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|
// 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/cpu"
"runtime/internal/atomic"
"runtime/internal/sys"
"unsafe"
)
// Functions called by C code.
//go:linkname main
//go:linkname goparkunlock
//go:linkname newextram
//go:linkname acquirep
//go:linkname releasep
//go:linkname incidlelocked
//go:linkname ginit
//go:linkname schedinit
//go:linkname ready
//go:linkname stopm
//go:linkname handoffp
//go:linkname wakep
//go:linkname stoplockedm
//go:linkname schedule
//go:linkname execute
//go:linkname goexit1
//go:linkname reentersyscall
//go:linkname reentersyscallblock
//go:linkname exitsyscall
//go:linkname gfget
//go:linkname kickoff
//go:linkname mstart1
//go:linkname mexit
//go:linkname globrunqput
//go:linkname pidleget
// Exported for test (see runtime/testdata/testprogcgo/dropm_stub.go).
//go:linkname getm
// Function called by misc/cgo/test.
//go:linkname lockedOSThread
// C functions for thread and context management.
func newosproc(*m)
//go:noescape
func malg(bool, bool, *unsafe.Pointer, *uintptr) *g
//go:noescape
func resetNewG(*g, *unsafe.Pointer, *uintptr)
func gogo(*g)
func setGContext()
func makeGContext(*g, unsafe.Pointer, uintptr)
func getTraceback(me, gp *g)
func gtraceback(*g)
func _cgo_notify_runtime_init_done()
func alreadyInCallers() bool
func stackfree(*g)
// Functions created by the compiler.
//extern __go_init_main
func main_init()
//extern main.main
func main_main()
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
raceprocctx0 uintptr
)
// 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
// 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(unsafe.Pointer) {
g := getg()
// 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
}
// Allow newproc to start new Ms.
mainStarted = true
if GOARCH != "wasm" { // no threads on wasm yet, so no sysmon
systemstack(func() {
newm(sysmon, nil)
})
}
// 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")
}
if nanotime() == 0 {
throw("nanotime returning zero")
}
// Defer unlock so that runtime.Goexit during init does the unlock too.
needUnlock := true
defer func() {
if needUnlock {
unlockOSThread()
}
}()
// Record when the world started.
runtimeInitTime = nanotime()
main_init_done = make(chan bool)
if iscgo {
// Start the template thread in case we enter Go from
// a C-created thread and need to create a new thread.
startTemplateThread()
_cgo_notify_runtime_init_done()
}
fn := main_init // make an indirect call, as the linker doesn't know the address of the main package when laying down the runtime
fn()
createGcRootsIndex()
close(main_init_done)
// For gccgo we have to wait until after main is initialized
// to enable GC, because initializing main registers the GC roots.
gcenable()
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() {
expectSystemGoroutine()
go forcegchelper()
}
func forcegchelper() {
setSystemGoroutine()
forcegc.g = getg()
for {
lock(&forcegc.lock)
if forcegc.idle != 0 {
throw("forcegc: phase error")
}
atomic.Store(&forcegc.idle, 1)
goparkunlock(&forcegc.lock, waitReasonForceGGIdle, 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.
// 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.
// 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.
//
// For gccgo note that this differs from the gc implementation; the gc
// implementation adds sys.PtrSize to the address of the interface
// value, but GCC's alias analysis decides that that can not be a
// reference to the second field of the interface, and in some cases
// it drops the initialization of the second field as a dead store.
//go:nosplit
func funcPC(f interface{}) uintptr {
i := (*iface)(unsafe.Pointer(&f))
r := *(*uintptr)(i.data)
if cpu.FunctionDescriptors {
// With PPC64 ELF ABI v1 function descriptors the
// function address is a pointer to a struct whose
// first field is the actual PC.
r = *(*uintptr)(unsafe.Pointer(r))
}
return r
}
func lockedOSThread() bool {
gp := getg()
return gp.lockedm != 0 && gp.m.lockedg != 0
}
var (
allgs []*g
allglock mutex
)
func allgadd(gp *g) {
if readgstatus(gp) == _Gidle {
throw("allgadd: bad status Gidle")
}
lock(&allglock)
allgs = append(allgs, gp)
allglen = uintptr(len(allgs))
unlock(&allglock)
}
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", "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)
}
func ginit() {
_m_ := &m0
_g_ := &g0
_m_.g0 = _g_
_m_.curg = _g_
_g_.m = _m_
setg(_g_)
}
// The bootstrap sequence is:
//
// call osinit
// call schedinit
// make & queue new G
// call runtime·mstart
//
// The new G calls runtime·main.
func schedinit() {
_g_ := getg()
sched.maxmcount = 10000
usestackmaps = probestackmaps()
mallocinit()
fastrandinit() // must run before mcommoninit
mcommoninit(_g_.m)
cpuinit() // must run before alginit
alginit() // maps must not be used before this call
msigsave(_g_.m)
initSigmask = _g_.m.sigmask
goargs()
goenvs()
parsedebugvars()
gcinit()
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")
}
// 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")
}
func checkmcount() {
// sched lock is held
if mcount() > sched.maxmcount {
print("runtime: program exceeds ", sched.maxmcount, "-thread limit\n")
throw("thread exhaustion")
}
}
func mcommoninit(mp *m) {
_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 sched.mnext+1 < sched.mnext {
throw("runtime: thread ID overflow")
}
mp.id = sched.mnext
sched.mnext++
checkmcount()
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)
// 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)
}
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)
if atomic.Load(&sched.npidle) != 0 && atomic.Load(&sched.nmspinning) == 0 {
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")
}
}
// 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 {
return atomic.Cas(&gp.atomicstatus, oldval, newval)
}
}
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")
})
}
// 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
}
}
}
// 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")
}
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.
semrelease(&worldsema)
getg().m.preemptoff = ""
}
// 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)
}
}
func startTheWorldWithSema(emitTraceEvent bool) int64 {
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)
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)
}
}
// 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.
if atomic.Load(&sched.npidle) != 0 && atomic.Load(&sched.nmspinning) == 0 {
wakep()
}
releasem(mp)
return startTime
}
// First function run by a new goroutine.
// This is passed to makecontext.
func kickoff() {
gp := getg()
if gp.traceback != 0 {
gtraceback(gp)
}
fv := gp.entry
param := gp.param
// When running on the g0 stack we can wind up here without a p,
// for example from mcall(exitsyscall0) in exitsyscall, in
// which case we can not run a write barrier.
// It is also possible for us to get here from the systemstack
// call in wbBufFlush, at which point the write barrier buffer
// is full and we can not run a write barrier.
// Setting gp.entry = nil or gp.param = nil will try to run a
// write barrier, so if we are on the g0 stack due to mcall
// (systemstack calls mcall) then clear the field using uintptr.
// This is OK when gp.param is gp.m.curg, as curg will be kept
// alive elsewhere, and gp.entry always points into g, or
// to a statically allocated value, or (in the case of mcall)
// to the stack.
if gp == gp.m.g0 && gp.param == unsafe.Pointer(gp.m.curg) {
*(*uintptr)(unsafe.Pointer(&gp.entry)) = 0
*(*uintptr)(unsafe.Pointer(&gp.param)) = 0
} else if gp.m.p == 0 {
throw("no p in kickoff")
} else {
gp.entry = nil
gp.param = nil
}
// Record the entry SP to help stack scan.
gp.entrysp = getsp()
fv(param)
goexit1()
}
func mstart1() {
_g_ := getg()
if _g_ != _g_.m.g0 {
throw("bad runtime·mstart")
}
asminit()
// Install signal handlers; after minit so that minit can
// prepare the thread to be able to handle the signals.
// For gccgo minit was called by C code.
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)
}
// 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)
notesleep(&m.park)
throw("locked m0 woke up")
}
sigblock()
unminit()
// Free the gsignal stack.
if m.gsignal != nil {
stackfree(m.gsignal)
// 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 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)
}
// 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)
}
// 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.
//
// 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(), allocatestack bool) (mp *m, g0Stack unsafe.Pointer, g0StackSize uintptr) {
_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(freem.g0)
freem = freem.freelink
}
sched.freem = newList
unlock(&sched.lock)
}
mp = new(m)
mp.mstartfn = fn
mcommoninit(mp)
mp.g0 = malg(allocatestack, false, &g0Stack, &g0StackSize)
mp.g0.m = mp
if _p_ == _g_.m.p.ptr() {
releasep()
}
releasem(_g_.m)
return mp, g0Stack, g0StackSize
}
// 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(x byte) {
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)
}
// 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())
// Save and block signals before installing g.
// 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.
msigsave(mp)
sigblock()
// Install g (= m->curg).
setg(mp.curg)
// Initialize this thread to use the m.
asminit()
minit()
setGContext()
// 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, g0SP, g0SPSize := allocm(nil, nil, true)
gp := malg(true, false, nil, nil)
// 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))
// put on allg for garbage collector
allgadd(gp)
// The context for gp will be set up in needm.
// Here we need to set the context for g0.
makeGContext(mp.g0, g0SP, g0SPSize)
// 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.
//
// CgocallBackDone calls this after releasing p, so no write barriers.
//go:nowritebarrierrec
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()
unminit()
// gccgo sets the stack to Gdead here, because the splitstack
// context is not initialized.
atomic.Store(&mp.curg.atomicstatus, _Gdead)
mp.curg.gcstack = 0
mp.curg.gcnextsp = 0
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
//go:nowritebarrierrec
func lockextra(nilokay bool) *m {
const locked = 1
incr := false
for {
old := atomic.Loaduintptr(&extram)
if old == locked {
yield := osyield
yield()
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))
}
yield := osyield
yield()
continue
}
}
//go:nosplit
//go:nowritebarrierrec
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.
//go:nowritebarrierrec
func newm(fn func(), _p_ *p) {
mp, _, _ := allocm(_p_, fn, false)
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) {
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
}
if !atomic.Cas(&newmHandoff.haveTemplateThread, 0, 1) {
return
}
newm(templateThread, nil)
}
// templateThread is a thread in a known-good state that exists solely
// to start new threads in known-good states when the calling thread
// may not be in a good state.
//
// Many programs never need this, so templateThread is started lazily
// when we first enter a state that might lead to running on a thread
// in an unknown state.
//
// templateThread runs on an M without a P, so it must not have write
// barriers.
//
//go:nowritebarrierrec
func templateThread() {
lock(&sched.lock)
sched.nmsys++
checkdead()
unlock(&sched.lock)
for {
lock(&newmHandoff.lock)
for newmHandoff.newm != 0 {
newm := newmHandoff.newm.ptr()
newmHandoff.newm = 0
unlock(&newmHandoff.lock)
for newm != nil {
next := newm.schedlink.ptr()
newm.schedlink = 0
newm1(newm)
newm = next
}
lock(&newmHandoff.lock)
}
newmHandoff.waiting = true
noteclear(&newmHandoff.wake)
unlock(&newmHandoff.lock)
notesleep(&newmHandoff.wake)
}
}
// Stops execution of the current m until new work is available.
// Returns with acquired P.
func stopm() {
_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)
notesleep(&_g_.m.park)
noteclear(&_g_.m.park)
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.
//go:nowritebarrierrec
func startm(_p_ *p, spinning bool) {
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")
}
}
return
}
}
mp := mget()
unlock(&sched.lock)
if mp == nil {
var fn func()
if spinning {
// The caller incremented nmspinning, so set m.spinning in the new M.
fn = mspinning
}
newm(fn, _p_)
return
}
if mp.spinning {
throw("startm: m is spinning")
}
if mp.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.
mp.spinning = spinning
mp.nextp.set(_p_)
notewakeup(&mp.park)
}
// 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
}
if when := nobarrierWakeTime(_p_); when != 0 {
wakeNetPoller(when)
}
pidleput(_p_)
unlock(&sched.lock)
}
// Tries to add one more P to execute G's.
// Called when a G is made runnable (newproc, ready).
func wakep() {
// be conservative about spinning threads
if !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.
notesleep(&_g_.m.park)
noteclear(&_g_.m.park)
status := readgstatus(_g_.m.lockedg.ptr())
if status&^_Gscan != _Grunnable {
print("runtime:stoplockedm: g is not Grunnable or Gscanrunnable\n")
dumpgstatus(_g_)
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
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)
}
// 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)
}
for i := 0; i < 4; i++ {
for enum := stealOrder.start(fastrand()); !enum.done(); enum.next() {
if sched.gcwaiting != 0 {
goto top
}
stealRunNextG := i > 2 // first look for ready queues with more than 1 g
p2 := allp[enum.position()]
if _p_ == p2 {
continue
}
if gp := runqsteal(_p_, p2, stealRunNextG); gp != nil {
return gp, false
}
// Consider stealing timers from p2.
// This call to checkTimers is the only place where
// we hold a lock on a different P's timers.
// Lock contention can be a problem here, so avoid
// grabbing the lock if p2 is running and not marked
// for preemption. If p2 is running and not being
// preempted we assume it will handle its own timers.
if i > 2 && shouldStealTimers(p2) {
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
}
}
}
}
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 && _p_.gcBgMarkWorker != 0 && gcMarkWorkAvailable(_p_) {
_p_.gcMarkWorkerMode = gcMarkWorkerIdleMode
gp := _p_.gcBgMarkWorker.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 pause execution until a callback was triggered.
if beforeIdle(delta) {
// At least one goroutine got woken.
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
// 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 the 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 _, _p_ := range allpSnapshot {
if !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
}
}
// Check for idle-priority GC work again.
if gcBlackenEnabled != 0 && gcMarkWorkAvailable(nil) {
lock(&sched.lock)
_p_ = pidleget()
if _p_ != nil && _p_.gcBgMarkWorker == 0 {
pidleput(_p_)
_p_ = nil
}
unlock(&sched.lock)
if _p_ != nil {
acquirep(_p_)
if wasSpinning {
_g_.m.spinning = true
atomic.Xadd(&sched.nmspinning, 1)
}
// Go back to idle GC check.
goto stop
}
}
// 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 there is one, and if it isn't going to wake up anyhow before
// the when argument.
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()
}
}
}
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.
if nmspinning == 0 && atomic.Load(&sched.npidle) > 0 {
wakep()
}
}
// Injects the list of runnable G's into the scheduler and clears glist.
// 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)
}
}
lock(&sched.lock)
var n int
for n = 0; !glist.empty(); n++ {
gp := glist.pop()
casgstatus(gp, _Gwaiting, _Grunnable)
globrunqput(gp)
}
unlock(&sched.lock)
for ; n != 0 && sched.npidle != 0; n-- {
startm(nil, false)
}
*glist = gList{}
}
// 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.
// Because gccgo does not implement preemption as a stack check,
// we need to check for preemption here for fairness.
// Otherwise goroutines on the local queue may starve
// goroutines on the global queue.
// Since we preempt by storing the goroutine on the global
// queue, this is the only place we need to check preempt.
// This does not call checkPreempt because gp is not running.
if gp != nil && gp.preempt {
gp.preempt = false
lock(&sched.lock)
globrunqput(gp)
unlock(&sched.lock)
goto top
}
}
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 {
if atomic.Load(&sched.npidle) != 0 && atomic.Load(&sched.nmspinning) == 0 {
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) {
lock(&pp.timersLock)
adjusttimers(pp)
rnow = now
if len(pp.timers) > 0 {
if rnow == 0 {
rnow = nanotime()
}
for len(pp.timers) > 0 {
// Note that runtimer may temporarily unlock
// pp.timersLock.
if tw := runtimer(pp, rnow); tw != 0 {
if tw > 0 {
pollUntil = tw
}
break
}
ran = true
}
}
unlock(&pp.timersLock)
return rnow, pollUntil, ran
}
// shouldStealTimers reports whether we should try stealing the timers from p2.
// We don't steal timers from a running P that is not marked for preemption,
// on the assumption that it will run its own timers. This reduces
// contention on the timers lock.
func shouldStealTimers(p2 *p) bool {
if p2.status != _Prunning {
return true
}
mp := p2.m.ptr()
if mp == nil || mp.locks > 0 {
return false
}
gp := mp.curg
if gp == nil || gp.atomicstatus != _Grunning || !gp.preempt {
return false
}
return true
}
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) // 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:
// - does not emit 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) {
pp := gp.m.p.ptr()
casgstatus(gp, _Grunning, _Grunnable)
dropg()
runqput(pp, gp, false)
schedule()
}
// Finishes execution of the current goroutine.
func goexit1() {
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.isSystemGoroutine = false
}
gp.m = nil
locked := gp.lockedm != 0
gp.lockedm = 0
_g_.m.lockedg = 0
gp.entry = nil
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.
scanCredit := int64(gcController.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.
_g_.m.exiting = true
gogo(_g_.m.g0)
} else {
// Clear lockedExt on plan9 since we may end up re-using
// this thread.
_g_.m.lockedExt = 0
}
}
schedule()
}
// 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.
//
// The entersyscall function is written in C, so that it can save the
// current register context so that the GC will see them.
// It calls reentersyscall.
//
// 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
//go:noinline
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++
_g_.syscallsp = sp
_g_.syscallpc = pc
casgstatus(_g_, _Grunning, _Gsyscall)
if trace.enabled {
systemstack(traceGoSysCall)
}
if atomic.Load(&sched.sysmonwait) != 0 {
systemstack(entersyscall_sysmon)
}
if _g_.m.p.ptr().runSafePointFn != 0 {
// runSafePointFn may stack split if run on this stack
systemstack(runSafePointFn)
}
_g_.m.syscalltick = _g_.m.p.ptr().syscalltick
_g_.sysblocktraced = true
_g_.m.mcache = nil
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)
}
_g_.m.locks--
}
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)
}
func reentersyscallblock(pc, sp uintptr) {
_g_ := getg()
_g_.m.locks++ // see comment in entersyscall
_g_.throwsplit = true
_g_.m.syscalltick = _g_.m.p.ptr().syscalltick
_g_.sysblocktraced = true
_g_.m.p.ptr().syscalltick++
// Leave SP around for GC and traceback.
_g_.syscallsp = sp
_g_.syscallpc = pc
casgstatus(_g_, _Grunning, _Gsyscall)
systemstack(entersyscallblock_handoff)
_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.
//
//go:nosplit
//go:nowritebarrierrec
func exitsyscall() {
_g_ := getg()
_g_.m.locks++ // see comment in entersyscall
_g_.waitsince = 0
oldp := _g_.m.oldp.ptr()
_g_.m.oldp = 0
if exitsyscallfast(oldp) {
if _g_.m.mcache == nil {
throw("lost mcache")
}
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)
exitsyscallclear(_g_)
_g_.m.locks--
_g_.throwsplit = false
// Check preemption, since unlike gc we don't check on
// every call.
if getg().preempt {
checkPreempt()
}
_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)
if _g_.m.mcache == nil {
throw("lost mcache")
}
// 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.
exitsyscallclear(_g_)
_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, _Gexitingsyscall)
dropg()
casgstatus(gp, _Gexitingsyscall, _Grunnable)
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.
}
// exitsyscallclear clears GC-related information that we only track
// during a syscall.
func exitsyscallclear(gp *g) {
// Garbage collector isn't running (since we are), so okay to
// clear syscallsp.
gp.syscallsp = 0
gp.gcstack = 0
gp.gcnextsp = 0
memclrNoHeapPointers(unsafe.Pointer(&gp.gcregs), unsafe.Sizeof(gp.gcregs))
}
// Code generated by cgo, and some library code, calls syscall.Entersyscall
// and syscall.Exitsyscall.
//go:linkname syscall_entersyscall syscall.Entersyscall
//go:nosplit
func syscall_entersyscall() {
entersyscall()
}
//go:linkname syscall_exitsyscall syscall.Exitsyscall
//go:nosplit
func syscall_exitsyscall() {
exitsyscall()
}
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++
msigsave(gp.m)
sigblock()
}
// 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
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
}
// 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()
}
// Called from syscall package after Exec.
//go:linkname syscall_runtime_AfterExec syscall.runtime_AfterExec
func syscall_runtime_AfterExec() {
execLock.unlock()
}
// panicgonil is used for gccgo as we need to use a compiler check for
// a nil func, in case we have to build a thunk.
//go:linkname panicgonil
func panicgonil() {
getg().m.throwing = -1 // do not dump full stacks
throw("go of nil func value")
}
// Create a new g running fn passing arg as the single argument.
// Put it on the queue of g's waiting to run.
// The compiler turns a go statement into a call to this.
//go:linkname newproc __go_go
func newproc(fn uintptr, arg unsafe.Pointer) *g {
_g_ := getg()
if fn == 0 {
_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
_p_ := _g_.m.p.ptr()
newg := gfget(_p_)
var (
sp unsafe.Pointer
spsize uintptr
)
if newg == nil {
newg = malg(true, false, &sp, &spsize)
casgstatus(newg, _Gidle, _Gdead)
allgadd(newg) // publishes with a g->status of Gdead so GC scanner doesn't look at uninitialized stack.
} else {
resetNewG(newg, &sp, &spsize)
}
newg.traceback = 0
if readgstatus(newg) != _Gdead {
throw("newproc1: new g is not Gdead")
}
// Store the C function pointer into entryfn, take the address
// of entryfn, convert it to a Go function value, and store
// that in entry.
newg.entryfn = fn
var entry func(unsafe.Pointer)
*(*unsafe.Pointer)(unsafe.Pointer(&entry)) = unsafe.Pointer(&newg.entryfn)
newg.entry = entry
newg.param = arg
newg.gopc = getcallerpc()
newg.ancestors = saveAncestors(_g_)
newg.startpc = 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 trace.enabled {
traceGoCreate(newg, newg.startpc)
}
makeGContext(newg, sp, spsize)
runqput(_p_, newg, true)
if atomic.Load(&sched.npidle) != 0 && atomic.Load(&sched.nmspinning) == 0 && mainStarted {
wakep()
}
releasem(_g_.m)
return newg
}
// expectedSystemGoroutines counts the number of goroutines expected
// to mark themselves as system goroutines. After they mark themselves
// by calling setSystemGoroutine, this is decremented. NumGoroutines
// uses this to wait for all system goroutines to mark themselves
// before it counts them.
var expectedSystemGoroutines uint32
// expectSystemGoroutine is called when starting a goroutine that will
// call setSystemGoroutine. It increments expectedSystemGoroutines.
func expectSystemGoroutine() {
atomic.Xadd(&expectedSystemGoroutines, +1)
}
// waitForSystemGoroutines waits for all currently expected system
// goroutines to register themselves.
func waitForSystemGoroutines() {
for atomic.Load(&expectedSystemGoroutines) > 0 {
Gosched()
osyield()
}
}
// setSystemGoroutine marks this goroutine as a "system goroutine".
// In the gc toolchain this is done by comparing startpc to a list of
// saved special PCs. In gccgo that approach does not work as startpc
// is often a thunk that invokes the real function with arguments,
// so the thunk address never matches the saved special PCs. Instead,
// since there are only a limited number of "system goroutines",
// we force each one to mark itself as special.
func setSystemGoroutine() {
getg().isSystemGoroutine = true
atomic.Xadd(&sched.ngsys, +1)
atomic.Xadd(&expectedSystemGoroutines, -1)
}
// 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
// FIXME: This should get a traceback of callergp.
// npcs := gcallers(callergp, 0, pcs[:])
npcs := 0
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)")
}
_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()
sched.gFree.list.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.list.empty() {
lock(&sched.gFree.lock)
// Move a batch of free Gs to the P.
for _p_.gFree.n < 32 {
gp := sched.gFree.list.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--
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--
sched.gFree.list.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(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() }
var _SystemPC = funcPC(_System)
var _ExternalCodePC = funcPC(_ExternalCode)
var _LostExternalCodePC = funcPC(_LostExternalCode)
var _GCPC = funcPC(_GC)
var _LostSIGPROFDuringAtomic64PC = funcPC(_LostSIGPROFDuringAtomic64)
// Called if we receive a SIGPROF signal.
// Called by the signal handler, may run during STW.
//go:nowritebarrierrec
func sigprof(pc uintptr, gp *g, mp *m) {
if prof.hz == 0 {
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++
traceback := true
// If SIGPROF arrived while already fetching runtime callers
// we can have trouble on older systems because the unwind
// library calls dl_iterate_phdr which was not reentrant in
// the past. alreadyInCallers checks for that.
if gp == nil || alreadyInCallers() {
traceback = false
}
var stk [maxCPUProfStack]uintptr
n := 0
if traceback {
var stklocs [maxCPUProfStack]location
n = callers(0, stklocs[:])
// Issue 26595: the stack trace we've just collected is going
// to include frames that we don't want to report in the CPU
// profile, including signal handler frames. Here is what we
// might typically see at the point of "callers" above for a
// signal delivered to the application routine "interesting"
// called by "main".
//
// 0: runtime.sigprof
// 1: runtime.sighandler
// 2: runtime.sigtrampgo
// 3: runtime.sigtramp
// 4: <signal handler called>
// 5: main.interesting_routine
// 6: main.main
//
// To ensure a sane profile, walk through the frames in
// "stklocs" until we find the "runtime.sigtramp" frame, then
// report only those frames below the frame one down from
// that. On systems that don't split stack, "sigtramp" can
// do a sibling call to "sigtrampgo", so use "sigtrampgo"
// if we don't find "sigtramp". If for some reason
// neither "runtime.sigtramp" nor "runtime.sigtrampgo" is
// present, don't make any changes.
framesToDiscard := 0
for i := 0; i < n; i++ {
if stklocs[i].function == "runtime.sigtrampgo" && i+2 < n {
framesToDiscard = i + 2
}
if stklocs[i].function == "runtime.sigtramp" && i+2 < n {
framesToDiscard = i + 2
break
}
}
n -= framesToDiscard
for i := 0; i < n; i++ {
stk[i] = stklocs[i+framesToDiscard].pc
}
}
if n <= 0 {
// Normal traceback is impossible or has failed.
// Account it against abstract "System" or "GC".
n = 2
stk[0] = pc
if mp.preemptoff != "" {
stk[1] = _GCPC + sys.PCQuantum
} else {
stk[1] = _SystemPC + sys.PCQuantum
}
}
if prof.hz != 0 {
cpuprof.add(gp, stk[:n])
}
getg().m.mallocing--
}
// Use global arrays rather than using up lots of stack space in the
// signal handler. This is safe since while we are executing a SIGPROF
// signal other SIGPROF signals are blocked.
var nonprofGoStklocs [maxCPUProfStack]location
var nonprofGoStk [maxCPUProfStack]uintptr
// 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(pc uintptr) {
if prof.hz != 0 {
n := callers(0, nonprofGoStklocs[:])
for i := 0; i < n; i++ {
nonprofGoStk[i] = nonprofGoStklocs[i].pc
}
if n <= 0 {
n = 2
nonprofGoStk[0] = pc
nonprofGoStk[1] = _ExternalCodePC + sys.PCQuantum
}
cpuprof.addNonGo(nonprofGoStk[:n])
}
}
// 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,
_ExternalCodePC + sys.PCQuantum,
}
cpuprof.addNonGo(stk)
}
}
// 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]
pp.deferpool = pp.deferpoolbuf[:0]
pp.wbBuf.reset()
if pp.mcache == nil {
if id == 0 {
if getg().m.mcache == nil {
throw("missing mcache?")
}
pp.mcache = getg().m.mcache // bootstrap
} else {
pp.mcache = allocmcache()
}
}
if raceenabled && pp.raceprocctx == 0 {
if id == 0 {
pp.raceprocctx = raceprocctx0
raceprocctx0 = 0 // bootstrap
} else {
pp.raceprocctx = raceproccreate()
}
}
}
// 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() {
// 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.adjustTimers = 0
unlock(&pp.timersLock)
unlock(&plocal.timersLock)
}
// If there's a background worker, make it runnable and put
// it on the global queue so it can clean itself up.
if gp := pp.gcBgMarkWorker.ptr(); gp != nil {
casgstatus(gp, _Gwaiting, _Grunnable)
if trace.enabled {
traceGoUnpark(gp, 0)
}
globrunqput(gp)
// This assignment doesn't race because the
// world is stopped.
pp.gcBgMarkWorker.set(nil)
}
// 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.deferpoolbuf {
pp.deferpoolbuf[i] = nil
}
pp.deferpool = pp.deferpoolbuf[:0]
systemstack(func() {
for i := 0; i < pp.mspancache.len; i++ {
// Safe to call since the world is stopped.
mheap_.spanalloc.free(unsafe.Pointer(pp.mspancache.buf[i]))
}
pp.mspancache.len = 0
pp.pcache.flush(&mheap_.pages)
})
freemcache(pp.mcache)
pp.mcache = nil
gfpurge(pp)
traceProcFree(pp)
pp.gcAssistTime = 0
pp.status = _Pdead
}
// Change number of processors. The world is stopped, sched is locked.
// gcworkbufs are not being modified by either the GC or
// the write barrier code.
// Returns list of Ps with local work, they need to be scheduled by the caller.
func procresize(nprocs int32) *p {
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
// 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
}
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
_g_.m.mcache = nil
p := allp[0]
p.m = 0
p.status = _Pidle
acquirep(p)
if trace.enabled {
traceGoStart()
}
}
// 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]
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 || _g_.m.mcache != nil {
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.mcache = _p_.mcache
_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 || _g_.m.mcache == nil {
throw("releasep: invalid arg")
}
_p_ := _g_.m.p.ptr()
if _p_.m.ptr() != _g_.m || _p_.mcache != _g_.m.mcache || _p_.status != _Prunning {
print("releasep: m=", _g_.m, " m->p=", _g_.m.p.ptr(), " p->m=", hex(_p_.m), " m->mcache=", _g_.m.mcache, " p->mcache=", _p_.mcache, " p->status=", _p_.status, "\n")
throw("releasep: invalid p state")
}
if trace.enabled {
traceProcStop(_g_.m.p.ptr())
}
_g_.m.p = 0
_g_.m.mcache = nil
_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() {
// 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:
unlock(&allglock)
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.
_p_ := timejump()
if _p_ != nil {
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)
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)
now := nanotime()
next := timeSleepUntil()
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) {
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)
}
notetsleep(&sched.sysmonnote, sleep)
if shouldRelax {
osRelax(false)
}
now = nanotime()
next = timeSleepUntil()
lock(&sched.lock)
atomic.Store(&sched.sysmonwait, 0)
noteclear(&sched.sysmonnote)
}
idle = 0
delay = 20
}
unlock(&sched.lock)
}
// 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)
}
}
if next < now {
// There are timers that should have already run,
// perhaps because there is an unpreemptible P.
// Try to start an M to run them.
startm(nil, false)
}
// 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)
}
}
}
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
// At this point the gc implementation sets gp.stackguard0 to
// a value that causes the goroutine to suspend itself.
// gccgo has no support for this, and it's hard to support.
// The split stack code reads a value from its TCB.
// We have no way to set a value in the TCB of a different thread.
// And, of course, not all systems support split stack anyhow.
// Checking the field in the g is expensive, since it requires
// loading the g from TLS. The best mechanism is likely to be
// setting a global variable and figuring out a way to efficiently
// check that global variable.
//
// For now we check gp.preempt in schedule, mallocgc, selectgo,
// and a few other places, which is at least better than doing
// nothing at all.
// 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.
func schedEnabled(gp *g) bool {
if sched.disable.user {
return isSystemGoroutine(gp, true)
}
return true
}
// Put mp on midle list.
// Sched must be locked.
// May run during STW, so write barriers are not allowed.
//go:nowritebarrierrec
func mput(mp *m) {
mp.schedlink = sched.midle
sched.midle.set(mp)
sched.nmidle++
checkdead()
}
// Try to get an m from midle list.
// Sched must be locked.
// May run during STW, so write barriers are not allowed.
//go:nowritebarrierrec
func mget() *m {
mp := sched.midle.ptr()
if mp != nil {
sched.midle = mp.schedlink
sched.nmidle--
}
return mp
}
// Put gp on the global runnable queue.
// Sched must be locked.
// May run during STW, so write barriers are not allowed.
//go:nowritebarrierrec
func globrunqput(gp *g) {
sched.runq.pushBack(gp)
sched.runqsize++
}
// Put gp at the head of the global runnable queue.
// Sched must be locked.
// May run during STW, so write barriers are not allowed.
//go:nowritebarrierrec
func globrunqputhead(gp *g) {
sched.runq.push(gp)
sched.runqsize++
}
// Put a batch of runnable goroutines on the global runnable queue.
// This clears *batch.
// Sched must be locked.
func globrunqputbatch(batch *gQueue, n int32) {
sched.runq.pushBackAll(*batch)
sched.runqsize += n
*batch = gQueue{}
}
// Try get a batch of G's from the global runnable queue.
// Sched must be locked.
func globrunqget(_p_ *p, max int32) *g {
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
}
// Put p to on _Pidle list.
// Sched must be locked.
// May run during STW, so write barriers are not allowed.
//go:nowritebarrierrec
func pidleput(_p_ *p) {
if !runqempty(_p_) {
throw("pidleput: P has non-empty run queue")
}
_p_.link = sched.pidle
sched.pidle.set(_p_)
atomic.Xadd(&sched.npidle, 1) // TODO: fast atomic
}
// Try get a p from _Pidle list.
// Sched must be locked.
// May run during STW, so write barriers are not allowed.
//go:nowritebarrierrec
func pidleget() *p {
_p_ := sched.pidle.ptr()
if _p_ != nil {
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
}
// 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..z2fdebug.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 {
// The gofrontend does not support experiments.
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..z2fatomic.runtime_procPin
//go:nosplit
func sync_atomic_runtime_procPin() int {
return procPin()
}
//go:linkname sync_atomic_runtime_procUnpin sync..z2fatomic.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
}
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