the G is genuinely blocked in a
4037 if sched.sysmonwait.Load() {
4038 systemstack(entersyscall_sysmon)
4042 if gp.m.p.ptr().runSafePointFn != 0 {
4043 // runSafePointFn may stack split if run on this stack
4044 systemstack(runSafePointFn)
4048 gp.m.syscalltick = gp.m.p.ptr().syscalltick
4053 atomic.Store(&pp.status, _Psyscall)
4054 if sched.gcwaiting.Load() {
4055 systemstack(entersyscall_gcwait)
4062 // Standard syscall entry used by the go syscall library and normal cgo calls.
4064 // This is exported via linkname to assembly in the syscall package and x/sys.
4067 //go:linkname entersyscall
4068 func entersyscall() {
4069 reentersyscall(getcallerpc(), getcallersp())
4072 func entersyscall_sysmon() {
4074 if sched.sysmonwait.Load() {
4075 sched.sysmonwait.Store(false)
4076 notewakeup(&sched.sysmonnote)
4081 func entersyscall_gcwait() {
4083 pp := gp.m.oldp.ptr()
4086 if sched.stopwait > 0 && atomic.Cas(&pp.status, _Psyscall, _Pgcstop) {
4092 if sched.stopwait--; sched.stopwait == 0 {
4093 notewakeup(&sched.stopnote)
4099 // The same as entersyscall(), but with a hint that the syscall is blocking.
4102 func entersyscallblock() {
4105 gp.m.locks++ // see comment in entersyscall
4106 gp.throwsplit = true
4107 gp.stackguard0 = stackPreempt // see comment in entersyscall
4108 gp.m.syscalltick = gp.m.p.ptr().syscalltick
4109 gp.m.p.ptr().syscalltick++
4111 // Leave SP around for GC and traceback.
4115 gp.syscallsp = gp.sched.sp
4116 gp.syscallpc = gp.sched.pc
4117 if gp.syscallsp < gp.stack.lo || gp.stack.hi < gp.syscallsp {
4121 systemstack(func() {
4122 print("entersyscallblock inconsistent ", hex(sp1), " ", hex(sp2), " ", hex(sp3), " [", hex(gp.stack.lo), ",", hex(gp.stack.hi), "]\n")
4123 throw("entersyscallblock")
4126 casgstatus(gp, _Grunning, _Gsyscall)
4127 if gp.syscallsp < gp.stack.lo || gp.stack.hi < gp.syscallsp {
4128 systemstack(func() {
4129 print("entersyscallblock inconsistent ", hex(sp), " ", hex(gp.sched.sp), " ", hex(gp.syscallsp), " [", hex(gp.stack.lo), ",", hex(gp.stack.hi), "]\n")
4130 throw("entersyscallblock")
4134 systemstack(entersyscallblock_handoff)
4136 // Resave for traceback during blocked call.
4137 save(getcallerpc(), getcallersp())
4142 func entersyscallblock_handoff() {
4145 traceGoSysBlock(getg().m.p.ptr())
4147 handoffp(releasep())
4150 // The goroutine g exited its system call.
4151 // Arrange for it to run on a cpu again.
4152 // This is called only from the go syscall library, not
4153 // from the low-level system calls used by the runtime.
4155 // Write barriers are not allowed because our P may have been stolen.
4157 // This is exported via linkname to assembly in the syscall package.
4160 //go:nowritebarrierrec
4161 //go:linkname exitsyscall
4162 func exitsyscall() {
4165 gp.m.locks++ // see comment in entersyscall
4166 if getcallersp() > gp.syscallsp {
4167 throw("exitsyscall: syscall frame is no longer valid")
4171 oldp := gp.m.oldp.ptr()
4173 if exitsyscallfast(oldp) {
4174 // When exitsyscallfast returns success, we have a P so can now use
4176 if goroutineProfile.active {
4177 // Make sure that gp has had its stack written out to the goroutine
4178 // profile, exactly as it was when the goroutine profiler first
4179 // stopped the world.
4180 systemstack(func() {
4181 tryRecordGoroutineProfileWB(gp)
4185 if oldp != gp.m.p.ptr() || gp.m.syscalltick != gp.m.p.ptr().syscalltick {
4186 systemstack(traceGoStart)
4189 // There's a cpu for us, so we can run.
4190 gp.m.p.ptr().syscalltick++
4191 // We need to cas the status and scan before resuming...
4192 casgstatus(gp, _Gsyscall, _Grunning)
4194 // Garbage collector isn't running (since we are),
4195 // so okay to clear syscallsp.
4199 // restore the preemption request in case we've cleared it in newstack
4200 gp.stackguard0 = stackPreempt
4202 // otherwise restore the real stackGuard, we've spoiled it in entersyscall/entersyscallblock
4203 gp.stackguard0 = gp.stack.lo + stackGuard
4205 gp.throwsplit = false
4207 if sched.disable.user && !schedEnabled(gp) {
4208 // Scheduling of this goroutine is disabled.
4216 // Wait till traceGoSysBlock event is emitted.
4217 // This ensures consistency of the trace (the goroutine is started after it is blocked).
4218 for oldp != nil && oldp.syscalltick == gp.m.syscalltick {
4221 // We can't trace syscall exit right now because we don't have a P.
4222 // Tracing code can invoke write barriers that cannot run without a P.
4223 // So instead we remember the syscall exit time and emit the event
4224 // in execute when we have a P.
4225 gp.trace.sysExitTime = traceClockNow()
4230 // Call the scheduler.
4233 // Scheduler returned, so we're allowed to run now.
4234 // Delete the syscallsp information that we left for
4235 // the garbage collector during the system call.
4236 // Must wait until now because until gosched returns
4237 // we don't know for sure that the garbage collector
4240 gp.m.p.ptr().syscalltick++
4241 gp.throwsplit = false
4245 func exitsyscallfast(oldp *p) bool {
4248 // Freezetheworld sets stopwait but does not retake P's.
4249 if sched.stopwait == freezeStopWait {
4253 // Try to re-acquire the last P.
4254 if oldp != nil && oldp.status == _Psyscall && atomic.Cas(&oldp.status, _Psyscall, _Pidle) {
4255 // There's a cpu for us, so we can run.
4257 exitsyscallfast_reacquired()
4261 // Try to get any other idle P.
4262 if sched.pidle != 0 {
4264 systemstack(func() {
4265 ok = exitsyscallfast_pidle()
4266 if ok && traceEnabled() {
4268 // Wait till traceGoSysBlock event is emitted.
4269 // This ensures consistency of the trace (the goroutine is started after it is blocked).
4270 for oldp.syscalltick == gp.m.syscalltick {
4284 // exitsyscallfast_reacquired is the exitsyscall path on which this G
4285 // has successfully reacquired the P it was running on before the
4289 func exitsyscallfast_reacquired() {
4291 if gp.m.syscalltick != gp.m.p.ptr().syscalltick {
4293 // The p was retaken and then enter into syscall again (since gp.m.syscalltick has changed).
4294 // traceGoSysBlock for this syscall was already emitted,
4295 // but here we effectively retake the p from the new syscall running on the same p.
4296 systemstack(func() {
4297 // Denote blocking of the new syscall.
4298 traceGoSysBlock(gp.m.p.ptr())
4299 // Denote completion of the current syscall.
4303 gp.m.p.ptr().syscalltick++
4307 func exitsyscallfast_pidle() bool {
4309 pp, _ := pidleget(0)
4310 if pp != nil && sched.sysmonwait.Load() {
4311 sched.sysmonwait.Store(false)
4312 notewakeup(&sched.sysmonnote)
4322 // exitsyscall slow path on g0.
4323 // Failed to acquire P, enqueue gp as runnable.
4325 // Called via mcall, so gp is the calling g from this M.
4327 //go:nowritebarrierrec
4328 func exitsyscall0(gp *g) {
4329 casgstatus(gp, _Gsyscall, _Grunnable)
4333 if schedEnabled(gp) {
4340 // Below, we stoplockedm if gp is locked. globrunqput releases
4341 // ownership of gp, so we must check if gp is locked prior to
4342 // committing the release by unlocking sched.lock, otherwise we
4343 // could race with another M transitioning gp from unlocked to
4345 locked = gp.lockedm != 0
4346 } else if sched.sysmonwait.Load() {
4347 sched.sysmonwait.Store(false)
4348 notewakeup(&sched.sysmonnote)
4353 execute(gp, false) // Never returns.
4356 // Wait until another thread schedules gp and so m again.
4358 // N.B. lockedm must be this M, as this g was running on this M
4359 // before entersyscall.
4361 execute(gp, false) // Never returns.
4364 schedule() // Never returns.
4367 // Called from syscall package before fork.
4369 //go:linkname syscall_runtime_BeforeFork syscall.runtime_BeforeFork
4371 func syscall_runtime_BeforeFork() {
4374 // Block signals during a fork, so that the child does not run
4375 // a signal handler before exec if a signal is sent to the process
4376 // group. See issue #18600.
4378 sigsave(&gp.m.sigmask)
4381 // This function is called before fork in syscall package.
4382 // Code between fork and exec must not allocate memory nor even try to grow stack.
4383 // Here we spoil g.stackguard0 to reliably detect any attempts to grow stack.
4384 // runtime_AfterFork will undo this in parent process, but not in child.
4385 gp.stackguard0 = stackFork
4388 // Called from syscall package after fork in parent.
4390 //go:linkname syscall_runtime_AfterFork syscall.runtime_AfterFork
4392 func syscall_runtime_AfterFork() {
4395 // See the comments in beforefork.
4396 gp.stackguard0 = gp.stack.lo + stackGuard
4398 msigrestore(gp.m.sigmask)
4403 // inForkedChild is true while manipulating signals in the child process.
4404 // This is used to avoid calling libc functions in case we are using vfork.
4405 var inForkedChild bool
4407 // Called from syscall package after fork in child.
4408 // It resets non-sigignored signals to the default handler, and
4409 // restores the signal mask in preparation for the exec.
4411 // Because this might be called during a vfork, and therefore may be
4412 // temporarily sharing address space with the parent process, this must
4413 // not change any global variables or calling into C code that may do so.
4415 //go:linkname syscall_runtime_AfterForkInChild syscall.runtime_AfterForkInChild
4417 //go:nowritebarrierrec
4418 func syscall_runtime_AfterForkInChild() {
4419 // It's OK to change the global variable inForkedChild here
4420 // because we are going to change it back. There is no race here,
4421 // because if we are sharing address space with the parent process,
4422 // then the parent process can not be running concurrently.
4423 inForkedChild = true
4425 clearSignalHandlers()
4427 // When we are the child we are the only thread running,
4428 // so we know that nothing else has changed gp.m.sigmask.
4429 msigrestore(getg().m.sigmask)
4431 inForkedChild = false
4434 // pendingPreemptSignals is the number of preemption signals
4435 // that have been sent but not received. This is only used on Darwin.
4437 var pendingPreemptSignals atomic.Int32
4439 // Called from syscall package before Exec.
4441 //go:linkname syscall_runtime_BeforeExec syscall.runtime_BeforeExec
4442 func syscall_runtime_BeforeExec() {
4443 // Prevent thread creation during exec.
4446 // On Darwin, wait for all pending preemption signals to
4447 // be received. See issue #41702.
4448 if GOOS == "darwin" || GOOS == "ios" {
4449 for pendingPreemptSignals.Load() > 0 {
4455 // Called from syscall package after Exec.
4457 //go:linkname syscall_runtime_AfterExec syscall.runtime_AfterExec
4458 func syscall_runtime_AfterExec() {
4462 // Allocate a new g, with a stack big enough for stacksize bytes.
4463 func malg(stacksize int32) *g {
4466 stacksize = round2(stackSystem + stacksize)
4467 systemstack(func() {
4468 newg.stack = stackalloc(uint32(stacksize))
4470 newg.stackguard0 = newg.stack.lo + stackGuard
4471 newg.stackguard1 = ^uintptr(0)
4472 // Clear the bottom word of the stack. We record g
4473 // there on gsignal stack during VDSO on ARM and ARM64.
4474 *(*uintptr)(unsafe.Pointer(newg.stack.lo)) = 0
4479 // Create a new g running fn.
4480 // Put it on the queue of g's waiting to run.
4481 // The compiler turns a go statement into a call to this.
4482 func newproc(fn *funcval) {
4485 systemstack(func() {
4486 newg := newproc1(fn, gp, pc)
4488 pp := getg().m.p.ptr()
4489 runqput(pp, newg, true)
4497 // Create a new g in state _Grunnable, starting at fn. callerpc is the
4498 // address of the go statement that created this. The caller is responsible
4499 // for adding the new g to the scheduler.
4500 func newproc1(fn *funcval, callergp *g, callerpc uintptr) *g {
4502 fatal("go of nil func value")
4505 mp := acquirem() // disable preemption because we hold M and P in local vars.
4509 newg = malg(stackMin)
4510 casgstatus(newg, _Gidle, _Gdead)
4511 allgadd(newg) // publishes with a g->status of Gdead so GC scanner doesn't look at uninitialized stack.
4513 if newg.stack.hi == 0 {
4514 throw("newproc1: newg missing stack")
4517 if readgstatus(newg) != _Gdead {
4518 throw("newproc1: new g is not Gdead")
4521 totalSize := uintptr(4*goarch.PtrSize + sys.MinFrameSize) // extra space in case of reads slightly beyond frame
4522 totalSize = alignUp(totalSize, sys.StackAlign)
4523 sp := newg.stack.hi - totalSize
4527 *(*uintptr)(unsafe.Pointer(sp)) = 0
4529 spArg += sys.MinFrameSize
4532 memclrNoHeapPointers(unsafe.Pointer(&newg.sched), unsafe.Sizeof(newg.sched))
4535 newg.sched.pc = abi.FuncPCABI0(goexit) + sys.PCQuantum // +PCQuantum so that previous instruction is in same function
4536 newg.sched.g = guintptr(unsafe.Pointer(newg))
4537 gostartcallfn(&newg.sched, fn)
4538 newg.parentGoid = callergp.goid
4539 newg.gopc = callerpc
4540 newg.ancestors = saveAncestors(callergp)
4541 newg.startpc = fn.fn
4542 if isSystemGoroutine(newg, false) {
4545 // Only user goroutines inherit pprof labels.
4547 newg.labels = mp.curg.labels
4549 if goroutineProfile.active {
4550 // A concurrent goroutine profile is running. It should include
4551 // exactly the set of goroutines that were alive when the goroutine
4552 // profiler first stopped the world. That does not include newg, so
4553 // mark it as not needing a profile before transitioning it from
4555 newg.goroutineProfiled.Store(goroutineProfileSatisfied)
4558 // Track initial transition?
4559 newg.trackingSeq = uint8(fastrand())
4560 if newg.trackingSeq%gTrackingPeriod == 0 {
4561 newg.tracking = true
4563 casgstatus(newg, _Gdead, _Grunnable)
4564 gcController.addScannableStack(pp, int64(newg.stack.hi-newg.stack.lo))
4566 if pp.goidcache == pp.goidcacheend {
4567 // Sched.goidgen is the last allocated id,
4568 // this batch must be [sched.goidgen+1, sched.goidgen+GoidCacheBatch].
4569 // At startup sched.goidgen=0, so main goroutine receives goid=1.
4570 pp.goidcache = sched.goidgen.Add(_GoidCacheBatch)
4571 pp.goidcache -= _GoidCacheBatch - 1
4572 pp.goidcacheend = pp.goidcache + _GoidCacheBatch
4574 newg.goid = pp.goidcache
4577 newg.racectx = racegostart(callerpc)
4579 if newg.labels != nil {
4580 // See note in proflabel.go on labelSync's role in synchronizing
4581 // with the reads in the signal handler.
4582 racereleasemergeg(newg, unsafe.Pointer(&labelSync))
4586 traceGoCreate(newg, newg.startpc)
4593 // saveAncestors copies previous ancestors of the given caller g and
4594 // includes info for the current caller into a new set of tracebacks for
4595 // a g being created.
4596 func saveAncestors(callergp *g) *[]ancestorInfo {
4597 // Copy all prior info, except for the root goroutine (goid 0).
4598 if debug.tracebackancestors <= 0 || callergp.goid == 0 {
4601 var callerAncestors []ancestorInfo
4602 if callergp.ancestors != nil {
4603 callerAncestors = *callergp.ancestors
4605 n := int32(len(callerAncestors)) + 1
4606 if n > debug.tracebackancestors {
4607 n = debug.tracebackancestors
4609 ancestors := make([]ancestorInfo, n)
4610 copy(ancestors[1:], callerAncestors)
4612 var pcs [tracebackInnerFrames]uintptr
4613 npcs := gcallers(callergp, 0, pcs[:])
4614 ipcs := make([]uintptr, npcs)
4616 ancestors[0] = ancestorInfo{
4618 goid: callergp.goid,
4619 gopc: callergp.gopc,
4622 ancestorsp := new([]ancestorInfo)
4623 *ancestorsp = ancestors
4627 // Put on gfree list.
4628 // If local list is too long, transfer a batch to the global list.
4629 func gfput(pp *p, gp *g) {
4630 if readgstatus(gp) != _Gdead {
4631 throw("gfput: bad status (not Gdead)")
4634 stksize := gp.stack.hi - gp.stack.lo
4636 if stksize != uintptr(startingStackSize) {
4637 // non-standard stack size - free it.
4646 if pp.gFree.n >= 64 {
4652 for pp.gFree.n >= 32 {
4653 gp := pp.gFree.pop()
4655 if gp.stack.lo == 0 {
4662 lock(&sched.gFree.lock)
4663 sched.gFree.noStack.pushAll(noStackQ)
4664 sched.gFree.stack.pushAll(stackQ)
4665 sched.gFree.n += inc
4666 unlock(&sched.gFree.lock)
4670 // Get from gfree list.
4671 // If local list is empty, grab a batch from global list.
4672 func gfget(pp *p) *g {
4674 if pp.gFree.empty() && (!sched.gFree.stack.empty() || !sched.gFree.noStack.empty()) {
4675 lock(&sched.gFree.lock)
4676 // Move a batch of free Gs to the P.
4677 for pp.gFree.n < 32 {
4678 // Prefer Gs with stacks.
4679 gp := sched.gFree.stack.pop()
4681 gp = sched.gFree.noStack.pop()
4690 unlock(&sched.gFree.lock)
4693 gp := pp.gFree.pop()
4698 if gp.stack.lo != 0 && gp.stack.hi-gp.stack.lo != uintptr(startingStackSize) {
4699 // Deallocate old stack. We kept it in gfput because it was the
4700 // right size when the goroutine was put on the free list, but
4701 // the right size has changed since then.
4702 systemstack(func() {
4709 if gp.stack.lo == 0 {
4710 // Stack was deallocated in gfput or just above. Allocate a new one.
4711 systemstack(func() {
4712 gp.stack = stackalloc(startingStackSize)
4714 gp.stackguard0 = gp.stack.lo + stackGuard
4717 racemalloc(unsafe.Pointer(gp.stack.lo), gp.stack.hi-gp.stack.lo)
4720 msanmalloc(unsafe.Pointer(gp.stack.lo), gp.stack.hi-gp.stack.lo)
4723 asanunpoison(unsafe.Pointer(gp.stack.lo), gp.stack.hi-gp.stack.lo)
4729 // Purge all cached G's from gfree list to the global list.
4730 func gfpurge(pp *p) {
4736 for !pp.gFree.empty() {
4737 gp := pp.gFree.pop()
4739 if gp.stack.lo == 0 {
4746 lock(&sched.gFree.lock)
4747 sched.gFree.noStack.pushAll(noStackQ)
4748 sched.gFree.stack.pushAll(stackQ)
4749 sched.gFree.n += inc
4750 unlock(&sched.gFree.lock)
4753 // Breakpoint executes a breakpoint trap.
4758 // dolockOSThread is called by LockOSThread and lockOSThread below
4759 // after they modify m.locked. Do not allow preemption during this call,
4760 // or else the m might be different in this function than in the caller.
4763 func dolockOSThread() {
4764 if GOARCH == "wasm" {
4765 return // no threads on wasm yet
4768 gp.m.lockedg.set(gp)
4769 gp.lockedm.set(gp.m)
4772 // LockOSThread wires the calling goroutine to its current operating system thread.
4773 // The calling goroutine will always execute in that thread,
4774 // and no other goroutine will execute in it,
4775 // until the calling goroutine has made as many calls to
4776 // UnlockOSThread as to LockOSThread.
4777 // If the calling goroutine exits without unlocking the thread,
4778 // the thread will be terminated.
4780 // All init functions are run on the startup thread. Calling LockOSThread
4781 // from an init function will cause the main function to be invoked on
4784 // A goroutine should call LockOSThread before calling OS services or
4785 // non-Go library functions that depend on per-thread state.
4788 func LockOSThread() {
4789 if atomic.Load(&newmHandoff.haveTemplateThread) == 0 && GOOS != "plan9" {
4790 // If we need to start a new thread from the locked
4791 // thread, we need the template thread. Start it now
4792 // while we're in a known-good state.
4793 startTemplateThread()
4797 if gp.m.lockedExt == 0 {
4799 panic("LockOSThread nesting overflow")
4805 func lockOSThread() {
4806 getg().m.lockedInt++
4810 // dounlockOSThread is called by UnlockOSThread and unlockOSThread below
4811 // after they update m->locked. Do not allow preemption during this call,
4812 // or else the m might be in different in this function than in the caller.
4815 func dounlockOSThread() {
4816 if GOARCH == "wasm" {
4817 return // no threads on wasm yet
4820 if gp.m.lockedInt != 0 || gp.m.lockedExt != 0 {
4827 // UnlockOSThread undoes an earlier call to LockOSThread.
4828 // If this drops the number of active LockOSThread calls on the
4829 // calling goroutine to zero, it unwires the calling goroutine from
4830 // its fixed operating system thread.
4831 // If there are no active LockOSThread calls, this is a no-op.
4833 // Before calling UnlockOSThread, the caller must ensure that the OS
4834 // thread is suitable for running other goroutines. If the caller made
4835 // any permanent changes to the state of the thread that would affect
4836 // other goroutines, it should not call this function and thus leave
4837 // the goroutine locked to the OS thread until the goroutine (and
4838 // hence the thread) exits.
4841 func UnlockOSThread() {
4843 if gp.m.lockedExt == 0 {
4851 func unlockOSThread() {
4853 if gp.m.lockedInt == 0 {
4854 systemstack(badunlockosthread)
4860 func badunlockosthread() {
4861 throw("runtime: internal error: misuse of lockOSThread/unlockOSThread")
4864 func gcount() int32 {
4865 n := int32(atomic.Loaduintptr(&allglen)) - sched.gFree.n - sched.ngsys.Load()
4866 for _, pp := range allp {
4870 // All these variables can be changed concurrently, so the result can be inconsistent.
4871 // But at least the current goroutine is running.
4878 func mcount() int32 {
4879 return int32(sched.mnext - sched.nmfreed)
4883 signalLock atomic.Uint32
4885 // Must hold signalLock to write. Reads may be lock-free, but
4886 // signalLock should be taken to synchronize with changes.
4890 func _System() { _System() }
4891 func _ExternalCode() { _ExternalCode() }
4892 func _LostExternalCode() { _LostExternalCode() }
4893 func _GC() { _GC() }
4894 func _LostSIGPROFDuringAtomic64() { _LostSIGPROFDuringAtomic64() }
4895 func _VDSO() { _VDSO() }
4897 // Called if we receive a SIGPROF signal.
4898 // Called by the signal handler, may run during STW.
4900 //go:nowritebarrierrec
4901 func sigprof(pc, sp, lr uintptr, gp *g, mp *m) {
4902 if prof.hz.Load() == 0 {
4906 // If mp.profilehz is 0, then profiling is not enabled for this thread.
4907 // We must check this to avoid a deadlock between setcpuprofilerate
4908 // and the call to cpuprof.add, below.
4909 if mp != nil && mp.profilehz == 0 {
4913 // On mips{,le}/arm, 64bit atomics are emulated with spinlocks, in
4914 // runtime/internal/atomic. If SIGPROF arrives while the program is inside
4915 // the critical section, it creates a deadlock (when writing the sample).
4916 // As a workaround, create a counter of SIGPROFs while in critical section
4917 // to store the count, and pass it to sigprof.add() later when SIGPROF is
4918 // received from somewhere else (with _LostSIGPROFDuringAtomic64 as pc).
4919 if GOARCH == "mips" || GOARCH == "mipsle" || GOARCH == "arm" {
4920 if f := findfunc(pc); f.valid() {
4921 if hasPrefix(funcname(f), "runtime/internal/atomic") {
4922 cpuprof.lostAtomic++
4926 if GOARCH == "arm" && goarm < 7 && GOOS == "linux" && pc&0xffff0000 == 0xffff0000 {
4927 // runtime/internal/atomic functions call into kernel
4928 // helpers on arm < 7. See
4929 // runtime/internal/atomic/sys_linux_arm.s.
4930 cpuprof.lostAtomic++
4935 // Profiling runs concurrently with GC, so it must not allocate.
4936 // Set a trap in case the code does allocate.
4937 // Note that on windows, one thread takes profiles of all the
4938 // other threads, so mp is usually not getg().m.
4939 // In fact mp may not even be stopped.
4940 // See golang.org/issue/17165.
4941 getg().m.mallocing++
4944 var stk [maxCPUProfStack]uintptr
4946 if mp.ncgo > 0 && mp.curg != nil && mp.curg.syscallpc != 0 && mp.curg.syscallsp != 0 {
4948 // Check cgoCallersUse to make sure that we are not
4949 // interrupting other code that is fiddling with
4950 // cgoCallers. We are running in a signal handler
4951 // with all signals blocked, so we don't have to worry
4952 // about any other code interrupting us.
4953 if mp.cgoCallersUse.Load() == 0 && mp.cgoCallers != nil && mp.cgoCallers[0] != 0 {
4954 for cgoOff < len(mp.cgoCallers) && mp.cgoCallers[cgoOff] != 0 {
4957 n += copy(stk[:], mp.cgoCallers[:cgoOff])
4958 mp.cgoCallers[0] = 0
4961 // Collect Go stack that leads to the cgo call.
4962 u.initAt(mp.curg.syscallpc, mp.curg.syscallsp, 0, mp.curg, unwindSilentErrors)
4963 } else if usesLibcall() && mp.libcallg != 0 && mp.libcallpc != 0 && mp.libcallsp != 0 {
4964 // Libcall, i.e. runtime syscall on windows.
4965 // Collect Go stack that leads to the call.
4966 u.initAt(mp.libcallpc, mp.libcallsp, 0, mp.libcallg.ptr(), unwindSilentErrors)
4967 } else if mp != nil && mp.vdsoSP != 0 {
4968 // VDSO call, e.g. nanotime1 on Linux.
4969 // Collect Go stack that leads to the call.
4970 u.initAt(mp.vdsoPC, mp.vdsoSP, 0, gp, unwindSilentErrors|unwindJumpStack)
4972 u.initAt(pc, sp, lr, gp, unwindSilentErrors|unwindTrap|unwindJumpStack)
4974 n += tracebackPCs(&u, 0, stk[n:])
4977 // Normal traceback is impossible or has failed.
4978 // Account it against abstract "System" or "GC".
4981 pc = abi.FuncPCABIInternal(_VDSO) + sys.PCQuantum
4982 } else if pc > firstmoduledata.etext {
4983 // "ExternalCode" is better than "etext".
4984 pc = abi.FuncPCABIInternal(_ExternalCode) + sys.PCQuantum
4987 if mp.preemptoff != "" {
4988 stk[1] = abi.FuncPCABIInternal(_GC) + sys.PCQuantum
4990 stk[1] = abi.FuncPCABIInternal(_System) + sys.PCQuantum
4994 if prof.hz.Load() != 0 {
4995 // Note: it can happen on Windows that we interrupted a system thread
4996 // with no g, so gp could nil. The other nil checks are done out of
4997 // caution, but not expected to be nil in practice.
4998 var tagPtr *unsafe.Pointer
4999 if gp != nil && gp.m != nil && gp.m.curg != nil {
5000 tagPtr = &gp.m.curg.labels
5002 cpuprof.add(tagPtr, stk[:n])
5006 if gp != nil && gp.m != nil {
5007 if gp.m.curg != nil {
5012 traceCPUSample(gprof, pp, stk[:n])
5014 getg().m.mallocing--
5017 // setcpuprofilerate sets the CPU profiling rate to hz times per second.
5018 // If hz <= 0, setcpuprofilerate turns off CPU profiling.
5019 func setcpuprofilerate(hz int32) {
5020 // Force sane arguments.
5025 // Disable preemption, otherwise we can be rescheduled to another thread
5026 // that has profiling enabled.
5030 // Stop profiler on this thread so that it is safe to lock prof.
5031 // if a profiling signal came in while we had prof locked,
5032 // it would deadlock.
5033 setThreadCPUProfiler(0)
5035 for !prof.signalLock.CompareAndSwap(0, 1) {
5038 if prof.hz.Load() != hz {
5039 setProcessCPUProfiler(hz)
5042 prof.signalLock.Store(0)
5045 sched.profilehz = hz
5049 setThreadCPUProfiler(hz)
5055 // init initializes pp, which may be a freshly allocated p or a
5056 // previously destroyed p, and transitions it to status _Pgcstop.
5057 func (pp *p) init(id int32) {
5059 pp.status = _Pgcstop
5060 pp.sudogcache = pp.sudogbuf[:0]
5061 pp.deferpool = pp.deferpoolbuf[:0]
5063 if pp.mcache == nil {
5066 throw("missing mcache?")
5068 // Use the bootstrap mcache0. Only one P will get
5069 // mcache0: the one with ID 0.
5072 pp.mcache = allocmcache()
5075 if raceenabled && pp.raceprocctx == 0 {
5077 pp.raceprocctx = raceprocctx0
5078 raceprocctx0 = 0 // bootstrap
5080 pp.raceprocctx = raceproccreate()
5083 lockInit(&pp.timersLock, lockRankTimers)
5085 // This P may get timers when it starts running. Set the mask here
5086 // since the P may not go through pidleget (notably P 0 on startup).
5088 // Similarly, we may not go through pidleget before this P starts
5089 // running if it is P 0 on startup.
5093 // destroy releases all of the resources associated with pp and
5094 // transitions it to status _Pdead.
5096 // sched.lock must be held and the world must be stopped.
5097 func (pp *p) destroy() {
5098 assertLockHeld(&sched.lock)
5099 assertWorldStopped()
5101 // Move all runnable goroutines to the global queue
5102 for pp.runqhead != pp.runqtail {
5103 // Pop from tail of local queue
5105 gp := pp.runq[pp.runqtail%uint32(len(pp.runq))].ptr()
5106 // Push onto head of global queue
5109 if pp.runnext != 0 {
5110 globrunqputhead(pp.runnext.ptr())
5113 if len(pp.timers) > 0 {
5114 plocal := getg().m.p.ptr()
5115 // The world is stopped, but we acquire timersLock to
5116 // protect against sysmon calling timeSleepUntil.
5117 // This is the only case where we hold the timersLock of
5118 // more than one P, so there are no deadlock concerns.
5119 lock(&plocal.timersLock)
5120 lock(&pp.timersLock)
5121 moveTimers(plocal, pp.timers)
5123 pp.numTimers.Store(0)
5124 pp.deletedTimers.Store(0)
5125 pp.timer0When.Store(0)
5126 unlock(&pp.timersLock)
5127 unlock(&plocal.timersLock)
5129 // Flush p's write barrier buffer.
5130 if gcphase != _GCoff {
5134 for i := range pp.sudogbuf {
5135 pp.sudogbuf[i] = nil
5137 pp.sudogcache = pp.sudogbuf[:0]
5138 pp.pinnerCache = nil
5139 for j := range pp.deferpoolbuf {
5140 pp.deferpoolbuf[j] = nil
5142 pp.deferpool = pp.deferpoolbuf[:0]
5143 systemstack(func() {
5144 for i := 0; i < pp.mspancache.len; i++ {
5145 // Safe to call since the world is stopped.
5146 mheap_.spanalloc.free(unsafe.Pointer(pp.mspancache.buf[i]))
5148 pp.mspancache.len = 0
5150 pp.pcache.flush(&mheap_.pages)
5151 unlock(&mheap_.lock)
5153 freemcache(pp.mcache)
5158 if pp.timerRaceCtx != 0 {
5159 // The race detector code uses a callback to fetch
5160 // the proc context, so arrange for that callback
5161 // to see the right thing.
5162 // This hack only works because we are the only
5168 racectxend(pp.timerRaceCtx)
5173 raceprocdestroy(pp.raceprocctx)
5180 // Change number of processors.
5182 // sched.lock must be held, and the world must be stopped.
5184 // gcworkbufs must not be being modified by either the GC or the write barrier
5185 // code, so the GC must not be running if the number of Ps actually changes.
5187 // Returns list of Ps with local work, they need to be scheduled by the caller.
5188 func procresize(nprocs int32) *p {
5189 assertLockHeld(&sched.lock)
5190 assertWorldStopped()
5193 if old < 0 || nprocs <= 0 {
5194 throw("procresize: invalid arg")
5197 traceGomaxprocs(nprocs)
5200 // update statistics
5202 if sched.procresizetime != 0 {
5203 sched.totaltime += int64(old) * (now - sched.procresizetime)
5205 sched.procresizetime = now
5207 maskWords := (nprocs + 31) / 32
5209 // Grow allp if necessary.
5210 if nprocs > int32(len(allp)) {
5211 // Synchronize with retake, which could be running
5212 // concurrently since it doesn't run on a P.
5214 if nprocs <= int32(cap(allp)) {
5215 allp = allp[:nprocs]
5217 nallp := make([]*p, nprocs)
5218 // Copy everything up to allp's cap so we
5219 // never lose old allocated Ps.
5220 copy(nallp, allp[:cap(allp)])
5224 if maskWords <= int32(cap(idlepMask)) {
5225 idlepMask = idlepMask[:maskWords]
5226 timerpMask = timerpMask[:maskWords]
5228 nidlepMask := make([]uint32, maskWords)
5229 // No need to copy beyond len, old Ps are irrelevant.
5230 copy(nidlepMask, idlepMask)
5231 idlepMask = nidlepMask
5233 ntimerpMask := make([]uint32, maskWords)
5234 copy(ntimerpMask, timerpMask)
5235 timerpMask = ntimerpMask
5240 // initialize new P's
5241 for i := old; i < nprocs; i++ {
5247 atomicstorep(unsafe.Pointer(&allp[i]), unsafe.Pointer(pp))
5251 if gp.m.p != 0 && gp.m.p.ptr().id < nprocs {
5252 // continue to use the current P
5253 gp.m.p.ptr().status = _Prunning
5254 gp.m.p.ptr().mcache.prepareForSweep()
5256 // release the current P and acquire allp[0].
5258 // We must do this before destroying our current P
5259 // because p.destroy itself has write barriers, so we
5260 // need to do that from a valid P.
5263 // Pretend that we were descheduled
5264 // and then scheduled again to keep
5267 traceProcStop(gp.m.p.ptr())
5281 // g.m.p is now set, so we no longer need mcache0 for bootstrapping.
5284 // release resources from unused P's
5285 for i := nprocs; i < old; i++ {
5288 // can't free P itself because it can be referenced by an M in syscall
5292 if int32(len(allp)) != nprocs {
5294 allp = allp[:nprocs]
5295 idlepMask = idlepMask[:maskWords]
5296 timerpMask = timerpMask[:maskWords]
5301 for i := nprocs - 1; i >= 0; i-- {
5303 if gp.m.p.ptr() == pp {
5311 pp.link.set(runnablePs)
5315 stealOrder.reset(uint32(nprocs))
5316 var int32p *int32 = &gomaxprocs // make compiler check that gomaxprocs is an int32
5317 atomic.Store((*uint32)(unsafe.Pointer(int32p)), uint32(nprocs))
5319 // Notify the limiter that the amount of procs has changed.
5320 gcCPULimiter.resetCapacity(now, nprocs)
5325 // Associate p and the current m.
5327 // This function is allowed to have write barriers even if the caller
5328 // isn't because it immediately acquires pp.
5330 //go:yeswritebarrierrec
5331 func acquirep(pp *p) {
5332 // Do the part that isn't allowed to have write barriers.
5335 // Have p; write barriers now allowed.
5337 // Perform deferred mcache flush before this P can allocate
5338 // from a potentially stale mcache.
5339 pp.mcache.prepareForSweep()
5346 // wirep is the first step of acquirep, which actually associates the
5347 // current M to pp. This is broken out so we can disallow write
5348 // barriers for this part, since we don't yet have a P.
5350 //go:nowritebarrierrec
5356 throw("wirep: already in go")
5358 if pp.m != 0 || pp.status != _Pidle {
5363 print("wirep: p->m=", pp.m, "(", id, ") p->status=", pp.status, "\n")
5364 throw("wirep: invalid p state")
5368 pp.status = _Prunning
5371 // Disassociate p and the current m.
5372 func releasep() *p {
5376 throw("releasep: invalid arg")
5379 if pp.m.ptr() != gp.m || pp.status != _Prunning {
5380 print("releasep: m=", gp.m, " m->p=", gp.m.p.ptr(), " p->m=", hex(pp.m), " p->status=", pp.status, "\n")
5381 throw("releasep: invalid p state")
5384 traceProcStop(gp.m.p.ptr())
5392 func incidlelocked(v int32) {
5394 sched.nmidlelocked += v
5401 // Check for deadlock situation.
5402 // The check is based on number of running M's, if 0 -> deadlock.
5403 // sched.lock must be held.
5405 assertLockHeld(&sched.lock)
5407 // For -buildmode=c-shared or -buildmode=c-archive it's OK if
5408 // there are no running goroutines. The calling program is
5409 // assumed to be running.
5410 if islibrary || isarchive {
5414 // If we are dying because of a signal caught on an already idle thread,
5415 // freezetheworld will cause all running threads to block.
5416 // And runtime will essentially enter into deadlock state,
5417 // except that there is a thread that will call exit soon.
5418 if panicking.Load() > 0 {
5422 // If we are not running under cgo, but we have an extra M then account
5423 // for it. (It is possible to have an extra M on Windows without cgo to
5424 // accommodate callbacks created by syscall.NewCallback. See issue #6751
5427 if !iscgo && cgoHasExtraM && extraMLength.Load() > 0 {
5431 run := mcount() - sched.nmidle - sched.nmidlelocked - sched.nmsys
5436 print("runtime: checkdead: nmidle=", sched.nmidle, " nmidlelocked=", sched.nmidlelocked, " mcount=", mcount(), " nmsys=", sched.nmsys, "\n")
5438 throw("checkdead: inconsistent counts")
5442 forEachG(func(gp *g) {
5443 if isSystemGoroutine(gp, false) {
5446 s := readgstatus(gp)
5447 switch s &^ _Gscan {
5454 print("runtime: checkdead: find g ", gp.goid, " in status ", s, "\n")
5456 throw("checkdead: runnable g")
5459 if grunning == 0 { // possible if main goroutine calls runtime·Goexit()
5460 unlock(&sched.lock) // unlock so that GODEBUG=scheddetail=1 doesn't hang
5461 fatal("no goroutines (main called runtime.Goexit) - deadlock!")
5464 // Maybe jump time forward for playground.
5466 if when := timeSleepUntil(); when < maxWhen {
5469 // Start an M to steal the timer.
5470 pp, _ := pidleget(faketime)
5472 // There should always be a free P since
5473 // nothing is running.
5475 throw("checkdead: no p for timer")
5479 // There should always be a free M since
5480 // nothing is running.
5482 throw("checkdead: no m for timer")
5484 // M must be spinning to steal. We set this to be
5485 // explicit, but since this is the only M it would
5486 // become spinning on its own anyways.
5487 sched.nmspinning.Add(1)
5490 notewakeup(&mp.park)
5495 // There are no goroutines running, so we can look at the P's.
5496 for _, pp := range allp {
5497 if len(pp.timers) > 0 {
5502 unlock(&sched.lock) // unlock so that GODEBUG=scheddetail=1 doesn't hang
5503 fatal("all goroutines are asleep - deadlock!")
5506 // forcegcperiod is the maximum time in nanoseconds between garbage
5507 // collections. If we go this long without a garbage collection, one
5508 // is forced to run.
5510 // This is a variable for testing purposes. It normally doesn't change.
5511 var forcegcperiod int64 = 2 * 60 * 1e9
5513 // needSysmonWorkaround is true if the workaround for
5514 // golang.org/issue/42515 is needed on NetBSD.
5515 var needSysmonWorkaround bool = false
5517 // Always runs without a P, so write barriers are not allowed.
5519 //go:nowritebarrierrec
5526 lasttrace := int64(0)
5527 idle := 0 // how many cycles in succession we had not wokeup somebody
5531 if idle == 0 { // start with 20us sleep...
5533 } else if idle > 50 { // start doubling the sleep after 1ms...
5536 if delay > 10*1000 { // up to 10ms
5541 // sysmon should not enter deep sleep if schedtrace is enabled so that
5542 // it can print that information at the right time.
5544 // It should also not enter deep sleep if there are any active P's so
5545 // that it can retake P's from syscalls, preempt long running G's, and
5546 // poll the network if all P's are busy for long stretches.
5548 // It should wakeup from deep sleep if any P's become active either due
5549 // to exiting a syscall or waking up due to a timer expiring so that it
5550 // can resume performing those duties. If it wakes from a syscall it
5551 // resets idle and delay as a bet that since it had retaken a P from a
5552 // syscall before, it may need to do it again shortly after the
5553 // application starts work again. It does not reset idle when waking
5554 // from a timer to avoid adding system load to applications that spend
5555 // most of their time sleeping.
5557 if debug.schedtrace <= 0 && (sched.gcwaiting.Load() || sched.npidle.Load() == gomaxprocs) {
5559 if sched.gcwaiting.Load() || sched.npidle.Load() == gomaxprocs {
5560 syscallWake := false
5561 next := timeSleepUntil()
5563 sched.sysmonwait.Store(true)
5565 // Make wake-up period small enough
5566 // for the sampling to be correct.
5567 sleep := forcegcperiod / 2
5568 if next-now < sleep {
5571 shouldRelax := sleep >= osRelaxMinNS
5575 syscallWake = notetsleep(&sched.sysmonnote, sleep)
5580 sched.sysmonwait.Store(false)
5581 noteclear(&sched.sysmonnote)
5591 lock(&sched.sysmonlock)
5592 // Update now in case we blocked on sysmonnote or spent a long time
5593 // blocked on schedlock or sysmonlock above.
5596 // trigger libc interceptors if needed
5597 if *cgo_yield != nil {
5598 asmcgocall(*cgo_yield, nil)
5600 // poll network if not polled for more than 10ms
5601 lastpoll := sched.lastpoll.Load()
5602 if netpollinited() && lastpoll != 0 && lastpoll+10*1000*1000 < now {
5603 sched.lastpoll.CompareAndSwap(lastpoll, now)
5604 list, delta := netpoll(0) // non-blocking - returns list of goroutines
5606 // Need to decrement number of idle locked M's
5607 // (pretending that one more is running) before injectglist.
5608 // Otherwise it can lead to the following situation:
5609 // injectglist grabs all P's but before it starts M's to run the P's,
5610 // another M returns from syscall, finishes running its G,
5611 // observes that there is no work to do and no other running M's
5612 // and reports deadlock.
5616 netpollAdjustWaiters(delta)
5619 if GOOS == "netbsd" && needSysmonWorkaround {
5620 // netpoll is responsible for waiting for timer
5621 // expiration, so we typically don't have to worry
5622 // about starting an M to service timers. (Note that
5623 // sleep for timeSleepUntil above simply ensures sysmon
5624 // starts running again when that timer expiration may
5625 // cause Go code to run again).
5627 // However, netbsd has a kernel bug that sometimes
5628 // misses netpollBreak wake-ups, which can lead to
5629 // unbounded delays servicing timers. If we detect this
5630 // overrun, then startm to get something to handle the
5633 // See issue 42515 and
5634 // https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=50094.
5635 if next := timeSleepUntil(); next < now {
5636 startm(nil, false, false)
5639 if scavenger.sysmonWake.Load() != 0 {
5640 // Kick the scavenger awake if someone requested it.
5643 // retake P's blocked in syscalls
5644 // and preempt long running G's
5645 if retake(now) != 0 {
5650 // check if we need to force a GC
5651 if t := (gcTrigger{kind: gcTriggerTime, now: now}); t.test() && forcegc.idle.Load() {
5653 forcegc.idle.Store(false)
5655 list.push(forcegc.g)
5657 unlock(&forcegc.lock)
5659 if debug.schedtrace > 0 && lasttrace+int64(debug.schedtrace)*1000000 <= now {
5661 schedtrace(debug.scheddetail > 0)
5663 unlock(&sched.sysmonlock)
5667 type sysmontick struct {
5674 // forcePreemptNS is the time slice given to a G before it is
5676 const forcePreemptNS = 10 * 1000 * 1000 // 10ms
5678 func retake(now int64) uint32 {
5680 // Prevent allp slice changes. This lock will be completely
5681 // uncontended unless we're already stopping the world.
5683 // We can't use a range loop over allp because we may
5684 // temporarily drop the allpLock. Hence, we need to re-fetch
5685 // allp each time around the loop.
5686 for i := 0; i < len(allp); i++ {
5689 // This can happen if procresize has grown
5690 // allp but not yet created new Ps.
5693 pd := &pp.sysmontick
5696 if s == _Prunning || s == _Psyscall {
5697 // Preempt G if it's running for too long.
5698 t := int64(pp.schedtick)
5699 if int64(pd.schedtick) != t {
5700 pd.schedtick = uint32(t)
5702 } else if pd.schedwhen+forcePreemptNS <= now {
5704 // In case of syscall, preemptone() doesn't
5705 // work, because there is no M wired to P.
5710 // Retake P from syscall if it's there for more than 1 sysmon tick (at least 20us).
5711 t := int64(pp.syscalltick)
5712 if !sysretake && int64(pd.syscalltick) != t {
5713 pd.syscalltick = uint32(t)
5714 pd.syscallwhen = now
5717 // On the one hand we don't want to retake Ps if there is no other work to do,
5718 // but on the other hand we want to retake them eventually
5719 // because they can prevent the sysmon thread from deep sleep.
5720 if runqempty(pp) && sched.nmspinning.Load()+sched.npidle.Load() > 0 && pd.syscallwhen+10*1000*1000 > now {
5723 // Drop allpLock so we can take sched.lock.
5725 // Need to decrement number of idle locked M's
5726 // (pretending that one more is running) before the CAS.
5727 // Otherwise the M from which we retake can exit the syscall,
5728 // increment nmidle and report deadlock.
5730 if atomic.Cas(&pp.status, s, _Pidle) {
5747 // Tell all goroutines that they have been preempted and they should stop.
5748 // This function is purely best-effort. It can fail to inform a goroutine if a
5749 // processor just started running it.
5750 // No locks need to be held.
5751 // Returns true if preemption request was issued to at least one goroutine.
5752 func preemptall() bool {
5754 for _, pp := range allp {
5755 if pp.status != _Prunning {
5765 // Tell the goroutine running on processor P to stop.
5766 // This function is purely best-effort. It can incorrectly fail to inform the
5767 // goroutine. It can inform the wrong goroutine. Even if it informs the
5768 // correct goroutine, that goroutine might ignore the request if it is
5769 // simultaneously executing newstack.
5770 // No lock needs to be held.
5771 // Returns true if preemption request was issued.
5772 // The actual preemption will happen at some point in the future
5773 // and will be indicated by the gp->status no longer being
5775 func preemptone(pp *p) bool {
5777 if mp == nil || mp == getg().m {
5781 if gp == nil || gp == mp.g0 {
5787 // Every call in a goroutine checks for stack overflow by
5788 // comparing the current stack pointer to gp->stackguard0.
5789 // Setting gp->stackguard0 to StackPreempt folds
5790 // preemption into the normal stack overflow check.
5791 gp.stackguard0 = stackPreempt
5793 // Request an async preemption of this P.
5794 if preemptMSupported && debug.asyncpreemptoff == 0 {
5804 func schedtrace(detailed bool) {
5811 print("SCHED ", (now-starttime)/1e6, "ms: gomaxprocs=", gomaxprocs, " idleprocs=", sched.npidle.Load(), " threads=", mcount(), " spinningthreads=", sched.nmspinning.Load(), " needspinning=", sched.needspinning.Load(), " idlethreads=", sched.nmidle, " runqueue=", sched.runqsize)
5813 print(" gcwaiting=", sched.gcwaiting.Load(), " nmidlelocked=", sched.nmidlelocked, " stopwait=", sched.stopwait, " sysmonwait=", sched.sysmonwait.Load(), "\n")
5815 // We must be careful while reading data from P's, M's and G's.
5816 // Even if we hold schedlock, most data can be changed concurrently.
5817 // E.g. (p->m ? p->m->id : -1) can crash if p->m changes from non-nil to nil.
5818 for i, pp := range allp {
5820 h := atomic.Load(&pp.runqhead)
5821 t := atomic.Load(&pp.runqtail)
5823 print(" P", i, ": status=", pp.status, " schedtick=", pp.schedtick, " syscalltick=", pp.syscalltick, " m=")
5829 print(" runqsize=", t-h, " gfreecnt=", pp.gFree.n, " timerslen=", len(pp.timers), "\n")
5831 // In non-detailed mode format lengths of per-P run queues as:
5832 // [len1 len2 len3 len4]
5838 if i == len(allp)-1 {
5849 for mp := allm; mp != nil; mp = mp.alllink {
5851 print(" M", mp.id, ": p=")
5863 print(" mallocing=", mp.mallocing, " throwing=", mp.throwing, " preemptoff=", mp.preemptoff, " locks=", mp.locks, " dying=", mp.dying, " spinning=", mp.spinning, " blocked=", mp.blocked, " lockedg=")
5864 if lockedg := mp.lockedg.ptr(); lockedg != nil {
5872 forEachG(func(gp *g) {
5873 print(" G", gp.goid, ": status=", readgstatus(gp), "(", gp.waitreason.String(), ") m=")
5880 if lockedm := gp.lockedm.ptr(); lockedm != nil {
5890 // schedEnableUser enables or disables the scheduling of user
5893 // This does not stop already running user goroutines, so the caller
5894 // should first stop the world when disabling user goroutines.
5895 func schedEnableUser(enable bool) {
5897 if sched.disable.user == !enable {
5901 sched.disable.user = !enable
5903 n := sched.disable.n
5905 globrunqputbatch(&sched.disable.runnable, n)
5907 for ; n != 0 && sched.npidle.Load() != 0; n-- {
5908 startm(nil, false, false)
5915 // schedEnabled reports whether gp should be scheduled. It returns
5916 // false is scheduling of gp is disabled.
5918 // sched.lock must be held.
5919 func schedEnabled(gp *g) bool {
5920 assertLockHeld(&sched.lock)
5922 if sched.disable.user {
5923 return isSystemGoroutine(gp, true)
5928 // Put mp on midle list.
5929 // sched.lock must be held.
5930 // May run during STW, so write barriers are not allowed.
5932 //go:nowritebarrierrec
5934 assertLockHeld(&sched.lock)
5936 mp.schedlink = sched.midle
5942 // Try to get an m from midle list.
5943 // sched.lock must be held.
5944 // May run during STW, so write barriers are not allowed.
5946 //go:nowritebarrierrec
5948 assertLockHeld(&sched.lock)
5950 mp := sched.midle.ptr()
5952 sched.midle = mp.schedlink
5958 // Put gp on the global runnable queue.
5959 // sched.lock must be held.
5960 // May run during STW, so write barriers are not allowed.
5962 //go:nowritebarrierrec
5963 func globrunqput(gp *g) {
5964 assertLockHeld(&sched.lock)
5966 sched.runq.pushBack(gp)
5970 // Put gp at the head of the global runnable queue.
5971 // sched.lock must be held.
5972 // May run during STW, so write barriers are not allowed.
5974 //go:nowritebarrierrec
5975 func globrunqputhead(gp *g) {
5976 assertLockHeld(&sched.lock)
5982 // Put a batch of runnable goroutines on the global runnable queue.
5983 // This clears *batch.
5984 // sched.lock must be held.
5985 // May run during STW, so write barriers are not allowed.
5987 //go:nowritebarrierrec
5988 func globrunqputbatch(batch *gQueue, n int32) {
5989 assertLockHeld(&sched.lock)
5991 sched.runq.pushBackAll(*batch)
5996 // Try get a batch of G's from the global runnable queue.
5997 // sched.lock must be held.
5998 func globrunqget(pp *p, max int32) *g {
5999 assertLockHeld(&sched.lock)
6001 if sched.runqsize == 0 {
6005 n := sched.runqsize/gomaxprocs + 1
6006 if n > sched.runqsize {
6009 if max > 0 && n > max {
6012 if n > int32(len(pp.runq))/2 {
6013 n = int32(len(pp.runq)) / 2
6018 gp := sched.runq.pop()
6021 gp1 := sched.runq.pop()
6022 runqput(pp, gp1, false)
6027 // pMask is an atomic bitstring with one bit per P.
6030 // read returns true if P id's bit is set.
6031 func (p pMask) read(id uint32) bool {
6033 mask := uint32(1) << (id % 32)
6034 return (atomic.Load(&p[word]) & mask) != 0
6037 // set sets P id's bit.
6038 func (p pMask) set(id int32) {
6040 mask := uint32(1) << (id % 32)
6041 atomic.Or(&p[word], mask)
6044 // clear clears P id's bit.
6045 func (p pMask) clear(id int32) {
6047 mask := uint32(1) << (id % 32)
6048 atomic.And(&p[word], ^mask)
6051 // updateTimerPMask clears pp's timer mask if it has no timers on its heap.
6053 // Ideally, the timer mask would be kept immediately consistent on any timer
6054 // operations. Unfortunately, updating a shared global data structure in the
6055 // timer hot path adds too much overhead in applications frequently switching
6056 // between no timers and some timers.
6058 // As a compromise, the timer mask is updated only on pidleget / pidleput. A
6059 // running P (returned by pidleget) may add a timer at any time, so its mask
6060 // must be set. An idle P (passed to pidleput) cannot add new timers while
6061 // idle, so if it has no timers at that time, its mask may be cleared.
6063 // Thus, we get the following effects on timer-stealing in findrunnable:
6065 // - Idle Ps with no timers when they go idle are never checked in findrunnable
6066 // (for work- or timer-stealing; this is the ideal case).
6067 // - Running Ps must always be checked.
6068 // - Idle Ps whose timers are stolen must continue to be checked until they run
6069 // again, even after timer expiration.
6071 // When the P starts running again, the mask should be set, as a timer may be
6072 // added at any time.
6074 // TODO(prattmic): Additional targeted updates may improve the above cases.
6075 // e.g., updating the mask when stealing a timer.
6076 func updateTimerPMask(pp *p) {
6077 if pp.numTimers.Load() > 0 {
6081 // Looks like there are no timers, however another P may transiently
6082 // decrement numTimers when handling a timerModified timer in
6083 // checkTimers. We must take timersLock to serialize with these changes.
6084 lock(&pp.timersLock)
6085 if pp.numTimers.Load() == 0 {
6086 timerpMask.clear(pp.id)
6088 unlock(&pp.timersLock)
6091 // pidleput puts p on the _Pidle list. now must be a relatively recent call
6092 // to nanotime or zero. Returns now or the current time if now was zero.
6094 // This releases ownership of p. Once sched.lock is released it is no longer
6097 // sched.lock must be held.
6099 // May run during STW, so write barriers are not allowed.
6101 //go:nowritebarrierrec
6102 func pidleput(pp *p, now int64) int64 {
6103 assertLockHeld(&sched.lock)
6106 throw("pidleput: P has non-empty run queue")
6111 updateTimerPMask(pp) // clear if there are no timers.
6112 idlepMask.set(pp.id)
6113 pp.link = sched.pidle
6116 if !pp.limiterEvent.start(limiterEventIdle, now) {
6117 throw("must be able to track idle limiter event")
6122 // pidleget tries to get a p from the _Pidle list, acquiring ownership.
6124 // sched.lock must be held.
6126 // May run during STW, so write barriers are not allowed.
6128 //go:nowritebarrierrec
6129 func pidleget(now int64) (*p, int64) {
6130 assertLockHeld(&sched.lock)
6132 pp := sched.pidle.ptr()
6134 // Timer may get added at any time now.
6138 timerpMask.set(pp.id)
6139 idlepMask.clear(pp.id)
6140 sched.pidle = pp.link
6141 sched.npidle.Add(-1)
6142 pp.limiterEvent.stop(limiterEventIdle, now)
6147 // pidlegetSpinning tries to get a p from the _Pidle list, acquiring ownership.
6148 // This is called by spinning Ms (or callers than need a spinning M) that have
6149 // found work. If no P is available, this must synchronized with non-spinning
6150 // Ms that may be preparing to drop their P without discovering this work.
6152 // sched.lock must be held.
6154 // May run during STW, so write barriers are not allowed.
6156 //go:nowritebarrierrec
6157 func pidlegetSpinning(now int64) (*p, int64) {
6158 assertLockHeld(&sched.lock)
6160 pp, now := pidleget(now)
6162 // See "Delicate dance" comment in findrunnable. We found work
6163 // that we cannot take, we must synchronize with non-spinning
6164 // Ms that may be preparing to drop their P.
6165 sched.needspinning.Store(1)
6172 // runqempty reports whether pp has no Gs on its local run queue.
6173 // It never returns true spuriously.
6174 func runqempty(pp *p) bool {
6175 // Defend against a race where 1) pp has G1 in runqnext but runqhead == runqtail,
6176 // 2) runqput on pp kicks G1 to the runq, 3) runqget on pp empties runqnext.
6177 // Simply observing that runqhead == runqtail and then observing that runqnext == nil
6178 // does not mean the queue is empty.
6180 head := atomic.Load(&pp.runqhead)
6181 tail := atomic.Load(&pp.runqtail)
6182 runnext := atomic.Loaduintptr((*uintptr)(unsafe.Pointer(&pp.runnext)))
6183 if tail == atomic.Load(&pp.runqtail) {
6184 return head == tail && runnext == 0
6189 // To shake out latent assumptions about scheduling order,
6190 // we introduce some randomness into scheduling decisions
6191 // when running with the race detector.
6192 // The need for this was made obvious by changing the
6193 // (deterministic) scheduling order in Go 1.5 and breaking
6194 // many poorly-written tests.
6195 // With the randomness here, as long as the tests pass
6196 // consistently with -race, they shouldn't have latent scheduling
6198 const randomizeScheduler = raceenabled
6200 // runqput tries to put g on the local runnable queue.
6201 // If next is false, runqput adds g to the tail of the runnable queue.
6202 // If next is true, runqput puts g in the pp.runnext slot.
6203 // If the run queue is full, runnext puts g on the global queue.
6204 // Executed only by the owner P.
6205 func runqput(pp *p, gp *g, next bool) {
6206 if randomizeScheduler && next && fastrandn(2) == 0 {
6212 oldnext := pp.runnext
6213 if !pp.runnext.cas(oldnext, guintptr(unsafe.Pointer(gp))) {
6219 // Kick the old runnext out to the regular run queue.
6224 h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with consumers
6226 if t-h < uint32(len(pp.runq)) {
6227 pp.runq[t%uint32(len(pp.runq))].set(gp)
6228 atomic.StoreRel(&pp.runqtail, t+1) // store-release, makes the item available for consumption
6231 if runqputslow(pp, gp, h, t) {
6234 // the queue is not full, now the put above must succeed
6238 // Put g and a batch of work from local runnable queue on global queue.
6239 // Executed only by the owner P.
6240 func runqputslow(pp *p, gp *g, h, t uint32) bool {
6241 var batch [len(pp.runq)/2 + 1]*g
6243 // First, grab a batch from local queue.
6246 if n != uint32(len(pp.runq)/2) {
6247 throw("runqputslow: queue is not full")
6249 for i := uint32(0); i < n; i++ {
6250 batch[i] = pp.runq[(h+i)%uint32(len(pp.runq))].ptr()
6252 if !atomic.CasRel(&pp.runqhead, h, h+n) { // cas-release, commits consume
6257 if randomizeScheduler {
6258 for i := uint32(1); i <= n; i++ {
6259 j := fastrandn(i + 1)
6260 batch[i], batch[j] = batch[j], batch[i]
6264 // Link the goroutines.
6265 for i := uint32(0); i < n; i++ {
6266 batch[i].schedlink.set(batch[i+1])
6269 q.head.set(batch[0])
6270 q.tail.set(batch[n])
6272 // Now put the batch on global queue.
6274 globrunqputbatch(&q, int32(n+1))
6279 // runqputbatch tries to put all the G's on q on the local runnable queue.
6280 // If the queue is full, they are put on the global queue; in that case
6281 // this will temporarily acquire the scheduler lock.
6282 // Executed only by the owner P.
6283 func runqputbatch(pp *p, q *gQueue, qsize int) {
6284 h := atomic.LoadAcq(&pp.runqhead)
6287 for !q.empty() && t-h < uint32(len(pp.runq)) {
6289 pp.runq[t%uint32(len(pp.runq))].set(gp)
6295 if randomizeScheduler {
6296 off := func(o uint32) uint32 {
6297 return (pp.runqtail + o) % uint32(len(pp.runq))
6299 for i := uint32(1); i < n; i++ {
6300 j := fastrandn(i + 1)
6301 pp.runq[off(i)], pp.runq[off(j)] = pp.runq[off(j)], pp.runq[off(i)]
6305 atomic.StoreRel(&pp.runqtail, t)
6308 globrunqputbatch(q, int32(qsize))
6313 // Get g from local runnable queue.
6314 // If inheritTime is true, gp should inherit the remaining time in the
6315 // current time slice. Otherwise, it should start a new time slice.
6316 // Executed only by the owner P.
6317 func runqget(pp *p) (gp *g, inheritTime bool) {
6318 // If there's a runnext, it's the next G to run.
6320 // If the runnext is non-0 and the CAS fails, it could only have been stolen by another P,
6321 // because other Ps can race to set runnext to 0, but only the current P can set it to non-0.
6322 // Hence, there's no need to retry this CAS if it fails.
6323 if next != 0 && pp.runnext.cas(next, 0) {
6324 return next.ptr(), true
6328 h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with other consumers
6333 gp := pp.runq[h%uint32(len(pp.runq))].ptr()
6334 if atomic.CasRel(&pp.runqhead, h, h+1) { // cas-release, commits consume
6340 // runqdrain drains the local runnable queue of pp and returns all goroutines in it.
6341 // Executed only by the owner P.
6342 func runqdrain(pp *p) (drainQ gQueue, n uint32) {
6343 oldNext := pp.runnext
6344 if oldNext != 0 && pp.runnext.cas(oldNext, 0) {
6345 drainQ.pushBack(oldNext.ptr())
6350 h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with other consumers
6356 if qn > uint32(len(pp.runq)) { // read inconsistent h and t
6360 if !atomic.CasRel(&pp.runqhead, h, h+qn) { // cas-release, commits consume
6364 // We've inverted the order in which it gets G's from the local P's runnable queue
6365 // and then advances the head pointer because we don't want to mess up the statuses of G's
6366 // while runqdrain() and runqsteal() are running in parallel.
6367 // Thus we should advance the head pointer before draining the local P into a gQueue,
6368 // so that we can update any gp.schedlink only after we take the full ownership of G,
6369 // meanwhile, other P's can't access to all G's in local P's runnable queue and steal them.
6370 // See https://groups.google.com/g/golang-dev/c/0pTKxEKhHSc/m/6Q85QjdVBQAJ for more details.
6371 for i := uint32(0); i < qn; i++ {
6372 gp := pp.runq[(h+i)%uint32(len(pp.runq))].ptr()
6379 // Grabs a batch of goroutines from pp's runnable queue into batch.
6380 // Batch is a ring buffer starting at batchHead.
6381 // Returns number of grabbed goroutines.
6382 // Can be executed by any P.
6383 func runqgrab(pp *p, batch *[256]guintptr, batchHead uint32, stealRunNextG bool) uint32 {
6385 h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with other consumers
6386 t := atomic.LoadAcq(&pp.runqtail) // load-acquire, synchronize with the producer
6391 // Try to steal from pp.runnext.
6392 if next := pp.runnext; next != 0 {
6393 if pp.status == _Prunning {
6394 // Sleep to ensure that pp isn't about to run the g
6395 // we are about to steal.
6396 // The important use case here is when the g running
6397 // on pp ready()s another g and then almost
6398 // immediately blocks. Instead of stealing runnext
6399 // in this window, back off to give pp a chance to
6400 // schedule runnext. This will avoid thrashing gs
6401 // between different Ps.
6402 // A sync chan send/recv takes ~50ns as of time of
6403 // writing, so 3us gives ~50x overshoot.
6404 if GOOS != "windows" && GOOS != "openbsd" && GOOS != "netbsd" {
6407 // On some platforms system timer granularity is
6408 // 1-15ms, which is way too much for this
6409 // optimization. So just yield.
6413 if !pp.runnext.cas(next, 0) {
6416 batch[batchHead%uint32(len(batch))] = next
6422 if n > uint32(len(pp.runq)/2) { // read inconsistent h and t
6425 for i := uint32(0); i < n; i++ {
6426 g := pp.runq[(h+i)%uint32(len(pp.runq))]
6427 batch[(batchHead+i)%uint32(len(batch))] = g
6429 if atomic.CasRel(&pp.runqhead, h, h+n) { // cas-release, commits consume
6435 // Steal half of elements from local runnable queue of p2
6436 // and put onto local runnable queue of p.
6437 // Returns one of the stolen elements (or nil if failed).
6438 func runqsteal(pp, p2 *p, stealRunNextG bool) *g {
6440 n := runqgrab(p2, &pp.runq, t, stealRunNextG)
6445 gp := pp.runq[(t+n)%uint32(len(pp.runq))].ptr()
6449 h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with consumers
6450 if t-h+n >= uint32(len(pp.runq)) {
6451 throw("runqsteal: runq overflow")
6453 atomic.StoreRel(&pp.runqtail, t+n) // store-release, makes the item available for consumption
6457 // A gQueue is a dequeue of Gs linked through g.schedlink. A G can only
6458 // be on one gQueue or gList at a time.
6459 type gQueue struct {
6464 // empty reports whether q is empty.
6465 func (q *gQueue) empty() bool {
6469 // push adds gp to the head of q.
6470 func (q *gQueue) push(gp *g) {
6471 gp.schedlink = q.head
6478 // pushBack adds gp to the tail of q.
6479 func (q *gQueue) pushBack(gp *g) {
6482 q.tail.ptr().schedlink.set(gp)
6489 // pushBackAll adds all Gs in q2 to the tail of q. After this q2 must
6491 func (q *gQueue) pushBackAll(q2 gQueue) {
6495 q2.tail.ptr().schedlink = 0
6497 q.tail.ptr().schedlink = q2.head
6504 // pop removes and returns the head of queue q. It returns nil if
6506 func (q *gQueue) pop() *g {
6509 q.head = gp.schedlink
6517 // popList takes all Gs in q and returns them as a gList.
6518 func (q *gQueue) popList() gList {
6519 stack := gList{q.head}
6524 // A gList is a list of Gs linked through g.schedlink. A G can only be
6525 // on one gQueue or gList at a time.
6530 // empty reports whether l is empty.
6531 func (l *gList) empty() bool {
6535 // push adds gp to the head of l.
6536 func (l *gList) push(gp *g) {
6537 gp.schedlink = l.head
6541 // pushAll prepends all Gs in q to l.
6542 func (l *gList) pushAll(q gQueue) {
6544 q.tail.ptr().schedlink = l.head
6549 // pop removes and returns the head of l. If l is empty, it returns nil.
6550 func (l *gList) pop() *g {
6553 l.head = gp.schedlink
6558 //go:linkname setMaxThreads runtime/debug.setMaxThreads
6559 func setMaxThreads(in int) (out int) {
6561 out = int(sched.maxmcount)
6562 if in > 0x7fffffff { // MaxInt32
6563 sched.maxmcount = 0x7fffffff
6565 sched.maxmcount = int32(in)
6573 func procPin() int {
6578 return int(mp.p.ptr().id)
6587 //go:linkname sync_runtime_procPin sync.runtime_procPin
6589 func sync_runtime_procPin() int {
6593 //go:linkname sync_runtime_procUnpin sync.runtime_procUnpin
6595 func sync_runtime_procUnpin() {
6599 //go:linkname sync_atomic_runtime_procPin sync/atomic.runtime_procPin
6601 func sync_atomic_runtime_procPin() int {
6605 //go:linkname sync_atomic_runtime_procUnpin sync/atomic.runtime_procUnpin
6607 func sync_atomic_runtime_procUnpin() {
6611 // Active spinning for sync.Mutex.
6613 //go:linkname sync_runtime_canSpin sync.runtime_canSpin
6615 func sync_runtime_canSpin(i int) bool {
6616 // sync.Mutex is cooperative, so we are conservative with spinning.
6617 // Spin only few times and only if running on a multicore machine and
6618 // GOMAXPROCS>1 and there is at least one other running P and local runq is empty.
6619 // As opposed to runtime mutex we don't do passive spinning here,
6620 // because there can be work on global runq or on other Ps.
6621 if i >= active_spin || ncpu <= 1 || gomaxprocs <= sched.npidle.Load()+sched.nmspinning.Load()+1 {
6624 if p := getg().m.p.ptr(); !runqempty(p) {
6630 //go:linkname sync_runtime_doSpin sync.runtime_doSpin
6632 func sync_runtime_doSpin() {
6633 procyield(active_spin_cnt)
6636 var stealOrder randomOrder
6638 // randomOrder/randomEnum are helper types for randomized work stealing.
6639 // They allow to enumerate all Ps in different pseudo-random orders without repetitions.
6640 // The algorithm is based on the fact that if we have X such that X and GOMAXPROCS
6641 // are coprime, then a sequences of (i + X) % GOMAXPROCS gives the required enumeration.
6642 type randomOrder struct {
6647 type randomEnum struct {
6654 func (ord *randomOrder) reset(count uint32) {
6656 ord.coprimes = ord.coprimes[:0]
6657 for i := uint32(1); i <= count; i++ {
6658 if gcd(i, count) == 1 {
6659 ord.coprimes = append(ord.coprimes, i)
6664 func (ord *randomOrder) start(i uint32) randomEnum {
6668 inc: ord.coprimes[i/ord.count%uint32(len(ord.coprimes))],
6672 func (enum *randomEnum) done() bool {
6673 return enum.i == enum.count
6676 func (enum *randomEnum) next() {
6678 enum.pos = (enum.pos + enum.inc) % enum.count
6681 func (enum *randomEnum) position() uint32 {
6685 func gcd(a, b uint32) uint32 {
6692 // An initTask represents the set of initializations that need to be done for a package.
6693 // Keep in sync with ../../test/noinit.go:initTask
6694 type initTask struct {
6695 state uint32 // 0 = uninitialized, 1 = in progress, 2 = done
6697 // followed by nfns pcs, uintptr sized, one per init function to run
6700 // inittrace stores statistics for init functions which are
6701 // updated by malloc and newproc when active is true.
6702 var inittrace tracestat
6704 type tracestat struct {
6705 active bool // init tracing activation status
6706 id uint64 // init goroutine id
6707 allocs uint64 // heap allocations
6708 bytes uint64 // heap allocated bytes
6711 func doInit(ts []*initTask) {
6712 for _, t := range ts {
6717 func doInit1(t *initTask) {
6719 case 2: // fully initialized
6721 case 1: // initialization in progress
6722 throw("recursive call during initialization - linker skew")
6723 default: // not initialized yet
6724 t.state = 1 // initialization in progress
6731 if inittrace.active {
6733 // Load stats non-atomically since tracinit is updated only by this init goroutine.
6738 // We should have pruned all of these in the linker.
6739 throw("inittask with no functions")
6742 firstFunc := add(unsafe.Pointer(t), 8)
6743 for i := uint32(0); i < t.nfns; i++ {
6744 p := add(firstFunc, uintptr(i)*goarch.PtrSize)
6745 f := *(*func())(unsafe.Pointer(&p))
6749 if inittrace.active {
6751 // Load stats non-atomically since tracinit is updated only by this init goroutine.
6754 f := *(*func())(unsafe.Pointer(&firstFunc))
6755 pkg := funcpkgpath(findfunc(abi.FuncPCABIInternal(f)))
6758 print("init ", pkg, " @")
6759 print(string(fmtNSAsMS(sbuf[:], uint64(start-runtimeInitTime))), " ms, ")
6760 print(string(fmtNSAsMS(sbuf[:], uint64(end-start))), " ms clock, ")
6761 print(string(itoa(sbuf[:], after.bytes-before.bytes)), " bytes, ")
6762 print(string(itoa(sbuf[:], after.allocs-before.allocs)), " allocs")
6766 t.state = 2 // initialization done