int32
runtime_helpgc(bool *extra)
{
M *mp;
int32 n, max;
// Figure out how many CPUs to use.
// Limited by gomaxprocs, number of actual CPUs, and MaxGcproc.
max = runtime_gomaxprocs;
if(max > runtime_ncpu)
max = runtime_ncpu > 0 ? runtime_ncpu : 1;
if(max > MaxGcproc)
max = MaxGcproc;
// We're going to use one CPU no matter what.
// Figure out the max number of additional CPUs.
max--;
runtime_lock(&runtime_sched);
n = 0;
while(n < max && (mp = mget(nil)) != nil) {
n++;
mp->helpgc = 1;
mp->waitnextg = 0;
runtime_notewakeup(&mp->havenextg);
}
runtime_unlock(&runtime_sched);
if(extra)
*extra = n != max;
return n;
}
// Unlock the scheduler.
static void
schedunlock(void)
{
M *m;
m = mwakeup;
mwakeup = nil;
runtime_unlock(&runtime_sched);
if(m != nil)
runtime_notewakeup(&m->havenextg);
}
// Pass g to m for running.
// Caller has already incremented mcpu.
static void
mnextg(M *m, G *g)
{
runtime_sched.grunning++;
m->nextg = g;
if(m->waitnextg) {
m->waitnextg = 0;
if(mwakeup != nil)
runtime_notewakeup(&mwakeup->havenextg);
mwakeup = m;
}
}
void
runtime_entersyscall(void)
{
uint32 v;
if(m->profilehz > 0)
runtime_setprof(false);
// Leave SP around for gc and traceback.
#ifdef USING_SPLIT_STACK
g->gcstack = __splitstack_find(nil, nil, &g->gcstack_size,
&g->gcnext_segment, &g->gcnext_sp,
&g->gcinitial_sp);
#else
g->gcnext_sp = (byte *) &v;
#endif
// Save the registers in the g structure so that any pointers
// held in registers will be seen by the garbage collector.
// We could use getcontext here, but setjmp is more efficient
// because it doesn't need to save the signal mask.
setjmp(g->gcregs);
g->status = Gsyscall;
// Fast path.
// The slow path inside the schedlock/schedunlock will get
// through without stopping if it does:
// mcpu--
// gwait not true
// waitstop && mcpu <= mcpumax not true
// If we can do the same with a single atomic add,
// then we can skip the locks.
v = runtime_xadd(&runtime_sched.atomic, -1<<mcpuShift);
if(!atomic_gwaiting(v) && (!atomic_waitstop(v) || atomic_mcpu(v) > atomic_mcpumax(v)))
return;
schedlock();
v = runtime_atomicload(&runtime_sched.atomic);
if(atomic_gwaiting(v)) {
matchmg();
v = runtime_atomicload(&runtime_sched.atomic);
}
if(atomic_waitstop(v) && atomic_mcpu(v) <= atomic_mcpumax(v)) {
runtime_xadd(&runtime_sched.atomic, -1<<waitstopShift);
runtime_notewakeup(&runtime_sched.stopped);
}
schedunlock();
}
// Get the next goroutine that m should run.
// Sched must be locked on entry, is unlocked on exit.
// Makes sure that at most $GOMAXPROCS g's are
// running on cpus (not in system calls) at any given time.
static G*
nextgandunlock(void)
{
G *gp;
uint32 v;
top:
if(atomic_mcpu(runtime_sched.atomic) >= maxgomaxprocs)
runtime_throw("negative mcpu");
// If there is a g waiting as m->nextg, the mcpu++
// happened before it was passed to mnextg.
if(m->nextg != nil) {
gp = m->nextg;
m->nextg = nil;
schedunlock();
return gp;
}
if(m->lockedg != nil) {
// We can only run one g, and it's not available.
// Make sure some other cpu is running to handle
// the ordinary run queue.
if(runtime_sched.gwait != 0) {
matchmg();
// m->lockedg might have been on the queue.
if(m->nextg != nil) {
gp = m->nextg;
m->nextg = nil;
schedunlock();
return gp;
}
}
} else {
// Look for work on global queue.
while(haveg() && canaddmcpu()) {
gp = gget();
if(gp == nil)
runtime_throw("gget inconsistency");
if(gp->lockedm) {
mnextg(gp->lockedm, gp);
continue;
}
runtime_sched.grunning++;
schedunlock();
return gp;
}
// The while loop ended either because the g queue is empty
// or because we have maxed out our m procs running go
// code (mcpu >= mcpumax). We need to check that
// concurrent actions by entersyscall/exitsyscall cannot
// invalidate the decision to end the loop.
//
// We hold the sched lock, so no one else is manipulating the
// g queue or changing mcpumax. Entersyscall can decrement
// mcpu, but if does so when there is something on the g queue,
// the gwait bit will be set, so entersyscall will take the slow path
// and use the sched lock. So it cannot invalidate our decision.
//
// Wait on global m queue.
mput(m);
}
// Look for deadlock situation.
// There is a race with the scavenger that causes false negatives:
// if the scavenger is just starting, then we have
// scvg != nil && grunning == 0 && gwait == 0
// and we do not detect a deadlock. It is possible that we should
// add that case to the if statement here, but it is too close to Go 1
// to make such a subtle change. Instead, we work around the
// false negative in trivial programs by calling runtime.gosched
// from the main goroutine just before main.main.
// See runtime_main above.
//
// On a related note, it is also possible that the scvg == nil case is
// wrong and should include gwait, but that does not happen in
// standard Go programs, which all start the scavenger.
//
if((scvg == nil && runtime_sched.grunning == 0) ||
(scvg != nil && runtime_sched.grunning == 1 && runtime_sched.gwait == 0 &&
(scvg->status == Grunning || scvg->status == Gsyscall))) {
runtime_throw("all goroutines are asleep - deadlock!");
}
m->nextg = nil;
m->waitnextg = 1;
runtime_noteclear(&m->havenextg);
// Stoptheworld is waiting for all but its cpu to go to stop.
// Entersyscall might have decremented mcpu too, but if so
// it will see the waitstop and take the slow path.
// Exitsyscall never increments mcpu beyond mcpumax.
v = runtime_atomicload(&runtime_sched.atomic);
if(atomic_waitstop(v) && atomic_mcpu(v) <= atomic_mcpumax(v)) {
// set waitstop = 0 (known to be 1)
runtime_xadd(&runtime_sched.atomic, -1<<waitstopShift);
runtime_notewakeup(&runtime_sched.stopped);
}
schedunlock();
runtime_notesleep(&m->havenextg);
if(m->helpgc) {
runtime_gchelper();
m->helpgc = 0;
runtime_lock(&runtime_sched);
goto top;
}
if((gp = m->nextg) == nil)
runtime_throw("bad m->nextg in nextgoroutine");
m->nextg = nil;
return gp;
}
// Get the next goroutine that m should run.
// Sched must be locked on entry, is unlocked on exit.
// Makes sure that at most $GOMAXPROCS g's are
// running on cpus (not in system calls) at any given time.
static G*
nextgandunlock(void)
{
G *gp;
uint32 v;
top:
if(atomic_mcpu(runtime_sched.atomic) >= maxgomaxprocs)
runtime_throw("negative mcpu");
// If there is a g waiting as m->nextg, the mcpu++
// happened before it was passed to mnextg.
if(m->nextg != nil) {
gp = m->nextg;
m->nextg = nil;
schedunlock();
return gp;
}
if(m->lockedg != nil) {
// We can only run one g, and it's not available.
// Make sure some other cpu is running to handle
// the ordinary run queue.
if(runtime_sched.gwait != 0) {
matchmg();
// m->lockedg might have been on the queue.
if(m->nextg != nil) {
gp = m->nextg;
m->nextg = nil;
schedunlock();
return gp;
}
}
} else {
// Look for work on global queue.
while(haveg() && canaddmcpu()) {
gp = gget();
if(gp == nil)
runtime_throw("gget inconsistency");
if(gp->lockedm) {
mnextg(gp->lockedm, gp);
continue;
}
runtime_sched.grunning++;
schedunlock();
return gp;
}
// The while loop ended either because the g queue is empty
// or because we have maxed out our m procs running go
// code (mcpu >= mcpumax). We need to check that
// concurrent actions by entersyscall/exitsyscall cannot
// invalidate the decision to end the loop.
//
// We hold the sched lock, so no one else is manipulating the
// g queue or changing mcpumax. Entersyscall can decrement
// mcpu, but if does so when there is something on the g queue,
// the gwait bit will be set, so entersyscall will take the slow path
// and use the sched lock. So it cannot invalidate our decision.
//
// Wait on global m queue.
mput(m);
}
v = runtime_atomicload(&runtime_sched.atomic);
if(runtime_sched.grunning == 0)
runtime_throw("all goroutines are asleep - deadlock!");
m->nextg = nil;
m->waitnextg = 1;
runtime_noteclear(&m->havenextg);
// Stoptheworld is waiting for all but its cpu to go to stop.
// Entersyscall might have decremented mcpu too, but if so
// it will see the waitstop and take the slow path.
// Exitsyscall never increments mcpu beyond mcpumax.
if(atomic_waitstop(v) && atomic_mcpu(v) <= atomic_mcpumax(v)) {
// set waitstop = 0 (known to be 1)
runtime_xadd(&runtime_sched.atomic, -1<<waitstopShift);
runtime_notewakeup(&runtime_sched.stopped);
}
schedunlock();
runtime_notesleep(&m->havenextg);
if(m->helpgc) {
runtime_gchelper();
m->helpgc = 0;
runtime_lock(&runtime_sched);
goto top;
}
if((gp = m->nextg) == nil)
runtime_throw("bad m->nextg in nextgoroutine");
m->nextg = nil;
return gp;
}
