diff options
Diffstat (limited to 'src/runtime/proc.go')
| -rw-r--r-- | src/runtime/proc.go | 6336 |
1 files changed, 6336 insertions, 0 deletions
diff --git a/src/runtime/proc.go b/src/runtime/proc.go new file mode 100644 index 0000000..32fe877 --- /dev/null +++ b/src/runtime/proc.go @@ -0,0 +1,6336 @@ +// 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/bytealg" + "internal/cpu" + "runtime/internal/atomic" + "runtime/internal/sys" + "unsafe" +) + +var buildVersion = sys.TheVersion + +// 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: +// We unpark an additional thread when we ready a goroutine if (1) there is an +// idle P and 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 global run queue/ +// 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 do some +// spinning looking for work in per-P run queues 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 readying goroutines. 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 a new goroutine, 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 goroutine readying is: submit a goroutine +// to local work queue, #StoreLoad-style memory barrier, check sched.nmspinning. +// The general pattern for spinning->non-spinning transition is: decrement nmspinning, +// #StoreLoad-style memory barrier, check all per-P work queues 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. + +var ( + m0 m + g0 g + mcache0 *mcache + raceprocctx0 uintptr +) + +//go:linkname runtime_inittask runtime..inittask +var runtime_inittask initTask + +//go:linkname main_inittask main..inittask +var main_inittask 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() { + g := getg() + + // Racectx of m0->g0 is used only as the parent of the main goroutine. + // It must not be used for anything else. + g.m.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 sys.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 + // For runtime_syscall_doAllThreadsSyscall, we + // register sysmon is not ready for the world to be + // stopped. + atomic.Store(&sched.sysmonStarting, 1) + 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 g.m != &m0 { + throw("runtime.main not on m0") + } + m0.doesPark = true + + // 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_inittask) // 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_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") + } + // 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) + } + + doInit(&main_inittask) + + // 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 { + 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 atomic.Load(&runningPanicDefers) != 0 { + // Running deferred functions should not take long. + for c := 0; c < 1000; c++ { + if atomic.Load(&runningPanicDefers) == 0 { + break + } + Gosched() + } + } + if atomic.Load(&panicking) != 0 { + gopark(nil, nil, waitReasonPanicWait, traceEvGoStop, 1) + } + + 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() { + if 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 != 0 { + throw("forcegc: phase error") + } + atomic.Store(&forcegc.idle, 1) + goparkunlock(&forcegc.lock, waitReasonForceGCIdle, traceEvGoBlock, 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()}) + } +} + +//go:nosplit + +// Gosched yields the processor, allowing other goroutines to run. It does not +// suspend the current goroutine, so execution resumes automatically. +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) +} + +// 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, traceEv byte, 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.waittraceev = traceEv + 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, traceEv byte, traceskip int) { + gopark(parkunlock_c, unsafe.Pointer(lock), reason, traceEv, 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) +} + +// funcPC returns the entry PC of the function f. +// It assumes that f is a func value. Otherwise the behavior is undefined. +// CAREFUL: In programs with plugins, funcPC can return different values +// for the same function (because there are actually multiple copies of +// the same function in the address space). To be safe, don't use the +// results of this function in any == expression. It is only safe to +// use the result as an address at which to start executing code. +//go:nosplit +func funcPC(f interface{}) uintptr { + return *(*uintptr)(efaceOf(&f).data) +} + +// 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")) +} + +var badmorestackg0Msg = "fatal: morestack on g0\n" + +//go:nosplit +//go:nowritebarrierrec +func badmorestackg0() { + sp := stringStructOf(&badmorestackg0Msg) + write(2, sp.str, int32(sp.len)) +} + +var badmorestackgsignalMsg = "fatal: morestack on gsignal\n" + +//go:nosplit +//go:nowritebarrierrec +func badmorestackgsignal() { + sp := stringStructOf(&badmorestackgsignalMsg) + write(2, sp.str, int32(sp.len)) +} + +//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(allg) and + // &allg[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) +} + +// 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*sys.PtrSize)) +} + +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 extracts the environment variable GODEBUG from the environment on +// Unix-like operating systems and calls internal/cpu.Initialize. +func cpuinit() { + const prefix = "GODEBUG=" + var env string + + switch GOOS { + case "aix", "darwin", "ios", "dragonfly", "freebsd", "netbsd", "openbsd", "illumos", "solaris", "linux": + cpu.DebugOptions = true + + // 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 := *(*string)(unsafe.Pointer(&stringStruct{unsafe.Pointer(p), findnull(p)})) + + if hasPrefix(s, prefix) { + env = gostring(p)[len(prefix):] + break + } + } + } + + 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. + x86HasPOPCNT = cpu.X86.HasPOPCNT + x86HasSSE41 = cpu.X86.HasSSE41 + x86HasFMA = cpu.X86.HasFMA + + armHasVFPv4 = cpu.ARM.HasVFPv4 + + arm64HasATOMICS = cpu.ARM64.HasATOMICS +} + +// 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(&trace.bufLock, lockRankTraceBuf) + lockInit(&trace.stringsLock, lockRankTraceStrings) + lockInit(&trace.lock, lockRankTrace) + lockInit(&cpuprof.lock, lockRankCpuprof) + lockInit(&trace.stackTab.lock, lockRankTraceStackTab) + // 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. + _g_ := getg() + if raceenabled { + _g_.racectx, raceprocctx0 = raceinit() + } + + sched.maxmcount = 10000 + + // The world starts stopped. + worldStopped() + + moduledataverify() + stackinit() + mallocinit() + fastrandinit() // must run before mcommoninit + mcommoninit(_g_.m, -1) + cpuinit() // must run before alginit + alginit() // maps must not be used before this call + modulesinit() // provides activeModules + typelinksinit() // uses maps, activeModules + itabsinit() // uses activeModules + + sigsave(&_g_.m.sigmask) + initSigmask = _g_.m.sigmask + + goargs() + goenvs() + parsedebugvars() + gcinit() + + lock(&sched.lock) + sched.lastpoll = uint64(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() + + // For cgocheck > 1, we turn on the write barrier at all times + // and check all pointer writes. We can't do this until after + // procresize because the write barrier needs a P. + if debug.cgocheck > 1 { + writeBarrier.cgo = true + writeBarrier.enabled = true + for _, p := range allp { + p.wbBuf.reset() + } + } + + 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) { + _g_ := getg() + print("runtime: gp: gp=", gp, ", goid=", gp.goid, ", gp->atomicstatus=", readgstatus(gp), "\n") + print("runtime: g: g=", _g_, ", goid=", _g_.goid, ", g->atomicstatus=", readgstatus(_g_), "\n") +} + +// sched.lock must be held. +func checkmcount() { + assertLockHeld(&sched.lock) + + if mcount() > 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) { + _g_ := getg() + + // g0 stack won't make sense for user (and is not necessary unwindable). + if _g_ != _g_.m.g0 { + callers(1, mp.createstack[:]) + } + + lock(&sched.lock) + + if id >= 0 { + mp.id = id + } else { + mp.id = mReserveID() + } + + mp.fastrand[0] = uint32(int64Hash(uint64(mp.id), fastrandseed)) + mp.fastrand[1] = uint32(int64Hash(uint64(cputicks()), ^fastrandseed)) + if mp.fastrand[0]|mp.fastrand[1] == 0 { + mp.fastrand[1] = 1 + } + + 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) + } +} + +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 trace.enabled { + traceGoUnpark(gp, traceskip) + } + + status := readgstatus(gp) + + // Mark runnable. + _g_ := getg() + 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(_g_.m.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 uint32 + +// 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() { + atomic.Store(&freezing, 1) + // 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 + atomic.Store(&sched.gcwaiting, 1) + // 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 atomic.Load(&gp.atomicstatus) +} + +// 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 = atomic.Cas(&gp.atomicstatus, 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 := atomic.Cas(&gp.atomicstatus, oldval, newval) + if r { + acquireLockRank(lockRankGscan) + } + return r + + } + } + print("runtime: castogscanstatus oldval=", hex(oldval), " newval=", hex(newval), "\n") + throw("castogscanstatus") + panic("not reached") +} + +// 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; !atomic.Cas(&gp.atomicstatus, oldval, newval); i++ { + if oldval == _Gwaiting && gp.atomicstatus == _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 != oldval; x++ { + procyield(1) + } + } else { + osyield() + nextYield = nanotime() + yieldDelay/2 + } + } +} + +// 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 atomic.Cas(&gp.atomicstatus, 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 !atomic.Cas(&gp.atomicstatus, _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") + } + return atomic.Cas(&gp.atomicstatus, _Gpreempted, _Gwaiting) +} + +// 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 string) { + semacquire(&worldsema) + gp := getg() + gp.m.preemptoff = reason + 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. + casgstatus(gp, _Grunning, _Gwaiting) + stopTheWorldWithSema() + casgstatus(gp, _Gwaiting, _Grunning) + }) +} + +// startTheWorld undoes the effects of stopTheWorld. +func startTheWorld() { + systemstack(func() { startTheWorldWithSema(false) }) + + // 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 string) { + 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() { + _g_ := 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 _g_.m.locks > 0 { + throw("stopTheWorld: holding locks") + } + + lock(&sched.lock) + sched.stopwait = gomaxprocs + atomic.Store(&sched.gcwaiting, 1) + preemptall() + // stop current P + _g_.m.p.ptr().status = _Pgcstop // Pgcstop is only diagnostic. + sched.stopwait-- + // try to retake all P's in Psyscall status + for _, p := range allp { + s := p.status + if s == _Psyscall && atomic.Cas(&p.status, s, _Pgcstop) { + if trace.enabled { + traceGoSysBlock(p) + traceProcStop(p) + } + p.syscalltick++ + sched.stopwait-- + } + } + // stop idle P's + for { + p := pidleget() + if p == nil { + break + } + p.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 _, p := range allp { + if p.status != _Pgcstop { + bad = "stopTheWorld: not stopped (status != _Pgcstop)" + } + } + } + if atomic.Load(&freezing) != 0 { + // 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(emitTraceEvent bool) 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 = 0 + if sched.sysmonwait != 0 { + sched.sysmonwait = 0 + 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 emitTraceEvent { + traceGCSTWDone() + } + + // 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 == "amd64" || 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 "amd64", "arm64": + return true + } + } + return false +} + +// mstart is the 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 mstart() { + _g_ := getg() + + osStack := _g_.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 := _g_.stack.hi + if size == 0 { + size = 8192 * sys.StackGuardMultiplier + } + _g_.stack.hi = uintptr(noescape(unsafe.Pointer(&size))) + _g_.stack.lo = _g_.stack.hi - size + 1024 + } + // Initialize stack guard so that we can start calling regular + // Go code. + _g_.stackguard0 = _g_.stack.lo + _StackGuard + // This is the g0, so we can also call go:systemstack + // functions, which check stackguard1. + _g_.stackguard1 = _g_.stackguard0 + mstart1() + + // Exit this thread. + if mStackIsSystemAllocated() { + // Windows, Solaris, illumos, Darwin, AIX and Plan 9 always system-allocate + // the stack, but put it in _g_.stack before mstart, + // so the logic above hasn't set osStack yet. + osStack = true + } + mexit(osStack) +} + +func mstart1() { + _g_ := getg() + + if _g_ != _g_.m.g0 { + throw("bad runtime·mstart") + } + + // Record the caller for use as the top of stack in mcall and + // for terminating the thread. + // We're never coming back to mstart1 after we call schedule, + // so other calls can reuse the current frame. + save(getcallerpc(), getcallersp()) + asminit() + minit() + + // Install signal handlers; after minit so that minit can + // prepare the thread to be able to handle the signals. + if _g_.m == &m0 { + mstartm0() + } + + if fn := _g_.m.mstartfn; fn != nil { + fn() + } + + if _g_.m != &m0 { + acquirep(_g_.m.nextp.ptr()) + _g_.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 - temporarily waking for +// fixups but otherwise waiting to be fully woken. This is the +// only way that m's should park themselves. +//go:nosplit +func mPark() { + g := getg() + for { + notesleep(&g.m.park) + // Note, because of signal handling by this parked m, + // a preemptive mDoFixup() may actually occur via + // mDoFixupAndOSYield(). (See golang.org/issue/44193) + noteclear(&g.m.park) + if !mDoFixup() { + return + } + } +} + +// 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(&_g_.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) { + g := getg() + m := g.m + + if m == &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 m.gsignal != nil { + stackfree(m.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. + m.gsignal = nil + } + + // Remove m from allm. + lock(&sched.lock) + for pprev := &allm; *pprev != nil; pprev = &(*pprev).alllink { + if *pprev == m { + *pprev = m.alllink + goto found + } + } + throw("m not found in allm") +found: + if !osStack { + // Delay reaping m until it's done with the stack. + // + // If this is using an OS stack, the OS will free it + // so there's no need for reaping. + atomic.Store(&m.freeWait, 1) + // Put m on the free list, though it will not be reaped until + // freeWait is 0. Note that the free list must not be linked + // through alllink because some functions walk allm without + // locking, so may be using alllink. + m.freelink = sched.freem + sched.freem = m + } + unlock(&sched.lock) + + // 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 atomic.Load(&m.signalPending) != 0 { + atomic.Xadd(&pendingPreemptSignals, -1) + } + } + + // Destroy all allocated resources. After this is called, we may no + // longer take any locks. + mdestroy(m) + + if osStack { + // 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(&m.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() + _p_ := 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 _, p := range allp { + if p != _p_ { + atomic.Store(&p.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(_p_) + + // Force Ps currently in _Psyscall into _Pidle and hand them + // off to induce safe point function execution. + for _, p := range allp { + s := p.status + if s == _Psyscall && p.runSafePointFn == 1 && atomic.Cas(&p.status, s, _Pidle) { + if trace.enabled { + traceGoSysBlock(p) + traceProcStop(p) + } + p.syscalltick++ + handoffp(p) + } + } + + // 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 _, p := range allp { + if p.runSafePointFn != 0 { + throw("forEachP: P did not run fn") + } + } + + lock(&sched.lock) + sched.safePointFn = nil + unlock(&sched.lock) + releasem(mp) +} + +// syscall_runtime_doAllThreadsSyscall serializes Go execution and +// executes a specified fn() call on all m's. +// +// The boolean argument to fn() indicates whether the function's +// return value will be consulted or not. That is, fn(true) should +// return true if fn() succeeds, and fn(true) should return false if +// it failed. When fn(false) is called, its return status will be +// ignored. +// +// syscall_runtime_doAllThreadsSyscall first invokes fn(true) on a +// single, coordinating, m, and only if it returns true does it go on +// to invoke fn(false) on all of the other m's known to the process. +// +//go:linkname syscall_runtime_doAllThreadsSyscall syscall.runtime_doAllThreadsSyscall +func syscall_runtime_doAllThreadsSyscall(fn func(bool) bool) { + if iscgo { + panic("doAllThreadsSyscall not supported with cgo enabled") + } + if fn == nil { + return + } + for atomic.Load(&sched.sysmonStarting) != 0 { + osyield() + } + + // We don't want this thread to handle signals for the + // duration of this critical section. The underlying issue + // being that this locked coordinating m is the one monitoring + // for fn() execution by all the other m's of the runtime, + // while no regular go code execution is permitted (the world + // is stopped). If this present m were to get distracted to + // run signal handling code, and find itself waiting for a + // second thread to execute go code before being able to + // return from that signal handling, a deadlock will result. + // (See golang.org/issue/44193.) + lockOSThread() + var sigmask sigset + sigsave(&sigmask) + sigblock(false) + + stopTheWorldGC("doAllThreadsSyscall") + if atomic.Load(&newmHandoff.haveTemplateThread) != 0 { + // Ensure that there are no in-flight thread + // creations: don't want to race with allm. + lock(&newmHandoff.lock) + for !newmHandoff.waiting { + unlock(&newmHandoff.lock) + osyield() + lock(&newmHandoff.lock) + } + unlock(&newmHandoff.lock) + } + if netpollinited() { + netpollBreak() + } + sigRecvPrepareForFixup() + _g_ := getg() + if raceenabled { + // For m's running without racectx, we loan out the + // racectx of this call. + lock(&mFixupRace.lock) + mFixupRace.ctx = _g_.racectx + unlock(&mFixupRace.lock) + } + if ok := fn(true); ok { + tid := _g_.m.procid + for mp := allm; mp != nil; mp = mp.alllink { + if mp.procid == tid { + // This m has already completed fn() + // call. + continue + } + // Be wary of mp's without procid values if + // they are known not to park. If they are + // marked as parking with a zero procid, then + // they will be racing with this code to be + // allocated a procid and we will annotate + // them with the need to execute the fn when + // they acquire a procid to run it. + if mp.procid == 0 && !mp.doesPark { + // Reaching here, we are either + // running Windows, or cgo linked + // code. Neither of which are + // currently supported by this API. + throw("unsupported runtime environment") + } + // stopTheWorldGC() doesn't guarantee stopping + // all the threads, so we lock here to avoid + // the possibility of racing with mp. + lock(&mp.mFixup.lock) + mp.mFixup.fn = fn + atomic.Store(&mp.mFixup.used, 1) + if mp.doesPark { + // For non-service threads this will + // cause the wakeup to be short lived + // (once the mutex is unlocked). The + // next real wakeup will occur after + // startTheWorldGC() is called. + notewakeup(&mp.park) + } + unlock(&mp.mFixup.lock) + } + for { + done := true + for mp := allm; done && mp != nil; mp = mp.alllink { + if mp.procid == tid { + continue + } + done = atomic.Load(&mp.mFixup.used) == 0 + } + if done { + break + } + // if needed force sysmon and/or newmHandoff to wakeup. + lock(&sched.lock) + if atomic.Load(&sched.sysmonwait) != 0 { + atomic.Store(&sched.sysmonwait, 0) + notewakeup(&sched.sysmonnote) + } + unlock(&sched.lock) + lock(&newmHandoff.lock) + if newmHandoff.waiting { + newmHandoff.waiting = false + notewakeup(&newmHandoff.wake) + } + unlock(&newmHandoff.lock) + osyield() + } + } + if raceenabled { + lock(&mFixupRace.lock) + mFixupRace.ctx = 0 + unlock(&mFixupRace.lock) + } + startTheWorldGC() + msigrestore(sigmask) + unlockOSThread() +} + +// 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 _p_. +// +//go:yeswritebarrierrec +func allocm(_p_ *p, fn func(), id int64) *m { + _g_ := getg() + acquirem() // disable GC because it can be called from sysmon + if _g_.m.p == 0 { + acquirep(_p_) // 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; { + if freem.freeWait != 0 { + next := freem.freelink + freem.freelink = newList + newList = freem + freem = next + continue + } + // 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(8192 * sys.StackGuardMultiplier) + } + mp.g0.m = mp + + if _p_ == _g_.m.p.ptr() { + releasep() + } + releasem(_g_.m) + + 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. +// +// When the callback is done with the m, it calls dropm to +// put the m back on the list. +//go:nosplit +func needm() { + 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. + write(2, unsafe.Pointer(&earlycgocallback[0]), int32(len(earlycgocallback))) + 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) + + // Lock extra list, take head, unlock popped list. + // nilokay=false is safe here because of the invariant above, + // that the extra list always contains or will soon contain + // at least one m. + mp := lockextra(false) + + // 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 = mp.schedlink == 0 + extraMCount-- + unlockextra(mp.schedlink.ptr()) + + // Store the original signal mask for use by minit. + mp.sigmask = sigmask + + // Install g (= m->g0) and set the stack bounds + // to match the current stack. We don't actually know + // how big the stack is, like we don't know how big any + // scheduling stack is, but we assume there's at least 32 kB, + // which is more than enough for us. + setg(mp.g0) + _g_ := getg() + _g_.stack.hi = getcallersp() + 1024 + _g_.stack.lo = getcallersp() - 32*1024 + _g_.stackguard0 = _g_.stack.lo + _StackGuard + + // Initialize this thread to use the m. + asminit() + minit() + + // mp.curg is now a real goroutine. + casgstatus(mp.curg, _Gdead, _Gsyscall) + atomic.Xadd(&sched.ngsys, -1) +} + +var earlycgocallback = []byte("fatal error: cgo callback before cgo call\n") + +// 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 := atomic.Xchg(&extraMWaiters, 0) + if c > 0 { + for i := uint32(0); i < c; i++ { + oneNewExtraM() + } + } else { + // Make sure there is at least one extra M. + mp := lockextra(true) + unlockextra(mp) + if mp == nil { + 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 = funcPC(goexit) + sys.PCQuantum + gp.sched.sp = gp.stack.hi + gp.sched.sp -= 4 * sys.RegSize // 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.lockedInt++ + mp.lockedg.set(gp) + gp.lockedm.set(mp) + gp.goid = int64(atomic.Xadd64(&sched.goidgen, 1)) + if raceenabled { + gp.racectx = racegostart(funcPC(newextram) + sys.PCQuantum) + } + // 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. + atomic.Xadd(&sched.ngsys, +1) + + // Add m to the extra list. + mnext := lockextra(true) + mp.schedlink.set(mnext) + extraMCount++ + unlockextra(mp) +} + +// 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. +// It puts the current m back onto the extra list. +// +// 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. +// +// TODO(rsc): An alternative would be to allocate a dummy pthread per-thread +// variable using pthread_key_create. Unlike the pthread keys we already use +// on OS X, this dummy key would never be read by Go code. It would exist +// only so that we could register at thread-exit-time destructor. +// That destructor would put the m back onto the extra list. +// This is purely a performance optimization. The current version, +// in which dropm happens on each cgo call, is still correct too. +// We may have to keep the current version on systems with cgo +// but without pthreads, like Windows. +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 + atomic.Xadd(&sched.ngsys, +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() + + mnext := lockextra(true) + extraMCount++ + mp.schedlink.set(mnext) + + setg(nil) + + // Commit the release of mp. + unlockextra(mp) + + msigrestore(sigmask) +} + +// A helper function for EnsureDropM. +func getm() uintptr { + return uintptr(unsafe.Pointer(getg().m)) +} + +var extram uintptr +var extraMCount uint32 // Protected by lockextra +var extraMWaiters 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 := atomic.Loaduintptr(&extram) + if old == locked { + osyield() + continue + } + if old == 0 && !nilokay { + if !incr { + // Add 1 to the number of threads + // waiting for an M. + // This is cleared by newextram. + atomic.Xadd(&extraMWaiters, 1) + incr = true + } + usleep(1) + continue + } + if atomic.Casuintptr(&extram, old, locked) { + return (*m)(unsafe.Pointer(old)) + } + osyield() + continue + } +} + +//go:nosplit +func unlockextra(mp *m) { + atomic.Storeuintptr(&extram, uintptr(unsafe.Pointer(mp))) +} + +// execLock serializes exec and clone to avoid bugs or unspecified behaviour +// around exec'ing while creating/destroying threads. See issue #19546. +var execLock rwmutex + +// 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(), _p_ *p, id int64) { + mp := allocm(_p_, fn, id) + mp.doesPark = (_p_ != nil) + mp.nextp.set(_p_) + 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) + return + } + newm1(mp) +} + +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(funcPC(mstart)) + if msanenabled { + msanwrite(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) +} + +// mFixupRace is used to temporarily borrow the race context from the +// coordinating m during a syscall_runtime_doAllThreadsSyscall and +// loan it out to each of the m's of the runtime so they can execute a +// mFixup.fn in that context. +var mFixupRace struct { + lock mutex + ctx uintptr +} + +// mDoFixup runs any outstanding fixup function for the running m. +// Returns true if a fixup was outstanding and actually executed. +// +// Note: to avoid deadlocks, and the need for the fixup function +// itself to be async safe, signals are blocked for the working m +// while it holds the mFixup lock. (See golang.org/issue/44193) +// +//go:nosplit +func mDoFixup() bool { + _g_ := getg() + if used := atomic.Load(&_g_.m.mFixup.used); used == 0 { + return false + } + + // slow path - if fixup fn is used, block signals and lock. + var sigmask sigset + sigsave(&sigmask) + sigblock(false) + lock(&_g_.m.mFixup.lock) + fn := _g_.m.mFixup.fn + if fn != nil { + if gcphase != _GCoff { + // We can't have a write barrier in this + // context since we may not have a P, but we + // clear fn to signal that we've executed the + // fixup. As long as fn is kept alive + // elsewhere, technically we should have no + // issues with the GC, but fn is likely + // generated in a different package altogether + // that may change independently. Just assert + // the GC is off so this lack of write barrier + // is more obviously safe. + throw("GC must be disabled to protect validity of fn value") + } + if _g_.racectx != 0 || !raceenabled { + fn(false) + } else { + // temporarily acquire the context of the + // originator of the + // syscall_runtime_doAllThreadsSyscall and + // block others from using it for the duration + // of the fixup call. + lock(&mFixupRace.lock) + _g_.racectx = mFixupRace.ctx + fn(false) + _g_.racectx = 0 + unlock(&mFixupRace.lock) + } + *(*uintptr)(unsafe.Pointer(&_g_.m.mFixup.fn)) = 0 + atomic.Store(&_g_.m.mFixup.used, 0) + } + unlock(&_g_.m.mFixup.lock) + msigrestore(sigmask) + return fn != nil +} + +// mDoFixupAndOSYield is called when an m is unable to send a signal +// because the allThreadsSyscall mechanism is in progress. That is, an +// mPark() has been interrupted with this signal handler so we need to +// ensure the fixup is executed from this context. +//go:nosplit +func mDoFixupAndOSYield() { + mDoFixup() + osyield() +} + +// 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) + mDoFixup() + } +} + +// Stops execution of the current m until new work is available. +// Returns with acquired P. +func stopm() { + _g_ := getg() + + if _g_.m.locks != 0 { + throw("stopm holding locks") + } + if _g_.m.p != 0 { + throw("stopm holding p") + } + if _g_.m.spinning { + throw("stopm spinning") + } + + lock(&sched.lock) + mput(_g_.m) + unlock(&sched.lock) + mPark() + acquirep(_g_.m.nextp.ptr()) + _g_.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 startm will +// either decrement nmspinning or 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. +// +// Must not have write barriers because this may be called without a P. +//go:nowritebarrierrec +func startm(_p_ *p, spinning 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() + lock(&sched.lock) + if _p_ == nil { + _p_ = pidleget() + if _p_ == nil { + unlock(&sched.lock) + if spinning { + // The caller incremented nmspinning, but there are no idle Ps, + // so it's okay to just undo the increment and give up. + if int32(atomic.Xadd(&sched.nmspinning, -1)) < 0 { + throw("startm: negative nmspinning") + } + } + 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. + // + // 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, _p_, id) + // Ownership transfer of _p_ committed by start in newm. + // Preemption is now safe. + releasem(mp) + return + } + unlock(&sched.lock) + if nmp.spinning { + throw("startm: m is spinning") + } + if nmp.nextp != 0 { + throw("startm: m has p") + } + if spinning && !runqempty(_p_) { + throw("startm: p has runnable gs") + } + // The caller incremented nmspinning, so set m.spinning in the new M. + nmp.spinning = spinning + nmp.nextp.set(_p_) + notewakeup(&nmp.park) + // Ownership transfer of _p_ 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(_p_ *p) { + // handoffp must start an M in any situation where + // findrunnable would return a G to run on _p_. + + // if it has local work, start it straight away + if !runqempty(_p_) || sched.runqsize != 0 { + startm(_p_, false) + return + } + // if it has GC work, start it straight away + if gcBlackenEnabled != 0 && gcMarkWorkAvailable(_p_) { + startm(_p_, false) + return + } + // no local work, check that there are no spinning/idle M's, + // otherwise our help is not required + if atomic.Load(&sched.nmspinning)+atomic.Load(&sched.npidle) == 0 && atomic.Cas(&sched.nmspinning, 0, 1) { // TODO: fast atomic + startm(_p_, true) + return + } + lock(&sched.lock) + if sched.gcwaiting != 0 { + _p_.status = _Pgcstop + sched.stopwait-- + if sched.stopwait == 0 { + notewakeup(&sched.stopnote) + } + unlock(&sched.lock) + return + } + if _p_.runSafePointFn != 0 && atomic.Cas(&_p_.runSafePointFn, 1, 0) { + sched.safePointFn(_p_) + sched.safePointWait-- + if sched.safePointWait == 0 { + notewakeup(&sched.safePointNote) + } + } + if sched.runqsize != 0 { + unlock(&sched.lock) + startm(_p_, 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 == uint32(gomaxprocs-1) && atomic.Load64(&sched.lastpoll) != 0 { + unlock(&sched.lock) + startm(_p_, false) + return + } + + // The scheduler lock cannot be held when calling wakeNetPoller below + // because wakeNetPoller may call wakep which may call startm. + when := nobarrierWakeTime(_p_) + pidleput(_p_) + 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). +func wakep() { + if atomic.Load(&sched.npidle) == 0 { + return + } + // be conservative about spinning threads + if atomic.Load(&sched.nmspinning) != 0 || !atomic.Cas(&sched.nmspinning, 0, 1) { + return + } + startm(nil, true) +} + +// Stops execution of the current m that is locked to a g until the g is runnable again. +// Returns with acquired P. +func stoplockedm() { + _g_ := getg() + + if _g_.m.lockedg == 0 || _g_.m.lockedg.ptr().lockedm.ptr() != _g_.m { + throw("stoplockedm: inconsistent locking") + } + if _g_.m.p != 0 { + // Schedule another M to run this p. + _p_ := releasep() + handoffp(_p_) + } + incidlelocked(1) + // Wait until another thread schedules lockedg again. + mPark() + status := readgstatus(_g_.m.lockedg.ptr()) + if status&^_Gscan != _Grunnable { + print("runtime:stoplockedm: lockedg (atomicstatus=", status, ") is not Grunnable or Gscanrunnable\n") + dumpgstatus(_g_.m.lockedg.ptr()) + throw("stoplockedm: not runnable") + } + acquirep(_g_.m.nextp.ptr()) + _g_.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) { + _g_ := getg() + + mp := gp.lockedm.ptr() + if mp == _g_.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) + _p_ := releasep() + mp.nextp.set(_p_) + notewakeup(&mp.park) + stopm() +} + +// Stops the current m for stopTheWorld. +// Returns when the world is restarted. +func gcstopm() { + _g_ := getg() + + if sched.gcwaiting == 0 { + throw("gcstopm: not waiting for gc") + } + if _g_.m.spinning { + _g_.m.spinning = false + // OK to just drop nmspinning here, + // startTheWorld will unpark threads as necessary. + if int32(atomic.Xadd(&sched.nmspinning, -1)) < 0 { + throw("gcstopm: negative nmspinning") + } + } + _p_ := releasep() + lock(&sched.lock) + _p_.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) { + _g_ := getg() + + // Assign gp.m before entering _Grunning so running Gs have an + // M. + _g_.m.curg = gp + gp.m = _g_.m + casgstatus(gp, _Grunnable, _Grunning) + gp.waitsince = 0 + gp.preempt = false + gp.stackguard0 = gp.stack.lo + _StackGuard + if !inheritTime { + _g_.m.p.ptr().schedtick++ + } + + // Check whether the profiler needs to be turned on or off. + hz := sched.profilehz + if _g_.m.profilehz != hz { + setThreadCPUProfiler(hz) + } + + if trace.enabled { + // GoSysExit has to happen when we have a P, but before GoStart. + // So we emit it here. + if gp.syscallsp != 0 && gp.sysblocktraced { + traceGoSysExit(gp.sysexitticks) + } + 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. +func findrunnable() (gp *g, inheritTime bool) { + _g_ := getg() + + // The conditions here and in handoffp must agree: if + // findrunnable would return a G to run, handoffp must start + // an M. + +top: + _p_ := _g_.m.p.ptr() + if sched.gcwaiting != 0 { + gcstopm() + goto top + } + if _p_.runSafePointFn != 0 { + runSafePointFn() + } + + now, pollUntil, _ := checkTimers(_p_, 0) + + if 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(_p_); gp != nil { + return gp, inheritTime + } + + // global runq + if sched.runqsize != 0 { + lock(&sched.lock) + gp := globrunqget(_p_, 0) + unlock(&sched.lock) + if gp != nil { + return gp, 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() && atomic.Load(&netpollWaiters) > 0 && atomic.Load64(&sched.lastpoll) != 0 { + if list := netpoll(0); !list.empty() { // non-blocking + gp := list.pop() + injectglist(&list) + casgstatus(gp, _Gwaiting, _Grunnable) + if trace.enabled { + traceGoUnpark(gp, 0) + } + return gp, false + } + } + + // Steal work from other P's. + procs := uint32(gomaxprocs) + ranTimer := false + // If number of spinning M's >= number of busy P's, block. + // This is necessary to prevent excessive CPU consumption + // when GOMAXPROCS>>1 but the program parallelism is low. + if !_g_.m.spinning && 2*atomic.Load(&sched.nmspinning) >= procs-atomic.Load(&sched.npidle) { + goto stop + } + if !_g_.m.spinning { + _g_.m.spinning = true + atomic.Xadd(&sched.nmspinning, 1) + } + 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 != 0 { + goto top + } + p2 := allp[enum.position()] + if _p_ == 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 is always has room to add + // stolen G's. So check now if there + // is a local G to run. + if gp, inheritTime := runqget(_p_); gp != nil { + return gp, inheritTime + } + ranTimer = true + } + } + + // Don't bother to attempt to steal if p2 is idle. + if !idlepMask.read(enum.position()) { + if gp := runqsteal(_p_, p2, stealTimersOrRunNextG); gp != nil { + return gp, false + } + } + } + } + if ranTimer { + // Running a timer may have made some goroutine ready. + goto top + } + +stop: + + // 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(_p_) { + node := (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop()) + if node != nil { + _p_.gcMarkWorkerMode = gcMarkWorkerIdleMode + gp := node.gp.ptr() + casgstatus(gp, _Gwaiting, _Grunnable) + if trace.enabled { + traceGoUnpark(gp, 0) + } + return gp, false + } + } + + delta := int64(-1) + if pollUntil != 0 { + // checkTimers ensures that polluntil > now. + delta = pollUntil - now + } + + // 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(delta) + if gp != nil { + casgstatus(gp, _Gwaiting, _Grunnable) + if trace.enabled { + traceGoUnpark(gp, 0) + } + return gp, 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 != 0 || _p_.runSafePointFn != 0 { + unlock(&sched.lock) + goto top + } + if sched.runqsize != 0 { + gp := globrunqget(_p_, 0) + unlock(&sched.lock) + return gp, false + } + if releasep() != _p_ { + throw("findrunnable: wrong p") + } + pidleput(_p_) + unlock(&sched.lock) + + // Delicate dance: thread transitions from spinning to non-spinning state, + // potentially concurrently with submission of new goroutines. We must + // drop nmspinning first and then check all per-P queues again (with + // #StoreLoad memory barrier in between). If we do it the other way around, + // another thread can submit a goroutine after we've checked all run queues + // but before we drop nmspinning; as a result nobody will unpark a thread + // to run the goroutine. + // 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, it is OK to just park the current thread: + // the system is fully loaded so no spinning threads are required. + // Also see "Worker thread parking/unparking" comment at the top of the file. + wasSpinning := _g_.m.spinning + if _g_.m.spinning { + _g_.m.spinning = false + if int32(atomic.Xadd(&sched.nmspinning, -1)) < 0 { + throw("findrunnable: negative nmspinning") + } + } + + // check all runqueues once again + for id, _p_ := range allpSnapshot { + if !idlepMaskSnapshot.read(uint32(id)) && !runqempty(_p_) { + lock(&sched.lock) + _p_ = pidleget() + unlock(&sched.lock) + if _p_ != nil { + acquirep(_p_) + if wasSpinning { + _g_.m.spinning = true + atomic.Xadd(&sched.nmspinning, 1) + } + goto top + } + break + } + } + + // Similar to above, 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. + for id, _p_ := range allpSnapshot { + if timerpMaskSnapshot.read(uint32(id)) { + w := nobarrierWakeTime(_p_) + if w != 0 && (pollUntil == 0 || w < pollUntil) { + pollUntil = w + } + } + } + if pollUntil != 0 { + if now == 0 { + now = nanotime() + } + delta = pollUntil - now + if delta < 0 { + delta = 0 + } + } + + // Check for idle-priority GC work again. + // + // N.B. Since we have no P, gcBlackenEnabled may change at any time; we + // must check again after acquiring a P. + if atomic.Load(&gcBlackenEnabled) != 0 && gcMarkWorkAvailable(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. 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. + lock(&sched.lock) + var node *gcBgMarkWorkerNode + _p_ = pidleget() + if _p_ != nil { + // Now that we own a P, gcBlackenEnabled can't change + // (as it requires STW). + if gcBlackenEnabled != 0 { + node = (*gcBgMarkWorkerNode)(gcBgMarkWorkerPool.pop()) + if node == nil { + pidleput(_p_) + _p_ = nil + } + } else { + pidleput(_p_) + _p_ = nil + } + } + unlock(&sched.lock) + if _p_ != nil { + acquirep(_p_) + if wasSpinning { + _g_.m.spinning = true + atomic.Xadd(&sched.nmspinning, 1) + } + + // Run the idle worker. + _p_.gcMarkWorkerMode = gcMarkWorkerIdleMode + gp := node.gp.ptr() + casgstatus(gp, _Gwaiting, _Grunnable) + if trace.enabled { + traceGoUnpark(gp, 0) + } + return gp, false + } + } + + // poll network + if netpollinited() && (atomic.Load(&netpollWaiters) > 0 || pollUntil != 0) && atomic.Xchg64(&sched.lastpoll, 0) != 0 { + atomic.Store64(&sched.pollUntil, uint64(pollUntil)) + if _g_.m.p != 0 { + throw("findrunnable: netpoll with p") + } + if _g_.m.spinning { + throw("findrunnable: netpoll with spinning") + } + if faketime != 0 { + // When using fake time, just poll. + delta = 0 + } + list := netpoll(delta) // block until new work is available + atomic.Store64(&sched.pollUntil, 0) + atomic.Store64(&sched.lastpoll, uint64(nanotime())) + 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) + _p_ = pidleget() + unlock(&sched.lock) + if _p_ == nil { + injectglist(&list) + } else { + acquirep(_p_) + if !list.empty() { + gp := list.pop() + injectglist(&list) + casgstatus(gp, _Gwaiting, _Grunnable) + if trace.enabled { + traceGoUnpark(gp, 0) + } + return gp, false + } + if wasSpinning { + _g_.m.spinning = true + atomic.Xadd(&sched.nmspinning, 1) + } + goto top + } + } else if pollUntil != 0 && netpollinited() { + pollerPollUntil := int64(atomic.Load64(&sched.pollUntil)) + 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() && atomic.Load(&netpollWaiters) > 0 && sched.lastpoll != 0 { + if list := netpoll(0); !list.empty() { + injectglist(&list) + return true + } + } + return false +} + +// 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 atomic.Load64(&sched.lastpoll) == 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 := int64(atomic.Load64(&sched.pollUntil)) + 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() { + _g_ := getg() + if !_g_.m.spinning { + throw("resetspinning: not a spinning m") + } + _g_.m.spinning = false + nmspinning := atomic.Xadd(&sched.nmspinning, -1) + if int32(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 trace.enabled { + 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 ; n != 0 && sched.npidle != 0; n-- { + startm(nil, false) + } + } + + pp := getg().m.p.ptr() + if pp == nil { + lock(&sched.lock) + globrunqputbatch(&q, int32(qsize)) + unlock(&sched.lock) + startIdle(qsize) + return + } + + npidle := int(atomic.Load(&sched.npidle)) + 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() { + _g_ := getg() + + if _g_.m.locks != 0 { + throw("schedule: holding locks") + } + + if _g_.m.lockedg != 0 { + stoplockedm() + execute(_g_.m.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 _g_.m.incgo { + throw("schedule: in cgo") + } + +top: + pp := _g_.m.p.ptr() + pp.preempt = false + + if sched.gcwaiting != 0 { + gcstopm() + goto top + } + if pp.runSafePointFn != 0 { + runSafePointFn() + } + + // Sanity 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 _g_.m.spinning && (pp.runnext != 0 || pp.runqhead != pp.runqtail) { + throw("schedule: spinning with local work") + } + + checkTimers(pp, 0) + + var gp *g + var inheritTime bool + + // Normal goroutines will check for need to wakeP in ready, + // but GCworkers and tracereaders will not, so the check must + // be done here instead. + tryWakeP := false + if trace.enabled || trace.shutdown { + gp = traceReader() + if gp != nil { + casgstatus(gp, _Gwaiting, _Grunnable) + traceGoUnpark(gp, 0) + tryWakeP = true + } + } + if gp == nil && gcBlackenEnabled != 0 { + gp = gcController.findRunnableGCWorker(_g_.m.p.ptr()) + tryWakeP = tryWakeP || gp != nil + } + if gp == nil { + // 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 _g_.m.p.ptr().schedtick%61 == 0 && sched.runqsize > 0 { + lock(&sched.lock) + gp = globrunqget(_g_.m.p.ptr(), 1) + unlock(&sched.lock) + } + } + if gp == nil { + gp, inheritTime = runqget(_g_.m.p.ptr()) + // We can see gp != nil here even if the M is spinning, + // if checkTimers added a local goroutine via goready. + } + if gp == nil { + gp, inheritTime = findrunnable() // blocks until work is available + } + + // 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 _g_.m.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() { + _g_ := getg() + + setMNoWB(&_g_.m.curg.m, nil) + setGNoWB(&_g_.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 current time or 0 if it is not known, +// 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 := int64(atomic.Load64(&pp.timer0When)) + nextAdj := int64(atomic.Load64(&pp.timerModifiedEarliest)) + 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(atomic.Load(&pp.deletedTimers)) <= int(atomic.Load(&pp.numTimers)/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(atomic.Load(&pp.deletedTimers)) > 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) { + _g_ := getg() + + if trace.enabled { + traceGoPark(_g_.m.waittraceev, _g_.m.waittraceskip) + } + + casgstatus(gp, _Grunning, _Gwaiting) + dropg() + + if fn := _g_.m.waitunlockf; fn != nil { + ok := fn(gp, _g_.m.waitlock) + _g_.m.waitunlockf = nil + _g_.m.waitlock = nil + if !ok { + if trace.enabled { + 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 trace.enabled { + 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 trace.enabled { + traceGoSched() + } + goschedImpl(gp) +} + +func gopreempt_m(gp *g) { + if trace.enabled { + traceGoPreempt() + } + goschedImpl(gp) +} + +// preemptPark parks gp and puts it in _Gpreempted. +// +//go:systemstack +func preemptPark(gp *g) { + if trace.enabled { + traceGoPark(traceEvGoBlock, 0) + } + status := readgstatus(gp) + if status&^_Gscan != _Grunning { + dumpgstatus(gp) + throw("bad g status") + } + gp.waitreason = waitReasonPreempted + // 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 trace.enabled { + 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 trace.enabled { + traceGoEnd() + } + mcall(goexit0) +} + +// goexit continuation on g0. +func goexit0(gp *g) { + _g_ := getg() + + casgstatus(gp, _Grunning, _Gdead) + if isSystemGoroutine(gp, false) { + atomic.Xadd(&sched.ngsys, -1) + } + gp.m = nil + locked := gp.lockedm != 0 + gp.lockedm = 0 + _g_.m.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 = 0 + 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 := float64frombits(atomic.Load64(&gcController.assistWorkPerByte)) + scanCredit := int64(assistWorkPerByte * float64(gp.gcAssistBytes)) + atomic.Xaddint64(&gcController.bgScanCredit, scanCredit) + gp.gcAssistBytes = 0 + } + + dropg() + + if GOARCH == "wasm" { // no threads yet on wasm + gfput(_g_.m.p.ptr(), gp) + schedule() // never returns + } + + if _g_.m.lockedInt != 0 { + print("invalid m->lockedInt = ", _g_.m.lockedInt, "\n") + throw("internal lockOSThread error") + } + gfput(_g_.m.p.ptr(), 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(&_g_.m.g0.sched) + } else { + // Clear lockedExt on plan9 since we may end up re-using + // this thread. + _g_.m.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) { + _g_ := getg() + + _g_.sched.pc = pc + _g_.sched.sp = sp + _g_.sched.lr = 0 + _g_.sched.ret = 0 + _g_.sched.g = guintptr(unsafe.Pointer(_g_)) + // 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 _g_.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 gosave 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 (_g_.m.syscalltick = _g_.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) { + _g_ := getg() + + // Disable preemption because during this function g is in Gsyscall status, + // but can have inconsistent g->sched, do not let GC observe it. + _g_.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. + _g_.stackguard0 = stackPreempt + _g_.throwsplit = true + + // Leave SP around for GC and traceback. + save(pc, sp) + _g_.syscallsp = sp + _g_.syscallpc = pc + casgstatus(_g_, _Grunning, _Gsyscall) + if _g_.syscallsp < _g_.stack.lo || _g_.stack.hi < _g_.syscallsp { + systemstack(func() { + print("entersyscall inconsistent ", hex(_g_.syscallsp), " [", hex(_g_.stack.lo), ",", hex(_g_.stack.hi), "]\n") + throw("entersyscall") + }) + } + + if trace.enabled { + 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 atomic.Load(&sched.sysmonwait) != 0 { + systemstack(entersyscall_sysmon) + save(pc, sp) + } + + if _g_.m.p.ptr().runSafePointFn != 0 { + // runSafePointFn may stack split if run on this stack + systemstack(runSafePointFn) + save(pc, sp) + } + + _g_.m.syscalltick = _g_.m.p.ptr().syscalltick + _g_.sysblocktraced = true + pp := _g_.m.p.ptr() + pp.m = 0 + _g_.m.oldp.set(pp) + _g_.m.p = 0 + atomic.Store(&pp.status, _Psyscall) + if sched.gcwaiting != 0 { + systemstack(entersyscall_gcwait) + save(pc, sp) + } + + _g_.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. +// +//go:nosplit +//go:linkname entersyscall +func entersyscall() { + reentersyscall(getcallerpc(), getcallersp()) +} + +func entersyscall_sysmon() { + lock(&sched.lock) + if atomic.Load(&sched.sysmonwait) != 0 { + atomic.Store(&sched.sysmonwait, 0) + notewakeup(&sched.sysmonnote) + } + unlock(&sched.lock) +} + +func entersyscall_gcwait() { + _g_ := getg() + _p_ := _g_.m.oldp.ptr() + + lock(&sched.lock) + if sched.stopwait > 0 && atomic.Cas(&_p_.status, _Psyscall, _Pgcstop) { + if trace.enabled { + traceGoSysBlock(_p_) + traceProcStop(_p_) + } + _p_.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() { + _g_ := getg() + + _g_.m.locks++ // see comment in entersyscall + _g_.throwsplit = true + _g_.stackguard0 = stackPreempt // see comment in entersyscall + _g_.m.syscalltick = _g_.m.p.ptr().syscalltick + _g_.sysblocktraced = true + _g_.m.p.ptr().syscalltick++ + + // Leave SP around for GC and traceback. + pc := getcallerpc() + sp := getcallersp() + save(pc, sp) + _g_.syscallsp = _g_.sched.sp + _g_.syscallpc = _g_.sched.pc + if _g_.syscallsp < _g_.stack.lo || _g_.stack.hi < _g_.syscallsp { + sp1 := sp + sp2 := _g_.sched.sp + sp3 := _g_.syscallsp + systemstack(func() { + print("entersyscallblock inconsistent ", hex(sp1), " ", hex(sp2), " ", hex(sp3), " [", hex(_g_.stack.lo), ",", hex(_g_.stack.hi), "]\n") + throw("entersyscallblock") + }) + } + casgstatus(_g_, _Grunning, _Gsyscall) + if _g_.syscallsp < _g_.stack.lo || _g_.stack.hi < _g_.syscallsp { + systemstack(func() { + print("entersyscallblock inconsistent ", hex(sp), " ", hex(_g_.sched.sp), " ", hex(_g_.syscallsp), " [", hex(_g_.stack.lo), ",", hex(_g_.stack.hi), "]\n") + throw("entersyscallblock") + }) + } + + systemstack(entersyscallblock_handoff) + + // Resave for traceback during blocked call. + save(getcallerpc(), getcallersp()) + + _g_.m.locks-- +} + +func entersyscallblock_handoff() { + if trace.enabled { + 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() { + _g_ := getg() + + _g_.m.locks++ // see comment in entersyscall + if getcallersp() > _g_.syscallsp { + throw("exitsyscall: syscall frame is no longer valid") + } + + _g_.waitsince = 0 + oldp := _g_.m.oldp.ptr() + _g_.m.oldp = 0 + if exitsyscallfast(oldp) { + if trace.enabled { + if oldp != _g_.m.p.ptr() || _g_.m.syscalltick != _g_.m.p.ptr().syscalltick { + systemstack(traceGoStart) + } + } + // There's a cpu for us, so we can run. + _g_.m.p.ptr().syscalltick++ + // We need to cas the status and scan before resuming... + casgstatus(_g_, _Gsyscall, _Grunning) + + // Garbage collector isn't running (since we are), + // so okay to clear syscallsp. + _g_.syscallsp = 0 + _g_.m.locks-- + if _g_.preempt { + // restore the preemption request in case we've cleared it in newstack + _g_.stackguard0 = stackPreempt + } else { + // otherwise restore the real _StackGuard, we've spoiled it in entersyscall/entersyscallblock + _g_.stackguard0 = _g_.stack.lo + _StackGuard + } + _g_.throwsplit = false + + if sched.disable.user && !schedEnabled(_g_) { + // Scheduling of this goroutine is disabled. + Gosched() + } + + return + } + + _g_.sysexitticks = 0 + if trace.enabled { + // 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 == _g_.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. + _g_.sysexitticks = cputicks() + } + + _g_.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. + _g_.syscallsp = 0 + _g_.m.p.ptr().syscalltick++ + _g_.throwsplit = false +} + +//go:nosplit +func exitsyscallfast(oldp *p) bool { + _g_ := 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 && trace.enabled { + 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 == _g_.m.syscalltick { + osyield() + } + } + traceGoSysExit(0) + } + }) + 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() { + _g_ := getg() + if _g_.m.syscalltick != _g_.m.p.ptr().syscalltick { + if trace.enabled { + // The p was retaken and then enter into syscall again (since _g_.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(_g_.m.p.ptr()) + // Denote completion of the current syscall. + traceGoSysExit(0) + }) + } + _g_.m.p.ptr().syscalltick++ + } +} + +func exitsyscallfast_pidle() bool { + lock(&sched.lock) + _p_ := pidleget() + if _p_ != nil && atomic.Load(&sched.sysmonwait) != 0 { + atomic.Store(&sched.sysmonwait, 0) + notewakeup(&sched.sysmonnote) + } + unlock(&sched.lock) + if _p_ != nil { + acquirep(_p_) + return true + } + return false +} + +// exitsyscall slow path on g0. +// Failed to acquire P, enqueue gp as runnable. +// +//go:nowritebarrierrec +func exitsyscall0(gp *g) { + _g_ := getg() + + casgstatus(gp, _Gsyscall, _Grunnable) + dropg() + lock(&sched.lock) + var _p_ *p + if schedEnabled(_g_) { + _p_ = pidleget() + } + if _p_ == nil { + globrunqput(gp) + } else if atomic.Load(&sched.sysmonwait) != 0 { + atomic.Store(&sched.sysmonwait, 0) + notewakeup(&sched.sysmonnote) + } + unlock(&sched.lock) + if _p_ != nil { + acquirep(_p_) + execute(gp, false) // Never returns. + } + if _g_.m.lockedg != 0 { + // Wait until another thread schedules gp and so m again. + stoplockedm() + execute(gp, false) // Never returns. + } + stopm() + schedule() // Never returns. +} + +func 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->_StackGuard 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 before fork. +//go:linkname syscall_runtime_BeforeFork syscall.runtime_BeforeFork +//go:nosplit +func syscall_runtime_BeforeFork() { + systemstack(beforefork) +} + +func afterfork() { + gp := getg().m.curg + + // See the comments in beforefork. + gp.stackguard0 = gp.stack.lo + _StackGuard + + msigrestore(gp.m.sigmask) + + gp.m.locks-- +} + +// Called from syscall package after fork in parent. +//go:linkname syscall_runtime_AfterFork syscall.runtime_AfterFork +//go:nosplit +func syscall_runtime_AfterFork() { + systemstack(afterfork) +} + +// 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 uint32 + +// 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 int32(atomic.Load(&pendingPreemptSignals)) > 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 with siz bytes of arguments. +// Put it on the queue of g's waiting to run. +// The compiler turns a go statement into a call to this. +// +// The stack layout of this call is unusual: it assumes that the +// arguments to pass to fn are on the stack sequentially immediately +// after &fn. Hence, they are logically part of newproc's argument +// frame, even though they don't appear in its signature (and can't +// because their types differ between call sites). +// +// This must be nosplit because this stack layout means there are +// untyped arguments in newproc's argument frame. Stack copies won't +// be able to adjust them and stack splits won't be able to copy them. +// +//go:nosplit +func newproc(siz int32, fn *funcval) { + argp := add(unsafe.Pointer(&fn), sys.PtrSize) + gp := getg() + pc := getcallerpc() + systemstack(func() { + newg := newproc1(fn, argp, siz, gp, pc) + + _p_ := getg().m.p.ptr() + runqput(_p_, newg, true) + + if mainStarted { + wakep() + } + }) +} + +// Create a new g in state _Grunnable, starting at fn, with narg bytes +// of arguments starting at argp. callerpc is the address of the go +// statement that created this. The caller is responsible for adding +// the new g to the scheduler. +// +// This must run on the system stack because it's the continuation of +// newproc, which cannot split the stack. +// +//go:systemstack +func newproc1(fn *funcval, argp unsafe.Pointer, narg int32, callergp *g, callerpc uintptr) *g { + _g_ := getg() + + if fn == nil { + _g_.m.throwing = -1 // do not dump full stacks + throw("go of nil func value") + } + acquirem() // disable preemption because it can be holding p in a local var + siz := narg + siz = (siz + 7) &^ 7 + + // We could allocate a larger initial stack if necessary. + // Not worth it: this is almost always an error. + // 4*sizeof(uintreg): extra space added below + // sizeof(uintreg): caller's LR (arm) or return address (x86, in gostartcall). + if siz >= _StackMin-4*sys.RegSize-sys.RegSize { + throw("newproc: function arguments too large for new goroutine") + } + + _p_ := _g_.m.p.ptr() + newg := gfget(_p_) + 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 := 4*sys.RegSize + uintptr(siz) + sys.MinFrameSize // extra space in case of reads slightly beyond frame + totalSize += -totalSize & (sys.SpAlign - 1) // align to spAlign + sp := newg.stack.hi - totalSize + spArg := sp + if usesLR { + // caller's LR + *(*uintptr)(unsafe.Pointer(sp)) = 0 + prepGoExitFrame(sp) + spArg += sys.MinFrameSize + } + if narg > 0 { + memmove(unsafe.Pointer(spArg), argp, uintptr(narg)) + // This is a stack-to-stack copy. If write barriers + // are enabled and the source stack is grey (the + // destination is always black), then perform a + // barrier copy. We do this *after* the memmove + // because the destination stack may have garbage on + // it. + if writeBarrier.needed && !_g_.m.curg.gcscandone { + f := findfunc(fn.fn) + stkmap := (*stackmap)(funcdata(f, _FUNCDATA_ArgsPointerMaps)) + if stkmap.nbit > 0 { + // We're in the prologue, so it's always stack map index 0. + bv := stackmapdata(stkmap, 0) + bulkBarrierBitmap(spArg, spArg, uintptr(bv.n)*sys.PtrSize, 0, bv.bytedata) + } + } + } + + memclrNoHeapPointers(unsafe.Pointer(&newg.sched), unsafe.Sizeof(newg.sched)) + newg.sched.sp = sp + newg.stktopsp = sp + newg.sched.pc = funcPC(goexit) + sys.PCQuantum // +PCQuantum so that previous instruction is in same function + newg.sched.g = guintptr(unsafe.Pointer(newg)) + gostartcallfn(&newg.sched, fn) + newg.gopc = callerpc + newg.ancestors = saveAncestors(callergp) + newg.startpc = fn.fn + if _g_.m.curg != nil { + newg.labels = _g_.m.curg.labels + } + if isSystemGoroutine(newg, false) { + atomic.Xadd(&sched.ngsys, +1) + } + casgstatus(newg, _Gdead, _Grunnable) + + if _p_.goidcache == _p_.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. + _p_.goidcache = atomic.Xadd64(&sched.goidgen, _GoidCacheBatch) + _p_.goidcache -= _GoidCacheBatch - 1 + _p_.goidcacheend = _p_.goidcache + _GoidCacheBatch + } + newg.goid = int64(_p_.goidcache) + _p_.goidcache++ + if raceenabled { + newg.racectx = racegostart(callerpc) + } + if trace.enabled { + traceGoCreate(newg, newg.startpc) + } + releasem(_g_.m) + + return newg +} + +// saveAncestors copies previous ancestors of the given caller g and +// includes infor 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 [_TracebackMaxFrames]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(_p_ *p, gp *g) { + if readgstatus(gp) != _Gdead { + throw("gfput: bad status (not Gdead)") + } + + stksize := gp.stack.hi - gp.stack.lo + + if stksize != _FixedStack { + // non-standard stack size - free it. + stackfree(gp.stack) + gp.stack.lo = 0 + gp.stack.hi = 0 + gp.stackguard0 = 0 + } + + _p_.gFree.push(gp) + _p_.gFree.n++ + if _p_.gFree.n >= 64 { + lock(&sched.gFree.lock) + for _p_.gFree.n >= 32 { + _p_.gFree.n-- + gp = _p_.gFree.pop() + if gp.stack.lo == 0 { + sched.gFree.noStack.push(gp) + } else { + sched.gFree.stack.push(gp) + } + sched.gFree.n++ + } + unlock(&sched.gFree.lock) + } +} + +// Get from gfree list. +// If local list is empty, grab a batch from global list. +func gfget(_p_ *p) *g { +retry: + if _p_.gFree.empty() && (!sched.gFree.stack.empty() || !sched.gFree.noStack.empty()) { + lock(&sched.gFree.lock) + // Move a batch of free Gs to the P. + for _p_.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-- + _p_.gFree.push(gp) + _p_.gFree.n++ + } + unlock(&sched.gFree.lock) + goto retry + } + gp := _p_.gFree.pop() + if gp == nil { + return nil + } + _p_.gFree.n-- + if gp.stack.lo == 0 { + // Stack was deallocated in gfput. Allocate a new one. + systemstack(func() { + gp.stack = stackalloc(_FixedStack) + }) + 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) + } + } + return gp +} + +// Purge all cached G's from gfree list to the global list. +func gfpurge(_p_ *p) { + lock(&sched.gFree.lock) + for !_p_.gFree.empty() { + gp := _p_.gFree.pop() + _p_.gFree.n-- + if gp.stack.lo == 0 { + sched.gFree.noStack.push(gp) + } else { + sched.gFree.stack.push(gp) + } + sched.gFree.n++ + } + 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 + } + _g_ := getg() + _g_.m.lockedg.set(_g_) + _g_.lockedm.set(_g_.m) +} + +//go:nosplit + +// 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. +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() + } + _g_ := getg() + _g_.m.lockedExt++ + if _g_.m.lockedExt == 0 { + _g_.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 + } + _g_ := getg() + if _g_.m.lockedInt != 0 || _g_.m.lockedExt != 0 { + return + } + _g_.m.lockedg = 0 + _g_.lockedm = 0 +} + +//go:nosplit + +// 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. +func UnlockOSThread() { + _g_ := getg() + if _g_.m.lockedExt == 0 { + return + } + _g_.m.lockedExt-- + dounlockOSThread() +} + +//go:nosplit +func unlockOSThread() { + _g_ := getg() + if _g_.m.lockedInt == 0 { + systemstack(badunlockosthread) + } + _g_.m.lockedInt-- + dounlockOSThread() +} + +func badunlockosthread() { + throw("runtime: internal error: misuse of lockOSThread/unlockOSThread") +} + +func gcount() int32 { + n := int32(atomic.Loaduintptr(&allglen)) - sched.gFree.n - int32(atomic.Load(&sched.ngsys)) + for _, _p_ := range allp { + n -= _p_.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 uint32 + hz 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 == 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++ + + // Define that a "user g" is a user-created goroutine, and a "system g" + // is one that is m->g0 or m->gsignal. + // + // We might be interrupted for profiling halfway through a + // goroutine switch. The switch involves updating three (or four) values: + // g, PC, SP, and (on arm) LR. The PC must be the last to be updated, + // because once it gets updated the new g is running. + // + // When switching from a user g to a system g, LR is not considered live, + // so the update only affects g, SP, and PC. Since PC must be last, there + // the possible partial transitions in ordinary execution are (1) g alone is updated, + // (2) both g and SP are updated, and (3) SP alone is updated. + // If SP or g alone is updated, we can detect the partial transition by checking + // whether the SP is within g's stack bounds. (We could also require that SP + // be changed only after g, but the stack bounds check is needed by other + // cases, so there is no need to impose an additional requirement.) + // + // There is one exceptional transition to a system g, not in ordinary execution. + // When a signal arrives, the operating system starts the signal handler running + // with an updated PC and SP. The g is updated last, at the beginning of the + // handler. There are two reasons this is okay. First, until g is updated the + // g and SP do not match, so the stack bounds check detects the partial transition. + // Second, signal handlers currently run with signals disabled, so a profiling + // signal cannot arrive during the handler. + // + // When switching from a system g to a user g, there are three possibilities. + // + // First, it may be that the g switch has no PC update, because the SP + // either corresponds to a user g throughout (as in asmcgocall) + // or because it has been arranged to look like a user g frame + // (as in cgocallback). In this case, since the entire + // transition is a g+SP update, a partial transition updating just one of + // those will be detected by the stack bounds check. + // + // Second, when returning from a signal handler, the PC and SP updates + // are performed by the operating system in an atomic update, so the g + // update must be done before them. The stack bounds check detects + // the partial transition here, and (again) signal handlers run with signals + // disabled, so a profiling signal cannot arrive then anyway. + // + // Third, the common case: it may be that the switch updates g, SP, and PC + // separately. If the PC is within any of the functions that does this, + // we don't ask for a traceback. C.F. the function setsSP for more about this. + // + // There is another apparently viable approach, recorded here in case + // the "PC within setsSP function" check turns out not to be usable. + // It would be possible to delay the update of either g or SP until immediately + // before the PC update instruction. Then, because of the stack bounds check, + // the only problematic interrupt point is just before that PC update instruction, + // and the sigprof handler can detect that instruction and simulate stepping past + // it in order to reach a consistent state. On ARM, the update of g must be made + // in two places (in R10 and also in a TLS slot), so the delayed update would + // need to be the SP update. The sigprof handler must read the instruction at + // the current PC and if it was the known instruction (for example, JMP BX or + // MOV R2, PC), use that other register in place of the PC value. + // The biggest drawback to this solution is that it requires that we can tell + // whether it's safe to read from the memory pointed at by PC. + // In a correct program, we can test PC == nil and otherwise read, + // but if a profiling signal happens at the instant that a program executes + // a bad jump (before the program manages to handle the resulting fault) + // the profiling handler could fault trying to read nonexistent memory. + // + // To recap, there are no constraints on the assembly being used for the + // transition. We simply require that g and SP match and that the PC is not + // in gogo. + traceback := true + if gp == nil || sp < gp.stack.lo || gp.stack.hi < sp || setsSP(pc) || (mp != nil && mp.vdsoSP != 0) { + traceback = false + } + 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 atomic.Load(&mp.cgoCallersUse) == 0 && mp.cgoCallers != nil && mp.cgoCallers[0] != 0 { + for cgoOff < len(mp.cgoCallers) && mp.cgoCallers[cgoOff] != 0 { + cgoOff++ + } + copy(stk[:], mp.cgoCallers[:cgoOff]) + mp.cgoCallers[0] = 0 + } + + // Collect Go stack that leads to the cgo call. + n = gentraceback(mp.curg.syscallpc, mp.curg.syscallsp, 0, mp.curg, 0, &stk[cgoOff], len(stk)-cgoOff, nil, nil, 0) + if n > 0 { + n += cgoOff + } + } else if traceback { + n = gentraceback(pc, sp, lr, gp, 0, &stk[0], len(stk), nil, nil, _TraceTrap|_TraceJumpStack) + } + + if n <= 0 { + // Normal traceback is impossible or has failed. + // See if it falls into several common cases. + n = 0 + 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. + n = gentraceback(mp.libcallpc, mp.libcallsp, 0, mp.libcallg.ptr(), 0, &stk[0], len(stk), nil, nil, 0) + } + if n == 0 && mp != nil && mp.vdsoSP != 0 { + n = gentraceback(mp.vdsoPC, mp.vdsoSP, 0, gp, 0, &stk[0], len(stk), nil, nil, _TraceTrap|_TraceJumpStack) + } + if n == 0 { + // If all of the above has failed, account it against abstract "System" or "GC". + n = 2 + if inVDSOPage(pc) { + pc = funcPC(_VDSO) + sys.PCQuantum + } else if pc > firstmoduledata.etext { + // "ExternalCode" is better than "etext". + pc = funcPC(_ExternalCode) + sys.PCQuantum + } + stk[0] = pc + if mp.preemptoff != "" { + stk[1] = funcPC(_GC) + sys.PCQuantum + } else { + stk[1] = funcPC(_System) + sys.PCQuantum + } + } + } + + if prof.hz != 0 { + cpuprof.add(gp, stk[:n]) + } + getg().m.mallocing-- +} + +// If the signal handler receives a SIGPROF signal on a non-Go thread, +// it tries to collect a traceback into sigprofCallers. +// sigprofCallersUse is set to non-zero while sigprofCallers holds a traceback. +var sigprofCallers cgoCallers +var sigprofCallersUse uint32 + +// sigprofNonGo is called if we receive a SIGPROF signal on a non-Go thread, +// and the signal handler collected a stack trace in sigprofCallers. +// When this is called, sigprofCallersUse will be non-zero. +// g is nil, and what we can do is very limited. +//go:nosplit +//go:nowritebarrierrec +func sigprofNonGo() { + if prof.hz != 0 { + n := 0 + for n < len(sigprofCallers) && sigprofCallers[n] != 0 { + n++ + } + cpuprof.addNonGo(sigprofCallers[:n]) + } + + atomic.Store(&sigprofCallersUse, 0) +} + +// sigprofNonGoPC is called when a profiling signal arrived on a +// non-Go thread and we have a single PC value, not a stack trace. +// g is nil, and what we can do is very limited. +//go:nosplit +//go:nowritebarrierrec +func sigprofNonGoPC(pc uintptr) { + if prof.hz != 0 { + stk := []uintptr{ + pc, + funcPC(_ExternalCode) + sys.PCQuantum, + } + cpuprof.addNonGo(stk) + } +} + +// Reports whether a function will set the SP +// to an absolute value. Important that +// we don't traceback when these are at the bottom +// of the stack since we can't be sure that we will +// find the caller. +// +// If the function is not on the bottom of the stack +// we assume that it will have set it up so that traceback will be consistent, +// either by being a traceback terminating function +// or putting one on the stack at the right offset. +func setsSP(pc uintptr) bool { + f := findfunc(pc) + if !f.valid() { + // couldn't find the function for this PC, + // so assume the worst and stop traceback + return true + } + switch f.funcID { + case funcID_gogo, funcID_systemstack, funcID_mcall, funcID_morestack: + return true + } + return false +} + +// 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. + _g_ := getg() + _g_.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 !atomic.Cas(&prof.signalLock, 0, 1) { + osyield() + } + if prof.hz != hz { + setProcessCPUProfiler(hz) + prof.hz = hz + } + atomic.Store(&prof.signalLock, 0) + + lock(&sched.lock) + sched.profilehz = hz + unlock(&sched.lock) + + if hz != 0 { + setThreadCPUProfiler(hz) + } + + _g_.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] + for i := range pp.deferpool { + pp.deferpool[i] = pp.deferpoolbuf[i][: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 = 0 + pp.deletedTimers = 0 + atomic.Store64(&pp.timer0When, 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] + for i := range pp.deferpool { + for j := range pp.deferpoolbuf[i] { + pp.deferpoolbuf[i][j] = nil + } + pp.deferpool[i] = pp.deferpoolbuf[i][: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 trace.enabled { + 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)) + } + + _g_ := getg() + if _g_.m.p != 0 && _g_.m.p.ptr().id < nprocs { + // continue to use the current P + _g_.m.p.ptr().status = _Prunning + _g_.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 _g_.m.p != 0 { + if trace.enabled { + // Pretend that we were descheduled + // and then scheduled again to keep + // the trace sane. + traceGoSched() + traceProcStop(_g_.m.p.ptr()) + } + _g_.m.p.ptr().m = 0 + } + _g_.m.p = 0 + p := allp[0] + p.m = 0 + p.status = _Pidle + acquirep(p) + if trace.enabled { + 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++ { + p := allp[i] + p.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-- { + p := allp[i] + if _g_.m.p.ptr() == p { + continue + } + p.status = _Pidle + if runqempty(p) { + pidleput(p) + } else { + p.m.set(mget()) + p.link.set(runnablePs) + runnablePs = p + } + } + stealOrder.reset(uint32(nprocs)) + var int32p *int32 = &gomaxprocs // make compiler check that gomaxprocs is an int32 + atomic.Store((*uint32)(unsafe.Pointer(int32p)), uint32(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 _p_. +// +//go:yeswritebarrierrec +func acquirep(_p_ *p) { + // Do the part that isn't allowed to have write barriers. + wirep(_p_) + + // Have p; write barriers now allowed. + + // Perform deferred mcache flush before this P can allocate + // from a potentially stale mcache. + _p_.mcache.prepareForSweep() + + if trace.enabled { + traceProcStart() + } +} + +// wirep is the first step of acquirep, which actually associates the +// current M to _p_. 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(_p_ *p) { + _g_ := getg() + + if _g_.m.p != 0 { + throw("wirep: already in go") + } + if _p_.m != 0 || _p_.status != _Pidle { + id := int64(0) + if _p_.m != 0 { + id = _p_.m.ptr().id + } + print("wirep: p->m=", _p_.m, "(", id, ") p->status=", _p_.status, "\n") + throw("wirep: invalid p state") + } + _g_.m.p.set(_p_) + _p_.m.set(_g_.m) + _p_.status = _Prunning +} + +// Disassociate p and the current m. +func releasep() *p { + _g_ := getg() + + if _g_.m.p == 0 { + throw("releasep: invalid arg") + } + _p_ := _g_.m.p.ptr() + if _p_.m.ptr() != _g_.m || _p_.status != _Prunning { + print("releasep: m=", _g_.m, " m->p=", _g_.m.p.ptr(), " p->m=", hex(_p_.m), " p->status=", _p_.status, "\n") + throw("releasep: invalid p state") + } + if trace.enabled { + traceProcStop(_g_.m.p.ptr()) + } + _g_.m.p = 0 + _p_.m = 0 + _p_.status = _Pidle + return _p_ +} + +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 > 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 { + mp := lockextra(true) + haveExtraM := extraMCount > 0 + unlockextra(mp) + if haveExtraM { + 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") + throw("checkdead: inconsistent counts") + } + + grunning := 0 + lock(&allglock) + for i := 0; i < len(allgs); i++ { + gp := allgs[i] + if isSystemGoroutine(gp, false) { + continue + } + 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") + throw("checkdead: runnable g") + } + } + unlock(&allglock) + if grunning == 0 { // possible if main goroutine calls runtime·Goexit() + unlock(&sched.lock) // unlock so that GODEBUG=scheddetail=1 doesn't hang + throw("no goroutines (main called runtime.Goexit) - deadlock!") + } + + // Maybe jump time forward for playground. + if faketime != 0 { + when, _p_ := timeSleepUntil() + if _p_ != nil { + faketime = when + for pp := &sched.pidle; *pp != 0; pp = &(*pp).ptr().link { + if (*pp).ptr() == _p_ { + *pp = _p_.link + break + } + } + mp := mget() + if mp == nil { + // There should always be a free M since + // nothing is running. + throw("checkdead: no m for timer") + } + mp.nextp.set(_p_) + notewakeup(&mp.park) + return + } + } + + // There are no goroutines running, so we can look at the P's. + for _, _p_ := range allp { + if len(_p_.timers) > 0 { + return + } + } + + getg().m.throwing = -1 // do not dump full stacks + unlock(&sched.lock) // unlock so that GODEBUG=scheddetail=1 doesn't hang + throw("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 + +// Always runs without a P, so write barriers are not allowed. +// +//go:nowritebarrierrec +func sysmon() { + lock(&sched.lock) + sched.nmsys++ + checkdead() + unlock(&sched.lock) + + // For syscall_runtime_doAllThreadsSyscall, sysmon is + // sufficiently up to participate in fixups. + atomic.Store(&sched.sysmonStarting, 0) + + 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) + mDoFixup() + + // 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 != 0 || atomic.Load(&sched.npidle) == uint32(gomaxprocs)) { + lock(&sched.lock) + if atomic.Load(&sched.gcwaiting) != 0 || atomic.Load(&sched.npidle) == uint32(gomaxprocs) { + syscallWake := false + next, _ := timeSleepUntil() + if next > now { + atomic.Store(&sched.sysmonwait, 1) + 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) + mDoFixup() + if shouldRelax { + osRelax(false) + } + lock(&sched.lock) + atomic.Store(&sched.sysmonwait, 0) + 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 := int64(atomic.Load64(&sched.lastpoll)) + if netpollinited() && lastpoll != 0 && lastpoll+10*1000*1000 < now { + atomic.Cas64(&sched.lastpoll, uint64(lastpoll), uint64(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) + } + } + mDoFixup() + if GOOS == "netbsd" { + // 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) + } + } + if atomic.Load(&scavenge.sysmonWake) != 0 { + // Kick the scavenger awake if someone requested it. + wakeScavenger() + } + // 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() && atomic.Load(&forcegc.idle) != 0 { + lock(&forcegc.lock) + forcegc.idle = 0 + 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++ { + _p_ := allp[i] + if _p_ == nil { + // This can happen if procresize has grown + // allp but not yet created new Ps. + continue + } + pd := &_p_.sysmontick + s := _p_.status + sysretake := false + if s == _Prunning || s == _Psyscall { + // Preempt G if it's running for too long. + t := int64(_p_.schedtick) + if int64(pd.schedtick) != t { + pd.schedtick = uint32(t) + pd.schedwhen = now + } else if pd.schedwhen+forcePreemptNS <= now { + preemptone(_p_) + // 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(_p_.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(_p_) && atomic.Load(&sched.nmspinning)+atomic.Load(&sched.npidle) > 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(&_p_.status, s, _Pidle) { + if trace.enabled { + traceGoSysBlock(_p_) + traceProcStop(_p_) + } + n++ + _p_.syscalltick++ + handoffp(_p_) + } + 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 _, _p_ := range allp { + if _p_.status != _Prunning { + continue + } + if preemptone(_p_) { + 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 send 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(_p_ *p) bool { + mp := _p_.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 go routine 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 { + _p_.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, " threads=", mcount(), " spinningthreads=", sched.nmspinning, " idlethreads=", sched.nmidle, " runqueue=", sched.runqsize) + if detailed { + print(" gcwaiting=", sched.gcwaiting, " nmidlelocked=", sched.nmidlelocked, " stopwait=", sched.stopwait, " sysmonwait=", sched.sysmonwait, "\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, _p_ := range allp { + mp := _p_.m.ptr() + h := atomic.Load(&_p_.runqhead) + t := atomic.Load(&_p_.runqtail) + if detailed { + id := int64(-1) + if mp != nil { + id = mp.id + } + print(" P", i, ": status=", _p_.status, " schedtick=", _p_.schedtick, " syscalltick=", _p_.syscalltick, " m=", id, " runqsize=", t-h, " gfreecnt=", _p_.gFree.n, " timerslen=", len(_p_.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 { + _p_ := mp.p.ptr() + gp := mp.curg + lockedg := mp.lockedg.ptr() + id1 := int32(-1) + if _p_ != nil { + id1 = _p_.id + } + id2 := int64(-1) + if gp != nil { + id2 = gp.goid + } + id3 := int64(-1) + if lockedg != nil { + id3 = lockedg.goid + } + print(" M", mp.id, ": p=", id1, " curg=", id2, " mallocing=", mp.mallocing, " throwing=", mp.throwing, " preemptoff=", mp.preemptoff, ""+" locks=", mp.locks, " dying=", mp.dying, " spinning=", mp.spinning, " blocked=", mp.blocked, " lockedg=", id3, "\n") + } + + lock(&allglock) + for gi := 0; gi < len(allgs); gi++ { + gp := allgs[gi] + mp := gp.m + lockedm := gp.lockedm.ptr() + id1 := int64(-1) + if mp != nil { + id1 = mp.id + } + id2 := int64(-1) + if lockedm != nil { + id2 = lockedm.id + } + print(" G", gp.goid, ": status=", readgstatus(gp), "(", gp.waitreason.String(), ") m=", id1, " lockedm=", id2, "\n") + } + unlock(&allglock) + 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 != 0; n-- { + startm(nil, 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. +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(_p_ *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(_p_.runq))/2 { + n = int32(len(_p_.runq)) / 2 + } + + sched.runqsize -= n + + gp := sched.runq.pop() + n-- + for ; n > 0; n-- { + gp1 := sched.runq.pop() + runqput(_p_, 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 atomic.Load(&pp.numTimers) > 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 atomic.Load(&pp.numTimers) == 0 { + timerpMask.clear(pp.id) + } + unlock(&pp.timersLock) +} + +// pidleput puts p to on the _Pidle list. +// +// 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(_p_ *p) { + assertLockHeld(&sched.lock) + + if !runqempty(_p_) { + throw("pidleput: P has non-empty run queue") + } + updateTimerPMask(_p_) // clear if there are no timers. + idlepMask.set(_p_.id) + _p_.link = sched.pidle + sched.pidle.set(_p_) + atomic.Xadd(&sched.npidle, 1) // TODO: fast atomic +} + +// 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() *p { + assertLockHeld(&sched.lock) + + _p_ := sched.pidle.ptr() + if _p_ != nil { + // Timer may get added at any time now. + timerpMask.set(_p_.id) + idlepMask.clear(_p_.id) + sched.pidle = _p_.link + atomic.Xadd(&sched.npidle, -1) // TODO: fast atomic + } + return _p_ +} + +// runqempty reports whether _p_ has no Gs on its local run queue. +// It never returns true spuriously. +func runqempty(_p_ *p) bool { + // Defend against a race where 1) _p_ has G1 in runqnext but runqhead == runqtail, + // 2) runqput on _p_ kicks G1 to the runq, 3) runqget on _p_ empties runqnext. + // Simply observing that runqhead == runqtail and then observing that runqnext == nil + // does not mean the queue is empty. + for { + head := atomic.Load(&_p_.runqhead) + tail := atomic.Load(&_p_.runqtail) + runnext := atomic.Loaduintptr((*uintptr)(unsafe.Pointer(&_p_.runnext))) + if tail == atomic.Load(&_p_.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 _p_.runnext slot. +// If the run queue is full, runnext puts g on the global queue. +// Executed only by the owner P. +func runqput(_p_ *p, gp *g, next bool) { + if randomizeScheduler && next && fastrand()%2 == 0 { + next = false + } + + if next { + retryNext: + oldnext := _p_.runnext + if !_p_.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(&_p_.runqhead) // load-acquire, synchronize with consumers + t := _p_.runqtail + if t-h < uint32(len(_p_.runq)) { + _p_.runq[t%uint32(len(_p_.runq))].set(gp) + atomic.StoreRel(&_p_.runqtail, t+1) // store-release, makes the item available for consumption + return + } + if runqputslow(_p_, 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(_p_ *p, gp *g, h, t uint32) bool { + var batch [len(_p_.runq)/2 + 1]*g + + // First, grab a batch from local queue. + n := t - h + n = n / 2 + if n != uint32(len(_p_.runq)/2) { + throw("runqputslow: queue is not full") + } + for i := uint32(0); i < n; i++ { + batch[i] = _p_.runq[(h+i)%uint32(len(_p_.runq))].ptr() + } + if !atomic.CasRel(&_p_.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(_p_ *p) (gp *g, inheritTime bool) { + // If there's a runnext, it's the next G to run. + for { + next := _p_.runnext + if next == 0 { + break + } + if _p_.runnext.cas(next, 0) { + return next.ptr(), true + } + } + + for { + h := atomic.LoadAcq(&_p_.runqhead) // load-acquire, synchronize with other consumers + t := _p_.runqtail + if t == h { + return nil, false + } + gp := _p_.runq[h%uint32(len(_p_.runq))].ptr() + if atomic.CasRel(&_p_.runqhead, h, h+1) { // cas-release, commits consume + return gp, false + } + } +} + +// Grabs a batch of goroutines from _p_'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(_p_ *p, batch *[256]guintptr, batchHead uint32, stealRunNextG bool) uint32 { + for { + h := atomic.LoadAcq(&_p_.runqhead) // load-acquire, synchronize with other consumers + t := atomic.LoadAcq(&_p_.runqtail) // load-acquire, synchronize with the producer + n := t - h + n = n - n/2 + if n == 0 { + if stealRunNextG { + // Try to steal from _p_.runnext. + if next := _p_.runnext; next != 0 { + if _p_.status == _Prunning { + // Sleep to ensure that _p_ isn't about to run the g + // we are about to steal. + // The important use case here is when the g running + // on _p_ ready()s another g and then almost + // immediately blocks. Instead of stealing runnext + // in this window, back off to give _p_ 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" { + usleep(3) + } else { + // On windows system timer granularity is + // 1-15ms, which is way too much for this + // optimization. So just yield. + osyield() + } + } + if !_p_.runnext.cas(next, 0) { + continue + } + batch[batchHead%uint32(len(batch))] = next + return 1 + } + } + return 0 + } + if n > uint32(len(_p_.runq)/2) { // read inconsistent h and t + continue + } + for i := uint32(0); i < n; i++ { + g := _p_.runq[(h+i)%uint32(len(_p_.runq))] + batch[(batchHead+i)%uint32(len(batch))] = g + } + if atomic.CasRel(&_p_.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(_p_, p2 *p, stealRunNextG bool) *g { + t := _p_.runqtail + n := runqgrab(p2, &_p_.runq, t, stealRunNextG) + if n == 0 { + return nil + } + n-- + gp := _p_.runq[(t+n)%uint32(len(_p_.runq))].ptr() + if n == 0 { + return gp + } + h := atomic.LoadAcq(&_p_.runqhead) // load-acquire, synchronize with consumers + if t-h+n >= uint32(len(_p_.runq)) { + throw("runqsteal: runq overflow") + } + atomic.StoreRel(&_p_.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 l2 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 +} + +func haveexperiment(name string) bool { + x := sys.Goexperiment + for x != "" { + xname := "" + i := bytealg.IndexByteString(x, ',') + if i < 0 { + xname, x = x, "" + } else { + xname, x = x[:i], x[i+1:] + } + if xname == name { + return true + } + if len(xname) > 2 && xname[:2] == "no" && xname[2:] == name { + return false + } + } + return false +} + +//go:nosplit +func procPin() int { + _g_ := getg() + mp := _g_.m + + mp.locks++ + return int(mp.p.ptr().id) +} + +//go:nosplit +func procUnpin() { + _g_ := getg() + _g_.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 <= int32(sched.npidle+sched.nmspinning)+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%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/initempty.go:initTask +type initTask struct { + // TODO: pack the first 3 fields more tightly? + state uintptr // 0 = uninitialized, 1 = in progress, 2 = done + ndeps uintptr + nfns uintptr + // followed by ndeps instances of an *initTask, one per package depended on + // followed by nfns pcs, 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 int64 // init go routine id + allocs uint64 // heap allocations + bytes uint64 // heap allocated bytes +} + +func doInit(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 + + for i := uintptr(0); i < t.ndeps; i++ { + p := add(unsafe.Pointer(t), (3+i)*sys.PtrSize) + t2 := *(**initTask)(p) + doInit(t2) + } + + if t.nfns == 0 { + t.state = 2 // initialization done + return + } + + var ( + start int64 + before tracestat + ) + + if inittrace.active { + start = nanotime() + // Load stats non-atomically since tracinit is updated only by this init go routine. + before = inittrace + } + + firstFunc := add(unsafe.Pointer(t), (3+t.ndeps)*sys.PtrSize) + for i := uintptr(0); i < t.nfns; i++ { + p := add(firstFunc, i*sys.PtrSize) + f := *(*func())(unsafe.Pointer(&p)) + f() + } + + if inittrace.active { + end := nanotime() + // Load stats non-atomically since tracinit is updated only by this init go routine. + after := inittrace + + pkg := funcpkgpath(findfunc(funcPC(firstFunc))) + + 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 + } +} |