runtime: merge proc1.go -> proc.go

from proc1.go to proc.go:
* prepend header comment explaining "Goroutine scheduler"
* insert m0 and g0 var defs after the comment
* append the rest

Updates #12952

Change-Id: I35ee9ae3287675cde0c1b6aeaca0a460393f2354
Reviewed-on: https://go-review.googlesource.com/16024
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

1 files changed, 3726 insertions, 0 deletions

diff --git a/src/runtime/proc.go b/src/runtime/proc.go
index c5b4a8c9af..24776375ca 100644
--- a/src/runtime/proc.go
+++ b/src/runtime/proc.go
@@ -6,6 +6,23 @@ package runtime
 
 import "unsafe"
 
+// 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.
+
+var (
+	m0 m
+	g0 g
+)
+
 //go:linkname runtime_init runtime.init
 func runtime_init()
 
@@ -323,3 +340,3712 @@ func allgadd(gp *g) {
 	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
+)
+
+// The bootstrap sequence is:
+//
+//	call osinit
+//	call schedinit
+//	make & queue new G
+//	call runtime·mstart
+//
+// The new G calls runtime·main.
+func schedinit() {
+	// raceinit must be the first call to race detector.
+	// In particular, it must be done before mallocinit below calls racemapshadow.
+	_g_ := getg()
+	if raceenabled {
+		_g_.racectx = raceinit()
+	}
+
+	sched.maxmcount = 10000
+
+	// Cache the framepointer experiment.  This affects stack unwinding.
+	framepointer_enabled = haveexperiment("framepointer")
+
+	tracebackinit()
+	moduledataverify()
+	stackinit()
+	mallocinit()
+	mcommoninit(_g_.m)
+
+	goargs()
+	goenvs()
+	parsedebugvars()
+	gcinit()
+
+	sched.lastpoll = uint64(nanotime())
+	procs := int(ncpu)
+	if n := atoi(gogetenv("GOMAXPROCS")); n > 0 {
+		if n > _MaxGomaxprocs {
+			n = _MaxGomaxprocs
+		}
+		procs = n
+	}
+	if procresize(int32(procs)) != nil {
+		throw("unknown runnable goroutine during bootstrap")
+	}
+
+	if buildVersion == "" {
+		// Condition should never trigger.  This code just serves
+		// to ensure runtime·buildVersion is kept in the resulting binary.
+		buildVersion = "unknown"
+	}
+}
+
+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 sched.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[:])
+	}
+
+	mp.fastrand = 0x49f6428a + uint32(mp.id) + uint32(cputicks())
+	if mp.fastrand == 0 {
+		mp.fastrand = 0x49f6428a
+	}
+
+	lock(&sched.lock)
+	mp.id = sched.mcount
+	sched.mcount++
+	checkmcount()
+	mpreinit(mp)
+	if mp.gsignal != nil {
+		mp.gsignal.stackguard1 = mp.gsignal.stack.lo + _StackGuard
+	}
+
+	// Add to allm so garbage collector doesn't free g->m
+	// when it is just in a register or thread-local storage.
+	mp.alllink = allm
+
+	// NumCgoCall() iterates over allm w/o schedlock,
+	// so we need to publish it safely.
+	atomicstorep(unsafe.Pointer(&allm), unsafe.Pointer(mp))
+	unlock(&sched.lock)
+}
+
+// Mark gp ready to run.
+func ready(gp *g, traceskip int) {
+	if trace.enabled {
+		traceGoUnpark(gp, traceskip)
+	}
+
+	status := readgstatus(gp)
+
+	// Mark runnable.
+	_g_ := getg()
+	_g_.m.locks++ // 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, true)
+	if atomicload(&sched.npidle) != 0 && atomicload(&sched.nmspinning) == 0 { // TODO: fast atomic
+		wakep()
+	}
+	_g_.m.locks--
+	if _g_.m.locks == 0 && _g_.preempt { // restore the preemption request in case we've cleared it in newstack
+		_g_.stackguard0 = stackPreempt
+	}
+}
+
+func gcprocs() int32 {
+	// Figure out how many CPUs to use during GC.
+	// Limited by gomaxprocs, number of actual CPUs, and MaxGcproc.
+	lock(&sched.lock)
+	n := gomaxprocs
+	if n > ncpu {
+		n = ncpu
+	}
+	if n > _MaxGcproc {
+		n = _MaxGcproc
+	}
+	if n > sched.nmidle+1 { // one M is currently running
+		n = sched.nmidle + 1
+	}
+	unlock(&sched.lock)
+	return n
+}
+
+func needaddgcproc() bool {
+	lock(&sched.lock)
+	n := gomaxprocs
+	if n > ncpu {
+		n = ncpu
+	}
+	if n > _MaxGcproc {
+		n = _MaxGcproc
+	}
+	n -= sched.nmidle + 1 // one M is currently running
+	unlock(&sched.lock)
+	return n > 0
+}
+
+func helpgc(nproc int32) {
+	_g_ := getg()
+	lock(&sched.lock)
+	pos := 0
+	for n := int32(1); n < nproc; n++ { // one M is currently running
+		if allp[pos].mcache == _g_.m.mcache {
+			pos++
+		}
+		mp := mget()
+		if mp == nil {
+			throw("gcprocs inconsistency")
+		}
+		mp.helpgc = n
+		mp.p.set(allp[pos])
+		mp.mcache = allp[pos].mcache
+		pos++
+		notewakeup(&mp.park)
+	}
+	unlock(&sched.lock)
+}
+
+// freezeStopWait is a large value that freezetheworld sets
+// sched.stopwait to in order to request that all Gs permanently stop.
+const freezeStopWait = 0x7fffffff
+
+// 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() {
+	// 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
+		atomicstore(&sched.gcwaiting, 1)
+		// this should stop running goroutines
+		if !preemptall() {
+			break // no running goroutines
+		}
+		usleep(1000)
+	}
+	// to be sure
+	usleep(1000)
+	preemptall()
+	usleep(1000)
+}
+
+func isscanstatus(status uint32) bool {
+	if status == _Gscan {
+		throw("isscanstatus: Bad status Gscan")
+	}
+	return status&_Gscan == _Gscan
+}
+
+// All reads and writes of g's status go through readgstatus, casgstatus
+// castogscanstatus, casfrom_Gscanstatus.
+//go:nosplit
+func readgstatus(gp *g) uint32 {
+	return atomicload(&gp.atomicstatus)
+}
+
+// Ownership of gscanvalid:
+//
+// If gp is running (meaning status == _Grunning or _Grunning|_Gscan),
+// then gp owns gp.gscanvalid, and other goroutines must not modify it.
+//
+// Otherwise, a second goroutine can lock the scan state by setting _Gscan
+// in the status bit and then modify gscanvalid, and then unlock the scan state.
+//
+// Note that the first condition implies an exception to the second:
+// if a second goroutine changes gp's status to _Grunning|_Gscan,
+// that second goroutine still does not have the right to modify gscanvalid.
+
+// 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:
+		if newval == oldval&^_Gscan {
+			success = cas(&gp.atomicstatus, oldval, newval)
+		}
+	case _Gscanenqueue:
+		if newval == _Gwaiting {
+			success = 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")
+	}
+	if newval == _Grunning {
+		gp.gcscanvalid = false
+	}
+}
+
+// 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,
+		_Gwaiting,
+		_Gsyscall:
+		if newval == oldval|_Gscan {
+			return cas(&gp.atomicstatus, oldval, newval)
+		}
+	case _Grunning:
+		if newval == _Gscanrunning || newval == _Gscanenqueue {
+			return 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")
+		})
+	}
+
+	if oldval == _Grunning && gp.gcscanvalid {
+		// If oldvall == _Grunning, then the actual status must be
+		// _Grunning or _Grunning|_Gscan; either way,
+		// we own gp.gcscanvalid, so it's safe to read.
+		// gp.gcscanvalid must not be true when we are running.
+		print("runtime: casgstatus ", hex(oldval), "->", hex(newval), " gp.status=", hex(gp.atomicstatus), " gp.gcscanvalid=true\n")
+		throw("casgstatus")
+	}
+
+	// loop if gp->atomicstatus is in a scan state giving
+	// GC time to finish and change the state to oldval.
+	for !cas(&gp.atomicstatus, oldval, newval) {
+		if oldval == _Gwaiting && gp.atomicstatus == _Grunnable {
+			systemstack(func() {
+				throw("casgstatus: waiting for Gwaiting but is Grunnable")
+			})
+		}
+		// Help GC if needed.
+		// if gp.preemptscan && !gp.gcworkdone && (oldval == _Grunning || oldval == _Gsyscall) {
+		// 	gp.preemptscan = false
+		// 	systemstack(func() {
+		// 		gcphasework(gp)
+		// 	})
+		// }
+	}
+	if newval == _Grunning {
+		gp.gcscanvalid = false
+	}
+}
+
+// casgstatus(gp, oldstatus, Gcopystack), assuming oldstatus is Gwaiting or Grunnable.
+// Returns old status. Cannot call casgstatus directly, because we are racing with an
+// async wakeup that might come in from netpoll. If we see Gwaiting from the readgstatus,
+// it might have become Grunnable by the time we get to the cas. If we called casgstatus,
+// it would loop waiting for the status to go back to Gwaiting, which it never will.
+//go:nosplit
+func casgcopystack(gp *g) uint32 {
+	for {
+		oldstatus := readgstatus(gp) &^ _Gscan
+		if oldstatus != _Gwaiting && oldstatus != _Grunnable {
+			throw("copystack: bad status, not Gwaiting or Grunnable")
+		}
+		if cas(&gp.atomicstatus, oldstatus, _Gcopystack) {
+			return oldstatus
+		}
+	}
+}
+
+// scang blocks until gp's stack has been scanned.
+// It might be scanned by scang or it might be scanned by the goroutine itself.
+// Either way, the stack scan has completed when scang returns.
+func scang(gp *g) {
+	// Invariant; we (the caller, markroot for a specific goroutine) own gp.gcscandone.
+	// Nothing is racing with us now, but gcscandone might be set to true left over
+	// from an earlier round of stack scanning (we scan twice per GC).
+	// We use gcscandone to record whether the scan has been done during this round.
+	// It is important that the scan happens exactly once: if called twice,
+	// the installation of stack barriers will detect the double scan and die.
+
+	gp.gcscandone = false
+
+	// Endeavor to get gcscandone set to true,
+	// either by doing the stack scan ourselves or by coercing gp to scan itself.
+	// gp.gcscandone can transition from false to true when we're not looking
+	// (if we asked for preemption), so any time we lock the status using
+	// castogscanstatus we have to double-check that the scan is still not done.
+	for !gp.gcscandone {
+		switch s := readgstatus(gp); s {
+		default:
+			dumpgstatus(gp)
+			throw("stopg: invalid status")
+
+		case _Gdead:
+			// No stack.
+			gp.gcscandone = true
+
+		case _Gcopystack:
+		// Stack being switched. Go around again.
+
+		case _Grunnable, _Gsyscall, _Gwaiting:
+			// Claim goroutine by setting scan bit.
+			// Racing with execution or readying of gp.
+			// The scan bit keeps them from running
+			// the goroutine until we're done.
+			if castogscanstatus(gp, s, s|_Gscan) {
+				if !gp.gcscandone {
+					// Coordinate with traceback
+					// in sigprof.
+					for !cas(&gp.stackLock, 0, 1) {
+						osyield()
+					}
+					scanstack(gp)
+					atomicstore(&gp.stackLock, 0)
+					gp.gcscandone = true
+				}
+				restartg(gp)
+			}
+
+		case _Gscanwaiting:
+		// newstack is doing a scan for us right now. Wait.
+
+		case _Grunning:
+			// Goroutine running. Try to preempt execution so it can scan itself.
+			// The preemption handler (in newstack) does the actual scan.
+
+			// Optimization: if there is already a pending preemption request
+			// (from the previous loop iteration), don't bother with the atomics.
+			if gp.preemptscan && gp.preempt && gp.stackguard0 == stackPreempt {
+				break
+			}
+
+			// Ask for preemption and self scan.
+			if castogscanstatus(gp, _Grunning, _Gscanrunning) {
+				if !gp.gcscandone {
+					gp.preemptscan = true
+					gp.preempt = true
+					gp.stackguard0 = stackPreempt
+				}
+				casfrom_Gscanstatus(gp, _Gscanrunning, _Grunning)
+			}
+		}
+	}
+
+	gp.preemptscan = false // cancel scan request if no longer needed
+}
+
+// The GC requests that this routine be moved from a scanmumble state to a mumble state.
+func restartg(gp *g) {
+	s := readgstatus(gp)
+	switch s {
+	default:
+		dumpgstatus(gp)
+		throw("restartg: unexpected status")
+
+	case _Gdead:
+	// ok
+
+	case _Gscanrunnable,
+		_Gscanwaiting,
+		_Gscansyscall:
+		casfrom_Gscanstatus(gp, s, s&^_Gscan)
+
+	// Scan is now completed.
+	// Goroutine now needs to be made runnable.
+	// We put it on the global run queue; ready blocks on the global scheduler lock.
+	case _Gscanenqueue:
+		casfrom_Gscanstatus(gp, _Gscanenqueue, _Gwaiting)
+		if gp != getg().m.curg {
+			throw("processing Gscanenqueue on wrong m")
+		}
+		dropg()
+		ready(gp, 0)
+	}
+}
+
+// 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, false)
+	getg().m.preemptoff = reason
+	systemstack(stopTheWorldWithSema)
+}
+
+// startTheWorld undoes the effects of stopTheWorld.
+func startTheWorld() {
+	systemstack(startTheWorldWithSema)
+	// worldsema must be held over startTheWorldWithSema to ensure
+	// gomaxprocs cannot change while worldsema is held.
+	semrelease(&worldsema)
+	getg().m.preemptoff = ""
+}
+
+// Holding worldsema grants an M the right to try to stop the world
+// and prevents gomaxprocs from changing concurrently.
+var worldsema 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, false)
+//	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
+	atomicstore(&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 i := 0; i < int(gomaxprocs); i++ {
+		p := allp[i]
+		s := p.status
+		if s == _Psyscall && 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()
+		}
+	}
+	if sched.stopwait != 0 {
+		throw("stopTheWorld: not stopped")
+	}
+	for i := 0; i < int(gomaxprocs); i++ {
+		p := allp[i]
+		if p.status != _Pgcstop {
+			throw("stopTheWorld: not stopped")
+		}
+	}
+}
+
+func mhelpgc() {
+	_g_ := getg()
+	_g_.m.helpgc = -1
+}
+
+func startTheWorldWithSema() {
+	_g_ := getg()
+
+	_g_.m.locks++        // disable preemption because it can be holding p in a local var
+	gp := netpoll(false) // non-blocking
+	injectglist(gp)
+	add := needaddgcproc()
+	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)
+			add = false
+		}
+	}
+
+	// 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 atomicload(&sched.npidle) != 0 && atomicload(&sched.nmspinning) == 0 {
+		wakep()
+	}
+
+	if add {
+		// If GC could have used another helper proc, start one now,
+		// in the hope that it will be available next time.
+		// It would have been even better to start it before the collection,
+		// but doing so requires allocating memory, so it's tricky to
+		// coordinate.  This lazy approach works out in practice:
+		// we don't mind if the first couple gc rounds don't have quite
+		// the maximum number of procs.
+		newm(mhelpgc, nil)
+	}
+	_g_.m.locks--
+	if _g_.m.locks == 0 && _g_.preempt { // restore the preemption request in case we've cleared it in newstack
+		_g_.stackguard0 = stackPreempt
+	}
+}
+
+// Called to start an M.
+//go:nosplit
+func mstart() {
+	_g_ := getg()
+
+	if _g_.stack.lo == 0 {
+		// Initialize stack bounds from system stack.
+		// Cgo may have left stack size in stack.hi.
+		size := _g_.stack.hi
+		if size == 0 {
+			size = 8192 * stackGuardMultiplier
+		}
+		_g_.stack.hi = uintptr(noescape(unsafe.Pointer(&size)))
+		_g_.stack.lo = _g_.stack.hi - size + 1024
+	}
+	// Initialize stack guards so that we can start calling
+	// both Go and C functions with stack growth prologues.
+	_g_.stackguard0 = _g_.stack.lo + _StackGuard
+	_g_.stackguard1 = _g_.stackguard0
+	mstart1()
+}
+
+func mstart1() {
+	_g_ := getg()
+
+	if _g_ != _g_.m.g0 {
+		throw("bad runtime·mstart")
+	}
+
+	// Record top of stack for use by mcall.
+	// Once we call schedule we're never coming back,
+	// so other calls can reuse this stack space.
+	gosave(&_g_.m.g0.sched)
+	_g_.m.g0.sched.pc = ^uintptr(0) // make sure it is never used
+	asminit()
+	minit()
+
+	// Install signal handlers; after minit so that minit can
+	// prepare the thread to be able to handle the signals.
+	if _g_.m == &m0 {
+		// Create an extra M for callbacks on threads not created by Go.
+		if iscgo && !cgoHasExtraM {
+			cgoHasExtraM = true
+			newextram()
+		}
+		initsig()
+	}
+
+	if fn := _g_.m.mstartfn; fn != nil {
+		fn()
+	}
+
+	if _g_.m.helpgc != 0 {
+		_g_.m.helpgc = 0
+		stopm()
+	} else if _g_.m != &m0 {
+		acquirep(_g_.m.nextp.ptr())
+		_g_.m.nextp = 0
+	}
+	schedule()
+}
+
+// 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.
+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[:gomaxprocs] {
+		if p != _p_ {
+			atomicstore(&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 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 i := 0; i < int(gomaxprocs); i++ {
+		p := allp[i]
+		s := p.status
+		if s == _Psyscall && p.runSafePointFn == 1 && 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.
+			if notetsleep(&sched.safePointNote, 100*1000) {
+				noteclear(&sched.safePointNote)
+				break
+			}
+			preemptall()
+		}
+	}
+	if sched.safePointWait != 0 {
+		throw("forEachP: not done")
+	}
+	for i := 0; i < int(gomaxprocs); i++ {
+		p := allp[i]
+		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 !cas(&p.runSafePointFn, 1, 0) {
+		return
+	}
+	sched.safePointFn(p)
+	lock(&sched.lock)
+	sched.safePointWait--
+	if sched.safePointWait == 0 {
+		notewakeup(&sched.safePointNote)
+	}
+	unlock(&sched.lock)
+}
+
+// When running with cgo, we call _cgo_thread_start
+// to start threads for us so that we can play nicely with
+// foreign code.
+var cgoThreadStart unsafe.Pointer
+
+type cgothreadstart struct {
+	g   guintptr
+	tls *uint64
+	fn  unsafe.Pointer
+}
+
+// Allocate a new m unassociated with any thread.
+// Can use p for allocation context if needed.
+// fn is recorded as the new m's m.mstartfn.
+func allocm(_p_ *p, fn func()) *m {
+	_g_ := getg()
+	_g_.m.locks++ // disable GC because it can be called from sysmon
+	if _g_.m.p == 0 {
+		acquirep(_p_) // temporarily borrow p for mallocs in this function
+	}
+	mp := new(m)
+	mp.mstartfn = fn
+	mcommoninit(mp)
+
+	// In case of cgo or Solaris, pthread_create will make us a stack.
+	// Windows and Plan 9 will layout sched stack on OS stack.
+	if iscgo || GOOS == "solaris" || GOOS == "windows" || GOOS == "plan9" {
+		mp.g0 = malg(-1)
+	} else {
+		mp.g0 = malg(8192 * stackGuardMultiplier)
+	}
+	mp.g0.m = mp
+
+	if _p_ == _g_.m.p.ptr() {
+		releasep()
+	}
+	_g_.m.locks--
+	if _g_.m.locks == 0 && _g_.preempt { // restore the preemption request in case we've cleared it in newstack
+		_g_.stackguard0 = stackPreempt
+	}
+
+	return mp
+}
+
+// needm is called when a cgo callback happens on a
+// thread without an m (a thread not created by Go).
+// In this case, needm is expected to find an m to use
+// and return with m, g initialized correctly.
+// Since m and g are not set now (likely nil, but see below)
+// needm is limited in what routines it can call. In particular
+// it can only call nosplit functions (textflag 7) and cannot
+// do any scheduling that requires an m.
+//
+// In order to avoid needing heavy lifting here, we adopt
+// the following strategy: there is a stack of available m's
+// that can be stolen. Using compare-and-swap
+// to pop from the stack has ABA races, so we simulate
+// a lock by doing an exchange (via casp) 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 && !cgoHasExtraM {
+		// Can happen if C/C++ code calls Go from a global ctor.
+		// 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
+	unlockextra(mp.schedlink.ptr())
+
+	// Install g (= m->g0) and set the stack bounds
+	// to match the current stack. We don't actually know
+	// how big the stack is, like we don't know how big any
+	// scheduling stack is, but we assume there's at least 32 kB,
+	// which is more than enough for us.
+	setg(mp.g0)
+	_g_ := getg()
+	_g_.stack.hi = uintptr(noescape(unsafe.Pointer(&x))) + 1024
+	_g_.stack.lo = uintptr(noescape(unsafe.Pointer(&x))) - 32*1024
+	_g_.stackguard0 = _g_.stack.lo + _StackGuard
+
+	msigsave(mp)
+	// Initialize this thread to use the m.
+	asminit()
+	minit()
+}
+
+var earlycgocallback = []byte("fatal error: cgo callback before cgo call\n")
+
+// newextram allocates an m and puts it 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() {
+	// Create extra goroutine locked to extra m.
+	// The goroutine is the context in which the cgo callback will run.
+	// The sched.pc will never be returned to, but setting it to
+	// goexit makes clear to the traceback routines where
+	// the goroutine stack ends.
+	mp := allocm(nil, nil)
+	gp := malg(4096)
+	gp.sched.pc = funcPC(goexit) + _PCQuantum
+	gp.sched.sp = gp.stack.hi
+	gp.sched.sp -= 4 * regSize // extra space in case of reads slightly beyond frame
+	gp.sched.lr = 0
+	gp.sched.g = guintptr(unsafe.Pointer(gp))
+	gp.syscallpc = gp.sched.pc
+	gp.syscallsp = gp.sched.sp
+	gp.stktopsp = gp.sched.sp
+	// malg returns status as Gidle, change to Gsyscall before adding to allg
+	// where GC will see it.
+	casgstatus(gp, _Gidle, _Gsyscall)
+	gp.m = mp
+	mp.curg = gp
+	mp.locked = _LockInternal
+	mp.lockedg = gp
+	gp.lockedm = mp
+	gp.goid = int64(xadd64(&sched.goidgen, 1))
+	if raceenabled {
+		gp.racectx = racegostart(funcPC(newextram))
+	}
+	// put on allg for garbage collector
+	allgadd(gp)
+
+	// Add m to the extra list.
+	mnext := lockextra(true)
+	mp.schedlink.set(mnext)
+	unlockextra(mp)
+}
+
+// dropm is called when a cgo callback has called needm but is now
+// done with the callback and returning back into the non-Go thread.
+// It puts the current m back onto the extra list.
+//
+// The main expense here is the call to signalstack to release the
+// m's signal stack, and then the call to needm on the next callback
+// from this thread. It is tempting to try to save the m for next time,
+// which would eliminate both these costs, but there might not be
+// a next time: the current thread (which Go does not control) might exit.
+// If we saved the m for that thread, there would be an m leak each time
+// such a thread exited. Instead, we acquire and release an m on each
+// call. These should typically not be scheduling operations, just a few
+// atomics, so the cost should be small.
+//
+// TODO(rsc): An alternative would be to allocate a dummy pthread per-thread
+// variable using pthread_key_create. Unlike the pthread keys we already use
+// on OS X, this dummy key would never be read by Go code. It would exist
+// only so that we could register at thread-exit-time destructor.
+// That destructor would put the m back onto the extra list.
+// This is purely a performance optimization. The current version,
+// in which dropm happens on each cgo call, is still correct too.
+// We may have to keep the current version on systems with cgo
+// but without pthreads, like Windows.
+func dropm() {
+	// Undo whatever initialization minit did during needm.
+	unminit()
+
+	// 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
+	mnext := lockextra(true)
+	mp.schedlink.set(mnext)
+
+	setg(nil)
+	unlockextra(mp)
+}
+
+var extram uintptr
+
+// lockextra locks the extra list and returns the list head.
+// The caller must unlock the list by storing a new list head
+// to extram. If nilokay is true, then lockextra will
+// return a nil list head if that's what it finds. If nilokay is false,
+// lockextra will keep waiting until the list head is no longer nil.
+//go:nosplit
+func lockextra(nilokay bool) *m {
+	const locked = 1
+
+	for {
+		old := atomicloaduintptr(&extram)
+		if old == locked {
+			yield := osyield
+			yield()
+			continue
+		}
+		if old == 0 && !nilokay {
+			usleep(1)
+			continue
+		}
+		if casuintptr(&extram, old, locked) {
+			return (*m)(unsafe.Pointer(old))
+		}
+		yield := osyield
+		yield()
+		continue
+	}
+}
+
+//go:nosplit
+func unlockextra(mp *m) {
+	atomicstoreuintptr(&extram, uintptr(unsafe.Pointer(mp)))
+}
+
+// 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:nowritebarrier
+func newm(fn func(), _p_ *p) {
+	mp := allocm(_p_, fn)
+	mp.nextp.set(_p_)
+	msigsave(mp)
+	if iscgo {
+		var ts cgothreadstart
+		if _cgo_thread_start == nil {
+			throw("_cgo_thread_start missing")
+		}
+		ts.g.set(mp.g0)
+		ts.tls = (*uint64)(unsafe.Pointer(&mp.tls[0]))
+		ts.fn = unsafe.Pointer(funcPC(mstart))
+		asmcgocall(_cgo_thread_start, unsafe.Pointer(&ts))
+		return
+	}
+	newosproc(mp, unsafe.Pointer(mp.g0.stack.hi))
+}
+
+// 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 {
+		_g_.m.spinning = false
+		xadd(&sched.nmspinning, -1)
+	}
+
+retry:
+	lock(&sched.lock)
+	mput(_g_.m)
+	unlock(&sched.lock)
+	notesleep(&_g_.m.park)
+	noteclear(&_g_.m.park)
+	if _g_.m.helpgc != 0 {
+		gchelper()
+		_g_.m.helpgc = 0
+		_g_.m.mcache = nil
+		_g_.m.p = 0
+		goto retry
+	}
+	acquirep(_g_.m.nextp.ptr())
+	_g_.m.nextp = 0
+}
+
+func mspinning() {
+	gp := getg()
+	if !runqempty(gp.m.nextp.ptr()) {
+		// Something (presumably the GC) was readied while the
+		// runtime was starting up this M, so the M is no
+		// longer spinning.
+		if int32(xadd(&sched.nmspinning, -1)) < 0 {
+			throw("mspinning: nmspinning underflowed")
+		}
+	} else {
+		gp.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.
+//go:nowritebarrier
+func startm(_p_ *p, spinning bool) {
+	lock(&sched.lock)
+	if _p_ == nil {
+		_p_ = pidleget()
+		if _p_ == nil {
+			unlock(&sched.lock)
+			if spinning {
+				xadd(&sched.nmspinning, -1)
+			}
+			return
+		}
+	}
+	mp := mget()
+	unlock(&sched.lock)
+	if mp == nil {
+		var fn func()
+		if spinning {
+			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")
+	}
+	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:nowritebarrier
+func handoffp(_p_ *p) {
+	// if it has local work, start it straight away
+	if !runqempty(_p_) || sched.runqsize != 0 {
+		startm(_p_, false)
+		return
+	}
+	// no local work, check that there are no spinning/idle M's,
+	// otherwise our help is not required
+	if atomicload(&sched.nmspinning)+atomicload(&sched.npidle) == 0 && 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 && 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) && atomicload64(&sched.lastpoll) != 0 {
+		unlock(&sched.lock)
+		startm(_p_, false)
+		return
+	}
+	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 !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 == nil || _g_.m.lockedg.lockedm != _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)
+	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:nowritebarrier
+func startlockedm(gp *g) {
+	_g_ := getg()
+
+	mp := gp.lockedm
+	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
+		xadd(&sched.nmspinning, -1)
+	}
+	_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.
+func execute(gp *g, inheritTime bool) {
+	_g_ := getg()
+
+	casgstatus(gp, _Grunnable, _Grunning)
+	gp.waitsince = 0
+	gp.preempt = false
+	gp.stackguard0 = gp.stack.lo + _StackGuard
+	if !inheritTime {
+		_g_.m.p.ptr().schedtick++
+	}
+	_g_.m.curg = gp
+	gp.m = _g_.m
+
+	// Check whether the profiler needs to be turned on or off.
+	hz := sched.profilehz
+	if _g_.m.profilehz != hz {
+		resetcpuprofiler(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 {
+			// Since gp.sysblocktraced is true, we must emit an event.
+			// There is a race between the code that initializes sysexitseq
+			// and sysexitticks (in exitsyscall, which runs without a P,
+			// and therefore is not stopped with the rest of the world)
+			// and the code that initializes a new trace.
+			// The recorded sysexitseq and sysexitticks must therefore
+			// be treated as "best effort". If they are valid for this trace,
+			// then great, use them for greater accuracy.
+			// But if they're not valid for this trace, assume that the
+			// trace was started after the actual syscall exit (but before
+			// we actually managed to start the goroutine, aka right now),
+			// and assign a fresh time stamp to keep the log consistent.
+			seq, ts := gp.sysexitseq, gp.sysexitticks
+			if seq == 0 || int64(seq)-int64(trace.seqStart) < 0 {
+				seq, ts = tracestamp()
+			}
+			traceGoSysExit(seq, ts)
+		}
+		traceGoStart()
+	}
+
+	gogo(&gp.sched)
+}
+
+// Finds a runnable goroutine to execute.
+// Tries to steal from other P's, get g from global queue, poll network.
+func findrunnable() (gp *g, inheritTime bool) {
+	_g_ := getg()
+
+top:
+	if sched.gcwaiting != 0 {
+		gcstopm()
+		goto top
+	}
+	if _g_.m.p.ptr().runSafePointFn != 0 {
+		runSafePointFn()
+	}
+	if fingwait && fingwake {
+		if gp := wakefing(); gp != nil {
+			ready(gp, 0)
+		}
+	}
+
+	// local runq
+	if gp, inheritTime := runqget(_g_.m.p.ptr()); gp != nil {
+		return gp, inheritTime
+	}
+
+	// global runq
+	if sched.runqsize != 0 {
+		lock(&sched.lock)
+		gp := globrunqget(_g_.m.p.ptr(), 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 a thread 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() && sched.lastpoll != 0 {
+		if gp := netpoll(false); gp != nil { // non-blocking
+			// netpoll returns list of goroutines linked by schedlink.
+			injectglist(gp.schedlink.ptr())
+			casgstatus(gp, _Gwaiting, _Grunnable)
+			if trace.enabled {
+				traceGoUnpark(gp, 0)
+			}
+			return gp, 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*atomicload(&sched.nmspinning) >= uint32(gomaxprocs)-atomicload(&sched.npidle) { // TODO: fast atomic
+		goto stop
+	}
+	if !_g_.m.spinning {
+		_g_.m.spinning = true
+		xadd(&sched.nmspinning, 1)
+	}
+	// random steal from other P's
+	for i := 0; i < int(4*gomaxprocs); i++ {
+		if sched.gcwaiting != 0 {
+			goto top
+		}
+		_p_ := allp[fastrand1()%uint32(gomaxprocs)]
+		var gp *g
+		if _p_ == _g_.m.p.ptr() {
+			gp, _ = runqget(_p_)
+		} else {
+			stealRunNextG := i > 2*int(gomaxprocs) // first look for ready queues with more than 1 g
+			gp = runqsteal(_g_.m.p.ptr(), _p_, stealRunNextG)
+		}
+		if gp != nil {
+			return gp, false
+		}
+	}
+
+stop:
+
+	// We have nothing to do. If we're in the GC mark phase and can
+	// safely scan and blacken objects, run idle-time marking
+	// rather than give up the P.
+	if _p_ := _g_.m.p.ptr(); gcBlackenEnabled != 0 && _p_.gcBgMarkWorker != nil && gcMarkWorkAvailable(_p_) {
+		_p_.gcMarkWorkerMode = gcMarkWorkerIdleMode
+		gp := _p_.gcBgMarkWorker
+		casgstatus(gp, _Gwaiting, _Grunnable)
+		if trace.enabled {
+			traceGoUnpark(gp, 0)
+		}
+		return gp, false
+	}
+
+	// return P and block
+	lock(&sched.lock)
+	if sched.gcwaiting != 0 || _g_.m.p.ptr().runSafePointFn != 0 {
+		unlock(&sched.lock)
+		goto top
+	}
+	if sched.runqsize != 0 {
+		gp := globrunqget(_g_.m.p.ptr(), 0)
+		unlock(&sched.lock)
+		return gp, false
+	}
+	_p_ := releasep()
+	pidleput(_p_)
+	unlock(&sched.lock)
+	if _g_.m.spinning {
+		_g_.m.spinning = false
+		xadd(&sched.nmspinning, -1)
+	}
+
+	// check all runqueues once again
+	for i := 0; i < int(gomaxprocs); i++ {
+		_p_ := allp[i]
+		if _p_ != nil && !runqempty(_p_) {
+			lock(&sched.lock)
+			_p_ = pidleget()
+			unlock(&sched.lock)
+			if _p_ != nil {
+				acquirep(_p_)
+				goto top
+			}
+			break
+		}
+	}
+
+	// poll network
+	if netpollinited() && xchg64(&sched.lastpoll, 0) != 0 {
+		if _g_.m.p != 0 {
+			throw("findrunnable: netpoll with p")
+		}
+		if _g_.m.spinning {
+			throw("findrunnable: netpoll with spinning")
+		}
+		gp := netpoll(true) // block until new work is available
+		atomicstore64(&sched.lastpoll, uint64(nanotime()))
+		if gp != nil {
+			lock(&sched.lock)
+			_p_ = pidleget()
+			unlock(&sched.lock)
+			if _p_ != nil {
+				acquirep(_p_)
+				injectglist(gp.schedlink.ptr())
+				casgstatus(gp, _Gwaiting, _Grunnable)
+				if trace.enabled {
+					traceGoUnpark(gp, 0)
+				}
+				return gp, false
+			}
+			injectglist(gp)
+		}
+	}
+	stopm()
+	goto top
+}
+
+func resetspinning() {
+	_g_ := getg()
+
+	var nmspinning uint32
+	if _g_.m.spinning {
+		_g_.m.spinning = false
+		nmspinning = xadd(&sched.nmspinning, -1)
+		if int32(nmspinning) < 0 {
+			throw("findrunnable: negative nmspinning")
+		}
+	} else {
+		nmspinning = atomicload(&sched.nmspinning)
+	}
+
+	// M wakeup policy is deliberately somewhat conservative (see nmspinning handling),
+	// so see if we need to wakeup another P here.
+	if nmspinning == 0 && atomicload(&sched.npidle) > 0 {
+		wakep()
+	}
+}
+
+// Injects the list of runnable G's into the scheduler.
+// Can run concurrently with GC.
+func injectglist(glist *g) {
+	if glist == nil {
+		return
+	}
+	if trace.enabled {
+		for gp := glist; gp != nil; gp = gp.schedlink.ptr() {
+			traceGoUnpark(gp, 0)
+		}
+	}
+	lock(&sched.lock)
+	var n int
+	for n = 0; glist != nil; n++ {
+		gp := glist
+		glist = gp.schedlink.ptr()
+		casgstatus(gp, _Gwaiting, _Grunnable)
+		globrunqput(gp)
+	}
+	unlock(&sched.lock)
+	for ; n != 0 && sched.npidle != 0; n-- {
+		startm(nil, false)
+	}
+}
+
+// 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 != nil {
+		stoplockedm()
+		execute(_g_.m.lockedg, false) // Never returns.
+	}
+
+top:
+	if sched.gcwaiting != 0 {
+		gcstopm()
+		goto top
+	}
+	if _g_.m.p.ptr().runSafePointFn != 0 {
+		runSafePointFn()
+	}
+
+	var gp *g
+	var inheritTime bool
+	if trace.enabled || trace.shutdown {
+		gp = traceReader()
+		if gp != nil {
+			casgstatus(gp, _Gwaiting, _Grunnable)
+			traceGoUnpark(gp, 0)
+			resetspinning()
+		}
+	}
+	if gp == nil && gcBlackenEnabled != 0 {
+		gp = gcController.findRunnableGCWorker(_g_.m.p.ptr())
+		if gp != nil {
+			resetspinning()
+		}
+	}
+	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 {
+				resetspinning()
+			}
+		}
+	}
+	if gp == nil {
+		gp, inheritTime = runqget(_g_.m.p.ptr())
+		if gp != nil && _g_.m.spinning {
+			throw("schedule: spinning with local work")
+		}
+	}
+	if gp == nil {
+		gp, inheritTime = findrunnable() // blocks until work is available
+		resetspinning()
+	}
+
+	if gp.lockedm != nil {
+		// 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()
+
+	if _g_.m.lockedg == nil {
+		_g_.m.curg.m = nil
+		_g_.m.curg = nil
+	}
+}
+
+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, gp)
+	}
+
+	casgstatus(gp, _Grunning, _Gwaiting)
+	dropg()
+
+	if _g_.m.waitunlockf != nil {
+		fn := *(*func(*g, unsafe.Pointer) bool)(unsafe.Pointer(&_g_.m.waitunlockf))
+		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)
+}
+
+func gopreempt_m(gp *g) {
+	if trace.enabled {
+		traceGoPreempt()
+	}
+	goschedImpl(gp)
+}
+
+// Finishes execution of the current goroutine.
+func goexit1() {
+	if raceenabled {
+		racegoend()
+	}
+	if trace.enabled {
+		traceGoEnd()
+	}
+	mcall(goexit0)
+}
+
+// goexit continuation on g0.
+func goexit0(gp *g) {
+	_g_ := getg()
+
+	casgstatus(gp, _Grunning, _Gdead)
+	gp.m = nil
+	gp.lockedm = nil
+	_g_.m.lockedg = nil
+	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 = ""
+	gp.param = nil
+
+	dropg()
+
+	if _g_.m.locked&^_LockExternal != 0 {
+		print("invalid m->locked = ", _g_.m.locked, "\n")
+		throw("internal lockOSThread error")
+	}
+	_g_.m.locked = 0
+	gfput(_g_.m.p.ptr(), gp)
+	schedule()
+}
+
+//go:nosplit
+//go:nowritebarrier
+func save(pc, sp uintptr) {
+	_g_ := getg()
+
+	_g_.sched.pc = pc
+	_g_.sched.sp = sp
+	_g_.sched.lr = 0
+	_g_.sched.ret = 0
+	_g_.sched.ctxt = nil
+	_g_.sched.g = guintptr(unsafe.Pointer(_g_))
+}
+
+// The goroutine g is about to enter a system call.
+// Record that it's not using the cpu anymore.
+// This is called only from the go syscall library and cgocall,
+// not from the low-level system calls used by the runtime.
+//
+// Entersyscall cannot split the stack: the gosave must
+// make g->sched refer to the caller's stack segment, because
+// entersyscall is going to return immediately after.
+//
+// Nothing entersyscall calls can split the stack either.
+// We cannot safely move the stack during an active call to syscall,
+// because we do not know which of the uintptr arguments are
+// really pointers (back into the stack).
+// In practice, this means that we make the fast path run through
+// entersyscall doing no-split things, and the slow path has to use systemstack
+// to run bigger things on the system stack.
+//
+// reentersyscall is the entry point used by cgo callbacks, where explicitly
+// saved SP and PC are restored. This is needed when exitsyscall will be called
+// from a function further up in the call stack than the parent, as g->syscallsp
+// must always point to a valid stack frame. entersyscall below is the normal
+// entry point for syscalls, which obtains the SP and PC from the caller.
+//
+// Syscall tracing:
+// At the start of a syscall we emit traceGoSysCall to capture the stack trace.
+// If the syscall does not block, that is it, we do not emit any other events.
+// If the syscall blocks (that is, P is retaken), retaker emits traceGoSysBlock;
+// when syscall returns we emit traceGoSysExit and when the goroutine starts running
+// (potentially instantly, if exitsyscallfast returns true) we emit traceGoStart.
+// To ensure that traceGoSysExit is emitted strictly after traceGoSysBlock,
+// we remember current value of syscalltick in m (_g_.m.syscalltick = _g_.m.p.ptr().syscalltick),
+// whoever emits traceGoSysBlock increments p.syscalltick afterwards;
+// and we wait for the increment before emitting traceGoSysExit.
+// Note that the increment is done even if tracing is not enabled,
+// because tracing can be enabled in the middle of syscall. We don't want the wait to hang.
+//
+//go:nosplit
+func reentersyscall(pc, sp uintptr) {
+	_g_ := getg()
+
+	// Disable preemption because during this function g is in Gsyscall status,
+	// but can have inconsistent g->sched, do not let GC observe it.
+	_g_.m.locks++
+
+	// Entersyscall must not call any function that might split/grow the stack.
+	// (See details in comment above.)
+	// Catch calls that might, by replacing the stack guard with something that
+	// will trip any stack check and leaving a flag to tell newstack to die.
+	_g_.stackguard0 = stackPreempt
+	_g_.throwsplit = true
+
+	// Leave SP around for GC and traceback.
+	save(pc, sp)
+	_g_.syscallsp = sp
+	_g_.syscallpc = pc
+	casgstatus(_g_, _Grunning, _Gsyscall)
+	if _g_.syscallsp < _g_.stack.lo || _g_.stack.hi < _g_.syscallsp {
+		systemstack(func() {
+			print("entersyscall inconsistent ", hex(_g_.syscallsp), " [", hex(_g_.stack.lo), ",", hex(_g_.stack.hi), "]\n")
+			throw("entersyscall")
+		})
+	}
+
+	if trace.enabled {
+		systemstack(traceGoSysCall)
+		// systemstack itself clobbers g.sched.{pc,sp} and we might
+		// need them later when the G is genuinely blocked in a
+		// syscall
+		save(pc, sp)
+	}
+
+	if atomicload(&sched.sysmonwait) != 0 { // TODO: fast atomic
+		systemstack(entersyscall_sysmon)
+		save(pc, sp)
+	}
+
+	if _g_.m.p.ptr().runSafePointFn != 0 {
+		// runSafePointFn may stack split if run on this stack
+		systemstack(runSafePointFn)
+		save(pc, sp)
+	}
+
+	_g_.m.syscalltick = _g_.m.p.ptr().syscalltick
+	_g_.sysblocktraced = true
+	_g_.m.mcache = nil
+	_g_.m.p.ptr().m = 0
+	atomicstore(&_g_.m.p.ptr().status, _Psyscall)
+	if sched.gcwaiting != 0 {
+		systemstack(entersyscall_gcwait)
+		save(pc, sp)
+	}
+
+	// Goroutines must not split stacks in Gsyscall status (it would corrupt g->sched).
+	// We set _StackGuard to StackPreempt so that first split stack check calls morestack.
+	// Morestack detects this case and throws.
+	_g_.stackguard0 = stackPreempt
+	_g_.m.locks--
+}
+
+// Standard syscall entry used by the go syscall library and normal cgo calls.
+//go:nosplit
+func entersyscall(dummy int32) {
+	reentersyscall(getcallerpc(unsafe.Pointer(&dummy)), getcallersp(unsafe.Pointer(&dummy)))
+}
+
+func entersyscall_sysmon() {
+	lock(&sched.lock)
+	if atomicload(&sched.sysmonwait) != 0 {
+		atomicstore(&sched.sysmonwait, 0)
+		notewakeup(&sched.sysmonnote)
+	}
+	unlock(&sched.lock)
+}
+
+func entersyscall_gcwait() {
+	_g_ := getg()
+	_p_ := _g_.m.p.ptr()
+
+	lock(&sched.lock)
+	if sched.stopwait > 0 && cas(&_p_.status, _Psyscall, _Pgcstop) {
+		if trace.enabled {
+			traceGoSysBlock(_p_)
+			traceProcStop(_p_)
+		}
+		_p_.syscalltick++
+		if sched.stopwait--; sched.stopwait == 0 {
+			notewakeup(&sched.stopnote)
+		}
+	}
+	unlock(&sched.lock)
+}
+
+// The same as entersyscall(), but with a hint that the syscall is blocking.
+//go:nosplit
+func entersyscallblock(dummy int32) {
+	_g_ := getg()
+
+	_g_.m.locks++ // see comment in entersyscall
+	_g_.throwsplit = true
+	_g_.stackguard0 = stackPreempt // see comment in entersyscall
+	_g_.m.syscalltick = _g_.m.p.ptr().syscalltick
+	_g_.sysblocktraced = true
+	_g_.m.p.ptr().syscalltick++
+
+	// Leave SP around for GC and traceback.
+	pc := getcallerpc(unsafe.Pointer(&dummy))
+	sp := getcallersp(unsafe.Pointer(&dummy))
+	save(pc, sp)
+	_g_.syscallsp = _g_.sched.sp
+	_g_.syscallpc = _g_.sched.pc
+	if _g_.syscallsp < _g_.stack.lo || _g_.stack.hi < _g_.syscallsp {
+		sp1 := sp
+		sp2 := _g_.sched.sp
+		sp3 := _g_.syscallsp
+		systemstack(func() {
+			print("entersyscallblock inconsistent ", hex(sp1), " ", hex(sp2), " ", hex(sp3), " [", hex(_g_.stack.lo), ",", hex(_g_.stack.hi), "]\n")
+			throw("entersyscallblock")
+		})
+	}
+	casgstatus(_g_, _Grunning, _Gsyscall)
+	if _g_.syscallsp < _g_.stack.lo || _g_.stack.hi < _g_.syscallsp {
+		systemstack(func() {
+			print("entersyscallblock inconsistent ", hex(sp), " ", hex(_g_.sched.sp), " ", hex(_g_.syscallsp), " [", hex(_g_.stack.lo), ",", hex(_g_.stack.hi), "]\n")
+			throw("entersyscallblock")
+		})
+	}
+
+	systemstack(entersyscallblock_handoff)
+
+	// Resave for traceback during blocked call.
+	save(getcallerpc(unsafe.Pointer(&dummy)), getcallersp(unsafe.Pointer(&dummy)))
+
+	_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
+//go:nosplit
+func exitsyscall(dummy int32) {
+	_g_ := getg()
+
+	_g_.m.locks++ // see comment in entersyscall
+	if getcallersp(unsafe.Pointer(&dummy)) > _g_.syscallsp {
+		throw("exitsyscall: syscall frame is no longer valid")
+	}
+
+	_g_.waitsince = 0
+	oldp := _g_.m.p.ptr()
+	if exitsyscallfast() {
+		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)
+
+		// Garbage collector isn't running (since we are),
+		// so okay to clear syscallsp.
+		_g_.syscallsp = 0
+		_g_.m.locks--
+		if _g_.preempt {
+			// restore the preemption request in case we've cleared it in newstack
+			_g_.stackguard0 = stackPreempt
+		} else {
+			// otherwise restore the real _StackGuard, we've spoiled it in entersyscall/entersyscallblock
+			_g_.stackguard0 = _g_.stack.lo + _StackGuard
+		}
+		_g_.throwsplit = false
+		return
+	}
+
+	_g_.sysexitticks = 0
+	_g_.sysexitseq = 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_.sysexitseq, _g_.sysexitticks = tracestamp()
+	}
+
+	_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.
+	_g_.syscallsp = 0
+	_g_.m.p.ptr().syscalltick++
+	_g_.throwsplit = false
+}
+
+//go:nosplit
+func exitsyscallfast() bool {
+	_g_ := getg()
+
+	// Freezetheworld sets stopwait but does not retake P's.
+	if sched.stopwait == freezeStopWait {
+		_g_.m.mcache = nil
+		_g_.m.p = 0
+		return false
+	}
+
+	// Try to re-acquire the last P.
+	if _g_.m.p != 0 && _g_.m.p.ptr().status == _Psyscall && cas(&_g_.m.p.ptr().status, _Psyscall, _Prunning) {
+		// There's a cpu for us, so we can run.
+		_g_.m.mcache = _g_.m.p.ptr().mcache
+		_g_.m.p.ptr().m.set(_g_.m)
+		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(tracestamp())
+				})
+			}
+			_g_.m.p.ptr().syscalltick++
+		}
+		return true
+	}
+
+	// Try to get any other idle P.
+	oldp := _g_.m.p.ptr()
+	_g_.m.mcache = nil
+	_g_.m.p = 0
+	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(tracestamp())
+			}
+		})
+		if ok {
+			return true
+		}
+	}
+	return false
+}
+
+func exitsyscallfast_pidle() bool {
+	lock(&sched.lock)
+	_p_ := pidleget()
+	if _p_ != nil && atomicload(&sched.sysmonwait) != 0 {
+		atomicstore(&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.
+func exitsyscall0(gp *g) {
+	_g_ := getg()
+
+	casgstatus(gp, _Gsyscall, _Grunnable)
+	dropg()
+	lock(&sched.lock)
+	_p_ := pidleget()
+	if _p_ == nil {
+		globrunqput(gp)
+	} else if atomicload(&sched.sysmonwait) != 0 {
+		atomicstore(&sched.sysmonwait, 0)
+		notewakeup(&sched.sysmonnote)
+	}
+	unlock(&sched.lock)
+	if _p_ != nil {
+		acquirep(_p_)
+		execute(gp, false) // Never returns.
+	}
+	if _g_.m.lockedg != nil {
+		// Wait until another thread schedules gp and so m again.
+		stoplockedm()
+		execute(gp, false) // Never returns.
+	}
+	stopm()
+	schedule() // Never returns.
+}
+
+func beforefork() {
+	gp := getg().m.curg
+
+	// Fork can hang if preempted with signals frequently enough (see issue 5517).
+	// Ensure that we stay on the same M where we disable profiling.
+	gp.m.locks++
+	if gp.m.profilehz != 0 {
+		resetcpuprofiler(0)
+	}
+
+	// This function is called before fork in syscall package.
+	// Code between fork and exec must not allocate memory nor even try to grow stack.
+	// Here we spoil g->_StackGuard to reliably detect any attempts to grow stack.
+	// runtime_AfterFork will undo this in parent process, but not in child.
+	gp.stackguard0 = stackFork
+}
+
+// Called from syscall package before fork.
+//go:linkname syscall_runtime_BeforeFork syscall.runtime_BeforeFork
+//go:nosplit
+func syscall_runtime_BeforeFork() {
+	systemstack(beforefork)
+}
+
+func afterfork() {
+	gp := getg().m.curg
+
+	// See the comment in beforefork.
+	gp.stackguard0 = gp.stack.lo + _StackGuard
+
+	hz := sched.profilehz
+	if hz != 0 {
+		resetcpuprofiler(hz)
+	}
+	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)
+}
+
+// Allocate a new g, with a stack big enough for stacksize bytes.
+func malg(stacksize int32) *g {
+	newg := new(g)
+	if stacksize >= 0 {
+		stacksize = round2(_StackSystem + stacksize)
+		systemstack(func() {
+			newg.stack, newg.stkbar = stackalloc(uint32(stacksize))
+		})
+		newg.stackguard0 = newg.stack.lo + _StackGuard
+		newg.stackguard1 = ^uintptr(0)
+		newg.stackAlloc = uintptr(stacksize)
+	}
+	return newg
+}
+
+// Create a new g running fn with siz bytes of arguments.
+// Put it on the queue of g's waiting to run.
+// The compiler turns a go statement into a call to this.
+// Cannot split the stack because it assumes that the arguments
+// are available sequentially after &fn; they would not be
+// copied if a stack split occurred.
+//go:nosplit
+func newproc(siz int32, fn *funcval) {
+	argp := add(unsafe.Pointer(&fn), ptrSize)
+	pc := getcallerpc(unsafe.Pointer(&siz))
+	systemstack(func() {
+		newproc1(fn, (*uint8)(argp), siz, 0, pc)
+	})
+}
+
+// Create a new g running fn with narg bytes of arguments starting
+// at argp and returning nret bytes of results.  callerpc is the
+// address of the go statement that created this.  The new g is put
+// on the queue of g's waiting to run.
+func newproc1(fn *funcval, argp *uint8, narg int32, nret int32, callerpc uintptr) *g {
+	_g_ := getg()
+
+	if fn == nil {
+		_g_.m.throwing = -1 // do not dump full stacks
+		throw("go of nil func value")
+	}
+	_g_.m.locks++ // disable preemption because it can be holding p in a local var
+	siz := narg + nret
+	siz = (siz + 7) &^ 7
+
+	// We could allocate a larger initial stack if necessary.
+	// Not worth it: this is almost always an error.
+	// 4*sizeof(uintreg): extra space added below
+	// sizeof(uintreg): caller's LR (arm) or return address (x86, in gostartcall).
+	if siz >= _StackMin-4*regSize-regSize {
+		throw("newproc: function arguments too large for new goroutine")
+	}
+
+	_p_ := _g_.m.p.ptr()
+	newg := gfget(_p_)
+	if newg == nil {
+		newg = malg(_StackMin)
+		casgstatus(newg, _Gidle, _Gdead)
+		allgadd(newg) // publishes with a g->status of Gdead so GC scanner doesn't look at uninitialized stack.
+	}
+	if newg.stack.hi == 0 {
+		throw("newproc1: newg missing stack")
+	}
+
+	if readgstatus(newg) != _Gdead {
+		throw("newproc1: new g is not Gdead")
+	}
+
+	totalSize := 4*regSize + uintptr(siz) + minFrameSize // extra space in case of reads slightly beyond frame
+	totalSize += -totalSize & (spAlign - 1)              // align to spAlign
+	sp := newg.stack.hi - totalSize
+	spArg := sp
+	if usesLR {
+		// caller's LR
+		*(*unsafe.Pointer)(unsafe.Pointer(sp)) = nil
+		spArg += minFrameSize
+	}
+	memmove(unsafe.Pointer(spArg), unsafe.Pointer(argp), uintptr(narg))
+
+	memclr(unsafe.Pointer(&newg.sched), unsafe.Sizeof(newg.sched))
+	newg.sched.sp = sp
+	newg.stktopsp = sp
+	newg.sched.pc = funcPC(goexit) + _PCQuantum // +PCQuantum so that previous instruction is in same function
+	newg.sched.g = guintptr(unsafe.Pointer(newg))
+	gostartcallfn(&newg.sched, fn)
+	newg.gopc = callerpc
+	newg.startpc = fn.fn
+	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 = xadd64(&sched.goidgen, _GoidCacheBatch)
+		_p_.goidcache -= _GoidCacheBatch - 1
+		_p_.goidcacheend = _p_.goidcache + _GoidCacheBatch
+	}
+	newg.goid = int64(_p_.goidcache)
+	_p_.goidcache++
+	if raceenabled {
+		newg.racectx = racegostart(callerpc)
+	}
+	if trace.enabled {
+		traceGoCreate(newg, newg.startpc)
+	}
+	runqput(_p_, newg, true)
+
+	if atomicload(&sched.npidle) != 0 && atomicload(&sched.nmspinning) == 0 && unsafe.Pointer(fn.fn) != unsafe.Pointer(funcPC(main)) { // TODO: fast atomic
+		wakep()
+	}
+	_g_.m.locks--
+	if _g_.m.locks == 0 && _g_.preempt { // restore the preemption request in case we've cleared it in newstack
+		_g_.stackguard0 = stackPreempt
+	}
+	return newg
+}
+
+// Put on gfree list.
+// If local list is too long, transfer a batch to the global list.
+func gfput(_p_ *p, gp *g) {
+	if readgstatus(gp) != _Gdead {
+		throw("gfput: bad status (not Gdead)")
+	}
+
+	stksize := gp.stackAlloc
+
+	if stksize != _FixedStack {
+		// non-standard stack size - free it.
+		stackfree(gp.stack, gp.stackAlloc)
+		gp.stack.lo = 0
+		gp.stack.hi = 0
+		gp.stackguard0 = 0
+		gp.stkbar = nil
+		gp.stkbarPos = 0
+	} else {
+		// Reset stack barriers.
+		gp.stkbar = gp.stkbar[:0]
+		gp.stkbarPos = 0
+	}
+
+	gp.schedlink.set(_p_.gfree)
+	_p_.gfree = gp
+	_p_.gfreecnt++
+	if _p_.gfreecnt >= 64 {
+		lock(&sched.gflock)
+		for _p_.gfreecnt >= 32 {
+			_p_.gfreecnt--
+			gp = _p_.gfree
+			_p_.gfree = gp.schedlink.ptr()
+			gp.schedlink.set(sched.gfree)
+			sched.gfree = gp
+			sched.ngfree++
+		}
+		unlock(&sched.gflock)
+	}
+}
+
+// Get from gfree list.
+// If local list is empty, grab a batch from global list.
+func gfget(_p_ *p) *g {
+retry:
+	gp := _p_.gfree
+	if gp == nil && sched.gfree != nil {
+		lock(&sched.gflock)
+		for _p_.gfreecnt < 32 && sched.gfree != nil {
+			_p_.gfreecnt++
+			gp = sched.gfree
+			sched.gfree = gp.schedlink.ptr()
+			sched.ngfree--
+			gp.schedlink.set(_p_.gfree)
+			_p_.gfree = gp
+		}
+		unlock(&sched.gflock)
+		goto retry
+	}
+	if gp != nil {
+		_p_.gfree = gp.schedlink.ptr()
+		_p_.gfreecnt--
+		if gp.stack.lo == 0 {
+			// Stack was deallocated in gfput.  Allocate a new one.
+			systemstack(func() {
+				gp.stack, gp.stkbar = stackalloc(_FixedStack)
+			})
+			gp.stackguard0 = gp.stack.lo + _StackGuard
+			gp.stackAlloc = _FixedStack
+		} else {
+			if raceenabled {
+				racemalloc(unsafe.Pointer(gp.stack.lo), gp.stackAlloc)
+			}
+		}
+	}
+	return gp
+}
+
+// Purge all cached G's from gfree list to the global list.
+func gfpurge(_p_ *p) {
+	lock(&sched.gflock)
+	for _p_.gfreecnt != 0 {
+		_p_.gfreecnt--
+		gp := _p_.gfree
+		_p_.gfree = gp.schedlink.ptr()
+		gp.schedlink.set(sched.gfree)
+		sched.gfree = gp
+		sched.ngfree++
+	}
+	unlock(&sched.gflock)
+}
+
+// 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() {
+	_g_ := getg()
+	_g_.m.lockedg = _g_
+	_g_.lockedm = _g_.m
+}
+
+//go:nosplit
+
+// LockOSThread wires the calling goroutine to its current operating system thread.
+// Until the calling goroutine exits or calls UnlockOSThread, it will always
+// execute in that thread, and no other goroutine can.
+func LockOSThread() {
+	getg().m.locked |= _LockExternal
+	dolockOSThread()
+}
+
+//go:nosplit
+func lockOSThread() {
+	getg().m.locked += _LockInternal
+	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() {
+	_g_ := getg()
+	if _g_.m.locked != 0 {
+		return
+	}
+	_g_.m.lockedg = nil
+	_g_.lockedm = nil
+}
+
+//go:nosplit
+
+// UnlockOSThread unwires the calling goroutine from its fixed operating system thread.
+// If the calling goroutine has not called LockOSThread, UnlockOSThread is a no-op.
+func UnlockOSThread() {
+	getg().m.locked &^= _LockExternal
+	dounlockOSThread()
+}
+
+//go:nosplit
+func unlockOSThread() {
+	_g_ := getg()
+	if _g_.m.locked < _LockInternal {
+		systemstack(badunlockosthread)
+	}
+	_g_.m.locked -= _LockInternal
+	dounlockOSThread()
+}
+
+func badunlockosthread() {
+	throw("runtime: internal error: misuse of lockOSThread/unlockOSThread")
+}
+
+func gcount() int32 {
+	n := int32(allglen) - sched.ngfree
+	for i := 0; ; i++ {
+		_p_ := allp[i]
+		if _p_ == nil {
+			break
+		}
+		n -= _p_.gfreecnt
+	}
+
+	// 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 sched.mcount
+}
+
+var prof struct {
+	lock uint32
+	hz   int32
+}
+
+func _System()       { _System() }
+func _ExternalCode() { _ExternalCode() }
+func _GC()           { _GC() }
+
+// Called if we receive a SIGPROF signal.
+func sigprof(pc, sp, lr uintptr, gp *g, mp *m) {
+	if prof.hz == 0 {
+		return
+	}
+
+	// Profiling runs concurrently with GC, so it must not allocate.
+	mp.mallocing++
+
+	// Coordinate with stack barrier insertion in scanstack.
+	for !cas(&gp.stackLock, 0, 1) {
+		osyield()
+	}
+
+	// Define that a "user g" is a user-created goroutine, and a "system g"
+	// is one that is m->g0 or m->gsignal.
+	//
+	// We might be interrupted for profiling halfway through a
+	// goroutine switch. The switch involves updating three (or four) values:
+	// g, PC, SP, and (on arm) LR. The PC must be the last to be updated,
+	// because once it gets updated the new g is running.
+	//
+	// When switching from a user g to a system g, LR is not considered live,
+	// so the update only affects g, SP, and PC. Since PC must be last, there
+	// the possible partial transitions in ordinary execution are (1) g alone is updated,
+	// (2) both g and SP are updated, and (3) SP alone is updated.
+	// If SP or g alone is updated, we can detect the partial transition by checking
+	// whether the SP is within g's stack bounds. (We could also require that SP
+	// be changed only after g, but the stack bounds check is needed by other
+	// cases, so there is no need to impose an additional requirement.)
+	//
+	// There is one exceptional transition to a system g, not in ordinary execution.
+	// When a signal arrives, the operating system starts the signal handler running
+	// with an updated PC and SP. The g is updated last, at the beginning of the
+	// handler. There are two reasons this is okay. First, until g is updated the
+	// g and SP do not match, so the stack bounds check detects the partial transition.
+	// Second, signal handlers currently run with signals disabled, so a profiling
+	// signal cannot arrive during the handler.
+	//
+	// When switching from a system g to a user g, there are three possibilities.
+	//
+	// First, it may be that the g switch has no PC update, because the SP
+	// either corresponds to a user g throughout (as in asmcgocall)
+	// or because it has been arranged to look like a user g frame
+	// (as in cgocallback_gofunc). In this case, since the entire
+	// transition is a g+SP update, a partial transition updating just one of
+	// those will be detected by the stack bounds check.
+	//
+	// Second, when returning from a signal handler, the PC and SP updates
+	// are performed by the operating system in an atomic update, so the g
+	// update must be done before them. The stack bounds check detects
+	// the partial transition here, and (again) signal handlers run with signals
+	// disabled, so a profiling signal cannot arrive then anyway.
+	//
+	// Third, the common case: it may be that the switch updates g, SP, and PC
+	// separately. If the PC is within any of the functions that does this,
+	// we don't ask for a traceback. C.F. the function setsSP for more about this.
+	//
+	// There is another apparently viable approach, recorded here in case
+	// the "PC within setsSP function" check turns out not to be usable.
+	// It would be possible to delay the update of either g or SP until immediately
+	// before the PC update instruction. Then, because of the stack bounds check,
+	// the only problematic interrupt point is just before that PC update instruction,
+	// and the sigprof handler can detect that instruction and simulate stepping past
+	// it in order to reach a consistent state. On ARM, the update of g must be made
+	// in two places (in R10 and also in a TLS slot), so the delayed update would
+	// need to be the SP update. The sigprof handler must read the instruction at
+	// the current PC and if it was the known instruction (for example, JMP BX or
+	// MOV R2, PC), use that other register in place of the PC value.
+	// The biggest drawback to this solution is that it requires that we can tell
+	// whether it's safe to read from the memory pointed at by PC.
+	// In a correct program, we can test PC == nil and otherwise read,
+	// but if a profiling signal happens at the instant that a program executes
+	// a bad jump (before the program manages to handle the resulting fault)
+	// the profiling handler could fault trying to read nonexistent memory.
+	//
+	// To recap, there are no constraints on the assembly being used for the
+	// transition. We simply require that g and SP match and that the PC is not
+	// in gogo.
+	traceback := true
+	if gp == nil || sp < gp.stack.lo || gp.stack.hi < sp || setsSP(pc) {
+		traceback = false
+	}
+	var stk [maxCPUProfStack]uintptr
+	n := 0
+	if mp.ncgo > 0 && mp.curg != nil && mp.curg.syscallpc != 0 && mp.curg.syscallsp != 0 {
+		// Cgo, we can't unwind and symbolize arbitrary C code,
+		// so instead collect Go stack that leads to the cgo call.
+		// This is especially important on windows, since all syscalls are cgo calls.
+		n = gentraceback(mp.curg.syscallpc, mp.curg.syscallsp, 0, mp.curg, 0, &stk[0], len(stk), nil, nil, 0)
+	} else if traceback {
+		n = gentraceback(pc, sp, lr, gp, 0, &stk[0], len(stk), nil, nil, _TraceTrap|_TraceJumpStack)
+	}
+	if !traceback || n <= 0 {
+		// Normal traceback is impossible or has failed.
+		// See if it falls into several common cases.
+		n = 0
+		if GOOS == "windows" && n == 0 && mp.libcallg != 0 && mp.libcallpc != 0 && mp.libcallsp != 0 {
+			// Libcall, i.e. runtime syscall on windows.
+			// Collect Go stack that leads to the call.
+			n = gentraceback(mp.libcallpc, mp.libcallsp, 0, mp.libcallg.ptr(), 0, &stk[0], len(stk), nil, nil, 0)
+		}
+		if n == 0 {
+			// If all of the above has failed, account it against abstract "System" or "GC".
+			n = 2
+			// "ExternalCode" is better than "etext".
+			if pc > firstmoduledata.etext {
+				pc = funcPC(_ExternalCode) + _PCQuantum
+			}
+			stk[0] = pc
+			if mp.preemptoff != "" || mp.helpgc != 0 {
+				stk[1] = funcPC(_GC) + _PCQuantum
+			} else {
+				stk[1] = funcPC(_System) + _PCQuantum
+			}
+		}
+	}
+	atomicstore(&gp.stackLock, 0)
+
+	if prof.hz != 0 {
+		// Simple cas-lock to coordinate with setcpuprofilerate.
+		for !cas(&prof.lock, 0, 1) {
+			osyield()
+		}
+		if prof.hz != 0 {
+			cpuprof.add(stk[:n])
+		}
+		atomicstore(&prof.lock, 0)
+	}
+	mp.mallocing--
+}
+
+// Reports whether a function will set the SP
+// to an absolute value. Important that
+// we don't traceback when these are at the bottom
+// of the stack since we can't be sure that we will
+// find the caller.
+//
+// If the function is not on the bottom of the stack
+// we assume that it will have set it up so that traceback will be consistent,
+// either by being a traceback terminating function
+// or putting one on the stack at the right offset.
+func setsSP(pc uintptr) bool {
+	f := findfunc(pc)
+	if f == nil {
+		// couldn't find the function for this PC,
+		// so assume the worst and stop traceback
+		return true
+	}
+	switch f.entry {
+	case gogoPC, systemstackPC, mcallPC, morestackPC:
+		return true
+	}
+	return false
+}
+
+// Arrange to call fn with a traceback hz times a second.
+func setcpuprofilerate_m(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.
+	resetcpuprofiler(0)
+
+	for !cas(&prof.lock, 0, 1) {
+		osyield()
+	}
+	prof.hz = hz
+	atomicstore(&prof.lock, 0)
+
+	lock(&sched.lock)
+	sched.profilehz = hz
+	unlock(&sched.lock)
+
+	if hz != 0 {
+		resetcpuprofiler(hz)
+	}
+
+	_g_.m.locks--
+}
+
+// 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 || old > _MaxGomaxprocs || nprocs <= 0 || nprocs > _MaxGomaxprocs {
+		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
+
+	// initialize new P's
+	for i := int32(0); i < nprocs; i++ {
+		pp := allp[i]
+		if pp == nil {
+			pp = new(p)
+			pp.id = i
+			pp.status = _Pgcstop
+			pp.sudogcache = pp.sudogbuf[:0]
+			for i := range pp.deferpool {
+				pp.deferpool[i] = pp.deferpoolbuf[i][:0]
+			}
+			atomicstorep(unsafe.Pointer(&allp[i]), unsafe.Pointer(pp))
+		}
+		if pp.mcache == nil {
+			if old == 0 && i == 0 {
+				if getg().m.mcache == nil {
+					throw("missing mcache?")
+				}
+				pp.mcache = getg().m.mcache // bootstrap
+			} else {
+				pp.mcache = allocmcache()
+			}
+		}
+	}
+
+	// free unused P's
+	for i := nprocs; i < old; i++ {
+		p := allp[i]
+		if trace.enabled {
+			if p == getg().m.p.ptr() {
+				// moving to p[0], pretend that we were descheduled
+				// and then scheduled again to keep the trace sane.
+				traceGoSched()
+				traceProcStop(p)
+			}
+		}
+		// move all runnable goroutines to the global queue
+		for p.runqhead != p.runqtail {
+			// pop from tail of local queue
+			p.runqtail--
+			gp := p.runq[p.runqtail%uint32(len(p.runq))]
+			// push onto head of global queue
+			globrunqputhead(gp)
+		}
+		if p.runnext != 0 {
+			globrunqputhead(p.runnext.ptr())
+			p.runnext = 0
+		}
+		// if there's a background worker, make it runnable and put
+		// it on the global queue so it can clean itself up
+		if p.gcBgMarkWorker != nil {
+			casgstatus(p.gcBgMarkWorker, _Gwaiting, _Grunnable)
+			if trace.enabled {
+				traceGoUnpark(p.gcBgMarkWorker, 0)
+			}
+			globrunqput(p.gcBgMarkWorker)
+			p.gcBgMarkWorker = nil
+		}
+		for i := range p.sudogbuf {
+			p.sudogbuf[i] = nil
+		}
+		p.sudogcache = p.sudogbuf[:0]
+		for i := range p.deferpool {
+			for j := range p.deferpoolbuf[i] {
+				p.deferpoolbuf[i][j] = nil
+			}
+			p.deferpool[i] = p.deferpoolbuf[i][:0]
+		}
+		freemcache(p.mcache)
+		p.mcache = nil
+		gfpurge(p)
+		traceProcFree(p)
+		p.status = _Pdead
+		// can't free P itself because it can be referenced by an M in syscall
+	}
+
+	_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
+	} else {
+		// release the current P and acquire allp[0]
+		if _g_.m.p != 0 {
+			_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()
+		}
+	}
+	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
+		}
+	}
+	var int32p *int32 = &gomaxprocs // make compiler check that gomaxprocs is an int32
+	atomicstore((*uint32)(unsafe.Pointer(int32p)), uint32(nprocs))
+	return runnablePs
+}
+
+// Associate p and the current m.
+func acquirep(_p_ *p) {
+	acquirep1(_p_)
+
+	// have p; write barriers now allowed
+	_g_ := getg()
+	_g_.m.mcache = _p_.mcache
+
+	if trace.enabled {
+		traceProcStart()
+	}
+}
+
+// May run during STW, so write barriers are not allowed.
+//go:nowritebarrier
+func acquirep1(_p_ *p) {
+	_g_ := getg()
+
+	if _g_.m.p != 0 || _g_.m.mcache != nil {
+		throw("acquirep: already in go")
+	}
+	if _p_.m != 0 || _p_.status != _Pidle {
+		id := int32(0)
+		if _p_.m != 0 {
+			id = _p_.m.ptr().id
+		}
+		print("acquirep: p->m=", _p_.m, "(", id, ") p->status=", _p_.status, "\n")
+		throw("acquirep: invalid p state")
+	}
+	_g_.m.p.set(_p_)
+	_p_.m.set(_g_.m)
+	_p_.status = _Prunning
+}
+
+// Disassociate p and the current m.
+func releasep() *p {
+	_g_ := getg()
+
+	if _g_.m.p == 0 || _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=", _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.
+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
+	}
+
+	// -1 for sysmon
+	run := sched.mcount - sched.nmidle - sched.nmidlelocked - 1
+	if run > 0 {
+		return
+	}
+	if run < 0 {
+		print("runtime: checkdead: nmidle=", sched.nmidle, " nmidlelocked=", sched.nmidlelocked, " mcount=", sched.mcount, "\n")
+		throw("checkdead: inconsistent counts")
+	}
+
+	grunning := 0
+	lock(&allglock)
+	for i := 0; i < len(allgs); i++ {
+		gp := allgs[i]
+		if isSystemGoroutine(gp) {
+			continue
+		}
+		s := readgstatus(gp)
+		switch s &^ _Gscan {
+		case _Gwaiting:
+			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()
+		throw("no goroutines (main called runtime.Goexit) - deadlock!")
+	}
+
+	// Maybe jump time forward for playground.
+	gp := timejump()
+	if gp != nil {
+		casgstatus(gp, _Gwaiting, _Grunnable)
+		globrunqput(gp)
+		_p_ := pidleget()
+		if _p_ == nil {
+			throw("checkdead: no p for timer")
+		}
+		mp := mget()
+		if mp == nil {
+			newm(nil, _p_)
+		} else {
+			mp.nextp.set(_p_)
+			notewakeup(&mp.park)
+		}
+		return
+	}
+
+	getg().m.throwing = -1 // do not dump full stacks
+	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
+
+func sysmon() {
+	// If a heap span goes unused for 5 minutes after a garbage collection,
+	// we hand it back to the operating system.
+	scavengelimit := int64(5 * 60 * 1e9)
+
+	if debug.scavenge > 0 {
+		// Scavenge-a-lot for testing.
+		forcegcperiod = 10 * 1e6
+		scavengelimit = 20 * 1e6
+	}
+
+	lastscavenge := nanotime()
+	nscavenge := 0
+
+	lasttrace := int64(0)
+	idle := 0 // how many cycles in succession we had not wokeup somebody
+	delay := uint32(0)
+	for {
+		if idle == 0 { // start with 20us sleep...
+			delay = 20
+		} else if idle > 50 { // start doubling the sleep after 1ms...
+			delay *= 2
+		}
+		if delay > 10*1000 { // up to 10ms
+			delay = 10 * 1000
+		}
+		usleep(delay)
+		if debug.schedtrace <= 0 && (sched.gcwaiting != 0 || atomicload(&sched.npidle) == uint32(gomaxprocs)) { // TODO: fast atomic
+			lock(&sched.lock)
+			if atomicload(&sched.gcwaiting) != 0 || atomicload(&sched.npidle) == uint32(gomaxprocs) {
+				atomicstore(&sched.sysmonwait, 1)
+				unlock(&sched.lock)
+				// Make wake-up period small enough
+				// for the sampling to be correct.
+				maxsleep := forcegcperiod / 2
+				if scavengelimit < forcegcperiod {
+					maxsleep = scavengelimit / 2
+				}
+				notetsleep(&sched.sysmonnote, maxsleep)
+				lock(&sched.lock)
+				atomicstore(&sched.sysmonwait, 0)
+				noteclear(&sched.sysmonnote)
+				idle = 0
+				delay = 20
+			}
+			unlock(&sched.lock)
+		}
+		// poll network if not polled for more than 10ms
+		lastpoll := int64(atomicload64(&sched.lastpoll))
+		now := nanotime()
+		unixnow := unixnanotime()
+		if lastpoll != 0 && lastpoll+10*1000*1000 < now {
+			cas64(&sched.lastpoll, uint64(lastpoll), uint64(now))
+			gp := netpoll(false) // non-blocking - returns list of goroutines
+			if gp != nil {
+				// 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(gp)
+				incidlelocked(1)
+			}
+		}
+		// 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
+		lastgc := int64(atomicload64(&memstats.last_gc))
+		if lastgc != 0 && unixnow-lastgc > forcegcperiod && atomicload(&forcegc.idle) != 0 && atomicloaduint(&bggc.working) == 0 {
+			lock(&forcegc.lock)
+			forcegc.idle = 0
+			forcegc.g.schedlink = 0
+			injectglist(forcegc.g)
+			unlock(&forcegc.lock)
+		}
+		// scavenge heap once in a while
+		if lastscavenge+scavengelimit/2 < now {
+			mHeap_Scavenge(int32(nscavenge), uint64(now), uint64(scavengelimit))
+			lastscavenge = now
+			nscavenge++
+		}
+		if debug.schedtrace > 0 && lasttrace+int64(debug.schedtrace*1000000) <= now {
+			lasttrace = now
+			schedtrace(debug.scheddetail > 0)
+		}
+	}
+}
+
+var pdesc [_MaxGomaxprocs]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
+	for i := int32(0); i < gomaxprocs; i++ {
+		_p_ := allp[i]
+		if _p_ == nil {
+			continue
+		}
+		pd := &pdesc[i]
+		s := _p_.status
+		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 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_) && atomicload(&sched.nmspinning)+atomicload(&sched.npidle) > 0 && pd.syscallwhen+10*1000*1000 > now {
+				continue
+			}
+			// 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 cas(&_p_.status, s, _Pidle) {
+				if trace.enabled {
+					traceGoSysBlock(_p_)
+					traceProcStop(_p_)
+				}
+				n++
+				_p_.syscalltick++
+				handoffp(_p_)
+			}
+			incidlelocked(1)
+		} else if s == _Prunning {
+			// 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
+				continue
+			}
+			if pd.schedwhen+forcePreemptNS > now {
+				continue
+			}
+			preemptone(_p_)
+		}
+	}
+	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 i := int32(0); i < gomaxprocs; i++ {
+		_p_ := allp[i]
+		if _p_ == nil || _p_.status != _Prunning {
+			continue
+		}
+		if preemptone(_p_) {
+			res = true
+		}
+	}
+	return res
+}
+
+// Tell the goroutine running on processor P to stop.
+// This function is purely best-effort.  It can incorrectly fail to inform the
+// goroutine.  It can send inform the wrong goroutine.  Even if it informs the
+// correct goroutine, that goroutine might ignore the request if it is
+// simultaneously executing newstack.
+// No lock needs to be held.
+// Returns true if preemption request was issued.
+// The actual preemption will happen at some point in the future
+// and will be indicated by the gp->status no longer being
+// Grunning
+func preemptone(_p_ *p) bool {
+	mp := _p_.m.ptr()
+	if mp == nil || mp == getg().m {
+		return false
+	}
+	gp := mp.curg
+	if gp == nil || gp == mp.g0 {
+		return false
+	}
+
+	gp.preempt = true
+
+	// Every call in a go routine checks for stack overflow by
+	// comparing the current stack pointer to gp->stackguard0.
+	// Setting gp->stackguard0 to StackPreempt folds
+	// preemption into the normal stack overflow check.
+	gp.stackguard0 = stackPreempt
+	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=", sched.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 := int32(0); i < gomaxprocs; i++ {
+		_p_ := allp[i]
+		if _p_ == nil {
+			continue
+		}
+		mp := _p_.m.ptr()
+		h := atomicload(&_p_.runqhead)
+		t := atomicload(&_p_.runqtail)
+		if detailed {
+			id := int32(-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_.gfreecnt, "\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 == gomaxprocs-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
+		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, " helpgc=", mp.helpgc, " spinning=", mp.spinning, " blocked=", getg().m.blocked, " lockedg=", id3, "\n")
+	}
+
+	lock(&allglock)
+	for gi := 0; gi < len(allgs); gi++ {
+		gp := allgs[gi]
+		mp := gp.m
+		lockedm := gp.lockedm
+		id1 := int32(-1)
+		if mp != nil {
+			id1 = mp.id
+		}
+		id2 := int32(-1)
+		if lockedm != nil {
+			id2 = lockedm.id
+		}
+		print("  G", gp.goid, ": status=", readgstatus(gp), "(", gp.waitreason, ") m=", id1, " lockedm=", id2, "\n")
+	}
+	unlock(&allglock)
+	unlock(&sched.lock)
+}
+
+// Put mp on midle list.
+// Sched must be locked.
+// May run during STW, so write barriers are not allowed.
+//go:nowritebarrier
+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:nowritebarrier
+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:nowritebarrier
+func globrunqput(gp *g) {
+	gp.schedlink = 0
+	if sched.runqtail != 0 {
+		sched.runqtail.ptr().schedlink.set(gp)
+	} else {
+		sched.runqhead.set(gp)
+	}
+	sched.runqtail.set(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:nowritebarrier
+func globrunqputhead(gp *g) {
+	gp.schedlink = sched.runqhead
+	sched.runqhead.set(gp)
+	if sched.runqtail == 0 {
+		sched.runqtail.set(gp)
+	}
+	sched.runqsize++
+}
+
+// Put a batch of runnable goroutines on the global runnable queue.
+// Sched must be locked.
+func globrunqputbatch(ghead *g, gtail *g, n int32) {
+	gtail.schedlink = 0
+	if sched.runqtail != 0 {
+		sched.runqtail.ptr().schedlink.set(ghead)
+	} else {
+		sched.runqhead.set(ghead)
+	}
+	sched.runqtail.set(gtail)
+	sched.runqsize += n
+}
+
+// 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
+	if sched.runqsize == 0 {
+		sched.runqtail = 0
+	}
+
+	gp := sched.runqhead.ptr()
+	sched.runqhead = gp.schedlink
+	n--
+	for ; n > 0; n-- {
+		gp1 := sched.runqhead.ptr()
+		sched.runqhead = gp1.schedlink
+		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:nowritebarrier
+func pidleput(_p_ *p) {
+	if !runqempty(_p_) {
+		throw("pidleput: P has non-empty run queue")
+	}
+	_p_.link = sched.pidle
+	sched.pidle.set(_p_)
+	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:nowritebarrier
+func pidleget() *p {
+	_p_ := sched.pidle.ptr()
+	if _p_ != nil {
+		sched.pidle = _p_.link
+		xadd(&sched.npidle, -1) // TODO: fast atomic
+	}
+	return _p_
+}
+
+// runqempty returns true if _p_ has no Gs on its local run queue.
+// Note that this test is generally racy.
+func runqempty(_p_ *p) bool {
+	return _p_.runqhead == _p_.runqtail && _p_.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 if 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 && fastrand1()%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 := atomicload(&_p_.runqhead) // load-acquire, synchronize with consumers
+	t := _p_.runqtail
+	if t-h < uint32(len(_p_.runq)) {
+		_p_.runq[t%uint32(len(_p_.runq))] = gp
+		atomicstore(&_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 suceed
+	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))]
+	}
+	if !cas(&_p_.runqhead, h, h+n) { // cas-release, commits consume
+		return false
+	}
+	batch[n] = gp
+
+	if randomizeScheduler {
+		for i := uint32(1); i <= n; i++ {
+			j := fastrand1() % (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])
+	}
+
+	// Now put the batch on global queue.
+	lock(&sched.lock)
+	globrunqputbatch(batch[0], batch[n], 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 := atomicload(&_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))]
+		if cas(&_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]*g, batchHead uint32, stealRunNextG bool) uint32 {
+	for {
+		h := atomicload(&_p_.runqhead) // load-acquire, synchronize with other consumers
+		t := atomicload(&_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 {
+					// 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.
+					usleep(100)
+					if !_p_.runnext.cas(next, 0) {
+						continue
+					}
+					batch[batchHead%uint32(len(batch))] = next.ptr()
+					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 cas(&_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))]
+	if n == 0 {
+		return gp
+	}
+	h := atomicload(&_p_.runqhead) // load-acquire, synchronize with consumers
+	if t-h+n >= uint32(len(_p_.runq)) {
+		throw("runqsteal: runq overflow")
+	}
+	atomicstore(&_p_.runqtail, t+n) // store-release, makes the item available for consumption
+	return gp
+}
+
+func testSchedLocalQueue() {
+	_p_ := new(p)
+	gs := make([]g, len(_p_.runq))
+	for i := 0; i < len(_p_.runq); i++ {
+		if g, _ := runqget(_p_); g != nil {
+			throw("runq is not empty initially")
+		}
+		for j := 0; j < i; j++ {
+			runqput(_p_, &gs[i], false)
+		}
+		for j := 0; j < i; j++ {
+			if g, _ := runqget(_p_); g != &gs[i] {
+				print("bad element at iter ", i, "/", j, "\n")
+				throw("bad element")
+			}
+		}
+		if g, _ := runqget(_p_); g != nil {
+			throw("runq is not empty afterwards")
+		}
+	}
+}
+
+func testSchedLocalQueueSteal() {
+	p1 := new(p)
+	p2 := new(p)
+	gs := make([]g, len(p1.runq))
+	for i := 0; i < len(p1.runq); i++ {
+		for j := 0; j < i; j++ {
+			gs[j].sig = 0
+			runqput(p1, &gs[j], false)
+		}
+		gp := runqsteal(p2, p1, true)
+		s := 0
+		if gp != nil {
+			s++
+			gp.sig++
+		}
+		for {
+			gp, _ = runqget(p2)
+			if gp == nil {
+				break
+			}
+			s++
+			gp.sig++
+		}
+		for {
+			gp, _ = runqget(p1)
+			if gp == nil {
+				break
+			}
+			gp.sig++
+		}
+		for j := 0; j < i; j++ {
+			if gs[j].sig != 1 {
+				print("bad element ", j, "(", gs[j].sig, ") at iter ", i, "\n")
+				throw("bad element")
+			}
+		}
+		if s != i/2 && s != i/2+1 {
+			print("bad steal ", s, ", want ", i/2, " or ", i/2+1, ", iter ", i, "\n")
+			throw("bad steal")
+		}
+	}
+}
+
+//go:linkname setMaxThreads runtime/debug.setMaxThreads
+func setMaxThreads(in int) (out int) {
+	lock(&sched.lock)
+	out = int(sched.maxmcount)
+	sched.maxmcount = int32(in)
+	checkmcount()
+	unlock(&sched.lock)
+	return
+}
+
+func haveexperiment(name string) bool {
+	x := goexperiment
+	for x != "" {
+		xname := ""
+		i := index(x, ",")
+		if i < 0 {
+			xname, x = x, ""
+		} else {
+			xname, x = x[:i], x[i+1:]
+		}
+		if xname == name {
+			return true
+		}
+	}
+	return false
+}
+
+//go:nosplit
+func procPin() int {
+	_g_ := getg()
+	mp := _g_.m
+
+	mp.locks++
+	return int(mp.p.ptr().id)
+}
+
+//go:nosplit
+func procUnpin() {
+	_g_ := getg()
+	_g_.m.locks--
+}
+
+//go:linkname sync_runtime_procPin sync.runtime_procPin
+//go:nosplit
+func sync_runtime_procPin() int {
+	return procPin()
+}
+
+//go:linkname sync_runtime_procUnpin sync.runtime_procUnpin
+//go:nosplit
+func sync_runtime_procUnpin() {
+	procUnpin()
+}
+
+//go:linkname sync_atomic_runtime_procPin sync/atomic.runtime_procPin
+//go:nosplit
+func sync_atomic_runtime_procPin() int {
+	return procPin()
+}
+
+//go:linkname sync_atomic_runtime_procUnpin sync/atomic.runtime_procUnpin
+//go:nosplit
+func sync_atomic_runtime_procUnpin() {
+	procUnpin()
+}
+
+// Active spinning for sync.Mutex.
+//go:linkname sync_runtime_canSpin sync.runtime_canSpin
+//go:nosplit
+func sync_runtime_canSpin(i int) bool {
+	// sync.Mutex is cooperative, so we are conservative with spinning.
+	// Spin only few times and only if running on a multicore machine and
+	// GOMAXPROCS>1 and there is at least one other running P and local runq is empty.
+	// As opposed to runtime mutex we don't do passive spinning here,
+	// because there can be work on global runq on 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)
+}