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Diffstat (limited to 'src/runtime/proc.go')
-rw-r--r-- | src/runtime/proc.go | 6757 |
1 files changed, 6757 insertions, 0 deletions
diff --git a/src/runtime/proc.go b/src/runtime/proc.go new file mode 100644 index 0000000..b408337 --- /dev/null +++ b/src/runtime/proc.go @@ -0,0 +1,6757 @@ +// Copyright 2014 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package runtime + +import ( + "internal/abi" + "internal/cpu" + "internal/goarch" + "runtime/internal/atomic" + "runtime/internal/sys" + "unsafe" +) + +// set using cmd/go/internal/modload.ModInfoProg +var modinfo string + +// Goroutine scheduler +// The scheduler's job is to distribute ready-to-run goroutines over worker threads. +// +// The main concepts are: +// G - goroutine. +// M - worker thread, or machine. +// P - processor, a resource that is required to execute Go code. +// M must have an associated P to execute Go code, however it can be +// blocked or in a syscall w/o an associated P. +// +// Design doc at https://golang.org/s/go11sched. + +// Worker thread parking/unparking. +// We need to balance between keeping enough running worker threads to utilize +// available hardware parallelism and parking excessive running worker threads +// to conserve CPU resources and power. This is not simple for two reasons: +// (1) scheduler state is intentionally distributed (in particular, per-P work +// queues), so it is not possible to compute global predicates on fast paths; +// (2) for optimal thread management we would need to know the future (don't park +// a worker thread when a new goroutine will be readied in near future). +// +// Three rejected approaches that would work badly: +// 1. Centralize all scheduler state (would inhibit scalability). +// 2. Direct goroutine handoff. That is, when we ready a new goroutine and there +// is a spare P, unpark a thread and handoff it the thread and the goroutine. +// This would lead to thread state thrashing, as the thread that readied the +// goroutine can be out of work the very next moment, we will need to park it. +// Also, it would destroy locality of computation as we want to preserve +// dependent goroutines on the same thread; and introduce additional latency. +// 3. Unpark an additional thread whenever we ready a goroutine and there is an +// idle P, but don't do handoff. This would lead to excessive thread parking/ +// unparking as the additional threads will instantly park without discovering +// any work to do. +// +// The current approach: +// +// This approach applies to three primary sources of potential work: readying a +// goroutine, new/modified-earlier timers, and idle-priority GC. See below for +// additional details. +// +// We unpark an additional thread when we submit work if (this is wakep()): +// 1. There is an idle P, and +// 2. There are no "spinning" worker threads. +// +// A worker thread is considered spinning if it is out of local work and did +// not find work in the global run queue or netpoller; the spinning state is +// denoted in m.spinning and in sched.nmspinning. Threads unparked this way are +// also considered spinning; we don't do goroutine handoff so such threads are +// out of work initially. Spinning threads spin on looking for work in per-P +// run queues and timer heaps or from the GC before parking. If a spinning +// thread finds work it takes itself out of the spinning state and proceeds to +// execution. If it does not find work it takes itself out of the spinning +// state and then parks. +// +// If there is at least one spinning thread (sched.nmspinning>1), we don't +// unpark new threads when submitting work. To compensate for that, if the last +// spinning thread finds work and stops spinning, it must unpark a new spinning +// thread. This approach smooths out unjustified spikes of thread unparking, +// but at the same time guarantees eventual maximal CPU parallelism +// utilization. +// +// The main implementation complication is that we need to be very careful +// during spinning->non-spinning thread transition. This transition can race +// with submission of new work, and either one part or another needs to unpark +// another worker thread. If they both fail to do that, we can end up with +// semi-persistent CPU underutilization. +// +// The general pattern for submission is: +// 1. Submit work to the local run queue, timer heap, or GC state. +// 2. #StoreLoad-style memory barrier. +// 3. Check sched.nmspinning. +// +// The general pattern for spinning->non-spinning transition is: +// 1. Decrement nmspinning. +// 2. #StoreLoad-style memory barrier. +// 3. Check all per-P work queues and GC for new work. +// +// Note that all this complexity does not apply to global run queue as we are +// not sloppy about thread unparking when submitting to global queue. Also see +// comments for nmspinning manipulation. +// +// How these different sources of work behave varies, though it doesn't affect +// the synchronization approach: +// * Ready goroutine: this is an obvious source of work; the goroutine is +// immediately ready and must run on some thread eventually. +// * New/modified-earlier timer: The current timer implementation (see time.go) +// uses netpoll in a thread with no work available to wait for the soonest +// timer. If there is no thread waiting, we want a new spinning thread to go +// wait. +// * Idle-priority GC: The GC wakes a stopped idle thread to contribute to +// background GC work (note: currently disabled per golang.org/issue/19112). +// Also see golang.org/issue/44313, as this should be extended to all GC +// workers. + +var ( + m0 m + g0 g + mcache0 *mcache + raceprocctx0 uintptr + raceFiniLock mutex +) + +// This slice records the initializing tasks that need to be +// done to start up the runtime. It is built by the linker. +var runtime_inittasks []*initTask + +// main_init_done is a signal used by cgocallbackg that initialization +// has been completed. It is made before _cgo_notify_runtime_init_done, +// so all cgo calls can rely on it existing. When main_init is complete, +// it is closed, meaning cgocallbackg can reliably receive from it. +var main_init_done chan bool + +//go:linkname main_main main.main +func main_main() + +// mainStarted indicates that the main M has started. +var mainStarted bool + +// runtimeInitTime is the nanotime() at which the runtime started. +var runtimeInitTime int64 + +// Value to use for signal mask for newly created M's. +var initSigmask sigset + +// The main goroutine. +func main() { + mp := getg().m + + // Racectx of m0->g0 is used only as the parent of the main goroutine. + // It must not be used for anything else. + mp.g0.racectx = 0 + + // Max stack size is 1 GB on 64-bit, 250 MB on 32-bit. + // Using decimal instead of binary GB and MB because + // they look nicer in the stack overflow failure message. + if goarch.PtrSize == 8 { + maxstacksize = 1000000000 + } else { + maxstacksize = 250000000 + } + + // An upper limit for max stack size. Used to avoid random crashes + // after calling SetMaxStack and trying to allocate a stack that is too big, + // since stackalloc works with 32-bit sizes. + maxstackceiling = 2 * maxstacksize + + // Allow newproc to start new Ms. + mainStarted = true + + if GOARCH != "wasm" { // no threads on wasm yet, so no sysmon + systemstack(func() { + newm(sysmon, nil, -1) + }) + } + + // Lock the main goroutine onto this, the main OS thread, + // during initialization. Most programs won't care, but a few + // do require certain calls to be made by the main thread. + // Those can arrange for main.main to run in the main thread + // by calling runtime.LockOSThread during initialization + // to preserve the lock. + lockOSThread() + + if mp != &m0 { + throw("runtime.main not on m0") + } + + // Record when the world started. + // Must be before doInit for tracing init. + runtimeInitTime = nanotime() + if runtimeInitTime == 0 { + throw("nanotime returning zero") + } + + if debug.inittrace != 0 { + inittrace.id = getg().goid + inittrace.active = true + } + + doInit(runtime_inittasks) // Must be before defer. + + // Defer unlock so that runtime.Goexit during init does the unlock too. + needUnlock := true + defer func() { + if needUnlock { + unlockOSThread() + } + }() + + gcenable() + + main_init_done = make(chan bool) + if iscgo { + if _cgo_pthread_key_created == nil { + throw("_cgo_pthread_key_created missing") + } + + if _cgo_thread_start == nil { + throw("_cgo_thread_start missing") + } + if GOOS != "windows" { + if _cgo_setenv == nil { + throw("_cgo_setenv missing") + } + if _cgo_unsetenv == nil { + throw("_cgo_unsetenv missing") + } + } + if _cgo_notify_runtime_init_done == nil { + throw("_cgo_notify_runtime_init_done missing") + } + + // Set the x_crosscall2_ptr C function pointer variable point to crosscall2. + if set_crosscall2 == nil { + throw("set_crosscall2 missing") + } + set_crosscall2() + + // Start the template thread in case we enter Go from + // a C-created thread and need to create a new thread. + startTemplateThread() + cgocall(_cgo_notify_runtime_init_done, nil) + } + + // Run the initializing tasks. Depending on build mode this + // list can arrive a few different ways, but it will always + // contain the init tasks computed by the linker for all the + // packages in the program (excluding those added at runtime + // by package plugin). + for _, m := range activeModules() { + doInit(m.inittasks) + } + + // Disable init tracing after main init done to avoid overhead + // of collecting statistics in malloc and newproc + inittrace.active = false + + close(main_init_done) + + needUnlock = false + unlockOSThread() + + if isarchive || islibrary { + // A program compiled with -buildmode=c-archive or c-shared + // has a main, but it is not executed. + return + } + fn := main_main // make an indirect call, as the linker doesn't know the address of the main package when laying down the runtime + fn() + if raceenabled { + runExitHooks(0) // run hooks now, since racefini does not return + racefini() + } + + // Make racy client program work: if panicking on + // another goroutine at the same time as main returns, + // let the other goroutine finish printing the panic trace. + // Once it does, it will exit. See issues 3934 and 20018. + if runningPanicDefers.Load() != 0 { + // Running deferred functions should not take long. + for c := 0; c < 1000; c++ { + if runningPanicDefers.Load() == 0 { + break + } + Gosched() + } + } + if panicking.Load() != 0 { + gopark(nil, nil, waitReasonPanicWait, traceBlockForever, 1) + } + runExitHooks(0) + + exit(0) + for { + var x *int32 + *x = 0 + } +} + +// os_beforeExit is called from os.Exit(0). +// +//go:linkname os_beforeExit os.runtime_beforeExit +func os_beforeExit(exitCode int) { + runExitHooks(exitCode) + if exitCode == 0 && raceenabled { + racefini() + } +} + +// start forcegc helper goroutine +func init() { + go forcegchelper() +} + +func forcegchelper() { + forcegc.g = getg() + lockInit(&forcegc.lock, lockRankForcegc) + for { + lock(&forcegc.lock) + if forcegc.idle.Load() { + throw("forcegc: phase error") + } + forcegc.idle.Store(true) + goparkunlock(&forcegc.lock, waitReasonForceGCIdle, traceBlockSystemGoroutine, 1) + // this goroutine is explicitly resumed by sysmon + if debug.gctrace > 0 { + println("GC forced") + } + // Time-triggered, fully concurrent. + gcStart(gcTrigger{kind: gcTriggerTime, now: nanotime()}) + } +} + +// Gosched yields the processor, allowing other goroutines to run. It does not +// suspend the current goroutine, so execution resumes automatically. +// +//go:nosplit +func Gosched() { + checkTimeouts() + mcall(gosched_m) +} + +// goschedguarded yields the processor like gosched, but also checks +// for forbidden states and opts out of the yield in those cases. +// +//go:nosplit +func goschedguarded() { + mcall(goschedguarded_m) +} + +// goschedIfBusy yields the processor like gosched, but only does so if +// there are no idle Ps or if we're on the only P and there's nothing in +// the run queue. In both cases, there is freely available idle time. +// +//go:nosplit +func goschedIfBusy() { + gp := getg() + // Call gosched if gp.preempt is set; we may be in a tight loop that + // doesn't otherwise yield. + if !gp.preempt && sched.npidle.Load() > 0 { + return + } + mcall(gosched_m) +} + +// Puts the current goroutine into a waiting state and calls unlockf on the +// system stack. +// +// If unlockf returns false, the goroutine is resumed. +// +// unlockf must not access this G's stack, as it may be moved between +// the call to gopark and the call to unlockf. +// +// Note that because unlockf is called after putting the G into a waiting +// state, the G may have already been readied by the time unlockf is called +// unless there is external synchronization preventing the G from being +// readied. If unlockf returns false, it must guarantee that the G cannot be +// externally readied. +// +// Reason explains why the goroutine has been parked. It is displayed in stack +// traces and heap dumps. Reasons should be unique and descriptive. Do not +// re-use reasons, add new ones. +func gopark(unlockf func(*g, unsafe.Pointer) bool, lock unsafe.Pointer, reason waitReason, traceReason traceBlockReason, traceskip int) { + if reason != waitReasonSleep { + checkTimeouts() // timeouts may expire while two goroutines keep the scheduler busy + } + mp := acquirem() + gp := mp.curg + status := readgstatus(gp) + if status != _Grunning && status != _Gscanrunning { + throw("gopark: bad g status") + } + mp.waitlock = lock + mp.waitunlockf = unlockf + gp.waitreason = reason + mp.waitTraceBlockReason = traceReason + mp.waitTraceSkip = traceskip + releasem(mp) + // can't do anything that might move the G between Ms here. + mcall(park_m) +} + +// Puts the current goroutine into a waiting state and unlocks the lock. +// The goroutine can be made runnable again by calling goready(gp). +func goparkunlock(lock *mutex, reason waitReason, traceReason traceBlockReason, traceskip int) { + gopark(parkunlock_c, unsafe.Pointer(lock), reason, traceReason, traceskip) +} + +func goready(gp *g, traceskip int) { + systemstack(func() { + ready(gp, traceskip, true) + }) +} + +//go:nosplit +func acquireSudog() *sudog { + // Delicate dance: the semaphore implementation calls + // acquireSudog, acquireSudog calls new(sudog), + // new calls malloc, malloc can call the garbage collector, + // and the garbage collector calls the semaphore implementation + // in stopTheWorld. + // Break the cycle by doing acquirem/releasem around new(sudog). + // The acquirem/releasem increments m.locks during new(sudog), + // which keeps the garbage collector from being invoked. + mp := acquirem() + pp := mp.p.ptr() + if len(pp.sudogcache) == 0 { + lock(&sched.sudoglock) + // First, try to grab a batch from central cache. + for len(pp.sudogcache) < cap(pp.sudogcache)/2 && sched.sudogcache != nil { + s := sched.sudogcache + sched.sudogcache = s.next + s.next = nil + pp.sudogcache = append(pp.sudogcache, s) + } + unlock(&sched.sudoglock) + // If the central cache is empty, allocate a new one. + if len(pp.sudogcache) == 0 { + pp.sudogcache = append(pp.sudogcache, new(sudog)) + } + } + n := len(pp.sudogcache) + s := pp.sudogcache[n-1] + pp.sudogcache[n-1] = nil + pp.sudogcache = pp.sudogcache[:n-1] + if s.elem != nil { + throw("acquireSudog: found s.elem != nil in cache") + } + releasem(mp) + return s +} + +//go:nosplit +func releaseSudog(s *sudog) { + if s.elem != nil { + throw("runtime: sudog with non-nil elem") + } + if s.isSelect { + throw("runtime: sudog with non-false isSelect") + } + if s.next != nil { + throw("runtime: sudog with non-nil next") + } + if s.prev != nil { + throw("runtime: sudog with non-nil prev") + } + if s.waitlink != nil { + throw("runtime: sudog with non-nil waitlink") + } + if s.c != nil { + throw("runtime: sudog with non-nil c") + } + gp := getg() + if gp.param != nil { + throw("runtime: releaseSudog with non-nil gp.param") + } + mp := acquirem() // avoid rescheduling to another P + pp := mp.p.ptr() + if len(pp.sudogcache) == cap(pp.sudogcache) { + // Transfer half of local cache to the central cache. + var first, last *sudog + for len(pp.sudogcache) > cap(pp.sudogcache)/2 { + n := len(pp.sudogcache) + p := pp.sudogcache[n-1] + pp.sudogcache[n-1] = nil + pp.sudogcache = pp.sudogcache[:n-1] + if first == nil { + first = p + } else { + last.next = p + } + last = p + } + lock(&sched.sudoglock) + last.next = sched.sudogcache + sched.sudogcache = first + unlock(&sched.sudoglock) + } + pp.sudogcache = append(pp.sudogcache, s) + releasem(mp) +} + +// called from assembly. +func badmcall(fn func(*g)) { + throw("runtime: mcall called on m->g0 stack") +} + +func badmcall2(fn func(*g)) { + throw("runtime: mcall function returned") +} + +func badreflectcall() { + panic(plainError("arg size to reflect.call more than 1GB")) +} + +//go:nosplit +//go:nowritebarrierrec +func badmorestackg0() { + writeErrStr("fatal: morestack on g0\n") +} + +//go:nosplit +//go:nowritebarrierrec +func badmorestackgsignal() { + writeErrStr("fatal: morestack on gsignal\n") +} + +//go:nosplit +func badctxt() { + throw("ctxt != 0") +} + +func lockedOSThread() bool { + gp := getg() + return gp.lockedm != 0 && gp.m.lockedg != 0 +} + +var ( + // allgs contains all Gs ever created (including dead Gs), and thus + // never shrinks. + // + // Access via the slice is protected by allglock or stop-the-world. + // Readers that cannot take the lock may (carefully!) use the atomic + // variables below. + allglock mutex + allgs []*g + + // allglen and allgptr are atomic variables that contain len(allgs) and + // &allgs[0] respectively. Proper ordering depends on totally-ordered + // loads and stores. Writes are protected by allglock. + // + // allgptr is updated before allglen. Readers should read allglen + // before allgptr to ensure that allglen is always <= len(allgptr). New + // Gs appended during the race can be missed. For a consistent view of + // all Gs, allglock must be held. + // + // allgptr copies should always be stored as a concrete type or + // unsafe.Pointer, not uintptr, to ensure that GC can still reach it + // even if it points to a stale array. + allglen uintptr + allgptr **g +) + +func allgadd(gp *g) { + if readgstatus(gp) == _Gidle { + throw("allgadd: bad status Gidle") + } + + lock(&allglock) + allgs = append(allgs, gp) + if &allgs[0] != allgptr { + atomicstorep(unsafe.Pointer(&allgptr), unsafe.Pointer(&allgs[0])) + } + atomic.Storeuintptr(&allglen, uintptr(len(allgs))) + unlock(&allglock) +} + +// allGsSnapshot returns a snapshot of the slice of all Gs. +// +// The world must be stopped or allglock must be held. +func allGsSnapshot() []*g { + assertWorldStoppedOrLockHeld(&allglock) + + // Because the world is stopped or allglock is held, allgadd + // cannot happen concurrently with this. allgs grows + // monotonically and existing entries never change, so we can + // simply return a copy of the slice header. For added safety, + // we trim everything past len because that can still change. + return allgs[:len(allgs):len(allgs)] +} + +// atomicAllG returns &allgs[0] and len(allgs) for use with atomicAllGIndex. +func atomicAllG() (**g, uintptr) { + length := atomic.Loaduintptr(&allglen) + ptr := (**g)(atomic.Loadp(unsafe.Pointer(&allgptr))) + return ptr, length +} + +// atomicAllGIndex returns ptr[i] with the allgptr returned from atomicAllG. +func atomicAllGIndex(ptr **g, i uintptr) *g { + return *(**g)(add(unsafe.Pointer(ptr), i*goarch.PtrSize)) +} + +// forEachG calls fn on every G from allgs. +// +// forEachG takes a lock to exclude concurrent addition of new Gs. +func forEachG(fn func(gp *g)) { + lock(&allglock) + for _, gp := range allgs { + fn(gp) + } + unlock(&allglock) +} + +// forEachGRace calls fn on every G from allgs. +// +// forEachGRace avoids locking, but does not exclude addition of new Gs during +// execution, which may be missed. +func forEachGRace(fn func(gp *g)) { + ptr, length := atomicAllG() + for i := uintptr(0); i < length; i++ { + gp := atomicAllGIndex(ptr, i) + fn(gp) + } + return +} + +const ( + // Number of goroutine ids to grab from sched.goidgen to local per-P cache at once. + // 16 seems to provide enough amortization, but other than that it's mostly arbitrary number. + _GoidCacheBatch = 16 +) + +// cpuinit sets up CPU feature flags and calls internal/cpu.Initialize. env should be the complete +// value of the GODEBUG environment variable. +func cpuinit(env string) { + switch GOOS { + case "aix", "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd", "illumos", "solaris", "linux": + cpu.DebugOptions = true + } + cpu.Initialize(env) + + // Support cpu feature variables are used in code generated by the compiler + // to guard execution of instructions that can not be assumed to be always supported. + switch GOARCH { + case "386", "amd64": + x86HasPOPCNT = cpu.X86.HasPOPCNT + x86HasSSE41 = cpu.X86.HasSSE41 + x86HasFMA = cpu.X86.HasFMA + + case "arm": + armHasVFPv4 = cpu.ARM.HasVFPv4 + + case "arm64": + arm64HasATOMICS = cpu.ARM64.HasATOMICS + } +} + +// getGodebugEarly extracts the environment variable GODEBUG from the environment on +// Unix-like operating systems and returns it. This function exists to extract GODEBUG +// early before much of the runtime is initialized. +func getGodebugEarly() string { + const prefix = "GODEBUG=" + var env string + switch GOOS { + case "aix", "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd", "illumos", "solaris", "linux": + // Similar to goenv_unix but extracts the environment value for + // GODEBUG directly. + // TODO(moehrmann): remove when general goenvs() can be called before cpuinit() + n := int32(0) + for argv_index(argv, argc+1+n) != nil { + n++ + } + + for i := int32(0); i < n; i++ { + p := argv_index(argv, argc+1+i) + s := unsafe.String(p, findnull(p)) + + if hasPrefix(s, prefix) { + env = gostring(p)[len(prefix):] + break + } + } + } + return env +} + +// The bootstrap sequence is: +// +// call osinit +// call schedinit +// make & queue new G +// call runtime·mstart +// +// The new G calls runtime·main. +func schedinit() { + lockInit(&sched.lock, lockRankSched) + lockInit(&sched.sysmonlock, lockRankSysmon) + lockInit(&sched.deferlock, lockRankDefer) + lockInit(&sched.sudoglock, lockRankSudog) + lockInit(&deadlock, lockRankDeadlock) + lockInit(&paniclk, lockRankPanic) + lockInit(&allglock, lockRankAllg) + lockInit(&allpLock, lockRankAllp) + lockInit(&reflectOffs.lock, lockRankReflectOffs) + lockInit(&finlock, lockRankFin) + lockInit(&cpuprof.lock, lockRankCpuprof) + allocmLock.init(lockRankAllocmR, lockRankAllocmRInternal, lockRankAllocmW) + execLock.init(lockRankExecR, lockRankExecRInternal, lockRankExecW) + traceLockInit() + // Enforce that this lock is always a leaf lock. + // All of this lock's critical sections should be + // extremely short. + lockInit(&memstats.heapStats.noPLock, lockRankLeafRank) + + // raceinit must be the first call to race detector. + // In particular, it must be done before mallocinit below calls racemapshadow. + gp := getg() + if raceenabled { + gp.racectx, raceprocctx0 = raceinit() + } + + sched.maxmcount = 10000 + + // The world starts stopped. + worldStopped() + + moduledataverify() + stackinit() + mallocinit() + godebug := getGodebugEarly() + initPageTrace(godebug) // must run after mallocinit but before anything allocates + cpuinit(godebug) // must run before alginit + alginit() // maps, hash, fastrand must not be used before this call + fastrandinit() // must run before mcommoninit + mcommoninit(gp.m, -1) + modulesinit() // provides activeModules + typelinksinit() // uses maps, activeModules + itabsinit() // uses activeModules + stkobjinit() // must run before GC starts + + sigsave(&gp.m.sigmask) + initSigmask = gp.m.sigmask + + goargs() + goenvs() + secure() + parsedebugvars() + gcinit() + + // if disableMemoryProfiling is set, update MemProfileRate to 0 to turn off memprofile. + // Note: parsedebugvars may update MemProfileRate, but when disableMemoryProfiling is + // set to true by the linker, it means that nothing is consuming the profile, it is + // safe to set MemProfileRate to 0. + if disableMemoryProfiling { + MemProfileRate = 0 + } + + lock(&sched.lock) + sched.lastpoll.Store(nanotime()) + procs := ncpu + if n, ok := atoi32(gogetenv("GOMAXPROCS")); ok && n > 0 { + procs = n + } + if procresize(procs) != nil { + throw("unknown runnable goroutine during bootstrap") + } + unlock(&sched.lock) + + // World is effectively started now, as P's can run. + worldStarted() + + if buildVersion == "" { + // Condition should never trigger. This code just serves + // to ensure runtime·buildVersion is kept in the resulting binary. + buildVersion = "unknown" + } + if len(modinfo) == 1 { + // Condition should never trigger. This code just serves + // to ensure runtime·modinfo is kept in the resulting binary. + modinfo = "" + } +} + +func dumpgstatus(gp *g) { + thisg := getg() + print("runtime: gp: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n") + print("runtime: getg: g=", thisg, ", goid=", thisg.goid, ", g->atomicstatus=", readgstatus(thisg), "\n") +} + +// sched.lock must be held. +func checkmcount() { + assertLockHeld(&sched.lock) + + // Exclude extra M's, which are used for cgocallback from threads + // created in C. + // + // The purpose of the SetMaxThreads limit is to avoid accidental fork + // bomb from something like millions of goroutines blocking on system + // calls, causing the runtime to create millions of threads. By + // definition, this isn't a problem for threads created in C, so we + // exclude them from the limit. See https://go.dev/issue/60004. + count := mcount() - int32(extraMInUse.Load()) - int32(extraMLength.Load()) + if count > sched.maxmcount { + print("runtime: program exceeds ", sched.maxmcount, "-thread limit\n") + throw("thread exhaustion") + } +} + +// mReserveID returns the next ID to use for a new m. This new m is immediately +// considered 'running' by checkdead. +// +// sched.lock must be held. +func mReserveID() int64 { + assertLockHeld(&sched.lock) + + if sched.mnext+1 < sched.mnext { + throw("runtime: thread ID overflow") + } + id := sched.mnext + sched.mnext++ + checkmcount() + return id +} + +// Pre-allocated ID may be passed as 'id', or omitted by passing -1. +func mcommoninit(mp *m, id int64) { + gp := getg() + + // g0 stack won't make sense for user (and is not necessary unwindable). + if gp != gp.m.g0 { + callers(1, mp.createstack[:]) + } + + lock(&sched.lock) + + if id >= 0 { + mp.id = id + } else { + mp.id = mReserveID() + } + + lo := uint32(int64Hash(uint64(mp.id), fastrandseed)) + hi := uint32(int64Hash(uint64(cputicks()), ^fastrandseed)) + if lo|hi == 0 { + hi = 1 + } + // Same behavior as for 1.17. + // TODO: Simplify this. + if goarch.BigEndian { + mp.fastrand = uint64(lo)<<32 | uint64(hi) + } else { + mp.fastrand = uint64(hi)<<32 | uint64(lo) + } + + mpreinit(mp) + if mp.gsignal != nil { + mp.gsignal.stackguard1 = mp.gsignal.stack.lo + stackGuard + } + + // Add to allm so garbage collector doesn't free g->m + // when it is just in a register or thread-local storage. + mp.alllink = allm + + // NumCgoCall() iterates over allm w/o schedlock, + // so we need to publish it safely. + atomicstorep(unsafe.Pointer(&allm), unsafe.Pointer(mp)) + unlock(&sched.lock) + + // Allocate memory to hold a cgo traceback if the cgo call crashes. + if iscgo || GOOS == "solaris" || GOOS == "illumos" || GOOS == "windows" { + mp.cgoCallers = new(cgoCallers) + } +} + +func (mp *m) becomeSpinning() { + mp.spinning = true + sched.nmspinning.Add(1) + sched.needspinning.Store(0) +} + +func (mp *m) hasCgoOnStack() bool { + return mp.ncgo > 0 || mp.isextra +} + +var fastrandseed uintptr + +func fastrandinit() { + s := (*[unsafe.Sizeof(fastrandseed)]byte)(unsafe.Pointer(&fastrandseed))[:] + getRandomData(s) +} + +// Mark gp ready to run. +func ready(gp *g, traceskip int, next bool) { + if traceEnabled() { + traceGoUnpark(gp, traceskip) + } + + status := readgstatus(gp) + + // Mark runnable. + mp := acquirem() // disable preemption because it can be holding p in a local var + if status&^_Gscan != _Gwaiting { + dumpgstatus(gp) + throw("bad g->status in ready") + } + + // status is Gwaiting or Gscanwaiting, make Grunnable and put on runq + casgstatus(gp, _Gwaiting, _Grunnable) + runqput(mp.p.ptr(), gp, next) + wakep() + releasem(mp) +} + +// freezeStopWait is a large value that freezetheworld sets +// sched.stopwait to in order to request that all Gs permanently stop. +const freezeStopWait = 0x7fffffff + +// freezing is set to non-zero if the runtime is trying to freeze the +// world. +var freezing atomic.Bool + +// Similar to stopTheWorld but best-effort and can be called several times. +// There is no reverse operation, used during crashing. +// This function must not lock any mutexes. +func freezetheworld() { + freezing.Store(true) + if debug.dontfreezetheworld > 0 { + // Don't prempt Ps to stop goroutines. That will perturb + // scheduler state, making debugging more difficult. Instead, + // allow goroutines to continue execution. + // + // fatalpanic will tracebackothers to trace all goroutines. It + // is unsafe to trace a running goroutine, so tracebackothers + // will skip running goroutines. That is OK and expected, we + // expect users of dontfreezetheworld to use core files anyway. + // + // However, allowing the scheduler to continue running free + // introduces a race: a goroutine may be stopped when + // tracebackothers checks its status, and then start running + // later when we are in the middle of traceback, potentially + // causing a crash. + // + // To mitigate this, when an M naturally enters the scheduler, + // schedule checks if freezing is set and if so stops + // execution. This guarantees that while Gs can transition from + // running to stopped, they can never transition from stopped + // to running. + // + // The sleep here allows racing Ms that missed freezing and are + // about to run a G to complete the transition to running + // before we start traceback. + usleep(1000) + return + } + + // stopwait and preemption requests can be lost + // due to races with concurrently executing threads, + // so try several times + for i := 0; i < 5; i++ { + // this should tell the scheduler to not start any new goroutines + sched.stopwait = freezeStopWait + sched.gcwaiting.Store(true) + // this should stop running goroutines + if !preemptall() { + break // no running goroutines + } + usleep(1000) + } + // to be sure + usleep(1000) + preemptall() + usleep(1000) +} + +// All reads and writes of g's status go through readgstatus, casgstatus +// castogscanstatus, casfrom_Gscanstatus. +// +//go:nosplit +func readgstatus(gp *g) uint32 { + return gp.atomicstatus.Load() +} + +// The Gscanstatuses are acting like locks and this releases them. +// If it proves to be a performance hit we should be able to make these +// simple atomic stores but for now we are going to throw if +// we see an inconsistent state. +func casfrom_Gscanstatus(gp *g, oldval, newval uint32) { + success := false + + // Check that transition is valid. + switch oldval { + default: + print("runtime: casfrom_Gscanstatus bad oldval gp=", gp, ", oldval=", hex(oldval), ", newval=", hex(newval), "\n") + dumpgstatus(gp) + throw("casfrom_Gscanstatus:top gp->status is not in scan state") + case _Gscanrunnable, + _Gscanwaiting, + _Gscanrunning, + _Gscansyscall, + _Gscanpreempted: + if newval == oldval&^_Gscan { + success = gp.atomicstatus.CompareAndSwap(oldval, newval) + } + } + if !success { + print("runtime: casfrom_Gscanstatus failed gp=", gp, ", oldval=", hex(oldval), ", newval=", hex(newval), "\n") + dumpgstatus(gp) + throw("casfrom_Gscanstatus: gp->status is not in scan state") + } + releaseLockRank(lockRankGscan) +} + +// This will return false if the gp is not in the expected status and the cas fails. +// This acts like a lock acquire while the casfromgstatus acts like a lock release. +func castogscanstatus(gp *g, oldval, newval uint32) bool { + switch oldval { + case _Grunnable, + _Grunning, + _Gwaiting, + _Gsyscall: + if newval == oldval|_Gscan { + r := gp.atomicstatus.CompareAndSwap(oldval, newval) + if r { + acquireLockRank(lockRankGscan) + } + return r + + } + } + print("runtime: castogscanstatus oldval=", hex(oldval), " newval=", hex(newval), "\n") + throw("castogscanstatus") + panic("not reached") +} + +// casgstatusAlwaysTrack is a debug flag that causes casgstatus to always track +// various latencies on every transition instead of sampling them. +var casgstatusAlwaysTrack = false + +// If asked to move to or from a Gscanstatus this will throw. Use the castogscanstatus +// and casfrom_Gscanstatus instead. +// casgstatus will loop if the g->atomicstatus is in a Gscan status until the routine that +// put it in the Gscan state is finished. +// +//go:nosplit +func casgstatus(gp *g, oldval, newval uint32) { + if (oldval&_Gscan != 0) || (newval&_Gscan != 0) || oldval == newval { + systemstack(func() { + print("runtime: casgstatus: oldval=", hex(oldval), " newval=", hex(newval), "\n") + throw("casgstatus: bad incoming values") + }) + } + + acquireLockRank(lockRankGscan) + releaseLockRank(lockRankGscan) + + // See https://golang.org/cl/21503 for justification of the yield delay. + const yieldDelay = 5 * 1000 + var nextYield int64 + + // loop if gp->atomicstatus is in a scan state giving + // GC time to finish and change the state to oldval. + for i := 0; !gp.atomicstatus.CompareAndSwap(oldval, newval); i++ { + if oldval == _Gwaiting && gp.atomicstatus.Load() == _Grunnable { + throw("casgstatus: waiting for Gwaiting but is Grunnable") + } + if i == 0 { + nextYield = nanotime() + yieldDelay + } + if nanotime() < nextYield { + for x := 0; x < 10 && gp.atomicstatus.Load() != oldval; x++ { + procyield(1) + } + } else { + osyield() + nextYield = nanotime() + yieldDelay/2 + } + } + + if oldval == _Grunning { + // Track every gTrackingPeriod time a goroutine transitions out of running. + if casgstatusAlwaysTrack || gp.trackingSeq%gTrackingPeriod == 0 { + gp.tracking = true + } + gp.trackingSeq++ + } + if !gp.tracking { + return + } + + // Handle various kinds of tracking. + // + // Currently: + // - Time spent in runnable. + // - Time spent blocked on a sync.Mutex or sync.RWMutex. + switch oldval { + case _Grunnable: + // We transitioned out of runnable, so measure how much + // time we spent in this state and add it to + // runnableTime. + now := nanotime() + gp.runnableTime += now - gp.trackingStamp + gp.trackingStamp = 0 + case _Gwaiting: + if !gp.waitreason.isMutexWait() { + // Not blocking on a lock. + break + } + // Blocking on a lock, measure it. Note that because we're + // sampling, we have to multiply by our sampling period to get + // a more representative estimate of the absolute value. + // gTrackingPeriod also represents an accurate sampling period + // because we can only enter this state from _Grunning. + now := nanotime() + sched.totalMutexWaitTime.Add((now - gp.trackingStamp) * gTrackingPeriod) + gp.trackingStamp = 0 + } + switch newval { + case _Gwaiting: + if !gp.waitreason.isMutexWait() { + // Not blocking on a lock. + break + } + // Blocking on a lock. Write down the timestamp. + now := nanotime() + gp.trackingStamp = now + case _Grunnable: + // We just transitioned into runnable, so record what + // time that happened. + now := nanotime() + gp.trackingStamp = now + case _Grunning: + // We're transitioning into running, so turn off + // tracking and record how much time we spent in + // runnable. + gp.tracking = false + sched.timeToRun.record(gp.runnableTime) + gp.runnableTime = 0 + } +} + +// casGToWaiting transitions gp from old to _Gwaiting, and sets the wait reason. +// +// Use this over casgstatus when possible to ensure that a waitreason is set. +func casGToWaiting(gp *g, old uint32, reason waitReason) { + // Set the wait reason before calling casgstatus, because casgstatus will use it. + gp.waitreason = reason + casgstatus(gp, old, _Gwaiting) +} + +// casgstatus(gp, oldstatus, Gcopystack), assuming oldstatus is Gwaiting or Grunnable. +// Returns old status. Cannot call casgstatus directly, because we are racing with an +// async wakeup that might come in from netpoll. If we see Gwaiting from the readgstatus, +// it might have become Grunnable by the time we get to the cas. If we called casgstatus, +// it would loop waiting for the status to go back to Gwaiting, which it never will. +// +//go:nosplit +func casgcopystack(gp *g) uint32 { + for { + oldstatus := readgstatus(gp) &^ _Gscan + if oldstatus != _Gwaiting && oldstatus != _Grunnable { + throw("copystack: bad status, not Gwaiting or Grunnable") + } + if gp.atomicstatus.CompareAndSwap(oldstatus, _Gcopystack) { + return oldstatus + } + } +} + +// casGToPreemptScan transitions gp from _Grunning to _Gscan|_Gpreempted. +// +// TODO(austin): This is the only status operation that both changes +// the status and locks the _Gscan bit. Rethink this. +func casGToPreemptScan(gp *g, old, new uint32) { + if old != _Grunning || new != _Gscan|_Gpreempted { + throw("bad g transition") + } + acquireLockRank(lockRankGscan) + for !gp.atomicstatus.CompareAndSwap(_Grunning, _Gscan|_Gpreempted) { + } +} + +// casGFromPreempted attempts to transition gp from _Gpreempted to +// _Gwaiting. If successful, the caller is responsible for +// re-scheduling gp. +func casGFromPreempted(gp *g, old, new uint32) bool { + if old != _Gpreempted || new != _Gwaiting { + throw("bad g transition") + } + gp.waitreason = waitReasonPreempted + return gp.atomicstatus.CompareAndSwap(_Gpreempted, _Gwaiting) +} + +// stwReason is an enumeration of reasons the world is stopping. +type stwReason uint8 + +// Reasons to stop-the-world. +// +// Avoid reusing reasons and add new ones instead. +const ( + stwUnknown stwReason = iota // "unknown" + stwGCMarkTerm // "GC mark termination" + stwGCSweepTerm // "GC sweep termination" + stwWriteHeapDump // "write heap dump" + stwGoroutineProfile // "goroutine profile" + stwGoroutineProfileCleanup // "goroutine profile cleanup" + stwAllGoroutinesStack // "all goroutines stack trace" + stwReadMemStats // "read mem stats" + stwAllThreadsSyscall // "AllThreadsSyscall" + stwGOMAXPROCS // "GOMAXPROCS" + stwStartTrace // "start trace" + stwStopTrace // "stop trace" + stwForTestCountPagesInUse // "CountPagesInUse (test)" + stwForTestReadMetricsSlow // "ReadMetricsSlow (test)" + stwForTestReadMemStatsSlow // "ReadMemStatsSlow (test)" + stwForTestPageCachePagesLeaked // "PageCachePagesLeaked (test)" + stwForTestResetDebugLog // "ResetDebugLog (test)" +) + +func (r stwReason) String() string { + return stwReasonStrings[r] +} + +// If you add to this list, also add it to src/internal/trace/parser.go. +// If you change the values of any of the stw* constants, bump the trace +// version number and make a copy of this. +var stwReasonStrings = [...]string{ + stwUnknown: "unknown", + stwGCMarkTerm: "GC mark termination", + stwGCSweepTerm: "GC sweep termination", + stwWriteHeapDump: "write heap dump", + stwGoroutineProfile: "goroutine profile", + stwGoroutineProfileCleanup: "goroutine profile cleanup", + stwAllGoroutinesStack: "all goroutines stack trace", + stwReadMemStats: "read mem stats", + stwAllThreadsSyscall: "AllThreadsSyscall", + stwGOMAXPROCS: "GOMAXPROCS", + stwStartTrace: "start trace", + stwStopTrace: "stop trace", + stwForTestCountPagesInUse: "CountPagesInUse (test)", + stwForTestReadMetricsSlow: "ReadMetricsSlow (test)", + stwForTestReadMemStatsSlow: "ReadMemStatsSlow (test)", + stwForTestPageCachePagesLeaked: "PageCachePagesLeaked (test)", + stwForTestResetDebugLog: "ResetDebugLog (test)", +} + +// stopTheWorld stops all P's from executing goroutines, interrupting +// all goroutines at GC safe points and records reason as the reason +// for the stop. On return, only the current goroutine's P is running. +// stopTheWorld must not be called from a system stack and the caller +// must not hold worldsema. The caller must call startTheWorld when +// other P's should resume execution. +// +// stopTheWorld is safe for multiple goroutines to call at the +// same time. Each will execute its own stop, and the stops will +// be serialized. +// +// This is also used by routines that do stack dumps. If the system is +// in panic or being exited, this may not reliably stop all +// goroutines. +func stopTheWorld(reason stwReason) { + semacquire(&worldsema) + gp := getg() + gp.m.preemptoff = reason.String() + systemstack(func() { + // Mark the goroutine which called stopTheWorld preemptible so its + // stack may be scanned. + // This lets a mark worker scan us while we try to stop the world + // since otherwise we could get in a mutual preemption deadlock. + // We must not modify anything on the G stack because a stack shrink + // may occur. A stack shrink is otherwise OK though because in order + // to return from this function (and to leave the system stack) we + // must have preempted all goroutines, including any attempting + // to scan our stack, in which case, any stack shrinking will + // have already completed by the time we exit. + // Don't provide a wait reason because we're still executing. + casGToWaiting(gp, _Grunning, waitReasonStoppingTheWorld) + stopTheWorldWithSema(reason) + casgstatus(gp, _Gwaiting, _Grunning) + }) +} + +// startTheWorld undoes the effects of stopTheWorld. +func startTheWorld() { + systemstack(func() { startTheWorldWithSema() }) + + // worldsema must be held over startTheWorldWithSema to ensure + // gomaxprocs cannot change while worldsema is held. + // + // Release worldsema with direct handoff to the next waiter, but + // acquirem so that semrelease1 doesn't try to yield our time. + // + // Otherwise if e.g. ReadMemStats is being called in a loop, + // it might stomp on other attempts to stop the world, such as + // for starting or ending GC. The operation this blocks is + // so heavy-weight that we should just try to be as fair as + // possible here. + // + // We don't want to just allow us to get preempted between now + // and releasing the semaphore because then we keep everyone + // (including, for example, GCs) waiting longer. + mp := acquirem() + mp.preemptoff = "" + semrelease1(&worldsema, true, 0) + releasem(mp) +} + +// stopTheWorldGC has the same effect as stopTheWorld, but blocks +// until the GC is not running. It also blocks a GC from starting +// until startTheWorldGC is called. +func stopTheWorldGC(reason stwReason) { + semacquire(&gcsema) + stopTheWorld(reason) +} + +// startTheWorldGC undoes the effects of stopTheWorldGC. +func startTheWorldGC() { + startTheWorld() + semrelease(&gcsema) +} + +// Holding worldsema grants an M the right to try to stop the world. +var worldsema uint32 = 1 + +// Holding gcsema grants the M the right to block a GC, and blocks +// until the current GC is done. In particular, it prevents gomaxprocs +// from changing concurrently. +// +// TODO(mknyszek): Once gomaxprocs and the execution tracer can handle +// being changed/enabled during a GC, remove this. +var gcsema uint32 = 1 + +// stopTheWorldWithSema is the core implementation of stopTheWorld. +// The caller is responsible for acquiring worldsema and disabling +// preemption first and then should stopTheWorldWithSema on the system +// stack: +// +// semacquire(&worldsema, 0) +// m.preemptoff = "reason" +// systemstack(stopTheWorldWithSema) +// +// When finished, the caller must either call startTheWorld or undo +// these three operations separately: +// +// m.preemptoff = "" +// systemstack(startTheWorldWithSema) +// semrelease(&worldsema) +// +// It is allowed to acquire worldsema once and then execute multiple +// startTheWorldWithSema/stopTheWorldWithSema pairs. +// Other P's are able to execute between successive calls to +// startTheWorldWithSema and stopTheWorldWithSema. +// Holding worldsema causes any other goroutines invoking +// stopTheWorld to block. +func stopTheWorldWithSema(reason stwReason) { + if traceEnabled() { + traceSTWStart(reason) + } + gp := getg() + + // If we hold a lock, then we won't be able to stop another M + // that is blocked trying to acquire the lock. + if gp.m.locks > 0 { + throw("stopTheWorld: holding locks") + } + + lock(&sched.lock) + sched.stopwait = gomaxprocs + sched.gcwaiting.Store(true) + preemptall() + // stop current P + gp.m.p.ptr().status = _Pgcstop // Pgcstop is only diagnostic. + sched.stopwait-- + // try to retake all P's in Psyscall status + for _, pp := range allp { + s := pp.status + if s == _Psyscall && atomic.Cas(&pp.status, s, _Pgcstop) { + if traceEnabled() { + traceGoSysBlock(pp) + traceProcStop(pp) + } + pp.syscalltick++ + sched.stopwait-- + } + } + // stop idle P's + now := nanotime() + for { + pp, _ := pidleget(now) + if pp == nil { + break + } + pp.status = _Pgcstop + sched.stopwait-- + } + wait := sched.stopwait > 0 + unlock(&sched.lock) + + // wait for remaining P's to stop voluntarily + if wait { + for { + // wait for 100us, then try to re-preempt in case of any races + if notetsleep(&sched.stopnote, 100*1000) { + noteclear(&sched.stopnote) + break + } + preemptall() + } + } + + // sanity checks + bad := "" + if sched.stopwait != 0 { + bad = "stopTheWorld: not stopped (stopwait != 0)" + } else { + for _, pp := range allp { + if pp.status != _Pgcstop { + bad = "stopTheWorld: not stopped (status != _Pgcstop)" + } + } + } + if freezing.Load() { + // Some other thread is panicking. This can cause the + // sanity checks above to fail if the panic happens in + // the signal handler on a stopped thread. Either way, + // we should halt this thread. + lock(&deadlock) + lock(&deadlock) + } + if bad != "" { + throw(bad) + } + + worldStopped() +} + +func startTheWorldWithSema() int64 { + assertWorldStopped() + + mp := acquirem() // disable preemption because it can be holding p in a local var + if netpollinited() { + list := netpoll(0) // non-blocking + injectglist(&list) + } + lock(&sched.lock) + + procs := gomaxprocs + if newprocs != 0 { + procs = newprocs + newprocs = 0 + } + p1 := procresize(procs) + sched.gcwaiting.Store(false) + if sched.sysmonwait.Load() { + sched.sysmonwait.Store(false) + notewakeup(&sched.sysmonnote) + } + unlock(&sched.lock) + + worldStarted() + + for p1 != nil { + p := p1 + p1 = p1.link.ptr() + if p.m != 0 { + mp := p.m.ptr() + p.m = 0 + if mp.nextp != 0 { + throw("startTheWorld: inconsistent mp->nextp") + } + mp.nextp.set(p) + notewakeup(&mp.park) + } else { + // Start M to run P. Do not start another M below. + newm(nil, p, -1) + } + } + + // Capture start-the-world time before doing clean-up tasks. + startTime := nanotime() + if traceEnabled() { + traceSTWDone() + } + + // Wakeup an additional proc in case we have excessive runnable goroutines + // in local queues or in the global queue. If we don't, the proc will park itself. + // If we have lots of excessive work, resetspinning will unpark additional procs as necessary. + wakep() + + releasem(mp) + + return startTime +} + +// usesLibcall indicates whether this runtime performs system calls +// via libcall. +func usesLibcall() bool { + switch GOOS { + case "aix", "darwin", "illumos", "ios", "solaris", "windows": + return true + case "openbsd": + return GOARCH == "386" || GOARCH == "amd64" || GOARCH == "arm" || GOARCH == "arm64" + } + return false +} + +// mStackIsSystemAllocated indicates whether this runtime starts on a +// system-allocated stack. +func mStackIsSystemAllocated() bool { + switch GOOS { + case "aix", "darwin", "plan9", "illumos", "ios", "solaris", "windows": + return true + case "openbsd": + switch GOARCH { + case "386", "amd64", "arm", "arm64": + return true + } + } + return false +} + +// mstart is the entry-point for new Ms. +// It is written in assembly, uses ABI0, is marked TOPFRAME, and calls mstart0. +func mstart() + +// mstart0 is the Go entry-point for new Ms. +// This must not split the stack because we may not even have stack +// bounds set up yet. +// +// May run during STW (because it doesn't have a P yet), so write +// barriers are not allowed. +// +//go:nosplit +//go:nowritebarrierrec +func mstart0() { + gp := getg() + + osStack := gp.stack.lo == 0 + if osStack { + // Initialize stack bounds from system stack. + // Cgo may have left stack size in stack.hi. + // minit may update the stack bounds. + // + // Note: these bounds may not be very accurate. + // We set hi to &size, but there are things above + // it. The 1024 is supposed to compensate this, + // but is somewhat arbitrary. + size := gp.stack.hi + if size == 0 { + size = 16384 * sys.StackGuardMultiplier + } + gp.stack.hi = uintptr(noescape(unsafe.Pointer(&size))) + gp.stack.lo = gp.stack.hi - size + 1024 + } + // Initialize stack guard so that we can start calling regular + // Go code. + gp.stackguard0 = gp.stack.lo + stackGuard + // This is the g0, so we can also call go:systemstack + // functions, which check stackguard1. + gp.stackguard1 = gp.stackguard0 + mstart1() + + // Exit this thread. + if mStackIsSystemAllocated() { + // Windows, Solaris, illumos, Darwin, AIX and Plan 9 always system-allocate + // the stack, but put it in gp.stack before mstart, + // so the logic above hasn't set osStack yet. + osStack = true + } + mexit(osStack) +} + +// The go:noinline is to guarantee the getcallerpc/getcallersp below are safe, +// so that we can set up g0.sched to return to the call of mstart1 above. +// +//go:noinline +func mstart1() { + gp := getg() + + if gp != gp.m.g0 { + throw("bad runtime·mstart") + } + + // Set up m.g0.sched as a label returning to just + // after the mstart1 call in mstart0 above, for use by goexit0 and mcall. + // We're never coming back to mstart1 after we call schedule, + // so other calls can reuse the current frame. + // And goexit0 does a gogo that needs to return from mstart1 + // and let mstart0 exit the thread. + gp.sched.g = guintptr(unsafe.Pointer(gp)) + gp.sched.pc = getcallerpc() + gp.sched.sp = getcallersp() + + asminit() + minit() + + // Install signal handlers; after minit so that minit can + // prepare the thread to be able to handle the signals. + if gp.m == &m0 { + mstartm0() + } + + if fn := gp.m.mstartfn; fn != nil { + fn() + } + + if gp.m != &m0 { + acquirep(gp.m.nextp.ptr()) + gp.m.nextp = 0 + } + schedule() +} + +// mstartm0 implements part of mstart1 that only runs on the m0. +// +// Write barriers are allowed here because we know the GC can't be +// running yet, so they'll be no-ops. +// +//go:yeswritebarrierrec +func mstartm0() { + // Create an extra M for callbacks on threads not created by Go. + // An extra M is also needed on Windows for callbacks created by + // syscall.NewCallback. See issue #6751 for details. + if (iscgo || GOOS == "windows") && !cgoHasExtraM { + cgoHasExtraM = true + newextram() + } + initsig(false) +} + +// mPark causes a thread to park itself, returning once woken. +// +//go:nosplit +func mPark() { + gp := getg() + notesleep(&gp.m.park) + noteclear(&gp.m.park) +} + +// mexit tears down and exits the current thread. +// +// Don't call this directly to exit the thread, since it must run at +// the top of the thread stack. Instead, use gogo(&gp.m.g0.sched) to +// unwind the stack to the point that exits the thread. +// +// It is entered with m.p != nil, so write barriers are allowed. It +// will release the P before exiting. +// +//go:yeswritebarrierrec +func mexit(osStack bool) { + mp := getg().m + + if mp == &m0 { + // This is the main thread. Just wedge it. + // + // On Linux, exiting the main thread puts the process + // into a non-waitable zombie state. On Plan 9, + // exiting the main thread unblocks wait even though + // other threads are still running. On Solaris we can + // neither exitThread nor return from mstart. Other + // bad things probably happen on other platforms. + // + // We could try to clean up this M more before wedging + // it, but that complicates signal handling. + handoffp(releasep()) + lock(&sched.lock) + sched.nmfreed++ + checkdead() + unlock(&sched.lock) + mPark() + throw("locked m0 woke up") + } + + sigblock(true) + unminit() + + // Free the gsignal stack. + if mp.gsignal != nil { + stackfree(mp.gsignal.stack) + // On some platforms, when calling into VDSO (e.g. nanotime) + // we store our g on the gsignal stack, if there is one. + // Now the stack is freed, unlink it from the m, so we + // won't write to it when calling VDSO code. + mp.gsignal = nil + } + + // Remove m from allm. + lock(&sched.lock) + for pprev := &allm; *pprev != nil; pprev = &(*pprev).alllink { + if *pprev == mp { + *pprev = mp.alllink + goto found + } + } + throw("m not found in allm") +found: + // Delay reaping m until it's done with the stack. + // + // Put mp on the free list, though it will not be reaped while freeWait + // is freeMWait. mp is no longer reachable via allm, so even if it is + // on an OS stack, we must keep a reference to mp alive so that the GC + // doesn't free mp while we are still using it. + // + // Note that the free list must not be linked through alllink because + // some functions walk allm without locking, so may be using alllink. + mp.freeWait.Store(freeMWait) + mp.freelink = sched.freem + sched.freem = mp + unlock(&sched.lock) + + atomic.Xadd64(&ncgocall, int64(mp.ncgocall)) + + // Release the P. + handoffp(releasep()) + // After this point we must not have write barriers. + + // Invoke the deadlock detector. This must happen after + // handoffp because it may have started a new M to take our + // P's work. + lock(&sched.lock) + sched.nmfreed++ + checkdead() + unlock(&sched.lock) + + if GOOS == "darwin" || GOOS == "ios" { + // Make sure pendingPreemptSignals is correct when an M exits. + // For #41702. + if mp.signalPending.Load() != 0 { + pendingPreemptSignals.Add(-1) + } + } + + // Destroy all allocated resources. After this is called, we may no + // longer take any locks. + mdestroy(mp) + + if osStack { + // No more uses of mp, so it is safe to drop the reference. + mp.freeWait.Store(freeMRef) + + // Return from mstart and let the system thread + // library free the g0 stack and terminate the thread. + return + } + + // mstart is the thread's entry point, so there's nothing to + // return to. Exit the thread directly. exitThread will clear + // m.freeWait when it's done with the stack and the m can be + // reaped. + exitThread(&mp.freeWait) +} + +// forEachP calls fn(p) for every P p when p reaches a GC safe point. +// If a P is currently executing code, this will bring the P to a GC +// safe point and execute fn on that P. If the P is not executing code +// (it is idle or in a syscall), this will call fn(p) directly while +// preventing the P from exiting its state. This does not ensure that +// fn will run on every CPU executing Go code, but it acts as a global +// memory barrier. GC uses this as a "ragged barrier." +// +// The caller must hold worldsema. +// +//go:systemstack +func forEachP(fn func(*p)) { + mp := acquirem() + pp := getg().m.p.ptr() + + lock(&sched.lock) + if sched.safePointWait != 0 { + throw("forEachP: sched.safePointWait != 0") + } + sched.safePointWait = gomaxprocs - 1 + sched.safePointFn = fn + + // Ask all Ps to run the safe point function. + for _, p2 := range allp { + if p2 != pp { + atomic.Store(&p2.runSafePointFn, 1) + } + } + preemptall() + + // Any P entering _Pidle or _Psyscall from now on will observe + // p.runSafePointFn == 1 and will call runSafePointFn when + // changing its status to _Pidle/_Psyscall. + + // Run safe point function for all idle Ps. sched.pidle will + // not change because we hold sched.lock. + for p := sched.pidle.ptr(); p != nil; p = p.link.ptr() { + if atomic.Cas(&p.runSafePointFn, 1, 0) { + fn(p) + sched.safePointWait-- + } + } + + wait := sched.safePointWait > 0 + unlock(&sched.lock) + + // Run fn for the current P. + fn(pp) + + // Force Ps currently in _Psyscall into _Pidle and hand them + // off to induce safe point function execution. + for _, p2 := range allp { + s := p2.status + if s == _Psyscall && p2.runSafePointFn == 1 && atomic.Cas(&p2.status, s, _Pidle) { + if traceEnabled() { + traceGoSysBlock(p2) + traceProcStop(p2) + } + p2.syscalltick++ + handoffp(p2) + } + } + + // Wait for remaining Ps to run fn. + if wait { + for { + // Wait for 100us, then try to re-preempt in + // case of any races. + // + // Requires system stack. + if notetsleep(&sched.safePointNote, 100*1000) { + noteclear(&sched.safePointNote) + break + } + preemptall() + } + } + if sched.safePointWait != 0 { + throw("forEachP: not done") + } + for _, p2 := range allp { + if p2.runSafePointFn != 0 { + throw("forEachP: P did not run fn") + } + } + + lock(&sched.lock) + sched.safePointFn = nil + unlock(&sched.lock) + releasem(mp) +} + +// runSafePointFn runs the safe point function, if any, for this P. +// This should be called like +// +// if getg().m.p.runSafePointFn != 0 { +// runSafePointFn() +// } +// +// runSafePointFn must be checked on any transition in to _Pidle or +// _Psyscall to avoid a race where forEachP sees that the P is running +// just before the P goes into _Pidle/_Psyscall and neither forEachP +// nor the P run the safe-point function. +func runSafePointFn() { + p := getg().m.p.ptr() + // Resolve the race between forEachP running the safe-point + // function on this P's behalf and this P running the + // safe-point function directly. + if !atomic.Cas(&p.runSafePointFn, 1, 0) { + return + } + sched.safePointFn(p) + lock(&sched.lock) + sched.safePointWait-- + if sched.safePointWait == 0 { + notewakeup(&sched.safePointNote) + } + unlock(&sched.lock) +} + +// When running with cgo, we call _cgo_thread_start +// to start threads for us so that we can play nicely with +// foreign code. +var cgoThreadStart unsafe.Pointer + +type cgothreadstart struct { + g guintptr + tls *uint64 + fn unsafe.Pointer +} + +// Allocate a new m unassociated with any thread. +// Can use p for allocation context if needed. +// fn is recorded as the new m's m.mstartfn. +// id is optional pre-allocated m ID. Omit by passing -1. +// +// This function is allowed to have write barriers even if the caller +// isn't because it borrows pp. +// +//go:yeswritebarrierrec +func allocm(pp *p, fn func(), id int64) *m { + allocmLock.rlock() + + // The caller owns pp, but we may borrow (i.e., acquirep) it. We must + // disable preemption to ensure it is not stolen, which would make the + // caller lose ownership. + acquirem() + + gp := getg() + if gp.m.p == 0 { + acquirep(pp) // temporarily borrow p for mallocs in this function + } + + // Release the free M list. We need to do this somewhere and + // this may free up a stack we can use. + if sched.freem != nil { + lock(&sched.lock) + var newList *m + for freem := sched.freem; freem != nil; { + wait := freem.freeWait.Load() + if wait == freeMWait { + next := freem.freelink + freem.freelink = newList + newList = freem + freem = next + continue + } + // Free the stack if needed. For freeMRef, there is + // nothing to do except drop freem from the sched.freem + // list. + if wait == freeMStack { + // stackfree must be on the system stack, but allocm is + // reachable off the system stack transitively from + // startm. + systemstack(func() { + stackfree(freem.g0.stack) + }) + } + freem = freem.freelink + } + sched.freem = newList + unlock(&sched.lock) + } + + mp := new(m) + mp.mstartfn = fn + mcommoninit(mp, id) + + // In case of cgo or Solaris or illumos or Darwin, pthread_create will make us a stack. + // Windows and Plan 9 will layout sched stack on OS stack. + if iscgo || mStackIsSystemAllocated() { + mp.g0 = malg(-1) + } else { + mp.g0 = malg(16384 * sys.StackGuardMultiplier) + } + mp.g0.m = mp + + if pp == gp.m.p.ptr() { + releasep() + } + + releasem(gp.m) + allocmLock.runlock() + return mp +} + +// needm is called when a cgo callback happens on a +// thread without an m (a thread not created by Go). +// In this case, needm is expected to find an m to use +// and return with m, g initialized correctly. +// Since m and g are not set now (likely nil, but see below) +// needm is limited in what routines it can call. In particular +// it can only call nosplit functions (textflag 7) and cannot +// do any scheduling that requires an m. +// +// In order to avoid needing heavy lifting here, we adopt +// the following strategy: there is a stack of available m's +// that can be stolen. Using compare-and-swap +// to pop from the stack has ABA races, so we simulate +// a lock by doing an exchange (via Casuintptr) to steal the stack +// head and replace the top pointer with MLOCKED (1). +// This serves as a simple spin lock that we can use even +// without an m. The thread that locks the stack in this way +// unlocks the stack by storing a valid stack head pointer. +// +// In order to make sure that there is always an m structure +// available to be stolen, we maintain the invariant that there +// is always one more than needed. At the beginning of the +// program (if cgo is in use) the list is seeded with a single m. +// If needm finds that it has taken the last m off the list, its job +// is - once it has installed its own m so that it can do things like +// allocate memory - to create a spare m and put it on the list. +// +// Each of these extra m's also has a g0 and a curg that are +// pressed into service as the scheduling stack and current +// goroutine for the duration of the cgo callback. +// +// It calls dropm to put the m back on the list, +// 1. when the callback is done with the m in non-pthread platforms, +// 2. or when the C thread exiting on pthread platforms. +// +// The signal argument indicates whether we're called from a signal +// handler. +// +//go:nosplit +func needm(signal bool) { + if (iscgo || GOOS == "windows") && !cgoHasExtraM { + // Can happen if C/C++ code calls Go from a global ctor. + // Can also happen on Windows if a global ctor uses a + // callback created by syscall.NewCallback. See issue #6751 + // for details. + // + // Can not throw, because scheduler is not initialized yet. + writeErrStr("fatal error: cgo callback before cgo call\n") + exit(1) + } + + // Save and block signals before getting an M. + // The signal handler may call needm itself, + // and we must avoid a deadlock. Also, once g is installed, + // any incoming signals will try to execute, + // but we won't have the sigaltstack settings and other data + // set up appropriately until the end of minit, which will + // unblock the signals. This is the same dance as when + // starting a new m to run Go code via newosproc. + var sigmask sigset + sigsave(&sigmask) + sigblock(false) + + // getExtraM is safe here because of the invariant above, + // that the extra list always contains or will soon contain + // at least one m. + mp, last := getExtraM() + + // Set needextram when we've just emptied the list, + // so that the eventual call into cgocallbackg will + // allocate a new m for the extra list. We delay the + // allocation until then so that it can be done + // after exitsyscall makes sure it is okay to be + // running at all (that is, there's no garbage collection + // running right now). + mp.needextram = last + + // Store the original signal mask for use by minit. + mp.sigmask = sigmask + + // Install TLS on some platforms (previously setg + // would do this if necessary). + osSetupTLS(mp) + + // Install g (= m->g0) and set the stack bounds + // to match the current stack. + setg(mp.g0) + sp := getcallersp() + callbackUpdateSystemStack(mp, sp, signal) + + // Should mark we are already in Go now. + // Otherwise, we may call needm again when we get a signal, before cgocallbackg1, + // which means the extram list may be empty, that will cause a deadlock. + mp.isExtraInC = false + + // Initialize this thread to use the m. + asminit() + minit() + + // mp.curg is now a real goroutine. + casgstatus(mp.curg, _Gdead, _Gsyscall) + sched.ngsys.Add(-1) +} + +// Acquire an extra m and bind it to the C thread when a pthread key has been created. +// +//go:nosplit +func needAndBindM() { + needm(false) + + if _cgo_pthread_key_created != nil && *(*uintptr)(_cgo_pthread_key_created) != 0 { + cgoBindM() + } +} + +// newextram allocates m's and puts them on the extra list. +// It is called with a working local m, so that it can do things +// like call schedlock and allocate. +func newextram() { + c := extraMWaiters.Swap(0) + if c > 0 { + for i := uint32(0); i < c; i++ { + oneNewExtraM() + } + } else if extraMLength.Load() == 0 { + // Make sure there is at least one extra M. + oneNewExtraM() + } +} + +// oneNewExtraM allocates an m and puts it on the extra list. +func oneNewExtraM() { + // Create extra goroutine locked to extra m. + // The goroutine is the context in which the cgo callback will run. + // The sched.pc will never be returned to, but setting it to + // goexit makes clear to the traceback routines where + // the goroutine stack ends. + mp := allocm(nil, nil, -1) + gp := malg(4096) + gp.sched.pc = abi.FuncPCABI0(goexit) + sys.PCQuantum + gp.sched.sp = gp.stack.hi + gp.sched.sp -= 4 * goarch.PtrSize // extra space in case of reads slightly beyond frame + gp.sched.lr = 0 + gp.sched.g = guintptr(unsafe.Pointer(gp)) + gp.syscallpc = gp.sched.pc + gp.syscallsp = gp.sched.sp + gp.stktopsp = gp.sched.sp + // malg returns status as _Gidle. Change to _Gdead before + // adding to allg where GC can see it. We use _Gdead to hide + // this from tracebacks and stack scans since it isn't a + // "real" goroutine until needm grabs it. + casgstatus(gp, _Gidle, _Gdead) + gp.m = mp + mp.curg = gp + mp.isextra = true + // mark we are in C by default. + mp.isExtraInC = true + mp.lockedInt++ + mp.lockedg.set(gp) + gp.lockedm.set(mp) + gp.goid = sched.goidgen.Add(1) + if raceenabled { + gp.racectx = racegostart(abi.FuncPCABIInternal(newextram) + sys.PCQuantum) + } + if traceEnabled() { + traceOneNewExtraM(gp) + } + // put on allg for garbage collector + allgadd(gp) + + // gp is now on the allg list, but we don't want it to be + // counted by gcount. It would be more "proper" to increment + // sched.ngfree, but that requires locking. Incrementing ngsys + // has the same effect. + sched.ngsys.Add(1) + + // Add m to the extra list. + addExtraM(mp) +} + +// dropm puts the current m back onto the extra list. +// +// 1. On systems without pthreads, like Windows +// dropm is called when a cgo callback has called needm but is now +// done with the callback and returning back into the non-Go thread. +// +// The main expense here is the call to signalstack to release the +// m's signal stack, and then the call to needm on the next callback +// from this thread. It is tempting to try to save the m for next time, +// which would eliminate both these costs, but there might not be +// a next time: the current thread (which Go does not control) might exit. +// If we saved the m for that thread, there would be an m leak each time +// such a thread exited. Instead, we acquire and release an m on each +// call. These should typically not be scheduling operations, just a few +// atomics, so the cost should be small. +// +// 2. On systems with pthreads +// dropm is called while a non-Go thread is exiting. +// We allocate a pthread per-thread variable using pthread_key_create, +// to register a thread-exit-time destructor. +// And store the g into a thread-specific value associated with the pthread key, +// when first return back to C. +// So that the destructor would invoke dropm while the non-Go thread is exiting. +// This is much faster since it avoids expensive signal-related syscalls. +// +// This always runs without a P, so //go:nowritebarrierrec is required. +// +// This may run with a different stack than was recorded in g0 (there is no +// call to callbackUpdateSystemStack prior to dropm), so this must be +// //go:nosplit to avoid the stack bounds check. +// +//go:nowritebarrierrec +//go:nosplit +func dropm() { + // Clear m and g, and return m to the extra list. + // After the call to setg we can only call nosplit functions + // with no pointer manipulation. + mp := getg().m + + // Return mp.curg to dead state. + casgstatus(mp.curg, _Gsyscall, _Gdead) + mp.curg.preemptStop = false + sched.ngsys.Add(1) + + // Block signals before unminit. + // Unminit unregisters the signal handling stack (but needs g on some systems). + // Setg(nil) clears g, which is the signal handler's cue not to run Go handlers. + // It's important not to try to handle a signal between those two steps. + sigmask := mp.sigmask + sigblock(false) + unminit() + + setg(nil) + + // Clear g0 stack bounds to ensure that needm always refreshes the + // bounds when reusing this M. + g0 := mp.g0 + g0.stack.hi = 0 + g0.stack.lo = 0 + g0.stackguard0 = 0 + g0.stackguard1 = 0 + + putExtraM(mp) + + msigrestore(sigmask) +} + +// bindm store the g0 of the current m into a thread-specific value. +// +// We allocate a pthread per-thread variable using pthread_key_create, +// to register a thread-exit-time destructor. +// We are here setting the thread-specific value of the pthread key, to enable the destructor. +// So that the pthread_key_destructor would dropm while the C thread is exiting. +// +// And the saved g will be used in pthread_key_destructor, +// since the g stored in the TLS by Go might be cleared in some platforms, +// before the destructor invoked, so, we restore g by the stored g, before dropm. +// +// We store g0 instead of m, to make the assembly code simpler, +// since we need to restore g0 in runtime.cgocallback. +// +// On systems without pthreads, like Windows, bindm shouldn't be used. +// +// NOTE: this always runs without a P, so, nowritebarrierrec required. +// +//go:nosplit +//go:nowritebarrierrec +func cgoBindM() { + if GOOS == "windows" || GOOS == "plan9" { + fatal("bindm in unexpected GOOS") + } + g := getg() + if g.m.g0 != g { + fatal("the current g is not g0") + } + if _cgo_bindm != nil { + asmcgocall(_cgo_bindm, unsafe.Pointer(g)) + } +} + +// A helper function for EnsureDropM. +func getm() uintptr { + return uintptr(unsafe.Pointer(getg().m)) +} + +var ( + // Locking linked list of extra M's, via mp.schedlink. Must be accessed + // only via lockextra/unlockextra. + // + // Can't be atomic.Pointer[m] because we use an invalid pointer as a + // "locked" sentinel value. M's on this list remain visible to the GC + // because their mp.curg is on allgs. + extraM atomic.Uintptr + // Number of M's in the extraM list. + extraMLength atomic.Uint32 + // Number of waiters in lockextra. + extraMWaiters atomic.Uint32 + + // Number of extra M's in use by threads. + extraMInUse atomic.Uint32 +) + +// lockextra locks the extra list and returns the list head. +// The caller must unlock the list by storing a new list head +// to extram. If nilokay is true, then lockextra will +// return a nil list head if that's what it finds. If nilokay is false, +// lockextra will keep waiting until the list head is no longer nil. +// +//go:nosplit +func lockextra(nilokay bool) *m { + const locked = 1 + + incr := false + for { + old := extraM.Load() + if old == locked { + osyield_no_g() + continue + } + if old == 0 && !nilokay { + if !incr { + // Add 1 to the number of threads + // waiting for an M. + // This is cleared by newextram. + extraMWaiters.Add(1) + incr = true + } + usleep_no_g(1) + continue + } + if extraM.CompareAndSwap(old, locked) { + return (*m)(unsafe.Pointer(old)) + } + osyield_no_g() + continue + } +} + +//go:nosplit +func unlockextra(mp *m, delta int32) { + extraMLength.Add(delta) + extraM.Store(uintptr(unsafe.Pointer(mp))) +} + +// Return an M from the extra M list. Returns last == true if the list becomes +// empty because of this call. +// +// Spins waiting for an extra M, so caller must ensure that the list always +// contains or will soon contain at least one M. +// +//go:nosplit +func getExtraM() (mp *m, last bool) { + mp = lockextra(false) + extraMInUse.Add(1) + unlockextra(mp.schedlink.ptr(), -1) + return mp, mp.schedlink.ptr() == nil +} + +// Returns an extra M back to the list. mp must be from getExtraM. Newly +// allocated M's should use addExtraM. +// +//go:nosplit +func putExtraM(mp *m) { + extraMInUse.Add(-1) + addExtraM(mp) +} + +// Adds a newly allocated M to the extra M list. +// +//go:nosplit +func addExtraM(mp *m) { + mnext := lockextra(true) + mp.schedlink.set(mnext) + unlockextra(mp, 1) +} + +var ( + // allocmLock is locked for read when creating new Ms in allocm and their + // addition to allm. Thus acquiring this lock for write blocks the + // creation of new Ms. + allocmLock rwmutex + + // execLock serializes exec and clone to avoid bugs or unspecified + // behaviour around exec'ing while creating/destroying threads. See + // issue #19546. + execLock rwmutex +) + +// These errors are reported (via writeErrStr) by some OS-specific +// versions of newosproc and newosproc0. +const ( + failthreadcreate = "runtime: failed to create new OS thread\n" + failallocatestack = "runtime: failed to allocate stack for the new OS thread\n" +) + +// newmHandoff contains a list of m structures that need new OS threads. +// This is used by newm in situations where newm itself can't safely +// start an OS thread. +var newmHandoff struct { + lock mutex + + // newm points to a list of M structures that need new OS + // threads. The list is linked through m.schedlink. + newm muintptr + + // waiting indicates that wake needs to be notified when an m + // is put on the list. + waiting bool + wake note + + // haveTemplateThread indicates that the templateThread has + // been started. This is not protected by lock. Use cas to set + // to 1. + haveTemplateThread uint32 +} + +// Create a new m. It will start off with a call to fn, or else the scheduler. +// fn needs to be static and not a heap allocated closure. +// May run with m.p==nil, so write barriers are not allowed. +// +// id is optional pre-allocated m ID. Omit by passing -1. +// +//go:nowritebarrierrec +func newm(fn func(), pp *p, id int64) { + // allocm adds a new M to allm, but they do not start until created by + // the OS in newm1 or the template thread. + // + // doAllThreadsSyscall requires that every M in allm will eventually + // start and be signal-able, even with a STW. + // + // Disable preemption here until we start the thread to ensure that + // newm is not preempted between allocm and starting the new thread, + // ensuring that anything added to allm is guaranteed to eventually + // start. + acquirem() + + mp := allocm(pp, fn, id) + mp.nextp.set(pp) + mp.sigmask = initSigmask + if gp := getg(); gp != nil && gp.m != nil && (gp.m.lockedExt != 0 || gp.m.incgo) && GOOS != "plan9" { + // We're on a locked M or a thread that may have been + // started by C. The kernel state of this thread may + // be strange (the user may have locked it for that + // purpose). We don't want to clone that into another + // thread. Instead, ask a known-good thread to create + // the thread for us. + // + // This is disabled on Plan 9. See golang.org/issue/22227. + // + // TODO: This may be unnecessary on Windows, which + // doesn't model thread creation off fork. + lock(&newmHandoff.lock) + if newmHandoff.haveTemplateThread == 0 { + throw("on a locked thread with no template thread") + } + mp.schedlink = newmHandoff.newm + newmHandoff.newm.set(mp) + if newmHandoff.waiting { + newmHandoff.waiting = false + notewakeup(&newmHandoff.wake) + } + unlock(&newmHandoff.lock) + // The M has not started yet, but the template thread does not + // participate in STW, so it will always process queued Ms and + // it is safe to releasem. + releasem(getg().m) + return + } + newm1(mp) + releasem(getg().m) +} + +func newm1(mp *m) { + if iscgo { + var ts cgothreadstart + if _cgo_thread_start == nil { + throw("_cgo_thread_start missing") + } + ts.g.set(mp.g0) + ts.tls = (*uint64)(unsafe.Pointer(&mp.tls[0])) + ts.fn = unsafe.Pointer(abi.FuncPCABI0(mstart)) + if msanenabled { + msanwrite(unsafe.Pointer(&ts), unsafe.Sizeof(ts)) + } + if asanenabled { + asanwrite(unsafe.Pointer(&ts), unsafe.Sizeof(ts)) + } + execLock.rlock() // Prevent process clone. + asmcgocall(_cgo_thread_start, unsafe.Pointer(&ts)) + execLock.runlock() + return + } + execLock.rlock() // Prevent process clone. + newosproc(mp) + execLock.runlock() +} + +// startTemplateThread starts the template thread if it is not already +// running. +// +// The calling thread must itself be in a known-good state. +func startTemplateThread() { + if GOARCH == "wasm" { // no threads on wasm yet + return + } + + // Disable preemption to guarantee that the template thread will be + // created before a park once haveTemplateThread is set. + mp := acquirem() + if !atomic.Cas(&newmHandoff.haveTemplateThread, 0, 1) { + releasem(mp) + return + } + newm(templateThread, nil, -1) + releasem(mp) +} + +// templateThread is a thread in a known-good state that exists solely +// to start new threads in known-good states when the calling thread +// may not be in a good state. +// +// Many programs never need this, so templateThread is started lazily +// when we first enter a state that might lead to running on a thread +// in an unknown state. +// +// templateThread runs on an M without a P, so it must not have write +// barriers. +// +//go:nowritebarrierrec +func templateThread() { + lock(&sched.lock) + sched.nmsys++ + checkdead() + unlock(&sched.lock) + + for { + lock(&newmHandoff.lock) + for newmHandoff.newm != 0 { + newm := newmHandoff.newm.ptr() + newmHandoff.newm = 0 + unlock(&newmHandoff.lock) + for newm != nil { + next := newm.schedlink.ptr() + newm.schedlink = 0 + newm1(newm) + newm = next + } + lock(&newmHandoff.lock) + } + newmHandoff.waiting = true + noteclear(&newmHandoff.wake) + unlock(&newmHandoff.lock) + notesleep(&newmHandoff.wake) + } +} + +// Stops execution of the current m until new work is available. +// Returns with acquired P. +func stopm() { + gp := getg() + + if gp.m.locks != 0 { + throw("stopm holding locks") + } + if gp.m.p != 0 { + throw("stopm holding p") + } + if gp.m.spinning { + throw("stopm spinning") + } + + lock(&sched.lock) + mput(gp.m) + unlock(&sched.lock) + mPark() + acquirep(gp.m.nextp.ptr()) + gp.m.nextp = 0 +} + +func mspinning() { + // startm's caller incremented nmspinning. Set the new M's spinning. + getg().m.spinning = true +} + +// Schedules some M to run the p (creates an M if necessary). +// If p==nil, tries to get an idle P, if no idle P's does nothing. +// May run with m.p==nil, so write barriers are not allowed. +// If spinning is set, the caller has incremented nmspinning and must provide a +// P. startm will set m.spinning in the newly started M. +// +// Callers passing a non-nil P must call from a non-preemptible context. See +// comment on acquirem below. +// +// Argument lockheld indicates whether the caller already acquired the +// scheduler lock. Callers holding the lock when making the call must pass +// true. The lock might be temporarily dropped, but will be reacquired before +// returning. +// +// Must not have write barriers because this may be called without a P. +// +//go:nowritebarrierrec +func startm(pp *p, spinning, lockheld bool) { + // Disable preemption. + // + // Every owned P must have an owner that will eventually stop it in the + // event of a GC stop request. startm takes transient ownership of a P + // (either from argument or pidleget below) and transfers ownership to + // a started M, which will be responsible for performing the stop. + // + // Preemption must be disabled during this transient ownership, + // otherwise the P this is running on may enter GC stop while still + // holding the transient P, leaving that P in limbo and deadlocking the + // STW. + // + // Callers passing a non-nil P must already be in non-preemptible + // context, otherwise such preemption could occur on function entry to + // startm. Callers passing a nil P may be preemptible, so we must + // disable preemption before acquiring a P from pidleget below. + mp := acquirem() + if !lockheld { + lock(&sched.lock) + } + if pp == nil { + if spinning { + // TODO(prattmic): All remaining calls to this function + // with _p_ == nil could be cleaned up to find a P + // before calling startm. + throw("startm: P required for spinning=true") + } + pp, _ = pidleget(0) + if pp == nil { + if !lockheld { + unlock(&sched.lock) + } + releasem(mp) + return + } + } + nmp := mget() + if nmp == nil { + // No M is available, we must drop sched.lock and call newm. + // However, we already own a P to assign to the M. + // + // Once sched.lock is released, another G (e.g., in a syscall), + // could find no idle P while checkdead finds a runnable G but + // no running M's because this new M hasn't started yet, thus + // throwing in an apparent deadlock. + // This apparent deadlock is possible when startm is called + // from sysmon, which doesn't count as a running M. + // + // Avoid this situation by pre-allocating the ID for the new M, + // thus marking it as 'running' before we drop sched.lock. This + // new M will eventually run the scheduler to execute any + // queued G's. + id := mReserveID() + unlock(&sched.lock) + + var fn func() + if spinning { + // The caller incremented nmspinning, so set m.spinning in the new M. + fn = mspinning + } + newm(fn, pp, id) + + if lockheld { + lock(&sched.lock) + } + // Ownership transfer of pp committed by start in newm. + // Preemption is now safe. + releasem(mp) + return + } + if !lockheld { + unlock(&sched.lock) + } + if nmp.spinning { + throw("startm: m is spinning") + } + if nmp.nextp != 0 { + throw("startm: m has p") + } + if spinning && !runqempty(pp) { + throw("startm: p has runnable gs") + } + // The caller incremented nmspinning, so set m.spinning in the new M. + nmp.spinning = spinning + nmp.nextp.set(pp) + notewakeup(&nmp.park) + // Ownership transfer of pp committed by wakeup. Preemption is now + // safe. + releasem(mp) +} + +// Hands off P from syscall or locked M. +// Always runs without a P, so write barriers are not allowed. +// +//go:nowritebarrierrec +func handoffp(pp *p) { + // handoffp must start an M in any situation where + // findrunnable would return a G to run on pp. + + // if it has local work, start it straight away + if !runqempty(pp) || sched.runqsize != 0 { + startm(pp, false, false) + return + } + // if there's trace work to do, start it straight away + if (traceEnabled() || traceShuttingDown()) && traceReaderAvailable() != nil { + startm(pp, false, false) + return + } + // if it has GC work, start it straight away + if gcBlackenEnabled != 0 && gcMarkWorkAvailable(pp) { + startm(pp, false, false) + return + } + // no local work, check that there are no spinning/idle M's, + // otherwise our help is not required + if sched.nmspinning.Load()+sched.npidle.Load() == 0 && sched.nmspinning.CompareAndSwap(0, 1) { // TODO: fast atomic + sched.needspinning.Store(0) + startm(pp, true, false) + return + } + lock(&sched.lock) + if sched.gcwaiting.Load() { + pp.status = _Pgcstop + sched.stopwait-- + if sched.stopwait == 0 { + notewakeup(&sched.stopnote) + } + unlock(&sched.lock) + return + } + if pp.runSafePointFn != 0 && atomic.Cas(&pp.runSafePointFn, 1, 0) { + sched.safePointFn(pp) + sched.safePointWait-- + if sched.safePointWait == 0 { + notewakeup(&sched.safePointNote) + } + } + if sched.runqsize != 0 { + unlock(&sched.lock) + startm(pp, false, false) + return + } + // If this is the last running P and nobody is polling network, + // need to wakeup another M to poll network. + if sched.npidle.Load() == gomaxprocs-1 && sched.lastpoll.Load() != 0 { + unlock(&sched.lock) + startm(pp, false, false) + return + } + + // The scheduler lock cannot be held when calling wakeNetPoller below + // because wakeNetPoller may call wakep which may call startm. + when := nobarrierWakeTime(pp) + pidleput(pp, 0) + unlock(&sched.lock) + + if when != 0 { + wakeNetPoller(when) + } +} + +// Tries to add one more P to execute G's. +// Called when a G is made runnable (newproc, ready). +// Must be called with a P. +func wakep() { + // Be conservative about spinning threads, only start one if none exist + // already. + if sched.nmspinning.Load() != 0 || !sched.nmspinning.CompareAndSwap(0, 1) { + return + } + + // Disable preemption until ownership of pp transfers to the next M in + // startm. Otherwise preemption here would leave pp stuck waiting to + // enter _Pgcstop. + // + // See preemption comment on acquirem in startm for more details. + mp := acquirem() + + var pp *p + lock(&sched.lock) + pp, _ = pidlegetSpinning(0) + if pp == nil { + if sched.nmspinning.Add(-1) < 0 { + throw("wakep: negative nmspinning") + } + unlock(&sched.lock) + releasem(mp) + return + } + // Since we always have a P, the race in the "No M is available" + // comment in startm doesn't apply during the small window between the + // unlock here and lock in startm. A checkdead in between will always + // see at least one running M (ours). + unlock(&sched.lock) + + startm(pp, true, false) + + releasem(mp) +} + +// Stops execution of the current m that is locked to a g until the g is runnable again. +// Returns with acquired P. +func stoplockedm() { + gp := getg() + + if gp.m.lockedg == 0 || gp.m.lockedg.ptr().lockedm.ptr() != gp.m { + throw("stoplockedm: inconsistent locking") + } + if gp.m.p != 0 { + // Schedule another M to run this p. + pp := releasep() + handoffp(pp) + } + incidlelocked(1) + // Wait until another thread schedules lockedg again. + mPark() + status := readgstatus(gp.m.lockedg.ptr()) + if status&^_Gscan != _Grunnable { + print("runtime:stoplockedm: lockedg (atomicstatus=", status, ") is not Grunnable or Gscanrunnable\n") + dumpgstatus(gp.m.lockedg.ptr()) + throw("stoplockedm: not runnable") + } + acquirep(gp.m.nextp.ptr()) + gp.m.nextp = 0 +} + +// Schedules the locked m to run the locked gp. +// May run during STW, so write barriers are not allowed. +// +//go:nowritebarrierrec +func startlockedm(gp *g) { + mp := gp.lockedm.ptr() + if mp == getg().m { + throw("startlockedm: locked to me") + } + if mp.nextp != 0 { + throw("startlockedm: m has p") + } + // directly handoff current P to the locked m + incidlelocked(-1) + pp := releasep() + mp.nextp.set(pp) + notewakeup(&mp.park) + stopm() +} + +// Stops the current m for stopTheWorld. +// Returns when the world is restarted. +func gcstopm() { + gp := getg() + + if !sched.gcwaiting.Load() { + throw("gcstopm: not waiting for gc") + } + if gp.m.spinning { + gp.m.spinning = false + // OK to just drop nmspinning here, + // startTheWorld will unpark threads as necessary. + if sched.nmspinning.Add(-1) < 0 { + throw("gcstopm: negative nmspinning") + } + } + pp := releasep() + lock(&sched.lock) + pp.status = _Pgcstop + sched.stopwait-- + if sched.stopwait == 0 { + notewakeup(&sched.stopnote) + } + unlock(&sched.lock) + stopm() +} + +// Schedules gp to run on the current M. +// If inheritTime is true, gp inherits the remaining time in the +// current time slice. Otherwise, it starts a new time slice. +// Never returns. +// +// Write barriers are allowed because this is called immediately after +// acquiring a P in several places. +// +//go:yeswritebarrierrec +func execute(gp *g, inheritTime bool) { + mp := getg().m + + if goroutineProfile.active { + // Make sure that gp has had its stack written out to the goroutine + // profile, exactly as it was when the goroutine profiler first stopped + // the world. + tryRecordGoroutineProfile(gp, osyield) + } + + // Assign gp.m before entering _Grunning so running Gs have an + // M. + mp.curg = gp + gp.m = mp + casgstatus(gp, _Grunnable, _Grunning) + gp.waitsince = 0 + gp.preempt = false + gp.stackguard0 = gp.stack.lo + stackGuard + if !inheritTime { + mp.p.ptr().schedtick++ + } + + // Check whether the profiler needs to be turned on or off. + hz := sched.profilehz + if mp.profilehz != hz { + setThreadCPUProfiler(hz) + } + + if traceEnabled() { + // GoSysExit has to happen when we have a P, but before GoStart. + // So we emit it here. + if gp.syscallsp != 0 { + traceGoSysExit() + } + traceGoStart() + } + + gogo(&gp.sched) +} + +// Finds a runnable goroutine to execute. +// Tries to steal from other P's, get g from local or global queue, poll network. +// tryWakeP indicates that the returned goroutine is not normal (GC worker, trace +// reader) so the caller should try to wake a P. +func findRunnable() (gp *g, inheritTime, tryWakeP bool) { + mp := getg().m + + // The conditions here and in handoffp must agree: if + // findrunnable would return a G to run, handoffp must start + // an M. + +top: + pp := mp.p.ptr() + if sched.gcwaiting.Load() { + gcstopm() + goto top + } + if pp.runSafePointFn != 0 { + runSafePointFn() + } + + // now and pollUntil are saved for work stealing later, + // which may steal timers. It's important that between now + // and then, nothing blocks, so these numbers remain mostly + // relevant. + now, pollUntil, _ := checkTimers(pp, 0) + + // Try to schedule the trace reader. + if traceEnabled() || traceShuttingDown() { + gp := traceReader() + if gp != nil { + casgstatus(gp, _Gwaiting, _Grunnable) + traceGoUnpark(gp, 0) + return gp, false, true + } + } + + // Try to schedule a GC worker. + if gcBlackenEnabled != 0 { + gp, tnow := gcController.findRunnableGCWorker(pp, now) + if gp != nil { + return gp, false, true + } + now = tnow + } + + // Check the global runnable queue once in a while to ensure fairness. + // Otherwise two goroutines can completely occupy the local runqueue + // by constantly respawning each other. + if pp.schedtick%61 == 0 && sched.runqsize > 0 { + lock(&sched.lock) + gp := globrunqget(pp, 1) + unlock(&sched.lock) + if gp != nil { + return gp, false, false + } + } + + // Wake up the finalizer G. + if fingStatus.Load()&(fingWait|fingWake) == fingWait|fingWake { + if gp := wakefing(); gp != nil { + ready(gp, 0, true) + } + } + if *cgo_yield != nil { + asmcgocall(*cgo_yield, nil) + } + + // local runq + if gp, inheritTime := runqget(pp); gp != nil { + return gp, inheritTime, false + } + + // global runq + if sched.runqsize != 0 { + lock(&sched.lock) + gp := globrunqget(pp, 0) + unlock(&sched.lock) + if gp != nil { + return gp, false, false + } + } + + // Poll network. + // This netpoll is only an optimization before we resort to stealing. + // We can safely skip it if there are no waiters or a thread is blocked + // in netpoll already. If there is any kind of logical race with that + // blocked thread (e.g. it has already returned from netpoll, but does + // not set lastpoll yet), this thread will do blocking netpoll below + // anyway. + if netpollinited() && netpollWaiters.Load() > 0 && sched.lastpoll.Load() != 0 { + if list := netpoll(0); !list.empty() { // non-blocking + gp := list.pop() + injectglist(&list) + casgstatus(gp, _Gwaiting, _Grunnable) + if traceEnabled() { + traceGoUnpark(gp, 0) + } + return gp, false, false + } + } + + // Spinning Ms: steal work from other Ps. + // + // Limit the number of spinning Ms to half the number of busy Ps. + // This is necessary to prevent excessive CPU consumption when + // GOMAXPROCS>>1 but the program parallelism is low. + if mp.spinning || 2*sched.nmspinning.Load() < gomaxprocs-sched.npidle.Load() { + if !mp.spinning { + mp.becomeSpinning() + } + + gp, inheritTime, tnow, w, newWork := stealWork(now) + if gp != nil { + // Successfully stole. + return gp, inheritTime, false + } + if newWork { + // There may be new timer or GC work; restart to + // discover. + goto top + } + + now = tnow + if w != 0 && (pollUntil == 0 || w < pollUntil) { + // Earlier timer to wait for. + pollUntil = w + } + } + + // We have nothing to do. + // + // If we're in the GC mark phase, can safely scan and blacken objects, + // and have work to do, run idle-time marking rather than give up the P. + if gcBlackenEnabled != 0 && gcMarkWorkAvailable(pp) && gcController.addIdleMarkWorker() { + node := (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop()) + if node != nil { + pp.gcMarkWorkerMode = gcMarkWorkerIdleMode + gp := node.gp.ptr() + casgstatus(gp, _Gwaiting, _Grunnable) + if traceEnabled() { + traceGoUnpark(gp, 0) + } + return gp, false, false + } + gcController.removeIdleMarkWorker() + } + + // wasm only: + // If a callback returned and no other goroutine is awake, + // then wake event handler goroutine which pauses execution + // until a callback was triggered. + gp, otherReady := beforeIdle(now, pollUntil) + if gp != nil { + casgstatus(gp, _Gwaiting, _Grunnable) + if traceEnabled() { + traceGoUnpark(gp, 0) + } + return gp, false, false + } + if otherReady { + goto top + } + + // Before we drop our P, make a snapshot of the allp slice, + // which can change underfoot once we no longer block + // safe-points. We don't need to snapshot the contents because + // everything up to cap(allp) is immutable. + allpSnapshot := allp + // Also snapshot masks. Value changes are OK, but we can't allow + // len to change out from under us. + idlepMaskSnapshot := idlepMask + timerpMaskSnapshot := timerpMask + + // return P and block + lock(&sched.lock) + if sched.gcwaiting.Load() || pp.runSafePointFn != 0 { + unlock(&sched.lock) + goto top + } + if sched.runqsize != 0 { + gp := globrunqget(pp, 0) + unlock(&sched.lock) + return gp, false, false + } + if !mp.spinning && sched.needspinning.Load() == 1 { + // See "Delicate dance" comment below. + mp.becomeSpinning() + unlock(&sched.lock) + goto top + } + if releasep() != pp { + throw("findrunnable: wrong p") + } + now = pidleput(pp, now) + unlock(&sched.lock) + + // Delicate dance: thread transitions from spinning to non-spinning + // state, potentially concurrently with submission of new work. We must + // drop nmspinning first and then check all sources again (with + // #StoreLoad memory barrier in between). If we do it the other way + // around, another thread can submit work after we've checked all + // sources but before we drop nmspinning; as a result nobody will + // unpark a thread to run the work. + // + // This applies to the following sources of work: + // + // * Goroutines added to a per-P run queue. + // * New/modified-earlier timers on a per-P timer heap. + // * Idle-priority GC work (barring golang.org/issue/19112). + // + // If we discover new work below, we need to restore m.spinning as a + // signal for resetspinning to unpark a new worker thread (because + // there can be more than one starving goroutine). + // + // However, if after discovering new work we also observe no idle Ps + // (either here or in resetspinning), we have a problem. We may be + // racing with a non-spinning M in the block above, having found no + // work and preparing to release its P and park. Allowing that P to go + // idle will result in loss of work conservation (idle P while there is + // runnable work). This could result in complete deadlock in the + // unlikely event that we discover new work (from netpoll) right as we + // are racing with _all_ other Ps going idle. + // + // We use sched.needspinning to synchronize with non-spinning Ms going + // idle. If needspinning is set when they are about to drop their P, + // they abort the drop and instead become a new spinning M on our + // behalf. If we are not racing and the system is truly fully loaded + // then no spinning threads are required, and the next thread to + // naturally become spinning will clear the flag. + // + // Also see "Worker thread parking/unparking" comment at the top of the + // file. + wasSpinning := mp.spinning + if mp.spinning { + mp.spinning = false + if sched.nmspinning.Add(-1) < 0 { + throw("findrunnable: negative nmspinning") + } + + // Note the for correctness, only the last M transitioning from + // spinning to non-spinning must perform these rechecks to + // ensure no missed work. However, the runtime has some cases + // of transient increments of nmspinning that are decremented + // without going through this path, so we must be conservative + // and perform the check on all spinning Ms. + // + // See https://go.dev/issue/43997. + + // Check all runqueues once again. + pp := checkRunqsNoP(allpSnapshot, idlepMaskSnapshot) + if pp != nil { + acquirep(pp) + mp.becomeSpinning() + goto top + } + + // Check for idle-priority GC work again. + pp, gp := checkIdleGCNoP() + if pp != nil { + acquirep(pp) + mp.becomeSpinning() + + // Run the idle worker. + pp.gcMarkWorkerMode = gcMarkWorkerIdleMode + casgstatus(gp, _Gwaiting, _Grunnable) + if traceEnabled() { + traceGoUnpark(gp, 0) + } + return gp, false, false + } + + // Finally, check for timer creation or expiry concurrently with + // transitioning from spinning to non-spinning. + // + // Note that we cannot use checkTimers here because it calls + // adjusttimers which may need to allocate memory, and that isn't + // allowed when we don't have an active P. + pollUntil = checkTimersNoP(allpSnapshot, timerpMaskSnapshot, pollUntil) + } + + // Poll network until next timer. + if netpollinited() && (netpollWaiters.Load() > 0 || pollUntil != 0) && sched.lastpoll.Swap(0) != 0 { + sched.pollUntil.Store(pollUntil) + if mp.p != 0 { + throw("findrunnable: netpoll with p") + } + if mp.spinning { + throw("findrunnable: netpoll with spinning") + } + delay := int64(-1) + if pollUntil != 0 { + if now == 0 { + now = nanotime() + } + delay = pollUntil - now + if delay < 0 { + delay = 0 + } + } + if faketime != 0 { + // When using fake time, just poll. + delay = 0 + } + list := netpoll(delay) // block until new work is available + // Refresh now again, after potentially blocking. + now = nanotime() + sched.pollUntil.Store(0) + sched.lastpoll.Store(now) + if faketime != 0 && list.empty() { + // Using fake time and nothing is ready; stop M. + // When all M's stop, checkdead will call timejump. + stopm() + goto top + } + lock(&sched.lock) + pp, _ := pidleget(now) + unlock(&sched.lock) + if pp == nil { + injectglist(&list) + } else { + acquirep(pp) + if !list.empty() { + gp := list.pop() + injectglist(&list) + casgstatus(gp, _Gwaiting, _Grunnable) + if traceEnabled() { + traceGoUnpark(gp, 0) + } + return gp, false, false + } + if wasSpinning { + mp.becomeSpinning() + } + goto top + } + } else if pollUntil != 0 && netpollinited() { + pollerPollUntil := sched.pollUntil.Load() + if pollerPollUntil == 0 || pollerPollUntil > pollUntil { + netpollBreak() + } + } + stopm() + goto top +} + +// pollWork reports whether there is non-background work this P could +// be doing. This is a fairly lightweight check to be used for +// background work loops, like idle GC. It checks a subset of the +// conditions checked by the actual scheduler. +func pollWork() bool { + if sched.runqsize != 0 { + return true + } + p := getg().m.p.ptr() + if !runqempty(p) { + return true + } + if netpollinited() && netpollWaiters.Load() > 0 && sched.lastpoll.Load() != 0 { + if list := netpoll(0); !list.empty() { + injectglist(&list) + return true + } + } + return false +} + +// stealWork attempts to steal a runnable goroutine or timer from any P. +// +// If newWork is true, new work may have been readied. +// +// If now is not 0 it is the current time. stealWork returns the passed time or +// the current time if now was passed as 0. +func stealWork(now int64) (gp *g, inheritTime bool, rnow, pollUntil int64, newWork bool) { + pp := getg().m.p.ptr() + + ranTimer := false + + const stealTries = 4 + for i := 0; i < stealTries; i++ { + stealTimersOrRunNextG := i == stealTries-1 + + for enum := stealOrder.start(fastrand()); !enum.done(); enum.next() { + if sched.gcwaiting.Load() { + // GC work may be available. + return nil, false, now, pollUntil, true + } + p2 := allp[enum.position()] + if pp == p2 { + continue + } + + // Steal timers from p2. This call to checkTimers is the only place + // where we might hold a lock on a different P's timers. We do this + // once on the last pass before checking runnext because stealing + // from the other P's runnext should be the last resort, so if there + // are timers to steal do that first. + // + // We only check timers on one of the stealing iterations because + // the time stored in now doesn't change in this loop and checking + // the timers for each P more than once with the same value of now + // is probably a waste of time. + // + // timerpMask tells us whether the P may have timers at all. If it + // can't, no need to check at all. + if stealTimersOrRunNextG && timerpMask.read(enum.position()) { + tnow, w, ran := checkTimers(p2, now) + now = tnow + if w != 0 && (pollUntil == 0 || w < pollUntil) { + pollUntil = w + } + if ran { + // Running the timers may have + // made an arbitrary number of G's + // ready and added them to this P's + // local run queue. That invalidates + // the assumption of runqsteal + // that it always has room to add + // stolen G's. So check now if there + // is a local G to run. + if gp, inheritTime := runqget(pp); gp != nil { + return gp, inheritTime, now, pollUntil, ranTimer + } + ranTimer = true + } + } + + // Don't bother to attempt to steal if p2 is idle. + if !idlepMask.read(enum.position()) { + if gp := runqsteal(pp, p2, stealTimersOrRunNextG); gp != nil { + return gp, false, now, pollUntil, ranTimer + } + } + } + } + + // No goroutines found to steal. Regardless, running a timer may have + // made some goroutine ready that we missed. Indicate the next timer to + // wait for. + return nil, false, now, pollUntil, ranTimer +} + +// Check all Ps for a runnable G to steal. +// +// On entry we have no P. If a G is available to steal and a P is available, +// the P is returned which the caller should acquire and attempt to steal the +// work to. +func checkRunqsNoP(allpSnapshot []*p, idlepMaskSnapshot pMask) *p { + for id, p2 := range allpSnapshot { + if !idlepMaskSnapshot.read(uint32(id)) && !runqempty(p2) { + lock(&sched.lock) + pp, _ := pidlegetSpinning(0) + if pp == nil { + // Can't get a P, don't bother checking remaining Ps. + unlock(&sched.lock) + return nil + } + unlock(&sched.lock) + return pp + } + } + + // No work available. + return nil +} + +// Check all Ps for a timer expiring sooner than pollUntil. +// +// Returns updated pollUntil value. +func checkTimersNoP(allpSnapshot []*p, timerpMaskSnapshot pMask, pollUntil int64) int64 { + for id, p2 := range allpSnapshot { + if timerpMaskSnapshot.read(uint32(id)) { + w := nobarrierWakeTime(p2) + if w != 0 && (pollUntil == 0 || w < pollUntil) { + pollUntil = w + } + } + } + + return pollUntil +} + +// Check for idle-priority GC, without a P on entry. +// +// If some GC work, a P, and a worker G are all available, the P and G will be +// returned. The returned P has not been wired yet. +func checkIdleGCNoP() (*p, *g) { + // N.B. Since we have no P, gcBlackenEnabled may change at any time; we + // must check again after acquiring a P. As an optimization, we also check + // if an idle mark worker is needed at all. This is OK here, because if we + // observe that one isn't needed, at least one is currently running. Even if + // it stops running, its own journey into the scheduler should schedule it + // again, if need be (at which point, this check will pass, if relevant). + if atomic.Load(&gcBlackenEnabled) == 0 || !gcController.needIdleMarkWorker() { + return nil, nil + } + if !gcMarkWorkAvailable(nil) { + return nil, nil + } + + // Work is available; we can start an idle GC worker only if there is + // an available P and available worker G. + // + // We can attempt to acquire these in either order, though both have + // synchronization concerns (see below). Workers are almost always + // available (see comment in findRunnableGCWorker for the one case + // there may be none). Since we're slightly less likely to find a P, + // check for that first. + // + // Synchronization: note that we must hold sched.lock until we are + // committed to keeping it. Otherwise we cannot put the unnecessary P + // back in sched.pidle without performing the full set of idle + // transition checks. + // + // If we were to check gcBgMarkWorkerPool first, we must somehow handle + // the assumption in gcControllerState.findRunnableGCWorker that an + // empty gcBgMarkWorkerPool is only possible if gcMarkDone is running. + lock(&sched.lock) + pp, now := pidlegetSpinning(0) + if pp == nil { + unlock(&sched.lock) + return nil, nil + } + + // Now that we own a P, gcBlackenEnabled can't change (as it requires STW). + if gcBlackenEnabled == 0 || !gcController.addIdleMarkWorker() { + pidleput(pp, now) + unlock(&sched.lock) + return nil, nil + } + + node := (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop()) + if node == nil { + pidleput(pp, now) + unlock(&sched.lock) + gcController.removeIdleMarkWorker() + return nil, nil + } + + unlock(&sched.lock) + + return pp, node.gp.ptr() +} + +// wakeNetPoller wakes up the thread sleeping in the network poller if it isn't +// going to wake up before the when argument; or it wakes an idle P to service +// timers and the network poller if there isn't one already. +func wakeNetPoller(when int64) { + if sched.lastpoll.Load() == 0 { + // In findrunnable we ensure that when polling the pollUntil + // field is either zero or the time to which the current + // poll is expected to run. This can have a spurious wakeup + // but should never miss a wakeup. + pollerPollUntil := sched.pollUntil.Load() + if pollerPollUntil == 0 || pollerPollUntil > when { + netpollBreak() + } + } else { + // There are no threads in the network poller, try to get + // one there so it can handle new timers. + if GOOS != "plan9" { // Temporary workaround - see issue #42303. + wakep() + } + } +} + +func resetspinning() { + gp := getg() + if !gp.m.spinning { + throw("resetspinning: not a spinning m") + } + gp.m.spinning = false + nmspinning := sched.nmspinning.Add(-1) + if nmspinning < 0 { + throw("findrunnable: negative nmspinning") + } + // M wakeup policy is deliberately somewhat conservative, so check if we + // need to wakeup another P here. See "Worker thread parking/unparking" + // comment at the top of the file for details. + wakep() +} + +// injectglist adds each runnable G on the list to some run queue, +// and clears glist. If there is no current P, they are added to the +// global queue, and up to npidle M's are started to run them. +// Otherwise, for each idle P, this adds a G to the global queue +// and starts an M. Any remaining G's are added to the current P's +// local run queue. +// This may temporarily acquire sched.lock. +// Can run concurrently with GC. +func injectglist(glist *gList) { + if glist.empty() { + return + } + if traceEnabled() { + for gp := glist.head.ptr(); gp != nil; gp = gp.schedlink.ptr() { + traceGoUnpark(gp, 0) + } + } + + // Mark all the goroutines as runnable before we put them + // on the run queues. + head := glist.head.ptr() + var tail *g + qsize := 0 + for gp := head; gp != nil; gp = gp.schedlink.ptr() { + tail = gp + qsize++ + casgstatus(gp, _Gwaiting, _Grunnable) + } + + // Turn the gList into a gQueue. + var q gQueue + q.head.set(head) + q.tail.set(tail) + *glist = gList{} + + startIdle := func(n int) { + for i := 0; i < n; i++ { + mp := acquirem() // See comment in startm. + lock(&sched.lock) + + pp, _ := pidlegetSpinning(0) + if pp == nil { + unlock(&sched.lock) + releasem(mp) + break + } + + startm(pp, false, true) + unlock(&sched.lock) + releasem(mp) + } + } + + pp := getg().m.p.ptr() + if pp == nil { + lock(&sched.lock) + globrunqputbatch(&q, int32(qsize)) + unlock(&sched.lock) + startIdle(qsize) + return + } + + npidle := int(sched.npidle.Load()) + var globq gQueue + var n int + for n = 0; n < npidle && !q.empty(); n++ { + g := q.pop() + globq.pushBack(g) + } + if n > 0 { + lock(&sched.lock) + globrunqputbatch(&globq, int32(n)) + unlock(&sched.lock) + startIdle(n) + qsize -= n + } + + if !q.empty() { + runqputbatch(pp, &q, qsize) + } +} + +// One round of scheduler: find a runnable goroutine and execute it. +// Never returns. +func schedule() { + mp := getg().m + + if mp.locks != 0 { + throw("schedule: holding locks") + } + + if mp.lockedg != 0 { + stoplockedm() + execute(mp.lockedg.ptr(), false) // Never returns. + } + + // We should not schedule away from a g that is executing a cgo call, + // since the cgo call is using the m's g0 stack. + if mp.incgo { + throw("schedule: in cgo") + } + +top: + pp := mp.p.ptr() + pp.preempt = false + + // Safety check: if we are spinning, the run queue should be empty. + // Check this before calling checkTimers, as that might call + // goready to put a ready goroutine on the local run queue. + if mp.spinning && (pp.runnext != 0 || pp.runqhead != pp.runqtail) { + throw("schedule: spinning with local work") + } + + gp, inheritTime, tryWakeP := findRunnable() // blocks until work is available + + if debug.dontfreezetheworld > 0 && freezing.Load() { + // See comment in freezetheworld. We don't want to perturb + // scheduler state, so we didn't gcstopm in findRunnable, but + // also don't want to allow new goroutines to run. + // + // Deadlock here rather than in the findRunnable loop so if + // findRunnable is stuck in a loop we don't perturb that + // either. + lock(&deadlock) + lock(&deadlock) + } + + // This thread is going to run a goroutine and is not spinning anymore, + // so if it was marked as spinning we need to reset it now and potentially + // start a new spinning M. + if mp.spinning { + resetspinning() + } + + if sched.disable.user && !schedEnabled(gp) { + // Scheduling of this goroutine is disabled. Put it on + // the list of pending runnable goroutines for when we + // re-enable user scheduling and look again. + lock(&sched.lock) + if schedEnabled(gp) { + // Something re-enabled scheduling while we + // were acquiring the lock. + unlock(&sched.lock) + } else { + sched.disable.runnable.pushBack(gp) + sched.disable.n++ + unlock(&sched.lock) + goto top + } + } + + // If about to schedule a not-normal goroutine (a GCworker or tracereader), + // wake a P if there is one. + if tryWakeP { + wakep() + } + if gp.lockedm != 0 { + // Hands off own p to the locked m, + // then blocks waiting for a new p. + startlockedm(gp) + goto top + } + + execute(gp, inheritTime) +} + +// dropg removes the association between m and the current goroutine m->curg (gp for short). +// Typically a caller sets gp's status away from Grunning and then +// immediately calls dropg to finish the job. The caller is also responsible +// for arranging that gp will be restarted using ready at an +// appropriate time. After calling dropg and arranging for gp to be +// readied later, the caller can do other work but eventually should +// call schedule to restart the scheduling of goroutines on this m. +func dropg() { + gp := getg() + + setMNoWB(&gp.m.curg.m, nil) + setGNoWB(&gp.m.curg, nil) +} + +// checkTimers runs any timers for the P that are ready. +// If now is not 0 it is the current time. +// It returns the passed time or the current time if now was passed as 0. +// and the time when the next timer should run or 0 if there is no next timer, +// and reports whether it ran any timers. +// If the time when the next timer should run is not 0, +// it is always larger than the returned time. +// We pass now in and out to avoid extra calls of nanotime. +// +//go:yeswritebarrierrec +func checkTimers(pp *p, now int64) (rnow, pollUntil int64, ran bool) { + // If it's not yet time for the first timer, or the first adjusted + // timer, then there is nothing to do. + next := pp.timer0When.Load() + nextAdj := pp.timerModifiedEarliest.Load() + if next == 0 || (nextAdj != 0 && nextAdj < next) { + next = nextAdj + } + + if next == 0 { + // No timers to run or adjust. + return now, 0, false + } + + if now == 0 { + now = nanotime() + } + if now < next { + // Next timer is not ready to run, but keep going + // if we would clear deleted timers. + // This corresponds to the condition below where + // we decide whether to call clearDeletedTimers. + if pp != getg().m.p.ptr() || int(pp.deletedTimers.Load()) <= int(pp.numTimers.Load()/4) { + return now, next, false + } + } + + lock(&pp.timersLock) + + if len(pp.timers) > 0 { + adjusttimers(pp, now) + for len(pp.timers) > 0 { + // Note that runtimer may temporarily unlock + // pp.timersLock. + if tw := runtimer(pp, now); tw != 0 { + if tw > 0 { + pollUntil = tw + } + break + } + ran = true + } + } + + // If this is the local P, and there are a lot of deleted timers, + // clear them out. We only do this for the local P to reduce + // lock contention on timersLock. + if pp == getg().m.p.ptr() && int(pp.deletedTimers.Load()) > len(pp.timers)/4 { + clearDeletedTimers(pp) + } + + unlock(&pp.timersLock) + + return now, pollUntil, ran +} + +func parkunlock_c(gp *g, lock unsafe.Pointer) bool { + unlock((*mutex)(lock)) + return true +} + +// park continuation on g0. +func park_m(gp *g) { + mp := getg().m + + if traceEnabled() { + traceGoPark(mp.waitTraceBlockReason, mp.waitTraceSkip) + } + + // N.B. Not using casGToWaiting here because the waitreason is + // set by park_m's caller. + casgstatus(gp, _Grunning, _Gwaiting) + dropg() + + if fn := mp.waitunlockf; fn != nil { + ok := fn(gp, mp.waitlock) + mp.waitunlockf = nil + mp.waitlock = nil + if !ok { + if traceEnabled() { + traceGoUnpark(gp, 2) + } + casgstatus(gp, _Gwaiting, _Grunnable) + execute(gp, true) // Schedule it back, never returns. + } + } + schedule() +} + +func goschedImpl(gp *g) { + status := readgstatus(gp) + if status&^_Gscan != _Grunning { + dumpgstatus(gp) + throw("bad g status") + } + casgstatus(gp, _Grunning, _Grunnable) + dropg() + lock(&sched.lock) + globrunqput(gp) + unlock(&sched.lock) + + schedule() +} + +// Gosched continuation on g0. +func gosched_m(gp *g) { + if traceEnabled() { + traceGoSched() + } + goschedImpl(gp) +} + +// goschedguarded is a forbidden-states-avoided version of gosched_m. +func goschedguarded_m(gp *g) { + + if !canPreemptM(gp.m) { + gogo(&gp.sched) // never return + } + + if traceEnabled() { + traceGoSched() + } + goschedImpl(gp) +} + +func gopreempt_m(gp *g) { + if traceEnabled() { + traceGoPreempt() + } + goschedImpl(gp) +} + +// preemptPark parks gp and puts it in _Gpreempted. +// +//go:systemstack +func preemptPark(gp *g) { + if traceEnabled() { + traceGoPark(traceBlockPreempted, 0) + } + status := readgstatus(gp) + if status&^_Gscan != _Grunning { + dumpgstatus(gp) + throw("bad g status") + } + + if gp.asyncSafePoint { + // Double-check that async preemption does not + // happen in SPWRITE assembly functions. + // isAsyncSafePoint must exclude this case. + f := findfunc(gp.sched.pc) + if !f.valid() { + throw("preempt at unknown pc") + } + if f.flag&abi.FuncFlagSPWrite != 0 { + println("runtime: unexpected SPWRITE function", funcname(f), "in async preempt") + throw("preempt SPWRITE") + } + } + + // Transition from _Grunning to _Gscan|_Gpreempted. We can't + // be in _Grunning when we dropg because then we'd be running + // without an M, but the moment we're in _Gpreempted, + // something could claim this G before we've fully cleaned it + // up. Hence, we set the scan bit to lock down further + // transitions until we can dropg. + casGToPreemptScan(gp, _Grunning, _Gscan|_Gpreempted) + dropg() + casfrom_Gscanstatus(gp, _Gscan|_Gpreempted, _Gpreempted) + schedule() +} + +// goyield is like Gosched, but it: +// - emits a GoPreempt trace event instead of a GoSched trace event +// - puts the current G on the runq of the current P instead of the globrunq +func goyield() { + checkTimeouts() + mcall(goyield_m) +} + +func goyield_m(gp *g) { + if traceEnabled() { + traceGoPreempt() + } + pp := gp.m.p.ptr() + casgstatus(gp, _Grunning, _Grunnable) + dropg() + runqput(pp, gp, false) + schedule() +} + +// Finishes execution of the current goroutine. +func goexit1() { + if raceenabled { + racegoend() + } + if traceEnabled() { + traceGoEnd() + } + mcall(goexit0) +} + +// goexit continuation on g0. +func goexit0(gp *g) { + mp := getg().m + pp := mp.p.ptr() + + casgstatus(gp, _Grunning, _Gdead) + gcController.addScannableStack(pp, -int64(gp.stack.hi-gp.stack.lo)) + if isSystemGoroutine(gp, false) { + sched.ngsys.Add(-1) + } + gp.m = nil + locked := gp.lockedm != 0 + gp.lockedm = 0 + mp.lockedg = 0 + gp.preemptStop = false + gp.paniconfault = false + gp._defer = nil // should be true already but just in case. + gp._panic = nil // non-nil for Goexit during panic. points at stack-allocated data. + gp.writebuf = nil + gp.waitreason = waitReasonZero + gp.param = nil + gp.labels = nil + gp.timer = nil + + if gcBlackenEnabled != 0 && gp.gcAssistBytes > 0 { + // Flush assist credit to the global pool. This gives + // better information to pacing if the application is + // rapidly creating an exiting goroutines. + assistWorkPerByte := gcController.assistWorkPerByte.Load() + scanCredit := int64(assistWorkPerByte * float64(gp.gcAssistBytes)) + gcController.bgScanCredit.Add(scanCredit) + gp.gcAssistBytes = 0 + } + + dropg() + + if GOARCH == "wasm" { // no threads yet on wasm + gfput(pp, gp) + schedule() // never returns + } + + if mp.lockedInt != 0 { + print("invalid m->lockedInt = ", mp.lockedInt, "\n") + throw("internal lockOSThread error") + } + gfput(pp, gp) + if locked { + // The goroutine may have locked this thread because + // it put it in an unusual kernel state. Kill it + // rather than returning it to the thread pool. + + // Return to mstart, which will release the P and exit + // the thread. + if GOOS != "plan9" { // See golang.org/issue/22227. + gogo(&mp.g0.sched) + } else { + // Clear lockedExt on plan9 since we may end up re-using + // this thread. + mp.lockedExt = 0 + } + } + schedule() +} + +// save updates getg().sched to refer to pc and sp so that a following +// gogo will restore pc and sp. +// +// save must not have write barriers because invoking a write barrier +// can clobber getg().sched. +// +//go:nosplit +//go:nowritebarrierrec +func save(pc, sp uintptr) { + gp := getg() + + if gp == gp.m.g0 || gp == gp.m.gsignal { + // m.g0.sched is special and must describe the context + // for exiting the thread. mstart1 writes to it directly. + // m.gsignal.sched should not be used at all. + // This check makes sure save calls do not accidentally + // run in contexts where they'd write to system g's. + throw("save on system g not allowed") + } + + gp.sched.pc = pc + gp.sched.sp = sp + gp.sched.lr = 0 + gp.sched.ret = 0 + // We need to ensure ctxt is zero, but can't have a write + // barrier here. However, it should always already be zero. + // Assert that. + if gp.sched.ctxt != nil { + badctxt() + } +} + +// The goroutine g is about to enter a system call. +// Record that it's not using the cpu anymore. +// This is called only from the go syscall library and cgocall, +// not from the low-level system calls used by the runtime. +// +// Entersyscall cannot split the stack: the save must +// make g->sched refer to the caller's stack segment, because +// entersyscall is going to return immediately after. +// +// Nothing entersyscall calls can split the stack either. +// We cannot safely move the stack during an active call to syscall, +// because we do not know which of the uintptr arguments are +// really pointers (back into the stack). +// In practice, this means that we make the fast path run through +// entersyscall doing no-split things, and the slow path has to use systemstack +// to run bigger things on the system stack. +// +// reentersyscall is the entry point used by cgo callbacks, where explicitly +// saved SP and PC are restored. This is needed when exitsyscall will be called +// from a function further up in the call stack than the parent, as g->syscallsp +// must always point to a valid stack frame. entersyscall below is the normal +// entry point for syscalls, which obtains the SP and PC from the caller. +// +// Syscall tracing: +// At the start of a syscall we emit traceGoSysCall to capture the stack trace. +// If the syscall does not block, that is it, we do not emit any other events. +// If the syscall blocks (that is, P is retaken), retaker emits traceGoSysBlock; +// when syscall returns we emit traceGoSysExit and when the goroutine starts running +// (potentially instantly, if exitsyscallfast returns true) we emit traceGoStart. +// To ensure that traceGoSysExit is emitted strictly after traceGoSysBlock, +// we remember current value of syscalltick in m (gp.m.syscalltick = gp.m.p.ptr().syscalltick), +// whoever emits traceGoSysBlock increments p.syscalltick afterwards; +// and we wait for the increment before emitting traceGoSysExit. +// Note that the increment is done even if tracing is not enabled, +// because tracing can be enabled in the middle of syscall. We don't want the wait to hang. +// +//go:nosplit +func reentersyscall(pc, sp uintptr) { + gp := getg() + + // Disable preemption because during this function g is in Gsyscall status, + // but can have inconsistent g->sched, do not let GC observe it. + gp.m.locks++ + + // Entersyscall must not call any function that might split/grow the stack. + // (See details in comment above.) + // Catch calls that might, by replacing the stack guard with something that + // will trip any stack check and leaving a flag to tell newstack to die. + gp.stackguard0 = stackPreempt + gp.throwsplit = true + + // Leave SP around for GC and traceback. + save(pc, sp) + gp.syscallsp = sp + gp.syscallpc = pc + casgstatus(gp, _Grunning, _Gsyscall) + if staticLockRanking { + // When doing static lock ranking casgstatus can call + // systemstack which clobbers g.sched. + save(pc, sp) + } + if gp.syscallsp < gp.stack.lo || gp.stack.hi < gp.syscallsp { + systemstack(func() { + print("entersyscall inconsistent ", hex(gp.syscallsp), " [", hex(gp.stack.lo), ",", hex(gp.stack.hi), "]\n") + throw("entersyscall") + }) + } + + if traceEnabled() { + systemstack(traceGoSysCall) + // systemstack itself clobbers g.sched.{pc,sp} and we might + // need them later when the G is genuinely blocked in a + // syscall + save(pc, sp) + } + + if sched.sysmonwait.Load() { + systemstack(entersyscall_sysmon) + save(pc, sp) + } + + if gp.m.p.ptr().runSafePointFn != 0 { + // runSafePointFn may stack split if run on this stack + systemstack(runSafePointFn) + save(pc, sp) + } + + gp.m.syscalltick = gp.m.p.ptr().syscalltick + pp := gp.m.p.ptr() + pp.m = 0 + gp.m.oldp.set(pp) + gp.m.p = 0 + atomic.Store(&pp.status, _Psyscall) + if sched.gcwaiting.Load() { + systemstack(entersyscall_gcwait) + save(pc, sp) + } + + gp.m.locks-- +} + +// Standard syscall entry used by the go syscall library and normal cgo calls. +// +// This is exported via linkname to assembly in the syscall package and x/sys. +// +//go:nosplit +//go:linkname entersyscall +func entersyscall() { + reentersyscall(getcallerpc(), getcallersp()) +} + +func entersyscall_sysmon() { + lock(&sched.lock) + if sched.sysmonwait.Load() { + sched.sysmonwait.Store(false) + notewakeup(&sched.sysmonnote) + } + unlock(&sched.lock) +} + +func entersyscall_gcwait() { + gp := getg() + pp := gp.m.oldp.ptr() + + lock(&sched.lock) + if sched.stopwait > 0 && atomic.Cas(&pp.status, _Psyscall, _Pgcstop) { + if traceEnabled() { + traceGoSysBlock(pp) + traceProcStop(pp) + } + pp.syscalltick++ + if sched.stopwait--; sched.stopwait == 0 { + notewakeup(&sched.stopnote) + } + } + unlock(&sched.lock) +} + +// The same as entersyscall(), but with a hint that the syscall is blocking. +// +//go:nosplit +func entersyscallblock() { + gp := getg() + + gp.m.locks++ // see comment in entersyscall + gp.throwsplit = true + gp.stackguard0 = stackPreempt // see comment in entersyscall + gp.m.syscalltick = gp.m.p.ptr().syscalltick + gp.m.p.ptr().syscalltick++ + + // Leave SP around for GC and traceback. + pc := getcallerpc() + sp := getcallersp() + save(pc, sp) + gp.syscallsp = gp.sched.sp + gp.syscallpc = gp.sched.pc + if gp.syscallsp < gp.stack.lo || gp.stack.hi < gp.syscallsp { + sp1 := sp + sp2 := gp.sched.sp + sp3 := gp.syscallsp + systemstack(func() { + print("entersyscallblock inconsistent ", hex(sp1), " ", hex(sp2), " ", hex(sp3), " [", hex(gp.stack.lo), ",", hex(gp.stack.hi), "]\n") + throw("entersyscallblock") + }) + } + casgstatus(gp, _Grunning, _Gsyscall) + if gp.syscallsp < gp.stack.lo || gp.stack.hi < gp.syscallsp { + systemstack(func() { + print("entersyscallblock inconsistent ", hex(sp), " ", hex(gp.sched.sp), " ", hex(gp.syscallsp), " [", hex(gp.stack.lo), ",", hex(gp.stack.hi), "]\n") + throw("entersyscallblock") + }) + } + + systemstack(entersyscallblock_handoff) + + // Resave for traceback during blocked call. + save(getcallerpc(), getcallersp()) + + gp.m.locks-- +} + +func entersyscallblock_handoff() { + if traceEnabled() { + traceGoSysCall() + traceGoSysBlock(getg().m.p.ptr()) + } + handoffp(releasep()) +} + +// The goroutine g exited its system call. +// Arrange for it to run on a cpu again. +// This is called only from the go syscall library, not +// from the low-level system calls used by the runtime. +// +// Write barriers are not allowed because our P may have been stolen. +// +// This is exported via linkname to assembly in the syscall package. +// +//go:nosplit +//go:nowritebarrierrec +//go:linkname exitsyscall +func exitsyscall() { + gp := getg() + + gp.m.locks++ // see comment in entersyscall + if getcallersp() > gp.syscallsp { + throw("exitsyscall: syscall frame is no longer valid") + } + + gp.waitsince = 0 + oldp := gp.m.oldp.ptr() + gp.m.oldp = 0 + if exitsyscallfast(oldp) { + // When exitsyscallfast returns success, we have a P so can now use + // write barriers + if goroutineProfile.active { + // Make sure that gp has had its stack written out to the goroutine + // profile, exactly as it was when the goroutine profiler first + // stopped the world. + systemstack(func() { + tryRecordGoroutineProfileWB(gp) + }) + } + if traceEnabled() { + if oldp != gp.m.p.ptr() || gp.m.syscalltick != gp.m.p.ptr().syscalltick { + systemstack(traceGoStart) + } + } + // There's a cpu for us, so we can run. + gp.m.p.ptr().syscalltick++ + // We need to cas the status and scan before resuming... + casgstatus(gp, _Gsyscall, _Grunning) + + // Garbage collector isn't running (since we are), + // so okay to clear syscallsp. + gp.syscallsp = 0 + gp.m.locks-- + if gp.preempt { + // restore the preemption request in case we've cleared it in newstack + gp.stackguard0 = stackPreempt + } else { + // otherwise restore the real stackGuard, we've spoiled it in entersyscall/entersyscallblock + gp.stackguard0 = gp.stack.lo + stackGuard + } + gp.throwsplit = false + + if sched.disable.user && !schedEnabled(gp) { + // Scheduling of this goroutine is disabled. + Gosched() + } + + return + } + + if traceEnabled() { + // Wait till traceGoSysBlock event is emitted. + // This ensures consistency of the trace (the goroutine is started after it is blocked). + for oldp != nil && oldp.syscalltick == gp.m.syscalltick { + osyield() + } + // We can't trace syscall exit right now because we don't have a P. + // Tracing code can invoke write barriers that cannot run without a P. + // So instead we remember the syscall exit time and emit the event + // in execute when we have a P. + gp.trace.sysExitTime = traceClockNow() + } + + gp.m.locks-- + + // Call the scheduler. + mcall(exitsyscall0) + + // Scheduler returned, so we're allowed to run now. + // Delete the syscallsp information that we left for + // the garbage collector during the system call. + // Must wait until now because until gosched returns + // we don't know for sure that the garbage collector + // is not running. + gp.syscallsp = 0 + gp.m.p.ptr().syscalltick++ + gp.throwsplit = false +} + +//go:nosplit +func exitsyscallfast(oldp *p) bool { + gp := getg() + + // Freezetheworld sets stopwait but does not retake P's. + if sched.stopwait == freezeStopWait { + return false + } + + // Try to re-acquire the last P. + if oldp != nil && oldp.status == _Psyscall && atomic.Cas(&oldp.status, _Psyscall, _Pidle) { + // There's a cpu for us, so we can run. + wirep(oldp) + exitsyscallfast_reacquired() + return true + } + + // Try to get any other idle P. + if sched.pidle != 0 { + var ok bool + systemstack(func() { + ok = exitsyscallfast_pidle() + if ok && traceEnabled() { + if oldp != nil { + // Wait till traceGoSysBlock event is emitted. + // This ensures consistency of the trace (the goroutine is started after it is blocked). + for oldp.syscalltick == gp.m.syscalltick { + osyield() + } + } + traceGoSysExit() + } + }) + if ok { + return true + } + } + return false +} + +// exitsyscallfast_reacquired is the exitsyscall path on which this G +// has successfully reacquired the P it was running on before the +// syscall. +// +//go:nosplit +func exitsyscallfast_reacquired() { + gp := getg() + if gp.m.syscalltick != gp.m.p.ptr().syscalltick { + if traceEnabled() { + // The p was retaken and then enter into syscall again (since gp.m.syscalltick has changed). + // traceGoSysBlock for this syscall was already emitted, + // but here we effectively retake the p from the new syscall running on the same p. + systemstack(func() { + // Denote blocking of the new syscall. + traceGoSysBlock(gp.m.p.ptr()) + // Denote completion of the current syscall. + traceGoSysExit() + }) + } + gp.m.p.ptr().syscalltick++ + } +} + +func exitsyscallfast_pidle() bool { + lock(&sched.lock) + pp, _ := pidleget(0) + if pp != nil && sched.sysmonwait.Load() { + sched.sysmonwait.Store(false) + notewakeup(&sched.sysmonnote) + } + unlock(&sched.lock) + if pp != nil { + acquirep(pp) + return true + } + return false +} + +// exitsyscall slow path on g0. +// Failed to acquire P, enqueue gp as runnable. +// +// Called via mcall, so gp is the calling g from this M. +// +//go:nowritebarrierrec +func exitsyscall0(gp *g) { + casgstatus(gp, _Gsyscall, _Grunnable) + dropg() + lock(&sched.lock) + var pp *p + if schedEnabled(gp) { + pp, _ = pidleget(0) + } + var locked bool + if pp == nil { + globrunqput(gp) + + // Below, we stoplockedm if gp is locked. globrunqput releases + // ownership of gp, so we must check if gp is locked prior to + // committing the release by unlocking sched.lock, otherwise we + // could race with another M transitioning gp from unlocked to + // locked. + locked = gp.lockedm != 0 + } else if sched.sysmonwait.Load() { + sched.sysmonwait.Store(false) + notewakeup(&sched.sysmonnote) + } + unlock(&sched.lock) + if pp != nil { + acquirep(pp) + execute(gp, false) // Never returns. + } + if locked { + // Wait until another thread schedules gp and so m again. + // + // N.B. lockedm must be this M, as this g was running on this M + // before entersyscall. + stoplockedm() + execute(gp, false) // Never returns. + } + stopm() + schedule() // Never returns. +} + +// Called from syscall package before fork. +// +//go:linkname syscall_runtime_BeforeFork syscall.runtime_BeforeFork +//go:nosplit +func syscall_runtime_BeforeFork() { + gp := getg().m.curg + + // Block signals during a fork, so that the child does not run + // a signal handler before exec if a signal is sent to the process + // group. See issue #18600. + gp.m.locks++ + sigsave(&gp.m.sigmask) + sigblock(false) + + // This function is called before fork in syscall package. + // Code between fork and exec must not allocate memory nor even try to grow stack. + // Here we spoil g.stackguard0 to reliably detect any attempts to grow stack. + // runtime_AfterFork will undo this in parent process, but not in child. + gp.stackguard0 = stackFork +} + +// Called from syscall package after fork in parent. +// +//go:linkname syscall_runtime_AfterFork syscall.runtime_AfterFork +//go:nosplit +func syscall_runtime_AfterFork() { + gp := getg().m.curg + + // See the comments in beforefork. + gp.stackguard0 = gp.stack.lo + stackGuard + + msigrestore(gp.m.sigmask) + + gp.m.locks-- +} + +// inForkedChild is true while manipulating signals in the child process. +// This is used to avoid calling libc functions in case we are using vfork. +var inForkedChild bool + +// Called from syscall package after fork in child. +// It resets non-sigignored signals to the default handler, and +// restores the signal mask in preparation for the exec. +// +// Because this might be called during a vfork, and therefore may be +// temporarily sharing address space with the parent process, this must +// not change any global variables or calling into C code that may do so. +// +//go:linkname syscall_runtime_AfterForkInChild syscall.runtime_AfterForkInChild +//go:nosplit +//go:nowritebarrierrec +func syscall_runtime_AfterForkInChild() { + // It's OK to change the global variable inForkedChild here + // because we are going to change it back. There is no race here, + // because if we are sharing address space with the parent process, + // then the parent process can not be running concurrently. + inForkedChild = true + + clearSignalHandlers() + + // When we are the child we are the only thread running, + // so we know that nothing else has changed gp.m.sigmask. + msigrestore(getg().m.sigmask) + + inForkedChild = false +} + +// pendingPreemptSignals is the number of preemption signals +// that have been sent but not received. This is only used on Darwin. +// For #41702. +var pendingPreemptSignals atomic.Int32 + +// Called from syscall package before Exec. +// +//go:linkname syscall_runtime_BeforeExec syscall.runtime_BeforeExec +func syscall_runtime_BeforeExec() { + // Prevent thread creation during exec. + execLock.lock() + + // On Darwin, wait for all pending preemption signals to + // be received. See issue #41702. + if GOOS == "darwin" || GOOS == "ios" { + for pendingPreemptSignals.Load() > 0 { + osyield() + } + } +} + +// Called from syscall package after Exec. +// +//go:linkname syscall_runtime_AfterExec syscall.runtime_AfterExec +func syscall_runtime_AfterExec() { + execLock.unlock() +} + +// Allocate a new g, with a stack big enough for stacksize bytes. +func malg(stacksize int32) *g { + newg := new(g) + if stacksize >= 0 { + stacksize = round2(stackSystem + stacksize) + systemstack(func() { + newg.stack = stackalloc(uint32(stacksize)) + }) + newg.stackguard0 = newg.stack.lo + stackGuard + newg.stackguard1 = ^uintptr(0) + // Clear the bottom word of the stack. We record g + // there on gsignal stack during VDSO on ARM and ARM64. + *(*uintptr)(unsafe.Pointer(newg.stack.lo)) = 0 + } + return newg +} + +// Create a new g running fn. +// Put it on the queue of g's waiting to run. +// The compiler turns a go statement into a call to this. +func newproc(fn *funcval) { + gp := getg() + pc := getcallerpc() + systemstack(func() { + newg := newproc1(fn, gp, pc) + + pp := getg().m.p.ptr() + runqput(pp, newg, true) + + if mainStarted { + wakep() + } + }) +} + +// Create a new g in state _Grunnable, starting at fn. callerpc is the +// address of the go statement that created this. The caller is responsible +// for adding the new g to the scheduler. +func newproc1(fn *funcval, callergp *g, callerpc uintptr) *g { + if fn == nil { + fatal("go of nil func value") + } + + mp := acquirem() // disable preemption because we hold M and P in local vars. + pp := mp.p.ptr() + newg := gfget(pp) + if newg == nil { + newg = malg(stackMin) + casgstatus(newg, _Gidle, _Gdead) + allgadd(newg) // publishes with a g->status of Gdead so GC scanner doesn't look at uninitialized stack. + } + if newg.stack.hi == 0 { + throw("newproc1: newg missing stack") + } + + if readgstatus(newg) != _Gdead { + throw("newproc1: new g is not Gdead") + } + + totalSize := uintptr(4*goarch.PtrSize + sys.MinFrameSize) // extra space in case of reads slightly beyond frame + totalSize = alignUp(totalSize, sys.StackAlign) + sp := newg.stack.hi - totalSize + spArg := sp + if usesLR { + // caller's LR + *(*uintptr)(unsafe.Pointer(sp)) = 0 + prepGoExitFrame(sp) + spArg += sys.MinFrameSize + } + + memclrNoHeapPointers(unsafe.Pointer(&newg.sched), unsafe.Sizeof(newg.sched)) + newg.sched.sp = sp + newg.stktopsp = sp + newg.sched.pc = abi.FuncPCABI0(goexit) + sys.PCQuantum // +PCQuantum so that previous instruction is in same function + newg.sched.g = guintptr(unsafe.Pointer(newg)) + gostartcallfn(&newg.sched, fn) + newg.parentGoid = callergp.goid + newg.gopc = callerpc + newg.ancestors = saveAncestors(callergp) + newg.startpc = fn.fn + if isSystemGoroutine(newg, false) { + sched.ngsys.Add(1) + } else { + // Only user goroutines inherit pprof labels. + if mp.curg != nil { + newg.labels = mp.curg.labels + } + if goroutineProfile.active { + // A concurrent goroutine profile is running. It should include + // exactly the set of goroutines that were alive when the goroutine + // profiler first stopped the world. That does not include newg, so + // mark it as not needing a profile before transitioning it from + // _Gdead. + newg.goroutineProfiled.Store(goroutineProfileSatisfied) + } + } + // Track initial transition? + newg.trackingSeq = uint8(fastrand()) + if newg.trackingSeq%gTrackingPeriod == 0 { + newg.tracking = true + } + casgstatus(newg, _Gdead, _Grunnable) + gcController.addScannableStack(pp, int64(newg.stack.hi-newg.stack.lo)) + + if pp.goidcache == pp.goidcacheend { + // Sched.goidgen is the last allocated id, + // this batch must be [sched.goidgen+1, sched.goidgen+GoidCacheBatch]. + // At startup sched.goidgen=0, so main goroutine receives goid=1. + pp.goidcache = sched.goidgen.Add(_GoidCacheBatch) + pp.goidcache -= _GoidCacheBatch - 1 + pp.goidcacheend = pp.goidcache + _GoidCacheBatch + } + newg.goid = pp.goidcache + pp.goidcache++ + if raceenabled { + newg.racectx = racegostart(callerpc) + newg.raceignore = 0 + if newg.labels != nil { + // See note in proflabel.go on labelSync's role in synchronizing + // with the reads in the signal handler. + racereleasemergeg(newg, unsafe.Pointer(&labelSync)) + } + } + if traceEnabled() { + traceGoCreate(newg, newg.startpc) + } + releasem(mp) + + return newg +} + +// saveAncestors copies previous ancestors of the given caller g and +// includes info for the current caller into a new set of tracebacks for +// a g being created. +func saveAncestors(callergp *g) *[]ancestorInfo { + // Copy all prior info, except for the root goroutine (goid 0). + if debug.tracebackancestors <= 0 || callergp.goid == 0 { + return nil + } + var callerAncestors []ancestorInfo + if callergp.ancestors != nil { + callerAncestors = *callergp.ancestors + } + n := int32(len(callerAncestors)) + 1 + if n > debug.tracebackancestors { + n = debug.tracebackancestors + } + ancestors := make([]ancestorInfo, n) + copy(ancestors[1:], callerAncestors) + + var pcs [tracebackInnerFrames]uintptr + npcs := gcallers(callergp, 0, pcs[:]) + ipcs := make([]uintptr, npcs) + copy(ipcs, pcs[:]) + ancestors[0] = ancestorInfo{ + pcs: ipcs, + goid: callergp.goid, + gopc: callergp.gopc, + } + + ancestorsp := new([]ancestorInfo) + *ancestorsp = ancestors + return ancestorsp +} + +// Put on gfree list. +// If local list is too long, transfer a batch to the global list. +func gfput(pp *p, gp *g) { + if readgstatus(gp) != _Gdead { + throw("gfput: bad status (not Gdead)") + } + + stksize := gp.stack.hi - gp.stack.lo + + if stksize != uintptr(startingStackSize) { + // non-standard stack size - free it. + stackfree(gp.stack) + gp.stack.lo = 0 + gp.stack.hi = 0 + gp.stackguard0 = 0 + } + + pp.gFree.push(gp) + pp.gFree.n++ + if pp.gFree.n >= 64 { + var ( + inc int32 + stackQ gQueue + noStackQ gQueue + ) + for pp.gFree.n >= 32 { + gp := pp.gFree.pop() + pp.gFree.n-- + if gp.stack.lo == 0 { + noStackQ.push(gp) + } else { + stackQ.push(gp) + } + inc++ + } + lock(&sched.gFree.lock) + sched.gFree.noStack.pushAll(noStackQ) + sched.gFree.stack.pushAll(stackQ) + sched.gFree.n += inc + unlock(&sched.gFree.lock) + } +} + +// Get from gfree list. +// If local list is empty, grab a batch from global list. +func gfget(pp *p) *g { +retry: + if pp.gFree.empty() && (!sched.gFree.stack.empty() || !sched.gFree.noStack.empty()) { + lock(&sched.gFree.lock) + // Move a batch of free Gs to the P. + for pp.gFree.n < 32 { + // Prefer Gs with stacks. + gp := sched.gFree.stack.pop() + if gp == nil { + gp = sched.gFree.noStack.pop() + if gp == nil { + break + } + } + sched.gFree.n-- + pp.gFree.push(gp) + pp.gFree.n++ + } + unlock(&sched.gFree.lock) + goto retry + } + gp := pp.gFree.pop() + if gp == nil { + return nil + } + pp.gFree.n-- + if gp.stack.lo != 0 && gp.stack.hi-gp.stack.lo != uintptr(startingStackSize) { + // Deallocate old stack. We kept it in gfput because it was the + // right size when the goroutine was put on the free list, but + // the right size has changed since then. + systemstack(func() { + stackfree(gp.stack) + gp.stack.lo = 0 + gp.stack.hi = 0 + gp.stackguard0 = 0 + }) + } + if gp.stack.lo == 0 { + // Stack was deallocated in gfput or just above. Allocate a new one. + systemstack(func() { + gp.stack = stackalloc(startingStackSize) + }) + gp.stackguard0 = gp.stack.lo + stackGuard + } else { + if raceenabled { + racemalloc(unsafe.Pointer(gp.stack.lo), gp.stack.hi-gp.stack.lo) + } + if msanenabled { + msanmalloc(unsafe.Pointer(gp.stack.lo), gp.stack.hi-gp.stack.lo) + } + if asanenabled { + asanunpoison(unsafe.Pointer(gp.stack.lo), gp.stack.hi-gp.stack.lo) + } + } + return gp +} + +// Purge all cached G's from gfree list to the global list. +func gfpurge(pp *p) { + var ( + inc int32 + stackQ gQueue + noStackQ gQueue + ) + for !pp.gFree.empty() { + gp := pp.gFree.pop() + pp.gFree.n-- + if gp.stack.lo == 0 { + noStackQ.push(gp) + } else { + stackQ.push(gp) + } + inc++ + } + lock(&sched.gFree.lock) + sched.gFree.noStack.pushAll(noStackQ) + sched.gFree.stack.pushAll(stackQ) + sched.gFree.n += inc + unlock(&sched.gFree.lock) +} + +// Breakpoint executes a breakpoint trap. +func Breakpoint() { + breakpoint() +} + +// dolockOSThread is called by LockOSThread and lockOSThread below +// after they modify m.locked. Do not allow preemption during this call, +// or else the m might be different in this function than in the caller. +// +//go:nosplit +func dolockOSThread() { + if GOARCH == "wasm" { + return // no threads on wasm yet + } + gp := getg() + gp.m.lockedg.set(gp) + gp.lockedm.set(gp.m) +} + +// LockOSThread wires the calling goroutine to its current operating system thread. +// The calling goroutine will always execute in that thread, +// and no other goroutine will execute in it, +// until the calling goroutine has made as many calls to +// UnlockOSThread as to LockOSThread. +// If the calling goroutine exits without unlocking the thread, +// the thread will be terminated. +// +// All init functions are run on the startup thread. Calling LockOSThread +// from an init function will cause the main function to be invoked on +// that thread. +// +// A goroutine should call LockOSThread before calling OS services or +// non-Go library functions that depend on per-thread state. +// +//go:nosplit +func LockOSThread() { + if atomic.Load(&newmHandoff.haveTemplateThread) == 0 && GOOS != "plan9" { + // If we need to start a new thread from the locked + // thread, we need the template thread. Start it now + // while we're in a known-good state. + startTemplateThread() + } + gp := getg() + gp.m.lockedExt++ + if gp.m.lockedExt == 0 { + gp.m.lockedExt-- + panic("LockOSThread nesting overflow") + } + dolockOSThread() +} + +//go:nosplit +func lockOSThread() { + getg().m.lockedInt++ + dolockOSThread() +} + +// dounlockOSThread is called by UnlockOSThread and unlockOSThread below +// after they update m->locked. Do not allow preemption during this call, +// or else the m might be in different in this function than in the caller. +// +//go:nosplit +func dounlockOSThread() { + if GOARCH == "wasm" { + return // no threads on wasm yet + } + gp := getg() + if gp.m.lockedInt != 0 || gp.m.lockedExt != 0 { + return + } + gp.m.lockedg = 0 + gp.lockedm = 0 +} + +// UnlockOSThread undoes an earlier call to LockOSThread. +// If this drops the number of active LockOSThread calls on the +// calling goroutine to zero, it unwires the calling goroutine from +// its fixed operating system thread. +// If there are no active LockOSThread calls, this is a no-op. +// +// Before calling UnlockOSThread, the caller must ensure that the OS +// thread is suitable for running other goroutines. If the caller made +// any permanent changes to the state of the thread that would affect +// other goroutines, it should not call this function and thus leave +// the goroutine locked to the OS thread until the goroutine (and +// hence the thread) exits. +// +//go:nosplit +func UnlockOSThread() { + gp := getg() + if gp.m.lockedExt == 0 { + return + } + gp.m.lockedExt-- + dounlockOSThread() +} + +//go:nosplit +func unlockOSThread() { + gp := getg() + if gp.m.lockedInt == 0 { + systemstack(badunlockosthread) + } + gp.m.lockedInt-- + dounlockOSThread() +} + +func badunlockosthread() { + throw("runtime: internal error: misuse of lockOSThread/unlockOSThread") +} + +func gcount() int32 { + n := int32(atomic.Loaduintptr(&allglen)) - sched.gFree.n - sched.ngsys.Load() + for _, pp := range allp { + n -= pp.gFree.n + } + + // All these variables can be changed concurrently, so the result can be inconsistent. + // But at least the current goroutine is running. + if n < 1 { + n = 1 + } + return n +} + +func mcount() int32 { + return int32(sched.mnext - sched.nmfreed) +} + +var prof struct { + signalLock atomic.Uint32 + + // Must hold signalLock to write. Reads may be lock-free, but + // signalLock should be taken to synchronize with changes. + hz atomic.Int32 +} + +func _System() { _System() } +func _ExternalCode() { _ExternalCode() } +func _LostExternalCode() { _LostExternalCode() } +func _GC() { _GC() } +func _LostSIGPROFDuringAtomic64() { _LostSIGPROFDuringAtomic64() } +func _VDSO() { _VDSO() } + +// Called if we receive a SIGPROF signal. +// Called by the signal handler, may run during STW. +// +//go:nowritebarrierrec +func sigprof(pc, sp, lr uintptr, gp *g, mp *m) { + if prof.hz.Load() == 0 { + return + } + + // If mp.profilehz is 0, then profiling is not enabled for this thread. + // We must check this to avoid a deadlock between setcpuprofilerate + // and the call to cpuprof.add, below. + if mp != nil && mp.profilehz == 0 { + return + } + + // On mips{,le}/arm, 64bit atomics are emulated with spinlocks, in + // runtime/internal/atomic. If SIGPROF arrives while the program is inside + // the critical section, it creates a deadlock (when writing the sample). + // As a workaround, create a counter of SIGPROFs while in critical section + // to store the count, and pass it to sigprof.add() later when SIGPROF is + // received from somewhere else (with _LostSIGPROFDuringAtomic64 as pc). + if GOARCH == "mips" || GOARCH == "mipsle" || GOARCH == "arm" { + if f := findfunc(pc); f.valid() { + if hasPrefix(funcname(f), "runtime/internal/atomic") { + cpuprof.lostAtomic++ + return + } + } + if GOARCH == "arm" && goarm < 7 && GOOS == "linux" && pc&0xffff0000 == 0xffff0000 { + // runtime/internal/atomic functions call into kernel + // helpers on arm < 7. See + // runtime/internal/atomic/sys_linux_arm.s. + cpuprof.lostAtomic++ + return + } + } + + // Profiling runs concurrently with GC, so it must not allocate. + // Set a trap in case the code does allocate. + // Note that on windows, one thread takes profiles of all the + // other threads, so mp is usually not getg().m. + // In fact mp may not even be stopped. + // See golang.org/issue/17165. + getg().m.mallocing++ + + var u unwinder + var stk [maxCPUProfStack]uintptr + n := 0 + if mp.ncgo > 0 && mp.curg != nil && mp.curg.syscallpc != 0 && mp.curg.syscallsp != 0 { + cgoOff := 0 + // Check cgoCallersUse to make sure that we are not + // interrupting other code that is fiddling with + // cgoCallers. We are running in a signal handler + // with all signals blocked, so we don't have to worry + // about any other code interrupting us. + if mp.cgoCallersUse.Load() == 0 && mp.cgoCallers != nil && mp.cgoCallers[0] != 0 { + for cgoOff < len(mp.cgoCallers) && mp.cgoCallers[cgoOff] != 0 { + cgoOff++ + } + n += copy(stk[:], mp.cgoCallers[:cgoOff]) + mp.cgoCallers[0] = 0 + } + + // Collect Go stack that leads to the cgo call. + u.initAt(mp.curg.syscallpc, mp.curg.syscallsp, 0, mp.curg, unwindSilentErrors) + } else if usesLibcall() && mp.libcallg != 0 && mp.libcallpc != 0 && mp.libcallsp != 0 { + // Libcall, i.e. runtime syscall on windows. + // Collect Go stack that leads to the call. + u.initAt(mp.libcallpc, mp.libcallsp, 0, mp.libcallg.ptr(), unwindSilentErrors) + } else if mp != nil && mp.vdsoSP != 0 { + // VDSO call, e.g. nanotime1 on Linux. + // Collect Go stack that leads to the call. + u.initAt(mp.vdsoPC, mp.vdsoSP, 0, gp, unwindSilentErrors|unwindJumpStack) + } else { + u.initAt(pc, sp, lr, gp, unwindSilentErrors|unwindTrap|unwindJumpStack) + } + n += tracebackPCs(&u, 0, stk[n:]) + + if n <= 0 { + // Normal traceback is impossible or has failed. + // Account it against abstract "System" or "GC". + n = 2 + if inVDSOPage(pc) { + pc = abi.FuncPCABIInternal(_VDSO) + sys.PCQuantum + } else if pc > firstmoduledata.etext { + // "ExternalCode" is better than "etext". + pc = abi.FuncPCABIInternal(_ExternalCode) + sys.PCQuantum + } + stk[0] = pc + if mp.preemptoff != "" { + stk[1] = abi.FuncPCABIInternal(_GC) + sys.PCQuantum + } else { + stk[1] = abi.FuncPCABIInternal(_System) + sys.PCQuantum + } + } + + if prof.hz.Load() != 0 { + // Note: it can happen on Windows that we interrupted a system thread + // with no g, so gp could nil. The other nil checks are done out of + // caution, but not expected to be nil in practice. + var tagPtr *unsafe.Pointer + if gp != nil && gp.m != nil && gp.m.curg != nil { + tagPtr = &gp.m.curg.labels + } + cpuprof.add(tagPtr, stk[:n]) + + gprof := gp + var pp *p + if gp != nil && gp.m != nil { + if gp.m.curg != nil { + gprof = gp.m.curg + } + pp = gp.m.p.ptr() + } + traceCPUSample(gprof, pp, stk[:n]) + } + getg().m.mallocing-- +} + +// setcpuprofilerate sets the CPU profiling rate to hz times per second. +// If hz <= 0, setcpuprofilerate turns off CPU profiling. +func setcpuprofilerate(hz int32) { + // Force sane arguments. + if hz < 0 { + hz = 0 + } + + // Disable preemption, otherwise we can be rescheduled to another thread + // that has profiling enabled. + gp := getg() + gp.m.locks++ + + // Stop profiler on this thread so that it is safe to lock prof. + // if a profiling signal came in while we had prof locked, + // it would deadlock. + setThreadCPUProfiler(0) + + for !prof.signalLock.CompareAndSwap(0, 1) { + osyield() + } + if prof.hz.Load() != hz { + setProcessCPUProfiler(hz) + prof.hz.Store(hz) + } + prof.signalLock.Store(0) + + lock(&sched.lock) + sched.profilehz = hz + unlock(&sched.lock) + + if hz != 0 { + setThreadCPUProfiler(hz) + } + + gp.m.locks-- +} + +// init initializes pp, which may be a freshly allocated p or a +// previously destroyed p, and transitions it to status _Pgcstop. +func (pp *p) init(id int32) { + pp.id = id + pp.status = _Pgcstop + pp.sudogcache = pp.sudogbuf[:0] + pp.deferpool = pp.deferpoolbuf[:0] + pp.wbBuf.reset() + if pp.mcache == nil { + if id == 0 { + if mcache0 == nil { + throw("missing mcache?") + } + // Use the bootstrap mcache0. Only one P will get + // mcache0: the one with ID 0. + pp.mcache = mcache0 + } else { + pp.mcache = allocmcache() + } + } + if raceenabled && pp.raceprocctx == 0 { + if id == 0 { + pp.raceprocctx = raceprocctx0 + raceprocctx0 = 0 // bootstrap + } else { + pp.raceprocctx = raceproccreate() + } + } + lockInit(&pp.timersLock, lockRankTimers) + + // This P may get timers when it starts running. Set the mask here + // since the P may not go through pidleget (notably P 0 on startup). + timerpMask.set(id) + // Similarly, we may not go through pidleget before this P starts + // running if it is P 0 on startup. + idlepMask.clear(id) +} + +// destroy releases all of the resources associated with pp and +// transitions it to status _Pdead. +// +// sched.lock must be held and the world must be stopped. +func (pp *p) destroy() { + assertLockHeld(&sched.lock) + assertWorldStopped() + + // Move all runnable goroutines to the global queue + for pp.runqhead != pp.runqtail { + // Pop from tail of local queue + pp.runqtail-- + gp := pp.runq[pp.runqtail%uint32(len(pp.runq))].ptr() + // Push onto head of global queue + globrunqputhead(gp) + } + if pp.runnext != 0 { + globrunqputhead(pp.runnext.ptr()) + pp.runnext = 0 + } + if len(pp.timers) > 0 { + plocal := getg().m.p.ptr() + // The world is stopped, but we acquire timersLock to + // protect against sysmon calling timeSleepUntil. + // This is the only case where we hold the timersLock of + // more than one P, so there are no deadlock concerns. + lock(&plocal.timersLock) + lock(&pp.timersLock) + moveTimers(plocal, pp.timers) + pp.timers = nil + pp.numTimers.Store(0) + pp.deletedTimers.Store(0) + pp.timer0When.Store(0) + unlock(&pp.timersLock) + unlock(&plocal.timersLock) + } + // Flush p's write barrier buffer. + if gcphase != _GCoff { + wbBufFlush1(pp) + pp.gcw.dispose() + } + for i := range pp.sudogbuf { + pp.sudogbuf[i] = nil + } + pp.sudogcache = pp.sudogbuf[:0] + pp.pinnerCache = nil + for j := range pp.deferpoolbuf { + pp.deferpoolbuf[j] = nil + } + pp.deferpool = pp.deferpoolbuf[:0] + systemstack(func() { + for i := 0; i < pp.mspancache.len; i++ { + // Safe to call since the world is stopped. + mheap_.spanalloc.free(unsafe.Pointer(pp.mspancache.buf[i])) + } + pp.mspancache.len = 0 + lock(&mheap_.lock) + pp.pcache.flush(&mheap_.pages) + unlock(&mheap_.lock) + }) + freemcache(pp.mcache) + pp.mcache = nil + gfpurge(pp) + traceProcFree(pp) + if raceenabled { + if pp.timerRaceCtx != 0 { + // The race detector code uses a callback to fetch + // the proc context, so arrange for that callback + // to see the right thing. + // This hack only works because we are the only + // thread running. + mp := getg().m + phold := mp.p.ptr() + mp.p.set(pp) + + racectxend(pp.timerRaceCtx) + pp.timerRaceCtx = 0 + + mp.p.set(phold) + } + raceprocdestroy(pp.raceprocctx) + pp.raceprocctx = 0 + } + pp.gcAssistTime = 0 + pp.status = _Pdead +} + +// Change number of processors. +// +// sched.lock must be held, and the world must be stopped. +// +// gcworkbufs must not be being modified by either the GC or the write barrier +// code, so the GC must not be running if the number of Ps actually changes. +// +// Returns list of Ps with local work, they need to be scheduled by the caller. +func procresize(nprocs int32) *p { + assertLockHeld(&sched.lock) + assertWorldStopped() + + old := gomaxprocs + if old < 0 || nprocs <= 0 { + throw("procresize: invalid arg") + } + if traceEnabled() { + traceGomaxprocs(nprocs) + } + + // update statistics + now := nanotime() + if sched.procresizetime != 0 { + sched.totaltime += int64(old) * (now - sched.procresizetime) + } + sched.procresizetime = now + + maskWords := (nprocs + 31) / 32 + + // Grow allp if necessary. + if nprocs > int32(len(allp)) { + // Synchronize with retake, which could be running + // concurrently since it doesn't run on a P. + lock(&allpLock) + if nprocs <= int32(cap(allp)) { + allp = allp[:nprocs] + } else { + nallp := make([]*p, nprocs) + // Copy everything up to allp's cap so we + // never lose old allocated Ps. + copy(nallp, allp[:cap(allp)]) + allp = nallp + } + + if maskWords <= int32(cap(idlepMask)) { + idlepMask = idlepMask[:maskWords] + timerpMask = timerpMask[:maskWords] + } else { + nidlepMask := make([]uint32, maskWords) + // No need to copy beyond len, old Ps are irrelevant. + copy(nidlepMask, idlepMask) + idlepMask = nidlepMask + + ntimerpMask := make([]uint32, maskWords) + copy(ntimerpMask, timerpMask) + timerpMask = ntimerpMask + } + unlock(&allpLock) + } + + // initialize new P's + for i := old; i < nprocs; i++ { + pp := allp[i] + if pp == nil { + pp = new(p) + } + pp.init(i) + atomicstorep(unsafe.Pointer(&allp[i]), unsafe.Pointer(pp)) + } + + gp := getg() + if gp.m.p != 0 && gp.m.p.ptr().id < nprocs { + // continue to use the current P + gp.m.p.ptr().status = _Prunning + gp.m.p.ptr().mcache.prepareForSweep() + } else { + // release the current P and acquire allp[0]. + // + // We must do this before destroying our current P + // because p.destroy itself has write barriers, so we + // need to do that from a valid P. + if gp.m.p != 0 { + if traceEnabled() { + // Pretend that we were descheduled + // and then scheduled again to keep + // the trace sane. + traceGoSched() + traceProcStop(gp.m.p.ptr()) + } + gp.m.p.ptr().m = 0 + } + gp.m.p = 0 + pp := allp[0] + pp.m = 0 + pp.status = _Pidle + acquirep(pp) + if traceEnabled() { + traceGoStart() + } + } + + // g.m.p is now set, so we no longer need mcache0 for bootstrapping. + mcache0 = nil + + // release resources from unused P's + for i := nprocs; i < old; i++ { + pp := allp[i] + pp.destroy() + // can't free P itself because it can be referenced by an M in syscall + } + + // Trim allp. + if int32(len(allp)) != nprocs { + lock(&allpLock) + allp = allp[:nprocs] + idlepMask = idlepMask[:maskWords] + timerpMask = timerpMask[:maskWords] + unlock(&allpLock) + } + + var runnablePs *p + for i := nprocs - 1; i >= 0; i-- { + pp := allp[i] + if gp.m.p.ptr() == pp { + continue + } + pp.status = _Pidle + if runqempty(pp) { + pidleput(pp, now) + } else { + pp.m.set(mget()) + pp.link.set(runnablePs) + runnablePs = pp + } + } + stealOrder.reset(uint32(nprocs)) + var int32p *int32 = &gomaxprocs // make compiler check that gomaxprocs is an int32 + atomic.Store((*uint32)(unsafe.Pointer(int32p)), uint32(nprocs)) + if old != nprocs { + // Notify the limiter that the amount of procs has changed. + gcCPULimiter.resetCapacity(now, nprocs) + } + return runnablePs +} + +// Associate p and the current m. +// +// This function is allowed to have write barriers even if the caller +// isn't because it immediately acquires pp. +// +//go:yeswritebarrierrec +func acquirep(pp *p) { + // Do the part that isn't allowed to have write barriers. + wirep(pp) + + // Have p; write barriers now allowed. + + // Perform deferred mcache flush before this P can allocate + // from a potentially stale mcache. + pp.mcache.prepareForSweep() + + if traceEnabled() { + traceProcStart() + } +} + +// wirep is the first step of acquirep, which actually associates the +// current M to pp. This is broken out so we can disallow write +// barriers for this part, since we don't yet have a P. +// +//go:nowritebarrierrec +//go:nosplit +func wirep(pp *p) { + gp := getg() + + if gp.m.p != 0 { + throw("wirep: already in go") + } + if pp.m != 0 || pp.status != _Pidle { + id := int64(0) + if pp.m != 0 { + id = pp.m.ptr().id + } + print("wirep: p->m=", pp.m, "(", id, ") p->status=", pp.status, "\n") + throw("wirep: invalid p state") + } + gp.m.p.set(pp) + pp.m.set(gp.m) + pp.status = _Prunning +} + +// Disassociate p and the current m. +func releasep() *p { + gp := getg() + + if gp.m.p == 0 { + throw("releasep: invalid arg") + } + pp := gp.m.p.ptr() + if pp.m.ptr() != gp.m || pp.status != _Prunning { + print("releasep: m=", gp.m, " m->p=", gp.m.p.ptr(), " p->m=", hex(pp.m), " p->status=", pp.status, "\n") + throw("releasep: invalid p state") + } + if traceEnabled() { + traceProcStop(gp.m.p.ptr()) + } + gp.m.p = 0 + pp.m = 0 + pp.status = _Pidle + return pp +} + +func incidlelocked(v int32) { + lock(&sched.lock) + sched.nmidlelocked += v + if v > 0 { + checkdead() + } + unlock(&sched.lock) +} + +// Check for deadlock situation. +// The check is based on number of running M's, if 0 -> deadlock. +// sched.lock must be held. +func checkdead() { + assertLockHeld(&sched.lock) + + // For -buildmode=c-shared or -buildmode=c-archive it's OK if + // there are no running goroutines. The calling program is + // assumed to be running. + if islibrary || isarchive { + return + } + + // If we are dying because of a signal caught on an already idle thread, + // freezetheworld will cause all running threads to block. + // And runtime will essentially enter into deadlock state, + // except that there is a thread that will call exit soon. + if panicking.Load() > 0 { + return + } + + // If we are not running under cgo, but we have an extra M then account + // for it. (It is possible to have an extra M on Windows without cgo to + // accommodate callbacks created by syscall.NewCallback. See issue #6751 + // for details.) + var run0 int32 + if !iscgo && cgoHasExtraM && extraMLength.Load() > 0 { + run0 = 1 + } + + run := mcount() - sched.nmidle - sched.nmidlelocked - sched.nmsys + if run > run0 { + return + } + if run < 0 { + print("runtime: checkdead: nmidle=", sched.nmidle, " nmidlelocked=", sched.nmidlelocked, " mcount=", mcount(), " nmsys=", sched.nmsys, "\n") + unlock(&sched.lock) + throw("checkdead: inconsistent counts") + } + + grunning := 0 + forEachG(func(gp *g) { + if isSystemGoroutine(gp, false) { + return + } + s := readgstatus(gp) + switch s &^ _Gscan { + case _Gwaiting, + _Gpreempted: + grunning++ + case _Grunnable, + _Grunning, + _Gsyscall: + print("runtime: checkdead: find g ", gp.goid, " in status ", s, "\n") + unlock(&sched.lock) + throw("checkdead: runnable g") + } + }) + if grunning == 0 { // possible if main goroutine calls runtime·Goexit() + unlock(&sched.lock) // unlock so that GODEBUG=scheddetail=1 doesn't hang + fatal("no goroutines (main called runtime.Goexit) - deadlock!") + } + + // Maybe jump time forward for playground. + if faketime != 0 { + if when := timeSleepUntil(); when < maxWhen { + faketime = when + + // Start an M to steal the timer. + pp, _ := pidleget(faketime) + if pp == nil { + // There should always be a free P since + // nothing is running. + unlock(&sched.lock) + throw("checkdead: no p for timer") + } + mp := mget() + if mp == nil { + // There should always be a free M since + // nothing is running. + unlock(&sched.lock) + throw("checkdead: no m for timer") + } + // M must be spinning to steal. We set this to be + // explicit, but since this is the only M it would + // become spinning on its own anyways. + sched.nmspinning.Add(1) + mp.spinning = true + mp.nextp.set(pp) + notewakeup(&mp.park) + return + } + } + + // There are no goroutines running, so we can look at the P's. + for _, pp := range allp { + if len(pp.timers) > 0 { + return + } + } + + unlock(&sched.lock) // unlock so that GODEBUG=scheddetail=1 doesn't hang + fatal("all goroutines are asleep - deadlock!") +} + +// forcegcperiod is the maximum time in nanoseconds between garbage +// collections. If we go this long without a garbage collection, one +// is forced to run. +// +// This is a variable for testing purposes. It normally doesn't change. +var forcegcperiod int64 = 2 * 60 * 1e9 + +// needSysmonWorkaround is true if the workaround for +// golang.org/issue/42515 is needed on NetBSD. +var needSysmonWorkaround bool = false + +// Always runs without a P, so write barriers are not allowed. +// +//go:nowritebarrierrec +func sysmon() { + lock(&sched.lock) + sched.nmsys++ + checkdead() + unlock(&sched.lock) + + lasttrace := int64(0) + idle := 0 // how many cycles in succession we had not wokeup somebody + delay := uint32(0) + + for { + if idle == 0 { // start with 20us sleep... + delay = 20 + } else if idle > 50 { // start doubling the sleep after 1ms... + delay *= 2 + } + if delay > 10*1000 { // up to 10ms + delay = 10 * 1000 + } + usleep(delay) + + // sysmon should not enter deep sleep if schedtrace is enabled so that + // it can print that information at the right time. + // + // It should also not enter deep sleep if there are any active P's so + // that it can retake P's from syscalls, preempt long running G's, and + // poll the network if all P's are busy for long stretches. + // + // It should wakeup from deep sleep if any P's become active either due + // to exiting a syscall or waking up due to a timer expiring so that it + // can resume performing those duties. If it wakes from a syscall it + // resets idle and delay as a bet that since it had retaken a P from a + // syscall before, it may need to do it again shortly after the + // application starts work again. It does not reset idle when waking + // from a timer to avoid adding system load to applications that spend + // most of their time sleeping. + now := nanotime() + if debug.schedtrace <= 0 && (sched.gcwaiting.Load() || sched.npidle.Load() == gomaxprocs) { + lock(&sched.lock) + if sched.gcwaiting.Load() || sched.npidle.Load() == gomaxprocs { + syscallWake := false + next := timeSleepUntil() + if next > now { + sched.sysmonwait.Store(true) + unlock(&sched.lock) + // Make wake-up period small enough + // for the sampling to be correct. + sleep := forcegcperiod / 2 + if next-now < sleep { + sleep = next - now + } + shouldRelax := sleep >= osRelaxMinNS + if shouldRelax { + osRelax(true) + } + syscallWake = notetsleep(&sched.sysmonnote, sleep) + if shouldRelax { + osRelax(false) + } + lock(&sched.lock) + sched.sysmonwait.Store(false) + noteclear(&sched.sysmonnote) + } + if syscallWake { + idle = 0 + delay = 20 + } + } + unlock(&sched.lock) + } + + lock(&sched.sysmonlock) + // Update now in case we blocked on sysmonnote or spent a long time + // blocked on schedlock or sysmonlock above. + now = nanotime() + + // trigger libc interceptors if needed + if *cgo_yield != nil { + asmcgocall(*cgo_yield, nil) + } + // poll network if not polled for more than 10ms + lastpoll := sched.lastpoll.Load() + if netpollinited() && lastpoll != 0 && lastpoll+10*1000*1000 < now { + sched.lastpoll.CompareAndSwap(lastpoll, now) + list := netpoll(0) // non-blocking - returns list of goroutines + if !list.empty() { + // Need to decrement number of idle locked M's + // (pretending that one more is running) before injectglist. + // Otherwise it can lead to the following situation: + // injectglist grabs all P's but before it starts M's to run the P's, + // another M returns from syscall, finishes running its G, + // observes that there is no work to do and no other running M's + // and reports deadlock. + incidlelocked(-1) + injectglist(&list) + incidlelocked(1) + } + } + if GOOS == "netbsd" && needSysmonWorkaround { + // netpoll is responsible for waiting for timer + // expiration, so we typically don't have to worry + // about starting an M to service timers. (Note that + // sleep for timeSleepUntil above simply ensures sysmon + // starts running again when that timer expiration may + // cause Go code to run again). + // + // However, netbsd has a kernel bug that sometimes + // misses netpollBreak wake-ups, which can lead to + // unbounded delays servicing timers. If we detect this + // overrun, then startm to get something to handle the + // timer. + // + // See issue 42515 and + // https://gnats.netbsd.org/cgi-bin/query-pr-single.pl?number=50094. + if next := timeSleepUntil(); next < now { + startm(nil, false, false) + } + } + if scavenger.sysmonWake.Load() != 0 { + // Kick the scavenger awake if someone requested it. + scavenger.wake() + } + // retake P's blocked in syscalls + // and preempt long running G's + if retake(now) != 0 { + idle = 0 + } else { + idle++ + } + // check if we need to force a GC + if t := (gcTrigger{kind: gcTriggerTime, now: now}); t.test() && forcegc.idle.Load() { + lock(&forcegc.lock) + forcegc.idle.Store(false) + var list gList + list.push(forcegc.g) + injectglist(&list) + unlock(&forcegc.lock) + } + if debug.schedtrace > 0 && lasttrace+int64(debug.schedtrace)*1000000 <= now { + lasttrace = now + schedtrace(debug.scheddetail > 0) + } + unlock(&sched.sysmonlock) + } +} + +type sysmontick struct { + schedtick uint32 + schedwhen int64 + syscalltick uint32 + syscallwhen int64 +} + +// forcePreemptNS is the time slice given to a G before it is +// preempted. +const forcePreemptNS = 10 * 1000 * 1000 // 10ms + +func retake(now int64) uint32 { + n := 0 + // Prevent allp slice changes. This lock will be completely + // uncontended unless we're already stopping the world. + lock(&allpLock) + // We can't use a range loop over allp because we may + // temporarily drop the allpLock. Hence, we need to re-fetch + // allp each time around the loop. + for i := 0; i < len(allp); i++ { + pp := allp[i] + if pp == nil { + // This can happen if procresize has grown + // allp but not yet created new Ps. + continue + } + pd := &pp.sysmontick + s := pp.status + sysretake := false + if s == _Prunning || s == _Psyscall { + // Preempt G if it's running for too long. + t := int64(pp.schedtick) + if int64(pd.schedtick) != t { + pd.schedtick = uint32(t) + pd.schedwhen = now + } else if pd.schedwhen+forcePreemptNS <= now { + preemptone(pp) + // In case of syscall, preemptone() doesn't + // work, because there is no M wired to P. + sysretake = true + } + } + if s == _Psyscall { + // Retake P from syscall if it's there for more than 1 sysmon tick (at least 20us). + t := int64(pp.syscalltick) + if !sysretake && int64(pd.syscalltick) != t { + pd.syscalltick = uint32(t) + pd.syscallwhen = now + continue + } + // On the one hand we don't want to retake Ps if there is no other work to do, + // but on the other hand we want to retake them eventually + // because they can prevent the sysmon thread from deep sleep. + if runqempty(pp) && sched.nmspinning.Load()+sched.npidle.Load() > 0 && pd.syscallwhen+10*1000*1000 > now { + continue + } + // Drop allpLock so we can take sched.lock. + unlock(&allpLock) + // Need to decrement number of idle locked M's + // (pretending that one more is running) before the CAS. + // Otherwise the M from which we retake can exit the syscall, + // increment nmidle and report deadlock. + incidlelocked(-1) + if atomic.Cas(&pp.status, s, _Pidle) { + if traceEnabled() { + traceGoSysBlock(pp) + traceProcStop(pp) + } + n++ + pp.syscalltick++ + handoffp(pp) + } + incidlelocked(1) + lock(&allpLock) + } + } + unlock(&allpLock) + return uint32(n) +} + +// Tell all goroutines that they have been preempted and they should stop. +// This function is purely best-effort. It can fail to inform a goroutine if a +// processor just started running it. +// No locks need to be held. +// Returns true if preemption request was issued to at least one goroutine. +func preemptall() bool { + res := false + for _, pp := range allp { + if pp.status != _Prunning { + continue + } + if preemptone(pp) { + res = true + } + } + return res +} + +// Tell the goroutine running on processor P to stop. +// This function is purely best-effort. It can incorrectly fail to inform the +// goroutine. It can inform the wrong goroutine. Even if it informs the +// correct goroutine, that goroutine might ignore the request if it is +// simultaneously executing newstack. +// No lock needs to be held. +// Returns true if preemption request was issued. +// The actual preemption will happen at some point in the future +// and will be indicated by the gp->status no longer being +// Grunning +func preemptone(pp *p) bool { + mp := pp.m.ptr() + if mp == nil || mp == getg().m { + return false + } + gp := mp.curg + if gp == nil || gp == mp.g0 { + return false + } + + gp.preempt = true + + // Every call in a goroutine checks for stack overflow by + // comparing the current stack pointer to gp->stackguard0. + // Setting gp->stackguard0 to StackPreempt folds + // preemption into the normal stack overflow check. + gp.stackguard0 = stackPreempt + + // Request an async preemption of this P. + if preemptMSupported && debug.asyncpreemptoff == 0 { + pp.preempt = true + preemptM(mp) + } + + return true +} + +var starttime int64 + +func schedtrace(detailed bool) { + now := nanotime() + if starttime == 0 { + starttime = now + } + + lock(&sched.lock) + print("SCHED ", (now-starttime)/1e6, "ms: gomaxprocs=", gomaxprocs, " idleprocs=", sched.npidle.Load(), " threads=", mcount(), " spinningthreads=", sched.nmspinning.Load(), " needspinning=", sched.needspinning.Load(), " idlethreads=", sched.nmidle, " runqueue=", sched.runqsize) + if detailed { + print(" gcwaiting=", sched.gcwaiting.Load(), " nmidlelocked=", sched.nmidlelocked, " stopwait=", sched.stopwait, " sysmonwait=", sched.sysmonwait.Load(), "\n") + } + // We must be careful while reading data from P's, M's and G's. + // Even if we hold schedlock, most data can be changed concurrently. + // E.g. (p->m ? p->m->id : -1) can crash if p->m changes from non-nil to nil. + for i, pp := range allp { + mp := pp.m.ptr() + h := atomic.Load(&pp.runqhead) + t := atomic.Load(&pp.runqtail) + if detailed { + print(" P", i, ": status=", pp.status, " schedtick=", pp.schedtick, " syscalltick=", pp.syscalltick, " m=") + if mp != nil { + print(mp.id) + } else { + print("nil") + } + print(" runqsize=", t-h, " gfreecnt=", pp.gFree.n, " timerslen=", len(pp.timers), "\n") + } else { + // In non-detailed mode format lengths of per-P run queues as: + // [len1 len2 len3 len4] + print(" ") + if i == 0 { + print("[") + } + print(t - h) + if i == len(allp)-1 { + print("]\n") + } + } + } + + if !detailed { + unlock(&sched.lock) + return + } + + for mp := allm; mp != nil; mp = mp.alllink { + pp := mp.p.ptr() + print(" M", mp.id, ": p=") + if pp != nil { + print(pp.id) + } else { + print("nil") + } + print(" curg=") + if mp.curg != nil { + print(mp.curg.goid) + } else { + print("nil") + } + print(" mallocing=", mp.mallocing, " throwing=", mp.throwing, " preemptoff=", mp.preemptoff, " locks=", mp.locks, " dying=", mp.dying, " spinning=", mp.spinning, " blocked=", mp.blocked, " lockedg=") + if lockedg := mp.lockedg.ptr(); lockedg != nil { + print(lockedg.goid) + } else { + print("nil") + } + print("\n") + } + + forEachG(func(gp *g) { + print(" G", gp.goid, ": status=", readgstatus(gp), "(", gp.waitreason.String(), ") m=") + if gp.m != nil { + print(gp.m.id) + } else { + print("nil") + } + print(" lockedm=") + if lockedm := gp.lockedm.ptr(); lockedm != nil { + print(lockedm.id) + } else { + print("nil") + } + print("\n") + }) + unlock(&sched.lock) +} + +// schedEnableUser enables or disables the scheduling of user +// goroutines. +// +// This does not stop already running user goroutines, so the caller +// should first stop the world when disabling user goroutines. +func schedEnableUser(enable bool) { + lock(&sched.lock) + if sched.disable.user == !enable { + unlock(&sched.lock) + return + } + sched.disable.user = !enable + if enable { + n := sched.disable.n + sched.disable.n = 0 + globrunqputbatch(&sched.disable.runnable, n) + unlock(&sched.lock) + for ; n != 0 && sched.npidle.Load() != 0; n-- { + startm(nil, false, false) + } + } else { + unlock(&sched.lock) + } +} + +// schedEnabled reports whether gp should be scheduled. It returns +// false is scheduling of gp is disabled. +// +// sched.lock must be held. +func schedEnabled(gp *g) bool { + assertLockHeld(&sched.lock) + + if sched.disable.user { + return isSystemGoroutine(gp, true) + } + return true +} + +// Put mp on midle list. +// sched.lock must be held. +// May run during STW, so write barriers are not allowed. +// +//go:nowritebarrierrec +func mput(mp *m) { + assertLockHeld(&sched.lock) + + mp.schedlink = sched.midle + sched.midle.set(mp) + sched.nmidle++ + checkdead() +} + +// Try to get an m from midle list. +// sched.lock must be held. +// May run during STW, so write barriers are not allowed. +// +//go:nowritebarrierrec +func mget() *m { + assertLockHeld(&sched.lock) + + mp := sched.midle.ptr() + if mp != nil { + sched.midle = mp.schedlink + sched.nmidle-- + } + return mp +} + +// Put gp on the global runnable queue. +// sched.lock must be held. +// May run during STW, so write barriers are not allowed. +// +//go:nowritebarrierrec +func globrunqput(gp *g) { + assertLockHeld(&sched.lock) + + sched.runq.pushBack(gp) + sched.runqsize++ +} + +// Put gp at the head of the global runnable queue. +// sched.lock must be held. +// May run during STW, so write barriers are not allowed. +// +//go:nowritebarrierrec +func globrunqputhead(gp *g) { + assertLockHeld(&sched.lock) + + sched.runq.push(gp) + sched.runqsize++ +} + +// Put a batch of runnable goroutines on the global runnable queue. +// This clears *batch. +// sched.lock must be held. +// May run during STW, so write barriers are not allowed. +// +//go:nowritebarrierrec +func globrunqputbatch(batch *gQueue, n int32) { + assertLockHeld(&sched.lock) + + sched.runq.pushBackAll(*batch) + sched.runqsize += n + *batch = gQueue{} +} + +// Try get a batch of G's from the global runnable queue. +// sched.lock must be held. +func globrunqget(pp *p, max int32) *g { + assertLockHeld(&sched.lock) + + if sched.runqsize == 0 { + return nil + } + + n := sched.runqsize/gomaxprocs + 1 + if n > sched.runqsize { + n = sched.runqsize + } + if max > 0 && n > max { + n = max + } + if n > int32(len(pp.runq))/2 { + n = int32(len(pp.runq)) / 2 + } + + sched.runqsize -= n + + gp := sched.runq.pop() + n-- + for ; n > 0; n-- { + gp1 := sched.runq.pop() + runqput(pp, gp1, false) + } + return gp +} + +// pMask is an atomic bitstring with one bit per P. +type pMask []uint32 + +// read returns true if P id's bit is set. +func (p pMask) read(id uint32) bool { + word := id / 32 + mask := uint32(1) << (id % 32) + return (atomic.Load(&p[word]) & mask) != 0 +} + +// set sets P id's bit. +func (p pMask) set(id int32) { + word := id / 32 + mask := uint32(1) << (id % 32) + atomic.Or(&p[word], mask) +} + +// clear clears P id's bit. +func (p pMask) clear(id int32) { + word := id / 32 + mask := uint32(1) << (id % 32) + atomic.And(&p[word], ^mask) +} + +// updateTimerPMask clears pp's timer mask if it has no timers on its heap. +// +// Ideally, the timer mask would be kept immediately consistent on any timer +// operations. Unfortunately, updating a shared global data structure in the +// timer hot path adds too much overhead in applications frequently switching +// between no timers and some timers. +// +// As a compromise, the timer mask is updated only on pidleget / pidleput. A +// running P (returned by pidleget) may add a timer at any time, so its mask +// must be set. An idle P (passed to pidleput) cannot add new timers while +// idle, so if it has no timers at that time, its mask may be cleared. +// +// Thus, we get the following effects on timer-stealing in findrunnable: +// +// - Idle Ps with no timers when they go idle are never checked in findrunnable +// (for work- or timer-stealing; this is the ideal case). +// - Running Ps must always be checked. +// - Idle Ps whose timers are stolen must continue to be checked until they run +// again, even after timer expiration. +// +// When the P starts running again, the mask should be set, as a timer may be +// added at any time. +// +// TODO(prattmic): Additional targeted updates may improve the above cases. +// e.g., updating the mask when stealing a timer. +func updateTimerPMask(pp *p) { + if pp.numTimers.Load() > 0 { + return + } + + // Looks like there are no timers, however another P may transiently + // decrement numTimers when handling a timerModified timer in + // checkTimers. We must take timersLock to serialize with these changes. + lock(&pp.timersLock) + if pp.numTimers.Load() == 0 { + timerpMask.clear(pp.id) + } + unlock(&pp.timersLock) +} + +// pidleput puts p on the _Pidle list. now must be a relatively recent call +// to nanotime or zero. Returns now or the current time if now was zero. +// +// This releases ownership of p. Once sched.lock is released it is no longer +// safe to use p. +// +// sched.lock must be held. +// +// May run during STW, so write barriers are not allowed. +// +//go:nowritebarrierrec +func pidleput(pp *p, now int64) int64 { + assertLockHeld(&sched.lock) + + if !runqempty(pp) { + throw("pidleput: P has non-empty run queue") + } + if now == 0 { + now = nanotime() + } + updateTimerPMask(pp) // clear if there are no timers. + idlepMask.set(pp.id) + pp.link = sched.pidle + sched.pidle.set(pp) + sched.npidle.Add(1) + if !pp.limiterEvent.start(limiterEventIdle, now) { + throw("must be able to track idle limiter event") + } + return now +} + +// pidleget tries to get a p from the _Pidle list, acquiring ownership. +// +// sched.lock must be held. +// +// May run during STW, so write barriers are not allowed. +// +//go:nowritebarrierrec +func pidleget(now int64) (*p, int64) { + assertLockHeld(&sched.lock) + + pp := sched.pidle.ptr() + if pp != nil { + // Timer may get added at any time now. + if now == 0 { + now = nanotime() + } + timerpMask.set(pp.id) + idlepMask.clear(pp.id) + sched.pidle = pp.link + sched.npidle.Add(-1) + pp.limiterEvent.stop(limiterEventIdle, now) + } + return pp, now +} + +// pidlegetSpinning tries to get a p from the _Pidle list, acquiring ownership. +// This is called by spinning Ms (or callers than need a spinning M) that have +// found work. If no P is available, this must synchronized with non-spinning +// Ms that may be preparing to drop their P without discovering this work. +// +// sched.lock must be held. +// +// May run during STW, so write barriers are not allowed. +// +//go:nowritebarrierrec +func pidlegetSpinning(now int64) (*p, int64) { + assertLockHeld(&sched.lock) + + pp, now := pidleget(now) + if pp == nil { + // See "Delicate dance" comment in findrunnable. We found work + // that we cannot take, we must synchronize with non-spinning + // Ms that may be preparing to drop their P. + sched.needspinning.Store(1) + return nil, now + } + + return pp, now +} + +// runqempty reports whether pp has no Gs on its local run queue. +// It never returns true spuriously. +func runqempty(pp *p) bool { + // Defend against a race where 1) pp has G1 in runqnext but runqhead == runqtail, + // 2) runqput on pp kicks G1 to the runq, 3) runqget on pp empties runqnext. + // Simply observing that runqhead == runqtail and then observing that runqnext == nil + // does not mean the queue is empty. + for { + head := atomic.Load(&pp.runqhead) + tail := atomic.Load(&pp.runqtail) + runnext := atomic.Loaduintptr((*uintptr)(unsafe.Pointer(&pp.runnext))) + if tail == atomic.Load(&pp.runqtail) { + return head == tail && runnext == 0 + } + } +} + +// To shake out latent assumptions about scheduling order, +// we introduce some randomness into scheduling decisions +// when running with the race detector. +// The need for this was made obvious by changing the +// (deterministic) scheduling order in Go 1.5 and breaking +// many poorly-written tests. +// With the randomness here, as long as the tests pass +// consistently with -race, they shouldn't have latent scheduling +// assumptions. +const randomizeScheduler = raceenabled + +// runqput tries to put g on the local runnable queue. +// If next is false, runqput adds g to the tail of the runnable queue. +// If next is true, runqput puts g in the pp.runnext slot. +// If the run queue is full, runnext puts g on the global queue. +// Executed only by the owner P. +func runqput(pp *p, gp *g, next bool) { + if randomizeScheduler && next && fastrandn(2) == 0 { + next = false + } + + if next { + retryNext: + oldnext := pp.runnext + if !pp.runnext.cas(oldnext, guintptr(unsafe.Pointer(gp))) { + goto retryNext + } + if oldnext == 0 { + return + } + // Kick the old runnext out to the regular run queue. + gp = oldnext.ptr() + } + +retry: + h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with consumers + t := pp.runqtail + if t-h < uint32(len(pp.runq)) { + pp.runq[t%uint32(len(pp.runq))].set(gp) + atomic.StoreRel(&pp.runqtail, t+1) // store-release, makes the item available for consumption + return + } + if runqputslow(pp, gp, h, t) { + return + } + // the queue is not full, now the put above must succeed + goto retry +} + +// Put g and a batch of work from local runnable queue on global queue. +// Executed only by the owner P. +func runqputslow(pp *p, gp *g, h, t uint32) bool { + var batch [len(pp.runq)/2 + 1]*g + + // First, grab a batch from local queue. + n := t - h + n = n / 2 + if n != uint32(len(pp.runq)/2) { + throw("runqputslow: queue is not full") + } + for i := uint32(0); i < n; i++ { + batch[i] = pp.runq[(h+i)%uint32(len(pp.runq))].ptr() + } + if !atomic.CasRel(&pp.runqhead, h, h+n) { // cas-release, commits consume + return false + } + batch[n] = gp + + if randomizeScheduler { + for i := uint32(1); i <= n; i++ { + j := fastrandn(i + 1) + batch[i], batch[j] = batch[j], batch[i] + } + } + + // Link the goroutines. + for i := uint32(0); i < n; i++ { + batch[i].schedlink.set(batch[i+1]) + } + var q gQueue + q.head.set(batch[0]) + q.tail.set(batch[n]) + + // Now put the batch on global queue. + lock(&sched.lock) + globrunqputbatch(&q, int32(n+1)) + unlock(&sched.lock) + return true +} + +// runqputbatch tries to put all the G's on q on the local runnable queue. +// If the queue is full, they are put on the global queue; in that case +// this will temporarily acquire the scheduler lock. +// Executed only by the owner P. +func runqputbatch(pp *p, q *gQueue, qsize int) { + h := atomic.LoadAcq(&pp.runqhead) + t := pp.runqtail + n := uint32(0) + for !q.empty() && t-h < uint32(len(pp.runq)) { + gp := q.pop() + pp.runq[t%uint32(len(pp.runq))].set(gp) + t++ + n++ + } + qsize -= int(n) + + if randomizeScheduler { + off := func(o uint32) uint32 { + return (pp.runqtail + o) % uint32(len(pp.runq)) + } + for i := uint32(1); i < n; i++ { + j := fastrandn(i + 1) + pp.runq[off(i)], pp.runq[off(j)] = pp.runq[off(j)], pp.runq[off(i)] + } + } + + atomic.StoreRel(&pp.runqtail, t) + if !q.empty() { + lock(&sched.lock) + globrunqputbatch(q, int32(qsize)) + unlock(&sched.lock) + } +} + +// Get g from local runnable queue. +// If inheritTime is true, gp should inherit the remaining time in the +// current time slice. Otherwise, it should start a new time slice. +// Executed only by the owner P. +func runqget(pp *p) (gp *g, inheritTime bool) { + // If there's a runnext, it's the next G to run. + next := pp.runnext + // If the runnext is non-0 and the CAS fails, it could only have been stolen by another P, + // because other Ps can race to set runnext to 0, but only the current P can set it to non-0. + // Hence, there's no need to retry this CAS if it fails. + if next != 0 && pp.runnext.cas(next, 0) { + return next.ptr(), true + } + + for { + h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with other consumers + t := pp.runqtail + if t == h { + return nil, false + } + gp := pp.runq[h%uint32(len(pp.runq))].ptr() + if atomic.CasRel(&pp.runqhead, h, h+1) { // cas-release, commits consume + return gp, false + } + } +} + +// runqdrain drains the local runnable queue of pp and returns all goroutines in it. +// Executed only by the owner P. +func runqdrain(pp *p) (drainQ gQueue, n uint32) { + oldNext := pp.runnext + if oldNext != 0 && pp.runnext.cas(oldNext, 0) { + drainQ.pushBack(oldNext.ptr()) + n++ + } + +retry: + h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with other consumers + t := pp.runqtail + qn := t - h + if qn == 0 { + return + } + if qn > uint32(len(pp.runq)) { // read inconsistent h and t + goto retry + } + + if !atomic.CasRel(&pp.runqhead, h, h+qn) { // cas-release, commits consume + goto retry + } + + // We've inverted the order in which it gets G's from the local P's runnable queue + // and then advances the head pointer because we don't want to mess up the statuses of G's + // while runqdrain() and runqsteal() are running in parallel. + // Thus we should advance the head pointer before draining the local P into a gQueue, + // so that we can update any gp.schedlink only after we take the full ownership of G, + // meanwhile, other P's can't access to all G's in local P's runnable queue and steal them. + // See https://groups.google.com/g/golang-dev/c/0pTKxEKhHSc/m/6Q85QjdVBQAJ for more details. + for i := uint32(0); i < qn; i++ { + gp := pp.runq[(h+i)%uint32(len(pp.runq))].ptr() + drainQ.pushBack(gp) + n++ + } + return +} + +// Grabs a batch of goroutines from pp's runnable queue into batch. +// Batch is a ring buffer starting at batchHead. +// Returns number of grabbed goroutines. +// Can be executed by any P. +func runqgrab(pp *p, batch *[256]guintptr, batchHead uint32, stealRunNextG bool) uint32 { + for { + h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with other consumers + t := atomic.LoadAcq(&pp.runqtail) // load-acquire, synchronize with the producer + n := t - h + n = n - n/2 + if n == 0 { + if stealRunNextG { + // Try to steal from pp.runnext. + if next := pp.runnext; next != 0 { + if pp.status == _Prunning { + // Sleep to ensure that pp isn't about to run the g + // we are about to steal. + // The important use case here is when the g running + // on pp ready()s another g and then almost + // immediately blocks. Instead of stealing runnext + // in this window, back off to give pp a chance to + // schedule runnext. This will avoid thrashing gs + // between different Ps. + // A sync chan send/recv takes ~50ns as of time of + // writing, so 3us gives ~50x overshoot. + if GOOS != "windows" && GOOS != "openbsd" && GOOS != "netbsd" { + usleep(3) + } else { + // On some platforms system timer granularity is + // 1-15ms, which is way too much for this + // optimization. So just yield. + osyield() + } + } + if !pp.runnext.cas(next, 0) { + continue + } + batch[batchHead%uint32(len(batch))] = next + return 1 + } + } + return 0 + } + if n > uint32(len(pp.runq)/2) { // read inconsistent h and t + continue + } + for i := uint32(0); i < n; i++ { + g := pp.runq[(h+i)%uint32(len(pp.runq))] + batch[(batchHead+i)%uint32(len(batch))] = g + } + if atomic.CasRel(&pp.runqhead, h, h+n) { // cas-release, commits consume + return n + } + } +} + +// Steal half of elements from local runnable queue of p2 +// and put onto local runnable queue of p. +// Returns one of the stolen elements (or nil if failed). +func runqsteal(pp, p2 *p, stealRunNextG bool) *g { + t := pp.runqtail + n := runqgrab(p2, &pp.runq, t, stealRunNextG) + if n == 0 { + return nil + } + n-- + gp := pp.runq[(t+n)%uint32(len(pp.runq))].ptr() + if n == 0 { + return gp + } + h := atomic.LoadAcq(&pp.runqhead) // load-acquire, synchronize with consumers + if t-h+n >= uint32(len(pp.runq)) { + throw("runqsteal: runq overflow") + } + atomic.StoreRel(&pp.runqtail, t+n) // store-release, makes the item available for consumption + return gp +} + +// A gQueue is a dequeue of Gs linked through g.schedlink. A G can only +// be on one gQueue or gList at a time. +type gQueue struct { + head guintptr + tail guintptr +} + +// empty reports whether q is empty. +func (q *gQueue) empty() bool { + return q.head == 0 +} + +// push adds gp to the head of q. +func (q *gQueue) push(gp *g) { + gp.schedlink = q.head + q.head.set(gp) + if q.tail == 0 { + q.tail.set(gp) + } +} + +// pushBack adds gp to the tail of q. +func (q *gQueue) pushBack(gp *g) { + gp.schedlink = 0 + if q.tail != 0 { + q.tail.ptr().schedlink.set(gp) + } else { + q.head.set(gp) + } + q.tail.set(gp) +} + +// pushBackAll adds all Gs in q2 to the tail of q. After this q2 must +// not be used. +func (q *gQueue) pushBackAll(q2 gQueue) { + if q2.tail == 0 { + return + } + q2.tail.ptr().schedlink = 0 + if q.tail != 0 { + q.tail.ptr().schedlink = q2.head + } else { + q.head = q2.head + } + q.tail = q2.tail +} + +// pop removes and returns the head of queue q. It returns nil if +// q is empty. +func (q *gQueue) pop() *g { + gp := q.head.ptr() + if gp != nil { + q.head = gp.schedlink + if q.head == 0 { + q.tail = 0 + } + } + return gp +} + +// popList takes all Gs in q and returns them as a gList. +func (q *gQueue) popList() gList { + stack := gList{q.head} + *q = gQueue{} + return stack +} + +// A gList is a list of Gs linked through g.schedlink. A G can only be +// on one gQueue or gList at a time. +type gList struct { + head guintptr +} + +// empty reports whether l is empty. +func (l *gList) empty() bool { + return l.head == 0 +} + +// push adds gp to the head of l. +func (l *gList) push(gp *g) { + gp.schedlink = l.head + l.head.set(gp) +} + +// pushAll prepends all Gs in q to l. +func (l *gList) pushAll(q gQueue) { + if !q.empty() { + q.tail.ptr().schedlink = l.head + l.head = q.head + } +} + +// pop removes and returns the head of l. If l is empty, it returns nil. +func (l *gList) pop() *g { + gp := l.head.ptr() + if gp != nil { + l.head = gp.schedlink + } + return gp +} + +//go:linkname setMaxThreads runtime/debug.setMaxThreads +func setMaxThreads(in int) (out int) { + lock(&sched.lock) + out = int(sched.maxmcount) + if in > 0x7fffffff { // MaxInt32 + sched.maxmcount = 0x7fffffff + } else { + sched.maxmcount = int32(in) + } + checkmcount() + unlock(&sched.lock) + return +} + +//go:nosplit +func procPin() int { + gp := getg() + mp := gp.m + + mp.locks++ + return int(mp.p.ptr().id) +} + +//go:nosplit +func procUnpin() { + gp := getg() + gp.m.locks-- +} + +//go:linkname sync_runtime_procPin sync.runtime_procPin +//go:nosplit +func sync_runtime_procPin() int { + return procPin() +} + +//go:linkname sync_runtime_procUnpin sync.runtime_procUnpin +//go:nosplit +func sync_runtime_procUnpin() { + procUnpin() +} + +//go:linkname sync_atomic_runtime_procPin sync/atomic.runtime_procPin +//go:nosplit +func sync_atomic_runtime_procPin() int { + return procPin() +} + +//go:linkname sync_atomic_runtime_procUnpin sync/atomic.runtime_procUnpin +//go:nosplit +func sync_atomic_runtime_procUnpin() { + procUnpin() +} + +// Active spinning for sync.Mutex. +// +//go:linkname sync_runtime_canSpin sync.runtime_canSpin +//go:nosplit +func sync_runtime_canSpin(i int) bool { + // sync.Mutex is cooperative, so we are conservative with spinning. + // Spin only few times and only if running on a multicore machine and + // GOMAXPROCS>1 and there is at least one other running P and local runq is empty. + // As opposed to runtime mutex we don't do passive spinning here, + // because there can be work on global runq or on other Ps. + if i >= active_spin || ncpu <= 1 || gomaxprocs <= sched.npidle.Load()+sched.nmspinning.Load()+1 { + return false + } + if p := getg().m.p.ptr(); !runqempty(p) { + return false + } + return true +} + +//go:linkname sync_runtime_doSpin sync.runtime_doSpin +//go:nosplit +func sync_runtime_doSpin() { + procyield(active_spin_cnt) +} + +var stealOrder randomOrder + +// randomOrder/randomEnum are helper types for randomized work stealing. +// They allow to enumerate all Ps in different pseudo-random orders without repetitions. +// The algorithm is based on the fact that if we have X such that X and GOMAXPROCS +// are coprime, then a sequences of (i + X) % GOMAXPROCS gives the required enumeration. +type randomOrder struct { + count uint32 + coprimes []uint32 +} + +type randomEnum struct { + i uint32 + count uint32 + pos uint32 + inc uint32 +} + +func (ord *randomOrder) reset(count uint32) { + ord.count = count + ord.coprimes = ord.coprimes[:0] + for i := uint32(1); i <= count; i++ { + if gcd(i, count) == 1 { + ord.coprimes = append(ord.coprimes, i) + } + } +} + +func (ord *randomOrder) start(i uint32) randomEnum { + return randomEnum{ + count: ord.count, + pos: i % ord.count, + inc: ord.coprimes[i/ord.count%uint32(len(ord.coprimes))], + } +} + +func (enum *randomEnum) done() bool { + return enum.i == enum.count +} + +func (enum *randomEnum) next() { + enum.i++ + enum.pos = (enum.pos + enum.inc) % enum.count +} + +func (enum *randomEnum) position() uint32 { + return enum.pos +} + +func gcd(a, b uint32) uint32 { + for b != 0 { + a, b = b, a%b + } + return a +} + +// An initTask represents the set of initializations that need to be done for a package. +// Keep in sync with ../../test/noinit.go:initTask +type initTask struct { + state uint32 // 0 = uninitialized, 1 = in progress, 2 = done + nfns uint32 + // followed by nfns pcs, uintptr sized, one per init function to run +} + +// inittrace stores statistics for init functions which are +// updated by malloc and newproc when active is true. +var inittrace tracestat + +type tracestat struct { + active bool // init tracing activation status + id uint64 // init goroutine id + allocs uint64 // heap allocations + bytes uint64 // heap allocated bytes +} + +func doInit(ts []*initTask) { + for _, t := range ts { + doInit1(t) + } +} + +func doInit1(t *initTask) { + switch t.state { + case 2: // fully initialized + return + case 1: // initialization in progress + throw("recursive call during initialization - linker skew") + default: // not initialized yet + t.state = 1 // initialization in progress + + var ( + start int64 + before tracestat + ) + + if inittrace.active { + start = nanotime() + // Load stats non-atomically since tracinit is updated only by this init goroutine. + before = inittrace + } + + if t.nfns == 0 { + // We should have pruned all of these in the linker. + throw("inittask with no functions") + } + + firstFunc := add(unsafe.Pointer(t), 8) + for i := uint32(0); i < t.nfns; i++ { + p := add(firstFunc, uintptr(i)*goarch.PtrSize) + f := *(*func())(unsafe.Pointer(&p)) + f() + } + + if inittrace.active { + end := nanotime() + // Load stats non-atomically since tracinit is updated only by this init goroutine. + after := inittrace + + f := *(*func())(unsafe.Pointer(&firstFunc)) + pkg := funcpkgpath(findfunc(abi.FuncPCABIInternal(f))) + + var sbuf [24]byte + print("init ", pkg, " @") + print(string(fmtNSAsMS(sbuf[:], uint64(start-runtimeInitTime))), " ms, ") + print(string(fmtNSAsMS(sbuf[:], uint64(end-start))), " ms clock, ") + print(string(itoa(sbuf[:], after.bytes-before.bytes)), " bytes, ") + print(string(itoa(sbuf[:], after.allocs-before.allocs)), " allocs") + print("\n") + } + + t.state = 2 // initialization done + } +} |