void
runtime·notetsleep(Note *n, int64 ns)
{
int64 deadline, now;
if(ns < 0) {
runtime·notesleep(n);
return;
}
if(runtime·atomicload(&n->key) != 0)
return;
if(m->profilehz > 0)
runtime·setprof(false);
deadline = runtime·nanotime() + ns;
for(;;) {
runtime·futexsleep(&n->key, 0, ns);
if(runtime·atomicload(&n->key) != 0)
break;
now = runtime·nanotime();
if(now >= deadline)
break;
ns = deadline - now;
}
if(m->profilehz > 0)
runtime·setprof(true);
}
void
runtime·stoptheworld(void)
{
uint32 v;
schedlock();
runtime·gcwaiting = 1;
setmcpumax(1);
// while mcpu > 1
for(;;) {
v = runtime·sched.atomic;
if(atomic_mcpu(v) <= 1)
break;
// It would be unsafe for multiple threads to be using
// the stopped note at once, but there is only
// ever one thread doing garbage collection.
runtime·noteclear(&runtime·sched.stopped);
if(atomic_waitstop(v))
runtime·throw("invalid waitstop");
// atomic { waitstop = 1 }, predicated on mcpu <= 1 check above
// still being true.
if(!runtime·cas(&runtime·sched.atomic, v, v+(1<<waitstopShift)))
continue;
schedunlock();
runtime·notesleep(&runtime·sched.stopped);
schedlock();
}
runtime·singleproc = runtime·gomaxprocs == 1;
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 gs are
// running on cpus (not in system calls) at any given time.
static G*
nextgandunlock(void)
{
G *gp;
if(runtime·sched.mcpu < 0)
runtime·throw("negative runtime·sched.mcpu");
// If there is a g waiting as m->nextg,
// mnextg took care of the runtime·sched.mcpu++.
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();
} else {
// Look for work on global queue.
while(runtime·sched.mcpu < runtime·sched.mcpumax && (gp=gget()) != nil) {
if(gp->lockedm) {
mnextg(gp->lockedm, gp);
continue;
}
runtime·sched.mcpu++; // this m will run gp
schedunlock();
return gp;
}
// Otherwise, wait on global m queue.
mput(m);
}
if(runtime·sched.mcpu == 0 && runtime·sched.msyscall == 0)
runtime·throw("all goroutines are asleep - deadlock!");
m->nextg = nil;
m->waitnextg = 1;
runtime·noteclear(&m->havenextg);
if(runtime·sched.waitstop && runtime·sched.mcpu <= runtime·sched.mcpumax) {
runtime·sched.waitstop = 0;
runtime·notewakeup(&runtime·sched.stopped);
}
schedunlock();
runtime·notesleep(&m->havenextg);
if((gp = m->nextg) == nil)
runtime·throw("bad m->nextg in nextgoroutine");
m->nextg = nil;
return gp;
}
// TODO(rsc): Remove. This is only temporary,
// for the mark and sweep collector.
void
runtime·stoptheworld(void)
{
schedlock();
runtime·gcwaiting = 1;
runtime·sched.mcpumax = 1;
while(runtime·sched.mcpu > 1) {
// It would be unsafe for multiple threads to be using
// the stopped note at once, but there is only
// ever one thread doing garbage collection,
// so this is okay.
runtime·noteclear(&runtime·sched.stopped);
runtime·sched.waitstop = 1;
schedunlock();
runtime·notesleep(&runtime·sched.stopped);
schedlock();
}
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;
}
void
runtime·notetsleep(Note *n, int64 ns)
{
M *mp;
int64 deadline, now;
if(ns < 0) {
runtime·notesleep(n);
return;
}
if(m->waitsema == 0)
m->waitsema = runtime·semacreate();
// Register for wakeup on n->waitm.
if(!runtime·casp((void**)&n->key, nil, m)) { // must be LOCKED (got wakeup already)
if(n->key != LOCKED)
runtime·throw("notetsleep - waitm out of sync");
return;
}
if(m->profilehz > 0)
runtime·setprof(false);
deadline = runtime·nanotime() + ns;
for(;;) {
// Registered. Sleep.
if(runtime·semasleep(ns) >= 0) {
// Acquired semaphore, semawakeup unregistered us.
// Done.
if(m->profilehz > 0)
runtime·setprof(true);
return;
}
// Interrupted or timed out. Still registered. Semaphore not acquired.
now = runtime·nanotime();
if(now >= deadline)
break;
// Deadline hasn't arrived. Keep sleeping.
ns = deadline - now;
}
if(m->profilehz > 0)
runtime·setprof(true);
// Deadline arrived. Still registered. Semaphore not acquired.
// Want to give up and return, but have to unregister first,
// so that any notewakeup racing with the return does not
// try to grant us the semaphore when we don't expect it.
for(;;) {
mp = runtime·atomicloadp((void**)&n->key);
if(mp == m) {
// No wakeup yet; unregister if possible.
if(runtime·casp((void**)&n->key, mp, nil))
return;
} else if(mp == (M*)LOCKED) {
// Wakeup happened so semaphore is available.
// Grab it to avoid getting out of sync.
if(runtime·semasleep(-1) < 0)
runtime·throw("runtime: unable to acquire - semaphore out of sync");
return;
} else {
runtime·throw("runtime: unexpected waitm - semaphore out of sync");
}
}
}
// 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: one single active g which happens to be scvg.
if(runtime·sched.grunning == 1 && runtime·sched.gwait == 0) {
if(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;
}
