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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
#include "runtime.h"
#include "arch_GOARCH.h"
#include "zaexperiment.h"
#include "malloc.h"
#include "stack.h"
#include "race.h"
#include "type.h"
#include "mgc0.h"
#include "textflag.h"
// 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 http://golang.org/s/go11sched.
enum
{
// Number of goroutine ids to grab from runtime·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,
};
SchedT runtime·sched;
int32 runtime·gomaxprocs;
uint32 runtime·needextram;
bool runtime·iscgo;
M runtime·m0;
G runtime·g0; // idle goroutine for m0
G* runtime·lastg;
M* runtime·allm;
M* runtime·extram;
P* runtime·allp[MaxGomaxprocs+1];
int8* runtime·goos;
int32 runtime·ncpu;
int32 runtime·newprocs;
Mutex runtime·allglock; // the following vars are protected by this lock or by stoptheworld
G** runtime·allg;
Slice runtime·allgs;
uintptr runtime·allglen;
ForceGCState runtime·forcegc;
void runtime·mstart(void);
static void runqput(P*, G*);
static G* runqget(P*);
static bool runqputslow(P*, G*, uint32, uint32);
static G* runqsteal(P*, P*);
static void mput(M*);
static M* mget(void);
static void mcommoninit(M*);
static void schedule(void);
static void procresize(int32);
static void acquirep(P*);
static P* releasep(void);
static void newm(void(*)(void), P*);
static void stopm(void);
static void startm(P*, bool);
static void handoffp(P*);
static void wakep(void);
static void stoplockedm(void);
static void startlockedm(G*);
static void sysmon(void);
static uint32 retake(int64);
static void incidlelocked(int32);
static void checkdead(void);
static void exitsyscall0(G*);
void runtime·park_m(G*);
static void goexit0(G*);
static void gfput(P*, G*);
static G* gfget(P*);
static void gfpurge(P*);
static void globrunqput(G*);
static void globrunqputbatch(G*, G*, int32);
static G* globrunqget(P*, int32);
static P* pidleget(void);
static void pidleput(P*);
static void injectglist(G*);
static bool preemptall(void);
static bool preemptone(P*);
static bool exitsyscallfast(void);
static bool haveexperiment(int8*);
void runtime·allgadd(G*);
static void dropg(void);
extern String runtime·buildVersion;
// For cgo-using programs with external linking,
// export "main" (defined in assembly) so that libc can handle basic
// C runtime startup and call the Go program as if it were
// the C main function.
#pragma cgo_export_static main
// Filled in by dynamic linker when Cgo is available.
void (*_cgo_init)(void);
void (*_cgo_malloc)(void);
void (*_cgo_free)(void);
// Copy for Go code.
void* runtime·cgoMalloc;
void* runtime·cgoFree;
// The bootstrap sequence is:
//
// call osinit
// call schedinit
// make & queue new G
// call runtime·mstart
//
// The new G calls runtime·main.
void
runtime·schedinit(void)
{
int32 n, procs;
byte *p;
// raceinit must be the first call to race detector.
// In particular, it must be done before mallocinit below calls racemapshadow.
if(raceenabled)
g->racectx = runtime·raceinit();
runtime·sched.maxmcount = 10000;
runtime·tracebackinit();
runtime·symtabinit();
runtime·stackinit();
runtime·mallocinit();
mcommoninit(g->m);
runtime·goargs();
runtime·goenvs();
runtime·parsedebugvars();
runtime·gcinit();
runtime·sched.lastpoll = runtime·nanotime();
procs = 1;
p = runtime·getenv("GOMAXPROCS");
if(p != nil && (n = runtime·atoi(p)) > 0) {
if(n > MaxGomaxprocs)
n = MaxGomaxprocs;
procs = n;
}
procresize(procs);
if(runtime·buildVersion.str == nil) {
// Condition should never trigger. This code just serves
// to ensure runtime·buildVersion is kept in the resulting binary.
runtime·buildVersion.str = (uint8*)"unknown";
runtime·buildVersion.len = 7;
}
runtime·cgoMalloc = _cgo_malloc;
runtime·cgoFree = _cgo_free;
}
void
runtime·newsysmon(void)
{
newm(sysmon, nil);
}
static void
dumpgstatus(G* gp)
{
runtime·printf("runtime: gp: gp=%p, goid=%D, gp->atomicstatus=%x\n", gp, gp->goid, runtime·readgstatus(gp));
runtime·printf("runtime: g: g=%p, goid=%D, g->atomicstatus=%x\n", g, g->goid, runtime·readgstatus(g));
}
static void
checkmcount(void)
{
// sched lock is held
if(runtime·sched.mcount > runtime·sched.maxmcount){
runtime·printf("runtime: program exceeds %d-thread limit\n", runtime·sched.maxmcount);
runtime·throw("thread exhaustion");
}
}
static void
mcommoninit(M *mp)
{
// g0 stack won't make sense for user (and is not necessary unwindable).
if(g != g->m->g0)
runtime·callers(1, mp->createstack, nelem(mp->createstack));
mp->fastrand = 0x49f6428aUL + mp->id + runtime·cputicks();
runtime·lock(&runtime·sched.lock);
mp->id = runtime·sched.mcount++;
checkmcount();
runtime·mpreinit(mp);
if(mp->gsignal)
mp->gsignal->stackguard1 = mp->gsignal->stack.lo + StackGuard;
// Add to runtime·allm so garbage collector doesn't free g->m
// when it is just in a register or thread-local storage.
mp->alllink = runtime·allm;
// runtime·NumCgoCall() iterates over allm w/o schedlock,
// so we need to publish it safely.
runtime·atomicstorep(&runtime·allm, mp);
runtime·unlock(&runtime·sched.lock);
}
// Mark gp ready to run.
void
runtime·ready(G *gp)
{
uint32 status;
status = runtime·readgstatus(gp);
// Mark runnable.
g->m->locks++; // disable preemption because it can be holding p in a local var
if((status&~Gscan) != Gwaiting){
dumpgstatus(gp);
runtime·throw("bad g->status in ready");
}
// status is Gwaiting or Gscanwaiting, make Grunnable and put on runq
runtime·casgstatus(gp, Gwaiting, Grunnable);
runqput(g->m->p, gp);
if(runtime·atomicload(&runtime·sched.npidle) != 0 && runtime·atomicload(&runtime·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;
}
void
runtime·ready_m(void)
{
G *gp;
gp = g->m->ptrarg[0];
g->m->ptrarg[0] = nil;
runtime·ready(gp);
}
int32
runtime·gcprocs(void)
{
int32 n;
// Figure out how many CPUs to use during GC.
// Limited by gomaxprocs, number of actual CPUs, and MaxGcproc.
runtime·lock(&runtime·sched.lock);
n = runtime·gomaxprocs;
if(n > runtime·ncpu)
n = runtime·ncpu;
if(n > MaxGcproc)
n = MaxGcproc;
if(n > runtime·sched.nmidle+1) // one M is currently running
n = runtime·sched.nmidle+1;
runtime·unlock(&runtime·sched.lock);
return n;
}
static bool
needaddgcproc(void)
{
int32 n;
runtime·lock(&runtime·sched.lock);
n = runtime·gomaxprocs;
if(n > runtime·ncpu)
n = runtime·ncpu;
if(n > MaxGcproc)
n = MaxGcproc;
n -= runtime·sched.nmidle+1; // one M is currently running
runtime·unlock(&runtime·sched.lock);
return n > 0;
}
void
runtime·helpgc(int32 nproc)
{
M *mp;
int32 n, pos;
runtime·lock(&runtime·sched.lock);
pos = 0;
for(n = 1; n < nproc; n++) { // one M is currently running
if(runtime·allp[pos]->mcache == g->m->mcache)
pos++;
mp = mget();
if(mp == nil)
runtime·throw("runtime·gcprocs inconsistency");
mp->helpgc = n;
mp->mcache = runtime·allp[pos]->mcache;
pos++;
runtime·notewakeup(&mp->park);
}
runtime·unlock(&runtime·sched.lock);
}
// 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.
void
runtime·freezetheworld(void)
{
int32 i;
if(runtime·gomaxprocs == 1)
return;
// stopwait and preemption requests can be lost
// due to races with concurrently executing threads,
// so try several times
for(i = 0; i < 5; i++) {
// this should tell the scheduler to not start any new goroutines
runtime·sched.stopwait = 0x7fffffff;
runtime·atomicstore((uint32*)&runtime·sched.gcwaiting, 1);
// this should stop running goroutines
if(!preemptall())
break; // no running goroutines
runtime·usleep(1000);
}
// to be sure
runtime·usleep(1000);
preemptall();
runtime·usleep(1000);
}
static bool
isscanstatus(uint32 status)
{
if(status == Gscan)
runtime·throw("isscanstatus: Bad status Gscan");
return (status&Gscan) == Gscan;
}
// All reads and writes of g's status go through readgstatus, casgstatus
// castogscanstatus, casfromgscanstatus.
#pragma textflag NOSPLIT
uint32
runtime·readgstatus(G *gp)
{
return runtime·atomicload(&gp->atomicstatus);
}
// The Gscanstatuses are acting like locks and this releases them.
// If it proves to be a performance hit we should be able to make these
// simple atomic stores but for now we are going to throw if
// we see an inconsistent state.
void
runtime·casfromgscanstatus(G *gp, uint32 oldval, uint32 newval)
{
bool success = false;
// Check that transition is valid.
switch(oldval) {
case Gscanrunnable:
case Gscanwaiting:
case Gscanrunning:
case Gscansyscall:
if(newval == (oldval&~Gscan))
success = runtime·cas(&gp->atomicstatus, oldval, newval);
break;
case Gscanenqueue:
if(newval == Gwaiting)
success = runtime·cas(&gp->atomicstatus, oldval, newval);
break;
}
if(!success){
runtime·printf("runtime: casfromgscanstatus failed gp=%p, oldval=%d, newval=%d\n",
gp, oldval, newval);
dumpgstatus(gp);
runtime·throw("casfromgscanstatus: gp->status is not in scan state");
}
}
// This will return false if the gp is not in the expected status and the cas fails.
// This acts like a lock acquire while the casfromgstatus acts like a lock release.
bool
runtime·castogscanstatus(G *gp, uint32 oldval, uint32 newval)
{
switch(oldval) {
case Grunnable:
case Gwaiting:
case Gsyscall:
if(newval == (oldval|Gscan))
return runtime·cas(&gp->atomicstatus, oldval, newval);
break;
case Grunning:
if(newval == Gscanrunning || newval == Gscanenqueue)
return runtime·cas(&gp->atomicstatus, oldval, newval);
break;
}
runtime·printf("runtime: castogscanstatus oldval=%d newval=%d\n", oldval, newval);
runtime·throw("castogscanstatus");
return false; // not reached
}
static void badcasgstatus(void);
static void helpcasgstatus(void);
// If asked to move to or from a Gscanstatus this will throw. Use the castogscanstatus
// and casfromgscanstatus 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.
#pragma textflag NOSPLIT
void
runtime·casgstatus(G *gp, uint32 oldval, uint32 newval)
{
void (*fn)(void);
if((oldval&Gscan) || (newval&Gscan) || oldval == newval) {
g->m->scalararg[0] = oldval;
g->m->scalararg[1] = newval;
fn = badcasgstatus;
runtime·onM(&fn);
}
// loop if gp->atomicstatus is in a scan state giving
// GC time to finish and change the state to oldval.
while(!runtime·cas(&gp->atomicstatus, oldval, newval)) {
// Help GC if needed.
if(gp->preemptscan && !gp->gcworkdone && (oldval == Grunning || oldval == Gsyscall)) {
gp->preemptscan = false;
g->m->ptrarg[0] = gp;
fn = helpcasgstatus;
runtime·onM(&fn);
}
}
}
static void
badcasgstatus(void)
{
uint32 oldval, newval;
oldval = g->m->scalararg[0];
newval = g->m->scalararg[1];
g->m->scalararg[0] = 0;
g->m->scalararg[1] = 0;
runtime·printf("casgstatus: oldval=%d, newval=%d\n", oldval, newval);
runtime·throw("casgstatus: bad incoming values");
}
static void
helpcasgstatus(void)
{
G *gp;
gp = g->m->ptrarg[0];
g->m->ptrarg[0] = 0;
runtime·gcphasework(gp);
}
// stopg ensures that gp is stopped at a GC safe point where its stack can be scanned
// or in the context of a moving collector the pointers can be flipped from pointing
// to old object to pointing to new objects.
// If stopg returns true, the caller knows gp is at a GC safe point and will remain there until
// the caller calls restartg.
// If stopg returns false, the caller is not responsible for calling restartg. This can happen
// if another thread, either the gp itself or another GC thread is taking the responsibility
// to do the GC work related to this thread.
bool
runtime·stopg(G *gp)
{
uint32 s;
for(;;) {
if(gp->gcworkdone)
return false;
s = runtime·readgstatus(gp);
switch(s) {
default:
dumpgstatus(gp);
runtime·throw("stopg: gp->atomicstatus is not valid");
case Gdead:
return false;
case Gcopystack:
// Loop until a new stack is in place.
break;
case Grunnable:
case Gsyscall:
case Gwaiting:
// Claim goroutine by setting scan bit.
if(!runtime·castogscanstatus(gp, s, s|Gscan))
break;
// In scan state, do work.
runtime·gcphasework(gp);
return true;
case Gscanrunnable:
case Gscanwaiting:
case Gscansyscall:
// Goroutine already claimed by another GC helper.
return false;
case Grunning:
// Claim goroutine, so we aren't racing with a status
// transition away from Grunning.
if(!runtime·castogscanstatus(gp, Grunning, Gscanrunning))
break;
// Mark gp for preemption.
if(!gp->gcworkdone) {
gp->preemptscan = true;
gp->preempt = true;
gp->stackguard0 = StackPreempt;
}
// Unclaim.
runtime·casfromgscanstatus(gp, Gscanrunning, Grunning);
return false;
}
}
// Should not be here....
}
// The GC requests that this routine be moved from a scanmumble state to a mumble state.
void
runtime·restartg (G *gp)
{
uint32 s;
s = runtime·readgstatus(gp);
switch(s) {
default:
dumpgstatus(gp);
runtime·throw("restartg: unexpected status");
case Gdead:
break;
case Gscanrunnable:
case Gscanwaiting:
case Gscansyscall:
runtime·casfromgscanstatus(gp, s, s&~Gscan);
break;
case Gscanenqueue:
// 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.
runtime·casfromgscanstatus(gp, Gscanenqueue, Gwaiting);
if(gp != g->m->curg)
runtime·throw("processing Gscanenqueue on wrong m");
dropg();
runtime·ready(gp);
break;
}
}
static void
stopscanstart(G* gp)
{
if(g == gp)
runtime·throw("GC not moved to G0");
if(runtime·stopg(gp)) {
if(!isscanstatus(runtime·readgstatus(gp))) {
dumpgstatus(gp);
runtime·throw("GC not in scan state");
}
runtime·restartg(gp);
}
}
// Runs on g0 and does the actual work after putting the g back on the run queue.
static void
mquiesce(G *gpmaster)
{
G* gp;
uint32 i;
uint32 status;
uint32 activeglen;
activeglen = runtime·allglen;
// enqueue the calling goroutine.
runtime·restartg(gpmaster);
for(i = 0; i < activeglen; i++) {
gp = runtime·allg[i];
if(runtime·readgstatus(gp) == Gdead)
gp->gcworkdone = true; // noop scan.
else
gp->gcworkdone = false;
stopscanstart(gp);
}
// Check that the G's gcwork (such as scanning) has been done. If not do it now.
// You can end up doing work here if the page trap on a Grunning Goroutine has
// not been sprung or in some race situations. For example a runnable goes dead
// and is started up again with a gp->gcworkdone set to false.
for(i = 0; i < activeglen; i++) {
gp = runtime·allg[i];
while (!gp->gcworkdone) {
status = runtime·readgstatus(gp);
if(status == Gdead) {
gp->gcworkdone = true; // scan is a noop
break;
//do nothing, scan not needed.
}
if(status == Grunning && gp->stackguard0 == (uintptr)StackPreempt && runtime·notetsleep(&runtime·sched.stopnote, 100*1000)) // nanosecond arg
runtime·noteclear(&runtime·sched.stopnote);
else
stopscanstart(gp);
}
}
for(i = 0; i < activeglen; i++) {
gp = runtime·allg[i];
status = runtime·readgstatus(gp);
if(isscanstatus(status)) {
runtime·printf("mstopandscang:bottom: post scan bad status gp=%p has status %x\n", gp, status);
dumpgstatus(gp);
}
if(!gp->gcworkdone && status != Gdead) {
runtime·printf("mstopandscang:bottom: post scan gp=%p->gcworkdone still false\n", gp);
dumpgstatus(gp);
}
}
schedule(); // Never returns.
}
// quiesce moves all the goroutines to a GC safepoint which for now is a at preemption point.
// If the global runtime·gcphase is GCmark quiesce will ensure that all of the goroutine's stacks
// have been scanned before it returns.
void
runtime·quiesce(G* mastergp)
{
void (*fn)(G*);
runtime·castogscanstatus(mastergp, Grunning, Gscanenqueue);
// Now move this to the g0 (aka m) stack.
// g0 will potentially scan this thread and put mastergp on the runqueue
fn = mquiesce;
runtime·mcall(&fn);
}
// This is used by the GC as well as the routines that do stack dumps. In the case
// of GC all the routines can be reliably stopped. This is not always the case
// when the system is in panic or being exited.
void
runtime·stoptheworld(void)
{
int32 i;
uint32 s;
P *p;
bool wait;
// 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)
runtime·throw("stoptheworld: holding locks");
runtime·lock(&runtime·sched.lock);
runtime·sched.stopwait = runtime·gomaxprocs;
runtime·atomicstore((uint32*)&runtime·sched.gcwaiting, 1);
preemptall();
// stop current P
g->m->p->status = Pgcstop; // Pgcstop is only diagnostic.
runtime·sched.stopwait--;
// try to retake all P's in Psyscall status
for(i = 0; i < runtime·gomaxprocs; i++) {
p = runtime·allp[i];
s = p->status;
if(s == Psyscall && runtime·cas(&p->status, s, Pgcstop))
runtime·sched.stopwait--;
}
// stop idle P's
while(p = pidleget()) {
p->status = Pgcstop;
runtime·sched.stopwait--;
}
wait = runtime·sched.stopwait > 0;
runtime·unlock(&runtime·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(runtime·notetsleep(&runtime·sched.stopnote, 100*1000)) {
runtime·noteclear(&runtime·sched.stopnote);
break;
}
preemptall();
}
}
if(runtime·sched.stopwait)
runtime·throw("stoptheworld: not stopped");
for(i = 0; i < runtime·gomaxprocs; i++) {
p = runtime·allp[i];
if(p->status != Pgcstop)
runtime·throw("stoptheworld: not stopped");
}
}
static void
mhelpgc(void)
{
g->m->helpgc = -1;
}
void
runtime·starttheworld(void)
{
P *p, *p1;
M *mp;
G *gp;
bool add;
g->m->locks++; // disable preemption because it can be holding p in a local var
gp = runtime·netpoll(false); // non-blocking
injectglist(gp);
add = needaddgcproc();
runtime·lock(&runtime·sched.lock);
if(runtime·newprocs) {
procresize(runtime·newprocs);
runtime·newprocs = 0;
} else
procresize(runtime·gomaxprocs);
runtime·sched.gcwaiting = 0;
p1 = nil;
while(p = pidleget()) {
// procresize() puts p's with work at the beginning of the list.
// Once we reach a p without a run queue, the rest don't have one either.
if(p->runqhead == p->runqtail) {
pidleput(p);
break;
}
p->m = mget();
p->link = p1;
p1 = p;
}
if(runtime·sched.sysmonwait) {
runtime·sched.sysmonwait = false;
runtime·notewakeup(&runtime·sched.sysmonnote);
}
runtime·unlock(&runtime·sched.lock);
while(p1) {
p = p1;
p1 = p1->link;
if(p->m) {
mp = p->m;
p->m = nil;
if(mp->nextp)
runtime·throw("starttheworld: inconsistent mp->nextp");
mp->nextp = p;
runtime·notewakeup(&mp->park);
} else {
// Start M to run P. Do not start another M below.
newm(nil, p);
add = false;
}
}
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;
}
static void mstart(void);
// Called to start an M.
#pragma textflag NOSPLIT
void
runtime·mstart(void)
{
uintptr x, size;
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;
g->stack.hi = (uintptr)&x;
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;
mstart();
}
static void
mstart(void)
{
if(g != g->m->g0)
runtime·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.
runtime·gosave(&g->m->g0->sched);
g->m->g0->sched.pc = (uintptr)-1; // make sure it is never used
runtime·asminit();
runtime·minit();
// Install signal handlers; after minit so that minit can
// prepare the thread to be able to handle the signals.
if(g->m == &runtime·m0)
runtime·initsig();
if(g->m->mstartfn)
g->m->mstartfn();
if(g->m->helpgc) {
g->m->helpgc = 0;
stopm();
} else if(g->m != &runtime·m0) {
acquirep(g->m->nextp);
g->m->nextp = nil;
}
schedule();
// TODO(brainman): This point is never reached, because scheduler
// does not release os threads at the moment. But once this path
// is enabled, we must remove our seh here.
}
// When running with cgo, we call _cgo_thread_start
// to start threads for us so that we can play nicely with
// foreign code.
void (*_cgo_thread_start)(void*);
typedef struct CgoThreadStart CgoThreadStart;
struct CgoThreadStart
{
G *g;
uintptr *tls;
void (*fn)(void);
};
M *runtime·newM(void); // in proc.go
// Allocate a new m unassociated with any thread.
// Can use p for allocation context if needed.
M*
runtime·allocm(P *p)
{
M *mp;
g->m->locks++; // disable GC because it can be called from sysmon
if(g->m->p == nil)
acquirep(p); // temporarily borrow p for mallocs in this function
mp = runtime·newM();
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(runtime·iscgo || Solaris || Windows || Plan9)
mp->g0 = runtime·malg(-1);
else
mp->g0 = runtime·malg(8192);
mp->g0->m = mp;
if(p == g->m->p)
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;
}
G *runtime·newG(void); // in proc.go
static G*
allocg(void)
{
return runtime·newG();
}
static M* lockextra(bool nilokay);
static void unlockextra(M*);
// 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.
#pragma textflag NOSPLIT
void
runtime·needm(byte x)
{
M *mp;
if(runtime·needextram) {
// Can happen if C/C++ code calls Go from a global ctor.
// Can not throw, because scheduler is not initialized yet.
runtime·write(2, "fatal error: cgo callback before cgo call\n",
sizeof("fatal error: cgo callback before cgo call\n")-1);
runtime·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 == nil;
unlockextra(mp->schedlink);
// 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.
runtime·setg(mp->g0);
g->stack.hi = (uintptr)(&x + 1024);
g->stack.lo = (uintptr)(&x - 32*1024);
g->stackguard0 = g->stack.lo + StackGuard;
// Initialize this thread to use the m.
runtime·asminit();
runtime·minit();
}
// 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.
void
runtime·newextram(void)
{
M *mp, *mnext;
G *gp;
// 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
// runtime.goexit makes clear to the traceback routines where
// the goroutine stack ends.
mp = runtime·allocm(nil);
gp = runtime·malg(4096);
gp->sched.pc = (uintptr)runtime·goexit;
gp->sched.sp = gp->stack.hi;
gp->sched.sp -= 4*sizeof(uintreg); // extra space in case of reads slightly beyond frame
gp->sched.lr = 0;
gp->sched.g = gp;
gp->syscallpc = gp->sched.pc;
gp->syscallsp = gp->sched.sp;
// malg returns status as Gidle, change to Gsyscall before adding to allg
// where GC will see it.
runtime·casgstatus(gp, Gidle, Gsyscall);
gp->m = mp;
mp->curg = gp;
mp->locked = LockInternal;
mp->lockedg = gp;
gp->lockedm = mp;
gp->goid = runtime·xadd64(&runtime·sched.goidgen, 1);
if(raceenabled)
gp->racectx = runtime·racegostart(runtime·newextram);
// put on allg for garbage collector
runtime·allgadd(gp);
// Add m to the extra list.
mnext = lockextra(true);
mp->schedlink = 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.
void
runtime·dropm(void)
{
M *mp, *mnext;
// Undo whatever initialization minit did during needm.
runtime·unminit();
// Clear m and g, and return m to the extra list.
// After the call to setmg we can only call nosplit functions.
mp = g->m;
runtime·setg(nil);
mnext = lockextra(true);
mp->schedlink = mnext;
unlockextra(mp);
}
#define MLOCKED ((M*)1)
// lockextra locks the extra list and returns the list head.
// The caller must unlock the list by storing a new list head
// to runtime.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.
#pragma textflag NOSPLIT
static M*
lockextra(bool nilokay)
{
M *mp;
void (*yield)(void);
for(;;) {
mp = runtime·atomicloadp(&runtime·extram);
if(mp == MLOCKED) {
yield = runtime·osyield;
yield();
continue;
}
if(mp == nil && !nilokay) {
runtime·usleep(1);
continue;
}
if(!runtime·casp(&runtime·extram, mp, MLOCKED)) {
yield = runtime·osyield;
yield();
continue;
}
break;
}
return mp;
}
#pragma textflag NOSPLIT
static void
unlockextra(M *mp)
{
runtime·atomicstorep(&runtime·extram, mp);
}
// Create a new m. It will start off with a call to fn, or else the scheduler.
static void
newm(void(*fn)(void), P *p)
{
M *mp;
mp = runtime·allocm(p);
mp->nextp = p;
mp->mstartfn = fn;
if(runtime·iscgo) {
CgoThreadStart ts;
if(_cgo_thread_start == nil)
runtime·throw("_cgo_thread_start missing");
ts.g = mp->g0;
ts.tls = mp->tls;
ts.fn = runtime·mstart;
runtime·asmcgocall(_cgo_thread_start, &ts);
return;
}
runtime·newosproc(mp, (byte*)mp->g0->stack.hi);
}
// Stops execution of the current m until new work is available.
// Returns with acquired P.
static void
stopm(void)
{
if(g->m->locks)
runtime·throw("stopm holding locks");
if(g->m->p)
runtime·throw("stopm holding p");
if(g->m->spinning) {
g->m->spinning = false;
runtime·xadd(&runtime·sched.nmspinning, -1);
}
retry:
runtime·lock(&runtime·sched.lock);
mput(g->m);
runtime·unlock(&runtime·sched.lock);
runtime·notesleep(&g->m->park);
runtime·noteclear(&g->m->park);
if(g->m->helpgc) {
runtime·gchelper();
g->m->helpgc = 0;
g->m->mcache = nil;
goto retry;
}
acquirep(g->m->nextp);
g->m->nextp = nil;
}
static void
mspinning(void)
{
g->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.
static void
startm(P *p, bool spinning)
{
M *mp;
void (*fn)(void);
runtime·lock(&runtime·sched.lock);
if(p == nil) {
p = pidleget();
if(p == nil) {
runtime·unlock(&runtime·sched.lock);
if(spinning)
runtime·xadd(&runtime·sched.nmspinning, -1);
return;
}
}
mp = mget();
runtime·unlock(&runtime·sched.lock);
if(mp == nil) {
fn = nil;
if(spinning)
fn = mspinning;
newm(fn, p);
return;
}
if(mp->spinning)
runtime·throw("startm: m is spinning");
if(mp->nextp)
runtime·throw("startm: m has p");
mp->spinning = spinning;
mp->nextp = p;
runtime·notewakeup(&mp->park);
}
// Hands off P from syscall or locked M.
static void
handoffp(P *p)
{
// if it has local work, start it straight away
if(p->runqhead != p->runqtail || runtime·sched.runqsize) {
startm(p, false);
return;
}
// no local work, check that there are no spinning/idle M's,
// otherwise our help is not required
if(runtime·atomicload(&runtime·sched.nmspinning) + runtime·atomicload(&runtime·sched.npidle) == 0 && // TODO: fast atomic
runtime·cas(&runtime·sched.nmspinning, 0, 1)){
startm(p, true);
return;
}
runtime·lock(&runtime·sched.lock);
if(runtime·sched.gcwaiting) {
p->status = Pgcstop;
if(--runtime·sched.stopwait == 0)
runtime·notewakeup(&runtime·sched.stopnote);
runtime·unlock(&runtime·sched.lock);
return;
}
if(runtime·sched.runqsize) {
runtime·unlock(&runtime·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(runtime·sched.npidle == runtime·gomaxprocs-1 && runtime·atomicload64(&runtime·sched.lastpoll) != 0) {
runtime·unlock(&runtime·sched.lock);
startm(p, false);
return;
}
pidleput(p);
runtime·unlock(&runtime·sched.lock);
}
// Tries to add one more P to execute G's.
// Called when a G is made runnable (newproc, ready).
static void
wakep(void)
{
// be conservative about spinning threads
if(!runtime·cas(&runtime·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.
static void
stoplockedm(void)
{
P *p;
uint32 status;
if(g->m->lockedg == nil || g->m->lockedg->lockedm != g->m)
runtime·throw("stoplockedm: inconsistent locking");
if(g->m->p) {
// Schedule another M to run this p.
p = releasep();
handoffp(p);
}
incidlelocked(1);
// Wait until another thread schedules lockedg again.
runtime·notesleep(&g->m->park);
runtime·noteclear(&g->m->park);
status = runtime·readgstatus(g->m->lockedg);
if((status&~Gscan) != Grunnable){
runtime·printf("runtime:stoplockedm: g is not Grunnable or Gscanrunnable");
dumpgstatus(g);
runtime·throw("stoplockedm: not runnable");
}
acquirep(g->m->nextp);
g->m->nextp = nil;
}
// Schedules the locked m to run the locked gp.
static void
startlockedm(G *gp)
{
M *mp;
P *p;
mp = gp->lockedm;
if(mp == g->m)
runtime·throw("startlockedm: locked to me");
if(mp->nextp)
runtime·throw("startlockedm: m has p");
// directly handoff current P to the locked m
incidlelocked(-1);
p = releasep();
mp->nextp = p;
runtime·notewakeup(&mp->park);
stopm();
}
// Stops the current m for stoptheworld.
// Returns when the world is restarted.
static void
gcstopm(void)
{
P *p;
if(!runtime·sched.gcwaiting)
runtime·throw("gcstopm: not waiting for gc");
if(g->m->spinning) {
g->m->spinning = false;
runtime·xadd(&runtime·sched.nmspinning, -1);
}
p = releasep();
runtime·lock(&runtime·sched.lock);
p->status = Pgcstop;
if(--runtime·sched.stopwait == 0)
runtime·notewakeup(&runtime·sched.stopnote);
runtime·unlock(&runtime·sched.lock);
stopm();
}
// Schedules gp to run on the current M.
// Never returns.
static void
execute(G *gp)
{
int32 hz;
runtime·casgstatus(gp, Grunnable, Grunning);
gp->waitsince = 0;
gp->preempt = false;
gp->stackguard0 = gp->stack.lo + StackGuard;
g->m->p->schedtick++;
g->m->curg = gp;
gp->m = g->m;
// Check whether the profiler needs to be turned on or off.
hz = runtime·sched.profilehz;
if(g->m->profilehz != hz)
runtime·resetcpuprofiler(hz);
runtime·gogo(&gp->sched);
}
// Finds a runnable goroutine to execute.
// Tries to steal from other P's, get g from global queue, poll network.
static G*
findrunnable(void)
{
G *gp;
P *p;
int32 i;
top:
if(runtime·sched.gcwaiting) {
gcstopm();
goto top;
}
if(runtime·fingwait && runtime·fingwake && (gp = runtime·wakefing()) != nil)
runtime·ready(gp);
// local runq
gp = runqget(g->m->p);
if(gp)
return gp;
// global runq
if(runtime·sched.runqsize) {
runtime·lock(&runtime·sched.lock);
gp = globrunqget(g->m->p, 0);
runtime·unlock(&runtime·sched.lock);
if(gp)
return gp;
}
// poll network
gp = runtime·netpoll(false); // non-blocking
if(gp) {
injectglist(gp->schedlink);
runtime·casgstatus(gp, Gwaiting, Grunnable);
return gp;
}
// 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 * runtime·atomicload(&runtime·sched.nmspinning) >= runtime·gomaxprocs - runtime·atomicload(&runtime·sched.npidle)) // TODO: fast atomic
goto stop;
if(!g->m->spinning) {
g->m->spinning = true;
runtime·xadd(&runtime·sched.nmspinning, 1);
}
// random steal from other P's
for(i = 0; i < 2*runtime·gomaxprocs; i++) {
if(runtime·sched.gcwaiting)
goto top;
p = runtime·allp[runtime·fastrand1()%runtime·gomaxprocs];
if(p == g->m->p)
gp = runqget(p);
else
gp = runqsteal(g->m->p, p);
if(gp)
return gp;
}
stop:
// return P and block
runtime·lock(&runtime·sched.lock);
if(runtime·sched.gcwaiting) {
runtime·unlock(&runtime·sched.lock);
goto top;
}
if(runtime·sched.runqsize) {
gp = globrunqget(g->m->p, 0);
runtime·unlock(&runtime·sched.lock);
return gp;
}
p = releasep();
pidleput(p);
runtime·unlock(&runtime·sched.lock);
if(g->m->spinning) {
g->m->spinning = false;
runtime·xadd(&runtime·sched.nmspinning, -1);
}
// check all runqueues once again
for(i = 0; i < runtime·gomaxprocs; i++) {
p = runtime·allp[i];
if(p && p->runqhead != p->runqtail) {
runtime·lock(&runtime·sched.lock);
p = pidleget();
runtime·unlock(&runtime·sched.lock);
if(p) {
acquirep(p);
goto top;
}
break;
}
}
// poll network
if(runtime·xchg64(&runtime·sched.lastpoll, 0) != 0) {
if(g->m->p)
runtime·throw("findrunnable: netpoll with p");
if(g->m->spinning)
runtime·throw("findrunnable: netpoll with spinning");
gp = runtime·netpoll(true); // block until new work is available
runtime·atomicstore64(&runtime·sched.lastpoll, runtime·nanotime());
if(gp) {
runtime·lock(&runtime·sched.lock);
p = pidleget();
runtime·unlock(&runtime·sched.lock);
if(p) {
acquirep(p);
injectglist(gp->schedlink);
runtime·casgstatus(gp, Gwaiting, Grunnable);
return gp;
}
injectglist(gp);
}
}
stopm();
goto top;
}
static void
resetspinning(void)
{
int32 nmspinning;
if(g->m->spinning) {
g->m->spinning = false;
nmspinning = runtime·xadd(&runtime·sched.nmspinning, -1);
if(nmspinning < 0)
runtime·throw("findrunnable: negative nmspinning");
} else
nmspinning = runtime·atomicload(&runtime·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 && runtime·atomicload(&runtime·sched.npidle) > 0)
wakep();
}
// Injects the list of runnable G's into the scheduler.
// Can run concurrently with GC.
static void
injectglist(G *glist)
{
int32 n;
G *gp;
if(glist == nil)
return;
runtime·lock(&runtime·sched.lock);
for(n = 0; glist; n++) {
gp = glist;
glist = gp->schedlink;
runtime·casgstatus(gp, Gwaiting, Grunnable);
globrunqput(gp);
}
runtime·unlock(&runtime·sched.lock);
for(; n && runtime·sched.npidle; n--)
startm(nil, false);
}
// One round of scheduler: find a runnable goroutine and execute it.
// Never returns.
static void
schedule(void)
{
G *gp;
uint32 tick;
if(g->m->locks)
runtime·throw("schedule: holding locks");
if(g->m->lockedg) {
stoplockedm();
execute(g->m->lockedg); // Never returns.
}
top:
if(runtime·sched.gcwaiting) {
gcstopm();
goto top;
}
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.
tick = g->m->p->schedtick;
// This is a fancy way to say tick%61==0,
// it uses 2 MUL instructions instead of a single DIV and so is faster on modern processors.
if(tick - (((uint64)tick*0x4325c53fu)>>36)*61 == 0 && runtime·sched.runqsize > 0) {
runtime·lock(&runtime·sched.lock);
gp = globrunqget(g->m->p, 1);
runtime·unlock(&runtime·sched.lock);
if(gp)
resetspinning();
}
if(gp == nil) {
gp = runqget(g->m->p);
if(gp && g->m->spinning)
runtime·throw("schedule: spinning with local work");
}
if(gp == nil) {
gp = findrunnable(); // blocks until work is available
resetspinning();
}
if(gp->lockedm) {
// Hands off own p to the locked m,
// then blocks waiting for a new p.
startlockedm(gp);
goto top;
}
execute(gp);
}
// 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 runtime·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.
static void
dropg(void)
{
if(g->m->lockedg == nil) {
g->m->curg->m = nil;
g->m->curg = nil;
}
}
// Puts the current goroutine into a waiting state and calls unlockf.
// If unlockf returns false, the goroutine is resumed.
void
runtime·park(bool(*unlockf)(G*, void*), void *lock, String reason)
{
void (*fn)(G*);
g->m->waitlock = lock;
g->m->waitunlockf = unlockf;
g->waitreason = reason;
fn = runtime·park_m;
runtime·mcall(&fn);
}
bool
runtime·parkunlock_c(G *gp, void *lock)
{
USED(gp);
runtime·unlock(lock);
return true;
}
// Puts the current goroutine into a waiting state and unlocks the lock.
// The goroutine can be made runnable again by calling runtime·ready(gp).
void
runtime·parkunlock(Mutex *lock, String reason)
{
runtime·park(runtime·parkunlock_c, lock, reason);
}
// runtime·park continuation on g0.
void
runtime·park_m(G *gp)
{
bool ok;
runtime·casgstatus(gp, Grunning, Gwaiting);
dropg();
if(g->m->waitunlockf) {
ok = g->m->waitunlockf(gp, g->m->waitlock);
g->m->waitunlockf = nil;
g->m->waitlock = nil;
if(!ok) {
runtime·casgstatus(gp, Gwaiting, Grunnable);
execute(gp); // Schedule it back, never returns.
}
}
schedule();
}
// Gosched continuation on g0.
void
runtime·gosched_m(G *gp)
{
uint32 status;
status = runtime·readgstatus(gp);
if((status&~Gscan) != Grunning){
dumpgstatus(gp);
runtime·throw("bad g status");
}
runtime·casgstatus(gp, Grunning, Grunnable);
dropg();
runtime·lock(&runtime·sched.lock);
globrunqput(gp);
runtime·unlock(&runtime·sched.lock);
schedule();
}
// Finishes execution of the current goroutine.
// Must be NOSPLIT because it is called from Go.
#pragma textflag NOSPLIT
void
runtime·goexit1(void)
{
void (*fn)(G*);
if(raceenabled)
runtime·racegoend();
fn = goexit0;
runtime·mcall(&fn);
}
// runtime·goexit continuation on g0.
static void
goexit0(G *gp)
{
runtime·casgstatus(gp, Grunning, Gdead);
gp->m = nil;
gp->lockedm = nil;
g->m->lockedg = nil;
gp->paniconfault = 0;
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.array = nil;
gp->writebuf.len = 0;
gp->writebuf.cap = 0;
gp->waitreason.str = nil;
gp->waitreason.len = 0;
gp->param = nil;
dropg();
if(g->m->locked & ~LockExternal) {
runtime·printf("invalid m->locked = %d\n", g->m->locked);
runtime·throw("internal lockOSThread error");
}
g->m->locked = 0;
gfput(g->m->p, gp);
schedule();
}
#pragma textflag NOSPLIT
static void
save(uintptr pc, uintptr sp)
{
g->sched.pc = pc;
g->sched.sp = sp;
g->sched.lr = 0;
g->sched.ret = 0;
g->sched.ctxt = 0;
g->sched.g = g;
}
static void entersyscall_bad(void);
static void entersyscall_sysmon(void);
static void entersyscall_gcwait(void);
// 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 runtime·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 onM
// to run bigger things on the m 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.
#pragma textflag NOSPLIT
void
runtime·reentersyscall(uintptr pc, uintptr sp)
{
void (*fn)(void);
// 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 = 1;
// Leave SP around for GC and traceback.
save(pc, sp);
g->syscallsp = sp;
g->syscallpc = pc;
runtime·casgstatus(g, Grunning, Gsyscall);
if(g->syscallsp < g->stack.lo || g->stack.hi < g->syscallsp) {
fn = entersyscall_bad;
runtime·onM(&fn);
}
if(runtime·atomicload(&runtime·sched.sysmonwait)) { // TODO: fast atomic
fn = entersyscall_sysmon;
runtime·onM(&fn);
save(pc, sp);
}
g->m->mcache = nil;
g->m->p->m = nil;
runtime·atomicstore(&g->m->p->status, Psyscall);
if(runtime·sched.gcwaiting) {
fn = entersyscall_gcwait;
runtime·onM(&fn);
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.
#pragma textflag NOSPLIT
void
·entersyscall(int32 dummy)
{
runtime·reentersyscall((uintptr)runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
}
static void
entersyscall_bad(void)
{
G *gp;
gp = g->m->curg;
runtime·printf("entersyscall inconsistent %p [%p,%p]\n",
gp->syscallsp, gp->stack.lo, gp->stack.hi);
runtime·throw("entersyscall");
}
static void
entersyscall_sysmon(void)
{
runtime·lock(&runtime·sched.lock);
if(runtime·atomicload(&runtime·sched.sysmonwait)) {
runtime·atomicstore(&runtime·sched.sysmonwait, 0);
runtime·notewakeup(&runtime·sched.sysmonnote);
}
runtime·unlock(&runtime·sched.lock);
}
static void
entersyscall_gcwait(void)
{
runtime·lock(&runtime·sched.lock);
if (runtime·sched.stopwait > 0 && runtime·cas(&g->m->p->status, Psyscall, Pgcstop)) {
if(--runtime·sched.stopwait == 0)
runtime·notewakeup(&runtime·sched.stopnote);
}
runtime·unlock(&runtime·sched.lock);
}
static void entersyscallblock_handoff(void);
// The same as runtime·entersyscall(), but with a hint that the syscall is blocking.
#pragma textflag NOSPLIT
void
·entersyscallblock(int32 dummy)
{
void (*fn)(void);
g->m->locks++; // see comment in entersyscall
g->throwsplit = 1;
g->stackguard0 = StackPreempt; // see comment in entersyscall
// Leave SP around for GC and traceback.
save((uintptr)runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
g->syscallsp = g->sched.sp;
g->syscallpc = g->sched.pc;
runtime·casgstatus(g, Grunning, Gsyscall);
if(g->syscallsp < g->stack.lo || g->stack.hi < g->syscallsp) {
fn = entersyscall_bad;
runtime·onM(&fn);
}
fn = entersyscallblock_handoff;
runtime·onM(&fn);
// Resave for traceback during blocked call.
save((uintptr)runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
g->m->locks--;
}
static void
entersyscallblock_handoff(void)
{
handoffp(releasep());
}
// The goroutine g exited its system call.
// Arrange for it to run on a cpu again.
// This is called only from the go syscall library, not
// from the low-level system calls used by the runtime.
#pragma textflag NOSPLIT
void
·exitsyscall(int32 dummy)
{
void (*fn)(G*);
g->m->locks++; // see comment in entersyscall
if(runtime·getcallersp(&dummy) > g->syscallsp)
runtime·throw("exitsyscall: syscall frame is no longer valid");
g->waitsince = 0;
if(exitsyscallfast()) {
// There's a cpu for us, so we can run.
g->m->p->syscalltick++;
// We need to cas the status and scan before resuming...
runtime·casgstatus(g, Gsyscall, Grunning);
// Garbage collector isn't running (since we are),
// so okay to clear syscallsp.
g->syscallsp = (uintptr)nil;
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 = 0;
return;
}
g->m->locks--;
// Call the scheduler.
fn = exitsyscall0;
runtime·mcall(&fn);
// 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 = (uintptr)nil;
g->m->p->syscalltick++;
g->throwsplit = 0;
}
static void exitsyscallfast_pidle(void);
#pragma textflag NOSPLIT
static bool
exitsyscallfast(void)
{
void (*fn)(void);
// Freezetheworld sets stopwait but does not retake P's.
if(runtime·sched.stopwait) {
g->m->p = nil;
return false;
}
// Try to re-acquire the last P.
if(g->m->p && g->m->p->status == Psyscall && runtime·cas(&g->m->p->status, Psyscall, Prunning)) {
// There's a cpu for us, so we can run.
g->m->mcache = g->m->p->mcache;
g->m->p->m = g->m;
return true;
}
// Try to get any other idle P.
g->m->p = nil;
if(runtime·sched.pidle) {
fn = exitsyscallfast_pidle;
runtime·onM(&fn);
if(g->m->scalararg[0]) {
g->m->scalararg[0] = 0;
return true;
}
}
return false;
}
static void
exitsyscallfast_pidle(void)
{
P *p;
runtime·lock(&runtime·sched.lock);
p = pidleget();
if(p && runtime·atomicload(&runtime·sched.sysmonwait)) {
runtime·atomicstore(&runtime·sched.sysmonwait, 0);
runtime·notewakeup(&runtime·sched.sysmonnote);
}
runtime·unlock(&runtime·sched.lock);
if(p) {
acquirep(p);
g->m->scalararg[0] = 1;
} else
g->m->scalararg[0] = 0;
}
// runtime·exitsyscall slow path on g0.
// Failed to acquire P, enqueue gp as runnable.
static void
exitsyscall0(G *gp)
{
P *p;
runtime·casgstatus(gp, Gsyscall, Grunnable);
dropg();
runtime·lock(&runtime·sched.lock);
p = pidleget();
if(p == nil)
globrunqput(gp);
else if(runtime·atomicload(&runtime·sched.sysmonwait)) {
runtime·atomicstore(&runtime·sched.sysmonwait, 0);
runtime·notewakeup(&runtime·sched.sysmonnote);
}
runtime·unlock(&runtime·sched.lock);
if(p) {
acquirep(p);
execute(gp); // Never returns.
}
if(g->m->lockedg) {
// Wait until another thread schedules gp and so m again.
stoplockedm();
execute(gp); // Never returns.
}
stopm();
schedule(); // Never returns.
}
static void
beforefork(void)
{
G *gp;
gp = g->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)
runtime·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.
#pragma textflag NOSPLIT
void
syscall·runtime_BeforeFork(void)
{
void (*fn)(void);
fn = beforefork;
runtime·onM(&fn);
}
static void
afterfork(void)
{
int32 hz;
G *gp;
gp = g->m->curg;
// See the comment in runtime_BeforeFork.
gp->stackguard0 = gp->stack.lo + StackGuard;
hz = runtime·sched.profilehz;
if(hz != 0)
runtime·resetcpuprofiler(hz);
gp->m->locks--;
}
// Called from syscall package after fork in parent.
#pragma textflag NOSPLIT
void
syscall·runtime_AfterFork(void)
{
void (*fn)(void);
fn = afterfork;
runtime·onM(&fn);
}
// Hook used by runtime·malg to call runtime·stackalloc on the
// scheduler stack. This exists because runtime·stackalloc insists
// on being called on the scheduler stack, to avoid trying to grow
// the stack while allocating a new stack segment.
static void
mstackalloc(G *gp)
{
G *newg;
uintptr size;
newg = g->m->ptrarg[0];
size = g->m->scalararg[0];
newg->stack = runtime·stackalloc(size);
runtime·gogo(&gp->sched);
}
// Allocate a new g, with a stack big enough for stacksize bytes.
G*
runtime·malg(int32 stacksize)
{
G *newg;
void (*fn)(G*);
newg = allocg();
if(stacksize >= 0) {
stacksize = runtime·round2(StackSystem + stacksize);
if(g == g->m->g0) {
// running on scheduler stack already.
newg->stack = runtime·stackalloc(stacksize);
} else {
// have to call stackalloc on scheduler stack.
g->m->scalararg[0] = stacksize;
g->m->ptrarg[0] = newg;
fn = mstackalloc;
runtime·mcall(&fn);
g->m->ptrarg[0] = nil;
}
newg->stackguard0 = newg->stack.lo + StackGuard;
newg->stackguard1 = ~(uintptr)0;
}
return newg;
}
static void
newproc_m(void)
{
byte *argp;
void *callerpc;
FuncVal *fn;
int32 siz;
siz = g->m->scalararg[0];
callerpc = (void*)g->m->scalararg[1];
argp = g->m->ptrarg[0];
fn = (FuncVal*)g->m->ptrarg[1];
runtime·newproc1(fn, argp, siz, 0, callerpc);
g->m->ptrarg[0] = nil;
g->m->ptrarg[1] = nil;
}
// 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.
#pragma textflag NOSPLIT
void
runtime·newproc(int32 siz, FuncVal* fn, ...)
{
byte *argp;
void (*mfn)(void);
if(thechar == '5')
argp = (byte*)(&fn+2); // skip caller's saved LR
else
argp = (byte*)(&fn+1);
g->m->locks++;
g->m->scalararg[0] = siz;
g->m->scalararg[1] = (uintptr)runtime·getcallerpc(&siz);
g->m->ptrarg[0] = argp;
g->m->ptrarg[1] = fn;
mfn = newproc_m;
runtime·onM(&mfn);
g->m->locks--;
}
void runtime·main(void);
// 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.
G*
runtime·newproc1(FuncVal *fn, byte *argp, int32 narg, int32 nret, void *callerpc)
{
byte *sp;
G *newg;
P *p;
int32 siz;
if(fn == nil) {
g->m->throwing = -1; // do not dump full stacks
runtime·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*sizeof(uintreg) - sizeof(uintreg))
runtime·throw("runtime.newproc: function arguments too large for new goroutine");
p = g->m->p;
if((newg = gfget(p)) == nil) {
newg = runtime·malg(StackMin);
runtime·casgstatus(newg, Gidle, Gdead);
runtime·allgadd(newg); // publishes with a g->status of Gdead so GC scanner doesn't look at uninitialized stack.
}
if(newg->stack.hi == 0)
runtime·throw("newproc1: newg missing stack");
if(runtime·readgstatus(newg) != Gdead)
runtime·throw("newproc1: new g is not Gdead");
sp = (byte*)newg->stack.hi;
sp -= 4*sizeof(uintreg); // extra space in case of reads slightly beyond frame
sp -= siz;
runtime·memmove(sp, argp, narg);
if(thechar == '5') {
// caller's LR
sp -= sizeof(void*);
*(void**)sp = nil;
}
runtime·memclr((byte*)&newg->sched, sizeof newg->sched);
newg->sched.sp = (uintptr)sp;
newg->sched.pc = (uintptr)runtime·goexit + PCQuantum; // +PCQuantum so that previous instruction is in same function
newg->sched.g = newg;
runtime·gostartcallfn(&newg->sched, fn);
newg->gopc = (uintptr)callerpc;
runtime·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 = runtime·xadd64(&runtime·sched.goidgen, GoidCacheBatch);
p->goidcache -= GoidCacheBatch - 1;
p->goidcacheend = p->goidcache + GoidCacheBatch;
}
newg->goid = p->goidcache++;
if(raceenabled)
newg->racectx = runtime·racegostart((void*)callerpc);
runqput(p, newg);
if(runtime·atomicload(&runtime·sched.npidle) != 0 && runtime·atomicload(&runtime·sched.nmspinning) == 0 && fn->fn != runtime·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.
static void
gfput(P *p, G *gp)
{
uintptr stksize;
if(runtime·readgstatus(gp) != Gdead)
runtime·throw("gfput: bad status (not Gdead)");
stksize = gp->stack.hi - gp->stack.lo;
if(stksize != FixedStack) {
// non-standard stack size - free it.
runtime·stackfree(gp->stack);
gp->stack.lo = 0;
gp->stack.hi = 0;
gp->stackguard0 = 0;
}
gp->schedlink = p->gfree;
p->gfree = gp;
p->gfreecnt++;
if(p->gfreecnt >= 64) {
runtime·lock(&runtime·sched.gflock);
while(p->gfreecnt >= 32) {
p->gfreecnt--;
gp = p->gfree;
p->gfree = gp->schedlink;
gp->schedlink = runtime·sched.gfree;
runtime·sched.gfree = gp;
runtime·sched.ngfree++;
}
runtime·unlock(&runtime·sched.gflock);
}
}
// Get from gfree list.
// If local list is empty, grab a batch from global list.
static G*
gfget(P *p)
{
G *gp;
void (*fn)(G*);
retry:
gp = p->gfree;
if(gp == nil && runtime·sched.gfree) {
runtime·lock(&runtime·sched.gflock);
while(p->gfreecnt < 32 && runtime·sched.gfree != nil) {
p->gfreecnt++;
gp = runtime·sched.gfree;
runtime·sched.gfree = gp->schedlink;
runtime·sched.ngfree--;
gp->schedlink = p->gfree;
p->gfree = gp;
}
runtime·unlock(&runtime·sched.gflock);
goto retry;
}
if(gp) {
p->gfree = gp->schedlink;
p->gfreecnt--;
if(gp->stack.lo == 0) {
// Stack was deallocated in gfput. Allocate a new one.
if(g == g->m->g0) {
gp->stack = runtime·stackalloc(FixedStack);
} else {
g->m->scalararg[0] = FixedStack;
g->m->ptrarg[0] = gp;
fn = mstackalloc;
runtime·mcall(&fn);
g->m->ptrarg[0] = nil;
}
gp->stackguard0 = gp->stack.lo + StackGuard;
} else {
if(raceenabled)
runtime·racemalloc((void*)gp->stack.lo, gp->stack.hi - gp->stack.lo);
}
}
return gp;
}
// Purge all cached G's from gfree list to the global list.
static void
gfpurge(P *p)
{
G *gp;
runtime·lock(&runtime·sched.gflock);
while(p->gfreecnt != 0) {
p->gfreecnt--;
gp = p->gfree;
p->gfree = gp->schedlink;
gp->schedlink = runtime·sched.gfree;
runtime·sched.gfree = gp;
runtime·sched.ngfree++;
}
runtime·unlock(&runtime·sched.gflock);
}
#pragma textflag NOSPLIT
void
runtime·Breakpoint(void)
{
runtime·breakpoint();
}
// lockOSThread is called by runtime.LockOSThread and runtime.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.
#pragma textflag NOSPLIT
static void
lockOSThread(void)
{
g->m->lockedg = g;
g->lockedm = g->m;
}
#pragma textflag NOSPLIT
void
runtime·LockOSThread(void)
{
g->m->locked |= LockExternal;
lockOSThread();
}
#pragma textflag NOSPLIT
void
runtime·lockOSThread(void)
{
g->m->locked += LockInternal;
lockOSThread();
}
// unlockOSThread is called by runtime.UnlockOSThread and runtime.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.
#pragma textflag NOSPLIT
static void
unlockOSThread(void)
{
if(g->m->locked != 0)
return;
g->m->lockedg = nil;
g->lockedm = nil;
}
#pragma textflag NOSPLIT
void
runtime·UnlockOSThread(void)
{
g->m->locked &= ~LockExternal;
unlockOSThread();
}
static void badunlockOSThread(void);
#pragma textflag NOSPLIT
void
runtime·unlockOSThread(void)
{
void (*fn)(void);
if(g->m->locked < LockInternal) {
fn = badunlockOSThread;
runtime·onM(&fn);
}
g->m->locked -= LockInternal;
unlockOSThread();
}
static void
badunlockOSThread(void)
{
runtime·throw("runtime: internal error: misuse of lockOSThread/unlockOSThread");
}
#pragma textflag NOSPLIT
int32
runtime·gcount(void)
{
P *p, **pp;
int32 n;
n = runtime·allglen - runtime·sched.ngfree;
for(pp=runtime·allp; p=*pp; pp++)
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;
}
int32
runtime·mcount(void)
{
return runtime·sched.mcount;
}
static struct ProfState {
uint32 lock;
int32 hz;
} prof;
static void System(void) {}
static void ExternalCode(void) {}
static void GC(void) {}
extern void runtime·cpuproftick(uintptr*, int32);
extern byte runtime·etext[];
// Called if we receive a SIGPROF signal.
void
runtime·sigprof(uint8 *pc, uint8 *sp, uint8 *lr, G *gp, M *mp)
{
int32 n;
bool traceback;
// Do not use global m in this function, use mp instead.
// On windows one m is sending reports about all the g's, so m means a wrong thing.
byte m;
uintptr stk[100];
m = 0;
USED(m);
if(prof.hz == 0)
return;
// Profiling runs concurrently with GC, so it must not allocate.
mp->mallocing++;
// Define that a "user g" is a user-created goroutine, and a "system g"
// is one that is m->g0 or m->gsignal. We've only made sure that we
// can unwind user g's, so exclude the system g's.
//
// It is not quite as easy as testing gp == m->curg (the current user g)
// because 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 g is updated, we'll see a system g and not look closer.
// If SP 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 runtime.asmcgocall)
// or because it has been arranged to look like a user g frame
// (as in runtime.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, as in runtime.gogo.
//
// Because runtime.gogo is the only instance, we check whether the PC lies
// within that function, and if so, not ask for a traceback. This approach
// requires knowing the size of the runtime.gogo function, which we
// record in arch_*.h and check in runtime_test.go.
//
// There is another apparently viable approach, recorded here in case
// the "PC within runtime.gogo" 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 runtime.gogo.
traceback = true;
if(gp == nil || gp != mp->curg ||
(uintptr)sp < gp->stack.lo || gp->stack.hi < (uintptr)sp ||
((uint8*)runtime·gogo <= pc && pc < (uint8*)runtime·gogo + RuntimeGogoBytes))
traceback = false;
n = 0;
if(traceback)
n = runtime·gentraceback((uintptr)pc, (uintptr)sp, (uintptr)lr, gp, 0, stk, nelem(stk), nil, nil, TraceTrap);
if(!traceback || n <= 0) {
// Normal traceback is impossible or has failed.
// See if it falls into several common cases.
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 = runtime·gentraceback(mp->curg->syscallpc, mp->curg->syscallsp, 0, mp->curg, 0, stk, nelem(stk), nil, nil, 0);
}
#ifdef GOOS_windows
if(n == 0 && mp->libcallg != nil && mp->libcallpc != 0 && mp->libcallsp != 0) {
// Libcall, i.e. runtime syscall on windows.
// Collect Go stack that leads to the call.
n = runtime·gentraceback(mp->libcallpc, mp->libcallsp, 0, mp->libcallg, 0, stk, nelem(stk), nil, nil, 0);
}
#endif
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((uintptr)pc > (uintptr)runtime·etext)
pc = (byte*)ExternalCode + PCQuantum;
stk[0] = (uintptr)pc;
if(mp->gcing || mp->helpgc)
stk[1] = (uintptr)GC + PCQuantum;
else
stk[1] = (uintptr)System + PCQuantum;
}
}
if(prof.hz != 0) {
// Simple cas-lock to coordinate with setcpuprofilerate.
while(!runtime·cas(&prof.lock, 0, 1))
runtime·osyield();
if(prof.hz != 0)
runtime·cpuproftick(stk, n);
runtime·atomicstore(&prof.lock, 0);
}
mp->mallocing--;
}
// Arrange to call fn with a traceback hz times a second.
void
runtime·setcpuprofilerate_m(void)
{
int32 hz;
hz = g->m->scalararg[0];
g->m->scalararg[0] = 0;
// Force sane arguments.
if(hz < 0)
hz = 0;
// Disable preemption, otherwise we can be rescheduled to another thread
// that has profiling enabled.
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.
runtime·resetcpuprofiler(0);
while(!runtime·cas(&prof.lock, 0, 1))
runtime·osyield();
prof.hz = hz;
runtime·atomicstore(&prof.lock, 0);
runtime·lock(&runtime·sched.lock);
runtime·sched.profilehz = hz;
runtime·unlock(&runtime·sched.lock);
if(hz != 0)
runtime·resetcpuprofiler(hz);
g->m->locks--;
}
P *runtime·newP(void);
// Change number of processors. The world is stopped, sched is locked.
static void
procresize(int32 new)
{
int32 i, old;
bool empty;
G *gp;
P *p;
old = runtime·gomaxprocs;
if(old < 0 || old > MaxGomaxprocs || new <= 0 || new >MaxGomaxprocs)
runtime·throw("procresize: invalid arg");
// initialize new P's
for(i = 0; i < new; i++) {
p = runtime·allp[i];
if(p == nil) {
p = runtime·newP();
p->id = i;
p->status = Pgcstop;
runtime·atomicstorep(&runtime·allp[i], p);
}
if(p->mcache == nil) {
if(old==0 && i==0)
p->mcache = g->m->mcache; // bootstrap
else
p->mcache = runtime·allocmcache();
}
}
// redistribute runnable G's evenly
// collect all runnable goroutines in global queue preserving FIFO order
// FIFO order is required to ensure fairness even during frequent GCs
// see http://golang.org/issue/7126
empty = false;
while(!empty) {
empty = true;
for(i = 0; i < old; i++) {
p = runtime·allp[i];
if(p->runqhead == p->runqtail)
continue;
empty = false;
// pop from tail of local queue
p->runqtail--;
gp = p->runq[p->runqtail%nelem(p->runq)];
// push onto head of global queue
gp->schedlink = runtime·sched.runqhead;
runtime·sched.runqhead = gp;
if(runtime·sched.runqtail == nil)
runtime·sched.runqtail = gp;
runtime·sched.runqsize++;
}
}
// fill local queues with at most nelem(p->runq)/2 goroutines
// start at 1 because current M already executes some G and will acquire allp[0] below,
// so if we have a spare G we want to put it into allp[1].
for(i = 1; i < new * nelem(p->runq)/2 && runtime·sched.runqsize > 0; i++) {
gp = runtime·sched.runqhead;
runtime·sched.runqhead = gp->schedlink;
if(runtime·sched.runqhead == nil)
runtime·sched.runqtail = nil;
runtime·sched.runqsize--;
runqput(runtime·allp[i%new], gp);
}
// free unused P's
for(i = new; i < old; i++) {
p = runtime·allp[i];
runtime·freemcache(p->mcache);
p->mcache = nil;
gfpurge(p);
p->status = Pdead;
// can't free P itself because it can be referenced by an M in syscall
}
if(g->m->p)
g->m->p->m = nil;
g->m->p = nil;
g->m->mcache = nil;
p = runtime·allp[0];
p->m = nil;
p->status = Pidle;
acquirep(p);
for(i = new-1; i > 0; i--) {
p = runtime·allp[i];
p->status = Pidle;
pidleput(p);
}
runtime·atomicstore((uint32*)&runtime·gomaxprocs, new);
}
// Associate p and the current m.
static void
acquirep(P *p)
{
if(g->m->p || g->m->mcache)
runtime·throw("acquirep: already in go");
if(p->m || p->status != Pidle) {
runtime·printf("acquirep: p->m=%p(%d) p->status=%d\n", p->m, p->m ? p->m->id : 0, p->status);
runtime·throw("acquirep: invalid p state");
}
g->m->mcache = p->mcache;
g->m->p = p;
p->m = g->m;
p->status = Prunning;
}
// Disassociate p and the current m.
static P*
releasep(void)
{
P *p;
if(g->m->p == nil || g->m->mcache == nil)
runtime·throw("releasep: invalid arg");
p = g->m->p;
if(p->m != g->m || p->mcache != g->m->mcache || p->status != Prunning) {
runtime·printf("releasep: m=%p m->p=%p p->m=%p m->mcache=%p p->mcache=%p p->status=%d\n",
g->m, g->m->p, p->m, g->m->mcache, p->mcache, p->status);
runtime·throw("releasep: invalid p state");
}
g->m->p = nil;
g->m->mcache = nil;
p->m = nil;
p->status = Pidle;
return p;
}
static void
incidlelocked(int32 v)
{
runtime·lock(&runtime·sched.lock);
runtime·sched.nmidlelocked += v;
if(v > 0)
checkdead();
runtime·unlock(&runtime·sched.lock);
}
// Check for deadlock situation.
// The check is based on number of running M's, if 0 -> deadlock.
static void
checkdead(void)
{
G *gp;
P *p;
M *mp;
int32 run, grunning, s;
uintptr i;
// -1 for sysmon
run = runtime·sched.mcount - runtime·sched.nmidle - runtime·sched.nmidlelocked - 1;
if(run > 0)
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 runtime·exit soon.
if(runtime·panicking > 0)
return;
if(run < 0) {
runtime·printf("runtime: checkdead: nmidle=%d nmidlelocked=%d mcount=%d\n",
runtime·sched.nmidle, runtime·sched.nmidlelocked, runtime·sched.mcount);
runtime·throw("checkdead: inconsistent counts");
}
grunning = 0;
runtime·lock(&runtime·allglock);
for(i = 0; i < runtime·allglen; i++) {
gp = runtime·allg[i];
if(gp->issystem)
continue;
s = runtime·readgstatus(gp);
switch(s&~Gscan) {
case Gwaiting:
grunning++;
break;
case Grunnable:
case Grunning:
case Gsyscall:
runtime·unlock(&runtime·allglock);
runtime·printf("runtime: checkdead: find g %D in status %d\n", gp->goid, s);
runtime·throw("checkdead: runnable g");
break;
}
}
runtime·unlock(&runtime·allglock);
if(grunning == 0) // possible if main goroutine calls runtime·Goexit()
runtime·throw("no goroutines (main called runtime.Goexit) - deadlock!");
// Maybe jump time forward for playground.
if((gp = runtime·timejump()) != nil) {
runtime·casgstatus(gp, Gwaiting, Grunnable);
globrunqput(gp);
p = pidleget();
if(p == nil)
runtime·throw("checkdead: no p for timer");
mp = mget();
if(mp == nil)
newm(nil, p);
else {
mp->nextp = p;
runtime·notewakeup(&mp->park);
}
return;
}
g->m->throwing = -1; // do not dump full stacks
runtime·throw("all goroutines are asleep - deadlock!");
}
static void
sysmon(void)
{
uint32 idle, delay, nscavenge;
int64 now, unixnow, lastpoll, lasttrace, lastgc;
int64 forcegcperiod, scavengelimit, lastscavenge, maxsleep;
G *gp;
// If we go two minutes without a garbage collection, force one to run.
forcegcperiod = 2*60*1e9;
// If a heap span goes unused for 5 minutes after a garbage collection,
// we hand it back to the operating system.
scavengelimit = 5*60*1e9;
if(runtime·debug.scavenge > 0) {
// Scavenge-a-lot for testing.
forcegcperiod = 10*1e6;
scavengelimit = 20*1e6;
}
lastscavenge = runtime·nanotime();
nscavenge = 0;
// Make wake-up period small enough for the sampling to be correct.
maxsleep = forcegcperiod/2;
if(scavengelimit < forcegcperiod)
maxsleep = scavengelimit/2;
lasttrace = 0;
idle = 0; // how many cycles in succession we had not wokeup somebody
delay = 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;
runtime·usleep(delay);
if(runtime·debug.schedtrace <= 0 &&
(runtime·sched.gcwaiting || runtime·atomicload(&runtime·sched.npidle) == runtime·gomaxprocs)) { // TODO: fast atomic
runtime·lock(&runtime·sched.lock);
if(runtime·atomicload(&runtime·sched.gcwaiting) || runtime·atomicload(&runtime·sched.npidle) == runtime·gomaxprocs) {
runtime·atomicstore(&runtime·sched.sysmonwait, 1);
runtime·unlock(&runtime·sched.lock);
runtime·notetsleep(&runtime·sched.sysmonnote, maxsleep);
runtime·lock(&runtime·sched.lock);
runtime·atomicstore(&runtime·sched.sysmonwait, 0);
runtime·noteclear(&runtime·sched.sysmonnote);
idle = 0;
delay = 20;
}
runtime·unlock(&runtime·sched.lock);
}
// poll network if not polled for more than 10ms
lastpoll = runtime·atomicload64(&runtime·sched.lastpoll);
now = runtime·nanotime();
unixnow = runtime·unixnanotime();
if(lastpoll != 0 && lastpoll + 10*1000*1000 < now) {
runtime·cas64(&runtime·sched.lastpoll, lastpoll, now);
gp = runtime·netpoll(false); // non-blocking
if(gp) {
// 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))
idle = 0;
else
idle++;
// check if we need to force a GC
lastgc = runtime·atomicload64(&mstats.last_gc);
if(lastgc != 0 && unixnow - lastgc > forcegcperiod && runtime·atomicload(&runtime·forcegc.idle)) {
runtime·lock(&runtime·forcegc.lock);
runtime·forcegc.idle = 0;
runtime·forcegc.g->schedlink = nil;
injectglist(runtime·forcegc.g);
runtime·unlock(&runtime·forcegc.lock);
}
// scavenge heap once in a while
if(lastscavenge + scavengelimit/2 < now) {
runtime·MHeap_Scavenge(nscavenge, now, scavengelimit);
lastscavenge = now;
nscavenge++;
}
if(runtime·debug.schedtrace > 0 && lasttrace + runtime·debug.schedtrace*1000000ll <= now) {
lasttrace = now;
runtime·schedtrace(runtime·debug.scheddetail);
}
}
}
typedef struct Pdesc Pdesc;
struct Pdesc
{
uint32 schedtick;
int64 schedwhen;
uint32 syscalltick;
int64 syscallwhen;
};
#pragma dataflag NOPTR
static Pdesc pdesc[MaxGomaxprocs];
static uint32
retake(int64 now)
{
uint32 i, s, n;
int64 t;
P *p;
Pdesc *pd;
n = 0;
for(i = 0; i < runtime·gomaxprocs; i++) {
p = runtime·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 = p->syscalltick;
if(pd->syscalltick != t) {
pd->syscalltick = 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(p->runqhead == p->runqtail &&
runtime·atomicload(&runtime·sched.nmspinning) + runtime·atomicload(&runtime·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(runtime·cas(&p->status, s, Pidle)) {
n++;
handoffp(p);
}
incidlelocked(1);
} else if(s == Prunning) {
// Preempt G if it's running for more than 10ms.
t = p->schedtick;
if(pd->schedtick != t) {
pd->schedtick = t;
pd->schedwhen = now;
continue;
}
if(pd->schedwhen + 10*1000*1000 > now)
continue;
preemptone(p);
}
}
return 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.
static bool
preemptall(void)
{
P *p;
int32 i;
bool res;
res = false;
for(i = 0; i < runtime·gomaxprocs; i++) {
p = runtime·allp[i];
if(p == nil || p->status != Prunning)
continue;
res |= preemptone(p);
}
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 runtime·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
static bool
preemptone(P *p)
{
M *mp;
G *gp;
mp = p->m;
if(mp == nil || mp == g->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;
}
void
runtime·schedtrace(bool detailed)
{
static int64 starttime;
int64 now;
int64 id1, id2, id3;
int32 i, t, h;
uintptr gi;
int8 *fmt;
M *mp, *lockedm;
G *gp, *lockedg;
P *p;
now = runtime·nanotime();
if(starttime == 0)
starttime = now;
runtime·lock(&runtime·sched.lock);
runtime·printf(