// 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 "../../cmd/ld/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.
typedef struct Sched Sched;
struct Sched {
Lock;
uint64 goidgen;
M* midle; // idle m's waiting for work
int32 nmidle; // number of idle m's waiting for work
int32 nmidlelocked; // number of locked m's waiting for work
int32 mcount; // number of m's that have been created
int32 maxmcount; // maximum number of m's allowed (or die)
P* pidle; // idle P's
uint32 npidle;
uint32 nmspinning;
// Global runnable queue.
G* runqhead;
G* runqtail;
int32 runqsize;
// Global cache of dead G's.
Lock gflock;
G* gfree;
uint32 gcwaiting; // gc is waiting to run
int32 stopwait;
Note stopnote;
uint32 sysmonwait;
Note sysmonnote;
uint64 lastpoll;
int32 profilehz; // cpu profiling rate
};
enum
{
// The max value of GOMAXPROCS.
// There are no fundamental restrictions on the value.
MaxGomaxprocs = 1<<8,
// 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,
};
Sched 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;
int8* runtime·goos;
int32 runtime·ncpu;
static int32 newprocs;
static Lock allglock; // the following vars are protected by this lock or by stoptheworld
G** runtime·allg;
uintptr runtime·allglen;
static uintptr allgcap;
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*);
static void park0(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*);
static void allgadd(G*);
// 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;
Eface i;
runtime·sched.maxmcount = 10000;
runtime·precisestack = true; // haveexperiment("precisestack");
runtime·symtabinit();
runtime·mallocinit();
mcommoninit(m);
// Initialize the itable value for newErrorCString,
// so that the next time it gets called, possibly
// in a fault during a garbage collection, it will not
// need to allocated memory.
runtime·newErrorCString(0, &i);
// Initialize the cached gotraceback value, since
// gotraceback calls getenv, which mallocs on Plan 9.
runtime·gotraceback(nil);
runtime·goargs();
runtime·goenvs();
runtime·parsedebugvars();
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;
}
runtime·allp = runtime·malloc((MaxGomaxprocs+1)*sizeof(runtime·allp[0]));
procresize(procs);
runtime·copystack = runtime·precisestack;
p = runtime·getenv("GOCOPYSTACK");
if(p != nil && !runtime·strcmp(p, (byte*)"0"))
runtime·copystack = false;
mstats.enablegc = 1;
if(raceenabled)
g->racectx = runtime·raceinit();
}
extern void main·init(void);
extern void main·main(void);
static FuncVal scavenger = {runtime·MHeap_Scavenger};
static FuncVal initDone = { runtime·unlockOSThread };
// The main goroutine.
// Note: C frames in general are not copyable during stack growth, for two reasons:
// 1) We don't know where in a frame to find pointers to other stack locations.
// 2) There's no guarantee that globals or heap values do not point into the frame.
//
// The C frame for runtime.main is copyable, because:
// 1) There are no pointers to other stack locations in the frame
// (d.fn points at a global, d.link is nil, d.argp is -1).
// 2) The only pointer into this frame is from the defer chain,
// which is explicitly handled during stack copying.
void
runtime·main(void)
{
Defer d;
// Max stack size is 1 GB on 64-bit, 250 MB on 32-bit.
// Using decimal instead of binary GB and MB because
// they look nicer in the stack overflow failure message.
if(sizeof(void*) == 8)
runtime·maxstacksize = 1000000000;
else
runtime·maxstacksize = 250000000;
newm(sysmon, nil);
// Lock the main goroutine onto this, the main OS thread,
// during initialization. Most programs won't care, but a few
// do require certain calls to be made by the main thread.
// Those can arrange for main.main to run in the main thread
// by calling runtime.LockOSThread during initialization
// to preserve the lock.
runtime·lockOSThread();
// Defer unlock so that runtime.Goexit during init does the unlock too.
d.fn = &initDone;
d.siz = 0;
d.link = g->defer;
d.argp = NoArgs;
d.special = true;
g->defer = &d;
if(m != &runtime·m0)
runtime·throw("runtime·main not on m0");
runtime·newproc1(&scavenger, nil, 0, 0, runtime·main);
main·init();
if(g->defer != &d || d.fn != &initDone)
runtime·throw("runtime: bad defer entry after init");
g->defer = d.link;
runtime·unlockOSThread();
main·main();
if(raceenabled)
runtime·racefini();
// Make racy client program work: if panicking on
// another goroutine at the same time as main returns,
// let the other goroutine finish printing the panic trace.
// Once it does, it will exit. See issue 3934.
if(runtime·panicking)
runtime·park(nil, nil, "panicwait");
runtime·exit(0);
for(;;)
*(int32*)runtime·main = 0;
}
void
runtime·goroutineheader(G *gp)
{
int8 *status;
int64 waitfor;
switch(gp->status) {
case Gidle:
status = "idle";
break;
case Grunnable:
status = "runnable";
break;
case Grunning:
status = "running";
break;
case Gsyscall:
status = "syscall";
break;
case Gwaiting:
if(gp->waitreason)
status = gp->waitreason;
else
status = "waiting";
break;
default:
status = "???";
break;
}
// approx time the G is blocked, in minutes
waitfor = 0;
if((gp->status == Gwaiting || gp->status == Gsyscall) && gp->waitsince != 0)
waitfor = (runtime·nanotime() - gp->waitsince) / (60LL*1000*1000*1000);
if(waitfor < 1)
runtime·printf("goroutine %D [%s]:\n", gp->goid, status);
else
runtime·printf("goroutine %D [%s, %D minutes]:\n", gp->goid, status, waitfor);
}
void
runtime·tracebackothers(G *me)
{
G *gp;
int32 traceback;
uintptr i;
traceback = runtime·gotraceback(nil);
// Show the current goroutine first, if we haven't already.
if((gp = m->curg) != nil && gp != me) {
runtime·printf("\n");
runtime·goroutineheader(gp);
runtime·traceback(~(uintptr)0, ~(uintptr)0, 0, gp);
}
runtime·lock(&allglock);
for(i = 0; i < runtime·allglen; i++) {
gp = runtime·allg[i];
if(gp == me || gp == m->curg || gp->status == Gdead)
continue;
if(gp->issystem && traceback < 2)
continue;
runtime·printf("\n");
runtime·goroutineheader(gp);
if(gp->status == Grunning) {
runtime·printf("\tgoroutine running on other thread; stack unavailable\n");
runtime·printcreatedby(gp);
} else
runtime·traceback(~(uintptr)0, ~(uintptr)0, 0, gp);
}
runtime·unlock(&allglock);
}
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)
{
// If there is no mcache runtime·callers() will crash,
// and we are most likely in sysmon thread so the stack is senseless anyway.
if(m->mcache)
runtime·callers(1, mp->createstack, nelem(mp->createstack));
mp->fastrand = 0x49f6428aUL + mp->id + runtime·cputicks();
runtime·lock(&runtime·sched);
mp->id = runtime·sched.mcount++;
checkmcount();
runtime·mpreinit(mp);
// Add to runtime·allm so garbage collector doesn't free 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);
}
// Mark gp ready to run.
void
runtime·ready(G *gp)
{
// Mark runnable.
m->locks++; // disable preemption because it can be holding p in a local var
if(gp->status != Gwaiting) {
runtime·printf("goroutine %D has status %d\n", gp->goid, gp->status);
runtime·throw("bad g->status in ready");
}
gp->status = Grunnable;
runqput(m->p, gp);
if(runtime·atomicload(&runtime·sched.npidle) != 0 && runtime·atomicload(&runtime·sched.nmspinning) == 0) // TODO: fast atomic
wakep();
m->locks--;
if(m->locks == 0 && g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
}
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);
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);
return n;
}
static bool
needaddgcproc(void)
{
int32 n;
runtime·lock(&runtime·sched);
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);
return n > 0;
}
void
runtime·helpgc(int32 nproc)
{
M *mp;
int32 n, pos;
runtime·lock(&runtime·sched);
pos = 0;
for(n = 1; n < nproc; n++) { // one M is currently running
if(runtime·allp[pos]->mcache == 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);
}
// 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);
}
void
runtime·stoptheworld(void)
{
int32 i;
uint32 s;
P *p;
bool wait;
runtime·lock(&runtime·sched);
runtime·sched.stopwait = runtime·gomaxprocs;
runtime·atomicstore((uint32*)&runtime·sched.gcwaiting, 1);
preemptall();
// stop current P
m->p->status = Pgcstop;
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);
// 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)
{
m->helpgc = -1;
}
void
runtime·starttheworld(void)
{
P *p, *p1;
M *mp;
G *gp;
bool add;
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);
if(newprocs) {
procresize(newprocs);
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);
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);
}
m->locks--;
if(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.
void
runtime·mstart(void)
{
if(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(&m->g0->sched);
m->g0->sched.pc = (uintptr)-1; // make sure it is never used
m->g0->stackguard = m->g0->stackguard0; // cgo sets only stackguard0, copy it to stackguard
runtime·asminit();
runtime·minit();
// Install signal handlers; after minit so that minit can
// prepare the thread to be able to handle the signals.
if(m == &runtime·m0)
runtime·initsig();
if(m->mstartfn)
m->mstartfn();
if(m->helpgc) {
m->helpgc = 0;
stopm();
} else if(m != &runtime·m0) {
acquirep(m->nextp);
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
{
M *m;
G *g;
uintptr *tls;
void (*fn)(void);
};
// Allocate a new m unassociated with any thread.
// Can use p for allocation context if needed.
M*
runtime·allocm(P *p)
{
M *mp;
static Type *mtype; // The Go type M
m->locks++; // disable GC because it can be called from sysmon
if(m->p == nil)
acquirep(p); // temporarily borrow p for mallocs in this function
if(mtype == nil) {
Eface e;
runtime·gc_m_ptr(&e);
mtype = ((PtrType*)e.type)->elem;
}
mp = runtime·cnew(mtype);
mcommoninit(mp);
// In case of cgo or Solaris, pthread_create will make us a stack.
// Windows will layout sched stack on OS stack.
if(runtime·iscgo || Solaris || Windows)
mp->g0 = runtime·malg(-1);
else
mp->g0 = runtime·malg(8192);
if(p == m->p)
releasep();
m->locks--;
if(m->locks == 0 && g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
return mp;
}
static G*
allocg(void)
{
G *gp;
static Type *gtype;
if(gtype == nil) {
Eface e;
runtime·gc_g_ptr(&e);
gtype = ((PtrType*)e.type)->elem;
}
gp = runtime·cnew(gtype);
return gp;
}
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 m and 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·setmg(mp, mp->g0);
g->stackbase = (uintptr)(&x + 1024);
g->stackguard = (uintptr)(&x - 32*1024);
g->stackguard0 = g->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->stackbase;
gp->sched.lr = 0;
gp->sched.g = gp;
gp->syscallpc = gp->sched.pc;
gp->syscallsp = gp->sched.sp;
gp->syscallstack = gp->stackbase;
gp->syscallguard = gp->stackguard;
gp->status = Gsyscall;
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
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 = m;
runtime·setmg(nil, 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.m = mp;
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->stackbase);
}
// Stops execution of the current m until new work is available.
// Returns with acquired P.
static void
stopm(void)
{
if(m->locks)
runtime·throw("stopm holding locks");
if(m->p)
runtime·throw("stopm holding p");
if(m->spinning) {
m->spinning = false;
runtime·xadd(&runtime·sched.nmspinning, -1);
}
retry:
runtime·lock(&runtime·sched);
mput(m);
runtime·unlock(&runtime·sched);
runtime·notesleep(&m->park);
runtime·noteclear(&m->park);
if(m->helpgc) {
runtime·gchelper();
m->helpgc = 0;
m->mcache = nil;
goto retry;
}
acquirep(m->nextp);
m->nextp = nil;
}
static void
mspinning(void)
{
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);
if(p == nil) {
p = pidleget();
if(p == nil) {
runtime·unlock(&runtime·sched);
if(spinning)
runtime·xadd(&runtime·sched.nmspinning, -1);
return;
}
}
mp = mget();
runtime·unlock(&runtime·sched);
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);
if(runtime·sched.gcwaiting) {
p->status = Pgcstop;
if(--runtime·sched.stopwait == 0)
runtime·notewakeup(&runtime·sched.stopnote);
runtime·unlock(&runtime·sched);
return;
}
if(runtime·sched.runqsize) {
runtime·unlock(&runtime·sched);
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);
startm(p, false);
return;
}
pidleput(p);
runtime·unlock(&runtime·sched);
}
// 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;
if(m->lockedg == nil || m->lockedg->lockedm != m)
runtime·throw("stoplockedm: inconsistent locking");
if(m->p) {
// Schedule another M to run this p.
p = releasep();
handoffp(p);
}
incidlelocked(1);
// Wait until another thread schedules lockedg again.
runtime·notesleep(&m->park);
runtime·noteclear(&m->park);
if(m->lockedg->status != Grunnable)
runtime·throw("stoplockedm: not runnable");
acquirep(m->nextp);
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 == 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(m->spinning) {
m->spinning = false;
runtime·xadd(&runtime·sched.nmspinning, -1);
}
p = releasep();
runtime·lock(&runtime·sched);
p->status = Pgcstop;
if(--runtime·sched.stopwait == 0)
runtime·notewakeup(&runtime·sched.stopnote);
runtime·unlock(&runtime·sched);
stopm();
}
// Schedules gp to run on the current M.
// Never returns.
static void
execute(G *gp)
{
int32 hz;
if(gp->status != Grunnable) {
runtime·printf("execute: bad g status %d\n", gp->status);
runtime·throw("execute: bad g status");
}
gp->status = Grunning;
gp->waitsince = 0;
gp->preempt = false;
gp->stackguard0 = gp->stackguard;
m->p->schedtick++;
m->curg = gp;
gp->m = m;
// Check whether the profiler needs to be turned on or off.
hz = runtime·sched.profilehz;
if(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(m->p);
if(gp)
return gp;
// global runq
if(runtime·sched.runqsize) {
runtime·lock(&runtime·sched);
gp = globrunqget(m->p, 0);
runtime·unlock(&runtime·sched);
if(gp)
return gp;
}
// poll network
gp = runtime·netpoll(false); // non-blocking
if(gp) {
injectglist(gp->schedlink);
gp->status = 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(!m->spinning && 2 * runtime·atomicload(&runtime·sched.nmspinning) >= runtime·gomaxprocs - runtime·atomicload(&runtime·sched.npidle)) // TODO: fast atomic
goto stop;
if(!m->spinning) {
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 == m->p)
gp = runqget(p);
else
gp = runqsteal(m->p, p);
if(gp)
return gp;
}
stop:
// return P and block
runtime·lock(&runtime·sched);
if(runtime·sched.gcwaiting) {
runtime·unlock(&runtime·sched);
goto top;
}
if(runtime·sched.runqsize) {
gp = globrunqget(m->p, 0);
runtime·unlock(&runtime·sched);
return gp;
}
p = releasep();
pidleput(p);
runtime·unlock(&runtime·sched);
if(m->spinning) {
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);
p = pidleget();
runtime·unlock(&runtime·sched);
if(p) {
acquirep(p);
goto top;
}
break;
}
}
// poll network
if(runtime·xchg64(&runtime·sched.lastpoll, 0) != 0) {
if(m->p)
runtime·throw("findrunnable: netpoll with p");
if(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);
p = pidleget();
runtime·unlock(&runtime·sched);
if(p) {
acquirep(p);
injectglist(gp->schedlink);
gp->status = Grunnable;
return gp;
}
injectglist(gp);
}
}
stopm();
goto top;
}
static void
resetspinning(void)
{
int32 nmspinning;
if(m->spinning) {
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);
for(n = 0; glist; n++) {
gp = glist;
glist = gp->schedlink;
gp->status = Grunnable;
globrunqput(gp);
}
runtime·unlock(&runtime·sched);
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(m->locks)
runtime·throw("schedule: holding locks");
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 = 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);
gp = globrunqget(m->p, 1);
runtime·unlock(&runtime·sched);
if(gp)
resetspinning();
}
if(gp == nil) {
gp = runqget(m->p);
if(gp && 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);
}
// 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, int8 *reason)
{
if(g->status != Grunning)
runtime·throw("bad g status");
m->waitlock = lock;
m->waitunlockf = unlockf;
g->waitreason = reason;
runtime·mcall(park0);
}
static bool
parkunlock(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(Lock *lock, int8 *reason)
{
runtime·park(parkunlock, lock, reason);
}
// runtime·park continuation on g0.
static void
park0(G *gp)
{
bool ok;
gp->status = Gwaiting;
gp->m = nil;
m->curg = nil;
if(m->waitunlockf) {
ok = m->waitunlockf(gp, m->waitlock);
m->waitunlockf = nil;
m->waitlock = nil;
if(!ok) {
gp->status = Grunnable;
execute(gp); // Schedule it back, never returns.
}
}
if(m->lockedg) {
stoplockedm();
execute(gp); // Never returns.
}
schedule();
}
// Scheduler yield.
void
runtime·gosched(void)
{
if(g->status != Grunning)
runtime·throw("bad g status");
runtime·mcall(runtime·gosched0);
}
// runtime·gosched continuation on g0.
void
runtime·gosched0(G *gp)
{
gp->status = Grunnable;
gp->m = nil;
m->curg = nil;
runtime·lock(&runtime·sched);
globrunqput(gp);
runtime·unlock(&runtime·sched);
if(m->lockedg) {
stoplockedm();
execute(gp); // Never returns.
}
schedule();
}
// Finishes execution of the current goroutine.
// Need to mark it as nosplit, because it runs with sp > stackbase (as runtime·lessstack).
// Since it does not return it does not matter. But if it is preempted
// at the split stack check, GC will complain about inconsistent sp.
#pragma textflag NOSPLIT
void
runtime·goexit(void)
{
if(g->status != Grunning)
runtime·throw("bad g status");
if(raceenabled)
runtime·racegoend();
runtime·mcall(goexit0);
}
// runtime·goexit continuation on g0.
static void
goexit0(G *gp)
{
gp->status = Gdead;
gp->m = nil;
gp->lockedm = 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->writenbuf = 0;
gp->writebuf = nil;
gp->waitreason = nil;
gp->param = nil;
m->curg = nil;
m->lockedg = nil;
if(m->locked & ~LockExternal) {
runtime·printf("invalid m->locked = %d\n", m->locked);
runtime·throw("internal lockOSThread error");
}
m->locked = 0;
runtime·unwindstack(gp, nil);
gfput(m->p, gp);
schedule();
}
#pragma textflag NOSPLIT
static void
save(void *pc, uintptr sp)
{
g->sched.pc = (uintptr)pc;
g->sched.sp = sp;
g->sched.lr = 0;
g->sched.ret = 0;
g->sched.ctxt = 0;
g->sched.g = 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 runtime·gosave must
// make g->sched refer to the caller's stack segment, because
// entersyscall is going to return immediately after.
#pragma textflag NOSPLIT
void
·entersyscall(int32 dummy)
{
// Disable preemption because during this function g is in Gsyscall status,
// but can have inconsistent g->sched, do not let GC observe it.
m->locks++;
// Leave SP around for GC and traceback.
save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
g->syscallsp = g->sched.sp;
g->syscallpc = g->sched.pc;
g->syscallstack = g->stackbase;
g->syscallguard = g->stackguard;
g->status = Gsyscall;
if(g->syscallsp < g->syscallguard-StackGuard || g->syscallstack < g->syscallsp) {
// runtime·printf("entersyscall inconsistent %p [%p,%p]\n",
// g->syscallsp, g->syscallguard-StackGuard, g->syscallstack);
runtime·throw("entersyscall");
}
if(runtime·atomicload(&runtime·sched.sysmonwait)) { // TODO: fast atomic
runtime·lock(&runtime·sched);
if(runtime·atomicload(&runtime·sched.sysmonwait)) {
runtime·atomicstore(&runtime·sched.sysmonwait, 0);
runtime·notewakeup(&runtime·sched.sysmonnote);
}
runtime·unlock(&runtime·sched);
save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
}
m->mcache = nil;
m->p->m = nil;
runtime·atomicstore(&m->p->status, Psyscall);
if(runtime·sched.gcwaiting) {
runtime·lock(&runtime·sched);
if (runtime·sched.stopwait > 0 && runtime·cas(&m->p->status, Psyscall, Pgcstop)) {
if(--runtime·sched.stopwait == 0)
runtime·notewakeup(&runtime·sched.stopnote);
}
runtime·unlock(&runtime·sched);
save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
}
// 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;
m->locks--;
}
// The same as runtime·entersyscall(), but with a hint that the syscall is blocking.
#pragma textflag NOSPLIT
void
·entersyscallblock(int32 dummy)
{
P *p;
m->locks++; // see comment in entersyscall
// Leave SP around for GC and traceback.
save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
g->syscallsp = g->sched.sp;
g->syscallpc = g->sched.pc;
g->syscallstack = g->stackbase;
g->syscallguard = g->stackguard;
g->status = Gsyscall;
if(g->syscallsp < g->syscallguard-StackGuard || g->syscallstack < g->syscallsp) {
// runtime·printf("entersyscall inconsistent %p [%p,%p]\n",
// g->syscallsp, g->syscallguard-StackGuard, g->syscallstack);
runtime·throw("entersyscallblock");
}
p = releasep();
handoffp(p);
if(g->isbackground) // do not consider blocked scavenger for deadlock detection
incidlelocked(1);
// Resave for traceback during blocked call.
save(runtime·getcallerpc(&dummy), runtime·getcallersp(&dummy));
g->stackguard0 = StackPreempt; // see comment in entersyscall
m->locks--;
}
// 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
runtime·exitsyscall(void)
{
m->locks++; // see comment in entersyscall
if(g->isbackground) // do not consider blocked scavenger for deadlock detection
incidlelocked(-1);
g->waitsince = 0;
if(exitsyscallfast()) {
// There's a cpu for us, so we can run.
m->p->syscalltick++;
g->status = Grunning;
// Garbage collector isn't running (since we are),
// so okay to clear gcstack and gcsp.
g->syscallstack = (uintptr)nil;
g->syscallsp = (uintptr)nil;
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->stackguard;
}
return;
}
m->locks--;
// Call the scheduler.
runtime·mcall(exitsyscall0);
// Scheduler returned, so we're allowed to run now.
// Delete the gcstack 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->syscallstack = (uintptr)nil;
g->syscallsp = (uintptr)nil;
m->p->syscalltick++;
}
#pragma textflag NOSPLIT
static bool
exitsyscallfast(void)
{
P *p;
// Freezetheworld sets stopwait but does not retake P's.
if(runtime·sched.stopwait) {
m->p = nil;
return false;
}
// Try to re-acquire the last P.
if(m->p && m->p->status == Psyscall && runtime·cas(&m->p->status, Psyscall, Prunning)) {
// There's a cpu for us, so we can run.
m->mcache = m->p->mcache;
m->p->m = m;
return true;
}
// Try to get any other idle P.
m->p = nil;
if(runtime·sched.pidle) {
runtime·lock(&runtime·sched);
p = pidleget();
if(p && runtime·atomicload(&runtime·sched.sysmonwait)) {
runtime·atomicstore(&runtime·sched.sysmonwait, 0);
runtime·notewakeup(&runtime·sched.sysmonnote);
}
runtime·unlock(&runtime·sched);
if(p) {
acquirep(p);
return true;
}
}
return false;
}
// runtime·exitsyscall slow path on g0.
// Failed to acquire P, enqueue gp as runnable.
static void
exitsyscall0(G *gp)
{
P *p;
gp->status = Grunnable;
gp->m = nil;
m->curg = nil;
runtime·lock(&runtime·sched);
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);
if(p) {
acquirep(p);
execute(gp); // Never returns.
}
if(m->lockedg) {
// Wait until another thread schedules gp and so m again.
stoplockedm();
execute(gp); // Never returns.
}
stopm();
schedule(); // Never returns.
}
// Called from syscall package before fork.
#pragma textflag NOSPLIT
void
syscall·runtime_BeforeFork(void)
{
// Fork can hang if preempted with signals frequently enough (see issue 5517).
// Ensure that we stay on the same M where we disable profiling.
m->locks++;
if(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.
m->forkstackguard = g->stackguard;
g->stackguard0 = StackPreempt-1;
g->stackguard = StackPreempt-1;
}
// Called from syscall package after fork in parent.
#pragma textflag NOSPLIT
void
syscall·runtime_AfterFork(void)
{
int32 hz;
// See the comment in runtime_BeforeFork.
g->stackguard0 = m->forkstackguard;
g->stackguard = m->forkstackguard;
m->forkstackguard = 0;
hz = runtime·sched.profilehz;
if(hz != 0)
runtime·resetcpuprofiler(hz);
m->locks--;
}
// 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*)gp->param;
size = newg->stacksize;
newg->stacksize = 0;
gp->param = runtime·stackalloc(newg, size);
runtime·gogo(&gp->sched);
}
// Allocate a new g, with a stack big enough for stacksize bytes.
G*
runtime·malg(int32 stacksize)
{
G *newg;
byte *stk;
if(StackTop < sizeof(Stktop)) {
runtime·printf("runtime: SizeofStktop=%d, should be >=%d\n", (int32)StackTop, (int32)sizeof(Stktop));
runtime·throw("runtime: bad stack.h");
}
newg = allocg();
if(stacksize >= 0) {
stacksize = runtime·round2(StackSystem + stacksize);
if(g == m->g0) {
// running on scheduler stack already.
stk = runtime·stackalloc(newg, stacksize);
} else {
// have to call stackalloc on scheduler stack.
newg->stacksize = stacksize;
g->param = newg;
runtime·mcall(mstackalloc);
stk = g->param;
g->param = nil;
}
newg->stack0 = (uintptr)stk;
newg->stackguard = (uintptr)stk + StackGuard;
newg->stackguard0 = newg->stackguard;
newg->stackbase = (uintptr)stk + stacksize - sizeof(Stktop);
}
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. It's OK for this to call
// functions that split the stack.
#pragma textflag NOSPLIT
void
runtime·newproc(int32 siz, FuncVal* fn, ...)
{
byte *argp;
if(thechar == '5')
argp = (byte*)(&fn+2); // skip caller's saved LR
else
argp = (byte*)(&fn+1);
runtime·newproc1(fn, argp, siz, 0, runtime·getcallerpc(&siz));
}
// 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;
//runtime·printf("newproc1 %p %p narg=%d nret=%d\n", fn->fn, argp, narg, nret);
if(fn == nil) {
m->throwing = -1; // do not dump full stacks
runtime·throw("go of nil func value");
}
m->locks++; // disable preemption because it can be holding p in a local var
siz = narg + nret;
siz = (siz+7) & ~7;
// We could instead create a secondary stack frame
// and make it look like goexit was on the original but
// the call to the actual goroutine function was split.
// Not worth it: this is almost always an error.
if(siz > StackMin - 1024)
runtime·throw("runtime.newproc: function arguments too large for new goroutine");
p = m->p;
if((newg = gfget(p)) != nil) {
if(newg->stackguard - StackGuard != newg->stack0)
runtime·throw("invalid stack in newg");
} else {
newg = runtime·malg(StackMin);
allgadd(newg);
}
sp = (byte*)newg->stackbase;
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;
newg->sched.g = newg;
runtime·gostartcallfn(&newg->sched, fn);
newg->gopc = (uintptr)callerpc;
newg->status = Grunnable;
if(p->goidcache == p->goidcacheend) {
p->goidcache = runtime·xadd64(&runtime·sched.goidgen, GoidCacheBatch);
p->goidcacheend = p->goidcache + GoidCacheBatch;
}
newg->goid = p->goidcache++;
newg->panicwrap = 0;
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();
m->locks--;
if(m->locks == 0 && g->preempt) // restore the preemption request in case we've cleared it in newstack
g->stackguard0 = StackPreempt;
return newg;
}
static void
allgadd(G *gp)
{
G **new;
uintptr cap;
runtime·lock(&allglock);
if(runtime·allglen >= allgcap) {
cap = 4096/sizeof(new[0]);
if(cap < 2*allgcap)
cap = 2*allgcap;
new = runtime·malloc(cap*sizeof(new[0]));
if(new == nil)
runtime·throw("runtime: cannot allocate memory");
if(runtime·allg != nil) {
runtime·memmove(new, runtime·allg, runtime·allglen*sizeof(new[0]));
runtime·free(runtime·allg);
}
runtime·allg = new;
allgcap = cap;
}
runtime·allg[runtime·allglen++] = gp;
runtime·unlock(&allglock);
}
// 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;
Stktop *top;
if(gp->stackguard - StackGuard != gp->stack0)
runtime·throw("invalid stack in gfput");
stksize = gp->stackbase + sizeof(Stktop) - gp->stack0;
if(stksize != gp->stacksize) {
runtime·printf("runtime: bad stacksize, goroutine %D, remain=%d, last=%d\n",
gp->goid, (int32)gp->stacksize, (int32)stksize);
runtime·throw("gfput: bad stacksize");
}
top = (Stktop*)gp->stackbase;
if(top->malloced) {
// non-standard stack size - free it.
runtime·stackfree(gp, (void*)gp->stack0, top);
gp->stack0 = 0;
gp->stackguard = 0;
gp->stackguard0 = 0;
gp->stackbase = 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·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;
byte *stk;
retry:
gp = p->gfree;
if(gp == nil && runtime·sched.gfree) {
runtime·lock(&runtime·sched.gflock);
while(p->gfreecnt < 32 && runtime·sched.gfree) {
p->gfreecnt++;
gp = runtime·sched.gfree;
runtime·sched.gfree = gp->schedlink;
gp->schedlink = p->gfree;
p->gfree = gp;
}
runtime·unlock(&runtime·sched.gflock);
goto retry;
}
if(gp) {
p->gfree = gp->schedlink;
p->gfreecnt--;
if(gp->stack0 == 0) {
// Stack was deallocated in gfput. Allocate a new one.
if(g == m->g0) {
stk = runtime·stackalloc(gp, FixedStack);
} else {
gp->stacksize = FixedStack;
g->param = gp;
runtime·mcall(mstackalloc);
stk = g->param;
g->param = nil;
}
gp->stack0 = (uintptr)stk;
gp->stackbase = (uintptr)stk + FixedStack - sizeof(Stktop);
gp->stackguard = (uintptr)stk + StackGuard;
gp->stackguard0 = gp->stackguard;
}
}
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) {
p->gfreecnt--;
gp = p->gfree;
p->gfree = gp->schedlink;
gp->schedlink = runtime·sched.gfree;
runtime·sched.gfree = gp;
}
runtime·unlock(&runtime·sched.gflock);
}
void
runtime·Breakpoint(void)
{
runtime·breakpoint();
}
void
runtime·Gosched(void)
{
runtime·gosched();
}
// Implementation of runtime.GOMAXPROCS.
// delete when scheduler is even stronger
int32
runtime·gomaxprocsfunc(int32 n)
{
int32 ret;
if(n > MaxGomaxprocs)
n = MaxGomaxprocs;
runtime·lock(&runtime·sched);
ret = runtime·gomaxprocs;
if(n <= 0 || n == ret) {
runtime·unlock(&runtime·sched);
return ret;
}
runtime·unlock(&runtime·sched);
runtime·semacquire(&runtime·worldsema, false);
m->gcing = 1;
runtime·stoptheworld();
newprocs = n;
m->gcing = 0;
runtime·semrelease(&runtime·worldsema);
runtime·starttheworld();
return ret;
}
// 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)
{
m->lockedg = g;
g->lockedm = m;
}
void
runtime·LockOSThread(void)
{
m->locked |= LockExternal;
lockOSThread();
}
void
runtime·lockOSThread(void)
{
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(m->locked != 0)
return;
m->lockedg = nil;
g->lockedm = nil;
}
void
runtime·UnlockOSThread(void)
{
m->locked &= ~LockExternal;
unlockOSThread();
}
void
runtime·unlockOSThread(void)
{
if(m->locked < LockInternal)
runtime·throw("runtime: internal error: misuse of lockOSThread/unlockOSThread");
m->locked -= LockInternal;
unlockOSThread();
}
bool
runtime·lockedOSThread(void)
{
return g->lockedm != nil && m->lockedg != nil;
}
int32
runtime·gcount(void)
{
G *gp;
int32 n, s;
uintptr i;
n = 0;
runtime·lock(&allglock);
// TODO(dvyukov): runtime.NumGoroutine() is O(N).
// We do not want to increment/decrement centralized counter in newproc/goexit,
// just to make runtime.NumGoroutine() faster.
// Compromise solution is to introduce per-P counters of active goroutines.
for(i = 0; i < runtime·allglen; i++) {
gp = runtime·allg[i];
s = gp->status;
if(s == Grunnable || s == Grunning || s == Gsyscall || s == Gwaiting)
n++;
}
runtime·unlock(&allglock);
return n;
}
int32
runtime·mcount(void)
{
return runtime·sched.mcount;
}
void
runtime·badmcall(void (*fn)(G*)) // called from assembly
{
USED(fn); // TODO: print fn?
runtime·throw("runtime: mcall called on m->g0 stack");
}
void
runtime·badmcall2(void (*fn)(G*)) // called from assembly
{
USED(fn);
runtime·throw("runtime: mcall function returned");
}
void
runtime·badreflectcall(void) // called from assembly
{
runtime·panicstring("runtime: arg size to reflect.call more than 1GB");
}
static struct {
Lock;
void (*fn)(uintptr*, int32);
int32 hz;
uintptr pcbuf[100];
} prof;
static void System(void) {}
static void ExternalCode(void) {}
static void GC(void) {}
extern byte 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;
m = 0;
USED(m);
if(prof.fn == nil || 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->stackguard - StackGuard || gp->stackbase < (uintptr)sp ||
((uint8*)runtime·gogo <= pc && pc < (uint8*)runtime·gogo + RuntimeGogoBytes))
traceback = false;
runtime·lock(&prof);
if(prof.fn == nil) {
runtime·unlock(&prof);
mp->mallocing--;
return;
}
n = 0;
if(traceback)
n = runtime·gentraceback((uintptr)pc, (uintptr)sp, (uintptr)lr, gp, 0, prof.pcbuf, nelem(prof.pcbuf), nil, nil, false);
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, prof.pcbuf, nelem(prof.pcbuf), nil, nil, false);
}
#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, prof.pcbuf, nelem(prof.pcbuf), nil, nil, false);
}
#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)etext)
pc = (byte*)ExternalCode + PCQuantum;
prof.pcbuf[0] = (uintptr)pc;
if(mp->gcing || mp->helpgc)
prof.pcbuf[1] = (uintptr)GC + PCQuantum;
else
prof.pcbuf[1] = (uintptr)System + PCQuantum;
}
}
prof.fn(prof.pcbuf, n);
runtime·unlock(&prof);
mp->mallocing--;
}
// Arrange to call fn with a traceback hz times a second.
void
runtime·setcpuprofilerate(void (*fn)(uintptr*, int32), int32 hz)
{
// Force sane arguments.
if(hz < 0)
hz = 0;
if(hz == 0)
fn = nil;
if(fn == nil)
hz = 0;
// Disable preemption, otherwise we can be rescheduled to another thread
// that has profiling enabled.
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);
runtime·lock(&prof);
prof.fn = fn;
prof.hz = hz;
runtime·unlock(&prof);
runtime·lock(&runtime·sched);
runtime·sched.profilehz = hz;
runtime·unlock(&runtime·sched);
if(hz != 0)
runtime·resetcpuprofiler(hz);
m->locks--;
}
// 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 = (P*)runtime·mallocgc(sizeof(*p), 0, FlagNoInvokeGC);
p->id = i;
p->status = Pgcstop;
runtime·atomicstorep(&runtime·allp[i], p);
}
if(p->mcache == nil) {
if(old==0 && i==0)
p->mcache = 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(m->p)
m->p->m = nil;
m->p = nil;
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(m->p || 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");
}
m->mcache = p->mcache;
m->p = p;
p->m = m;
p->status = Prunning;
}
// Disassociate p and the current m.
static P*
releasep(void)
{
P *p;
if(m->p == nil || m->mcache == nil)
runtime·throw("releasep: invalid arg");
p = m->p;
if(p->m != m || p->mcache != 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",
m, m->p, p->m, m->mcache, p->mcache, p->status);
runtime·throw("releasep: invalid p state");
}
m->p = nil;
m->mcache = nil;
p->m = nil;
p->status = Pidle;
return p;
}
static void
incidlelocked(int32 v)
{
runtime·lock(&runtime·sched);
runtime·sched.nmidlelocked += v;
if(v > 0)
checkdead();
runtime·unlock(&runtime·sched);
}
// Check for deadlock situation.
// The check is based on number of running M's, if 0 -> deadlock.
static void
checkdead(void)
{
G *gp;
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(&allglock);
for(i = 0; i < runtime·allglen; i++) {
gp = runtime·allg[i];
if(gp->isbackground)
continue;
s = gp->status;
if(s == Gwaiting)
grunning++;
else if(s == Grunnable || s == Grunning || s == Gsyscall) {
runtime·unlock(&allglock);
runtime·printf("runtime: checkdead: find g %D in status %d\n", gp->goid, s);
runtime·throw("checkdead: runnable g");
}
}
runtime·unlock(&allglock);
if(grunning == 0) // possible if main goroutine calls runtime·Goexit()
runtime·throw("no goroutines (main called runtime.Goexit) - deadlock!");
m->throwing = -1; // do not dump full stacks
runtime·throw("all goroutines are asleep - deadlock!");
}
static void
sysmon(void)
{
uint32 idle, delay;
int64 now, lastpoll, lasttrace;
G *gp;
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);
if(runtime·atomicload(&runtime·sched.gcwaiting) || runtime·atomicload(&runtime·sched.npidle) == runtime·gomaxprocs) {
runtime·atomicstore(&runtime·sched.sysmonwait, 1);
runtime·unlock(&runtime·sched);
runtime·notesleep(&runtime·sched.sysmonnote);
runtime·noteclear(&runtime·sched.sysmonnote);
idle = 0;
delay = 20;
} else
runtime·unlock(&runtime·sched);
}
// poll network if not polled for more than 10ms
lastpoll = runtime·atomicload64(&runtime·sched.lastpoll);
now = runtime·nanotime();
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++;
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.
static bool
preemptone(P *p)
{
M *mp;
G *gp;
mp = p->m;
if(mp == nil || mp == m)
return false;
gp = mp->curg;
if(gp == nil || gp == mp->g0)
return false;
gp->preempt = true;
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);
runtime·printf("SCHED %Dms: gomaxprocs=%d idleprocs=%d threads=%d idlethreads=%d runqueue=%d",
(now-starttime)/1000000, runtime·gomaxprocs, runtime·sched.npidle, runtime·sched.mcount,
runtime·sched.nmidle, runtime·sched.runqsize);
if(detailed) {
runtime·printf(" gcwaiting=%d nmidlelocked=%d nmspinning=%d stopwait=%d sysmonwait=%d\n",
runtime·sched.gcwaiting, runtime·sched.nmidlelocked, runtime·sched.nmspinning,
runtime·sched.stopwait, runtime·sched.sysmonwait);
}
// 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 = 0; i < runtime·gomaxprocs; i++) {
p = runtime·allp[i];
if(p == nil)
continue;
mp = p->m;
h = runtime·atomicload(&p->runqhead);
t = runtime·atomicload(&p->runqtail);
if(detailed)
runtime·printf(" P%d: status=%d schedtick=%d syscalltick=%d m=%d runqsize=%d gfreecnt=%d\n",
i, p->status, p->schedtick, p->syscalltick, mp ? mp->id : -1, t-h, p->gfreecnt);
else {
// In non-detailed mode format lengths of per-P run queues as:
// [len1 len2 len3 len4]
fmt = " %d";
if(runtime·gomaxprocs == 1)
fmt = " [%d]\n";
else if(i == 0)
fmt = " [%d";
else if(i == runtime·gomaxprocs-1)
fmt = " %d]\n";
runtime·printf(fmt, t-h);
}
}
if(!detailed) {
runtime·unlock(&runtime·sched);
return;
}
for(mp = runtime·allm; mp; mp = mp->alllink) {
p = mp->p;
gp = mp->curg;
lockedg = mp->lockedg;
id1 = -1;
if(p)
id1 = p->id;
id2 = -1;
if(gp)
id2 = gp->goid;
id3 = -1;
if(lockedg)
id3 = lockedg->goid;
runtime·printf(" M%d: p=%D curg=%D mallocing=%d throwing=%d gcing=%d"
" locks=%d dying=%d helpgc=%d spinning=%d blocked=%d lockedg=%D\n",
mp->id, id1, id2,
mp->mallocing, mp->throwing, mp->gcing, mp->locks, mp->dying, mp->helpgc,
mp->spinning, m->blocked, id3);
}
runtime·lock(&allglock);
for(gi = 0; gi < runtime·allglen; gi++) {
gp = runtime·allg[gi];
mp = gp->m;
lockedm = gp->lockedm;
runtime·printf(" G%D: status=%d(%s) m=%d lockedm=%d\n",
gp->goid, gp->status, gp->waitreason, mp ? mp->id : -1,
lockedm ? lockedm->id : -1);
}
runtime·unlock(&allglock);
runtime·unlock(&runtime·sched);
}
// Put mp on midle list.
// Sched must be locked.
static void
mput(M *mp)
{
mp->schedlink = runtime·sched.midle;
runtime·sched.midle = mp;
runtime·sched.nmidle++;
checkdead();
}
// Try to get an m from midle list.
// Sched must be locked.
static M*
mget(void)
{
M *mp;
if((mp = runtime·sched.midle) != nil){
runtime·sched.midle = mp->schedlink;
runtime·sched.nmidle--;
}
return mp;
}
// Put gp on the global runnable queue.
// Sched must be locked.
static void
globrunqput(G *gp)
{
gp->schedlink = nil;
if(runtime·sched.runqtail)
runtime·sched.runqtail->schedlink = gp;
else
runtime·sched.runqhead = gp;
runtime·sched.runqtail = gp;
runtime·sched.runqsize++;
}
// Put a batch of runnable goroutines on the global runnable queue.
// Sched must be locked.
static void
globrunqputbatch(G *ghead, G *gtail, int32 n)
{
gtail->schedlink = nil;
if(runtime·sched.runqtail)
runtime·sched.runqtail->schedlink = ghead;
else
runtime·sched.runqhead = ghead;
runtime·sched.runqtail = gtail;
runtime·sched.runqsize += n;
}
// Try get a batch of G's from the global runnable queue.
// Sched must be locked.
static G*
globrunqget(P *p, int32 max)
{
G *gp, *gp1;
int32 n;
if(runtime·sched.runqsize == 0)
return nil;
n = runtime·sched.runqsize/runtime·gomaxprocs+1;
if(n > runtime·sched.runqsize)
n = runtime·sched.runqsize;
if(max > 0 && n > max)
n = max;
if(n > nelem(p->runq)/2)
n = nelem(p->runq)/2;
runtime·sched.runqsize -= n;
if(runtime·sched.runqsize == 0)
runtime·sched.runqtail = nil;
gp = runtime·sched.runqhead;
runtime·sched.runqhead = gp->schedlink;
n--;
while(n--) {
gp1 = runtime·sched.runqhead;
runtime·sched.runqhead = gp1->schedlink;
runqput(p, gp1);
}
return gp;
}
// Put p to on pidle list.
// Sched must be locked.
static void
pidleput(P *p)
{
p->link = runtime·sched.pidle;
runtime·sched.pidle = p;
runtime·xadd(&runtime·sched.npidle, 1); // TODO: fast atomic
}
// Try get a p from pidle list.
// Sched must be locked.
static P*
pidleget(void)
{
P *p;
p = runtime·sched.pidle;
if(p) {
runtime·sched.pidle = p->link;
runtime·xadd(&runtime·sched.npidle, -1); // TODO: fast atomic
}
return p;
}
// Try to put g on local runnable queue.
// If it's full, put onto global queue.
// Executed only by the owner P.
static void
runqput(P *p, G *gp)
{
uint32 h, t;
retry:
h = runtime·atomicload(&p->runqhead); // load-acquire, synchronize with consumers
t = p->runqtail;
if(t - h < nelem(p->runq)) {
p->runq[t%nelem(p->runq)] = gp;
runtime·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.
static bool
runqputslow(P *p, G *gp, uint32 h, uint32 t)
{
G *batch[nelem(p->runq)/2+1];
uint32 n, i;
// First, grab a batch from local queue.
n = t-h;
n = n/2;
if(n != nelem(p->runq)/2)
runtime·throw("runqputslow: queue is not full");
for(i=0; i<n; i++)
batch[i] = p->runq[(h+i)%nelem(p->runq)];
if(!runtime·cas(&p->runqhead, h, h+n)) // cas-release, commits consume
return false;
batch[n] = gp;
// Link the goroutines.
for(i=0; i<n; i++)
batch[i]->schedlink = batch[i+1];
// Now put the batch on global queue.
runtime·lock(&runtime·sched);
globrunqputbatch(batch[0], batch[n], n+1);
runtime·unlock(&runtime·sched);
return true;
}
// Get g from local runnable queue.
// Executed only by the owner P.
static G*
runqget(P *p)
{
G *gp;
uint32 t, h;
for(;;) {
h = runtime·atomicload(&p->runqhead); // load-acquire, synchronize with other consumers
t = p->runqtail;
if(t == h)
return nil;
gp = p->runq[h%nelem(p->runq)];
if(runtime·cas(&p->runqhead, h, h+1)) // cas-release, commits consume
return gp;
}
}
// Grabs a batch of goroutines from local runnable queue.
// batch array must be of size nelem(p->runq)/2. Returns number of grabbed goroutines.
// Can be executed by any P.
static uint32
runqgrab(P *p, G **batch)
{
uint32 t, h, n, i;
for(;;) {
h = runtime·atomicload(&p->runqhead); // load-acquire, synchronize with other consumers
t = runtime·atomicload(&p->runqtail); // load-acquire, synchronize with the producer
n = t-h;
n = n - n/2;
if(n == 0)
break;
if(n > nelem(p->runq)/2) // read inconsistent h and t
continue;
for(i=0; i<n; i++)
batch[i] = p->runq[(h+i)%nelem(p->runq)];
if(runtime·cas(&p->runqhead, h, h+n)) // cas-release, commits consume
break;
}
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).
static G*
runqsteal(P *p, P *p2)
{
G *gp;
G *batch[nelem(p->runq)/2];
uint32 t, h, n, i;
n = runqgrab(p2, batch);
if(n == 0)
return nil;
n--;
gp = batch[n];
if(n == 0)
return gp;
h = runtime·atomicload(&p->runqhead); // load-acquire, synchronize with consumers
t = p->runqtail;
if(t - h + n >= nelem(p->runq))
runtime·throw("runqsteal: runq overflow");
for(i=0; i<n; i++, t++)
p->runq[t%nelem(p->runq)] = batch[i];
runtime·atomicstore(&p->runqtail, t); // store-release, makes the item available for consumption
return gp;
}
void
runtime·testSchedLocalQueue(void)
{
P p;
G gs[nelem(p.runq)];
int32 i, j;
runtime·memclr((byte*)&p, sizeof(p));
for(i = 0; i < nelem(gs); i++) {
if(runqget(&p) != nil)
runtime·throw("runq is not empty initially");
for(j = 0; j < i; j++)
runqput(&p, &gs[i]);
for(j = 0; j < i; j++) {
if(runqget(&p) != &gs[i]) {
runtime·printf("bad element at iter %d/%d\n", i, j);
runtime·throw("bad element");
}
}
if(runqget(&p) != nil)
runtime·throw("runq is not empty afterwards");
}
}
void
runtime·testSchedLocalQueueSteal(void)
{
P p1, p2;
G gs[nelem(p1.runq)], *gp;
int32 i, j, s;
runtime·memclr((byte*)&p1, sizeof(p1));
runtime·memclr((byte*)&p2, sizeof(p2));
for(i = 0; i < nelem(gs); i++) {
for(j = 0; j < i; j++) {
gs[j].sig = 0;
runqput(&p1, &gs[j]);
}
gp = runqsteal(&p2, &p1);
s = 0;
if(gp) {
s++;
gp->sig++;
}
while(gp = runqget(&p2)) {
s++;
gp->sig++;
}
while(gp = runqget(&p1))
gp->sig++;
for(j = 0; j < i; j++) {
if(gs[j].sig != 1) {
runtime·printf("bad element %d(%d) at iter %d\n", j, gs[j].sig, i);
runtime·throw("bad element");
}
}
if(s != i/2 && s != i/2+1) {
runtime·printf("bad steal %d, want %d or %d, iter %d\n",
s, i/2, i/2+1, i);
runtime·throw("bad steal");
}
}
}
extern void runtime·morestack(void);
uintptr runtime·externalthreadhandlerp;
// Does f mark the top of a goroutine stack?
bool
runtime·topofstack(Func *f)
{
return f->entry == (uintptr)runtime·goexit ||
f->entry == (uintptr)runtime·mstart ||
f->entry == (uintptr)runtime·mcall ||
f->entry == (uintptr)runtime·morestack ||
f->entry == (uintptr)runtime·lessstack ||
f->entry == (uintptr)_rt0_go ||
(runtime·externalthreadhandlerp != 0 && f->entry == runtime·externalthreadhandlerp);
}
int32
runtime·setmaxthreads(int32 in)
{
int32 out;
runtime·lock(&runtime·sched);
out = runtime·sched.maxmcount;
runtime·sched.maxmcount = in;
checkmcount();
runtime·unlock(&runtime·sched);
return out;
}
static int8 experiment[] = GOEXPERIMENT; // defined in zaexperiment.h
static bool
haveexperiment(int8 *name)
{
int32 i, j;
for(i=0; i<sizeof(experiment); i++) {
if((i == 0 || experiment[i-1] == ',') && experiment[i] == name[0]) {
for(j=0; name[j]; j++)
if(experiment[i+j] != name[j])
goto nomatch;
if(experiment[i+j] != '\0' && experiment[i+j] != ',')
goto nomatch;
return 1;
}
nomatch:;
}
return 0;
}