Exemple #1
0
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();
}
Exemple #2
0
void
runtime·entersyscall(void)
{
	uint32 v;

	if(m->profilehz > 0)
		runtime·setprof(false);

	// Leave SP around for gc and traceback.
	runtime·gosave(&g->sched);
	g->gcsp = g->sched.sp;
	g->gcstack = g->stackbase;
	g->gcguard = g->stackguard;
	g->status = Gsyscall;
	if(g->gcsp < g->gcguard-StackGuard || g->gcstack < g->gcsp) {
		// runtime·printf("entersyscall inconsistent %p [%p,%p]\n",
		//	g->gcsp, g->gcguard-StackGuard, g->gcstack);
		runtime·throw("entersyscall");
	}

	// 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);
	}

	// Re-save sched in case one of the calls
	// (notewakeup, matchmg) triggered something using it.
	runtime·gosave(&g->sched);

	schedunlock();
}
Exemple #3
0
// 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.
void
runtime_exitsyscall(void)
{
	G *gp;
	uint32 v;

	// Fast path.
	// If we can do the mcpu++ bookkeeping and
	// find that we still have mcpu <= mcpumax, then we can
	// start executing Go code immediately, without having to
	// schedlock/schedunlock.
	// Also do fast return if any locks are held, so that
	// panic code can use syscalls to open a file.
	gp = g;
	v = runtime_xadd(&runtime_sched.atomic, (1<<mcpuShift));
	if((m->profilehz == runtime_sched.profilehz && atomic_mcpu(v) <= atomic_mcpumax(v)) || m->locks > 0) {
		// There's a cpu for us, so we can run.
		gp->status = Grunning;
		// Garbage collector isn't running (since we are),
		// so okay to clear gcstack.
#ifdef USING_SPLIT_STACK
		gp->gcstack = nil;
#endif
		gp->gcnext_sp = nil;
		runtime_memclr(&gp->gcregs, sizeof gp->gcregs);

		if(m->profilehz > 0)
			runtime_setprof(true);
		return;
	}

	// Tell scheduler to put g back on the run queue:
	// mostly equivalent to g->status = Grunning,
	// but keeps the garbage collector from thinking
	// that g is running right now, which it's not.
	gp->readyonstop = 1;

	// All the cpus are taken.
	// The scheduler will ready g and put this m to sleep.
	// When the scheduler takes g away from m,
	// it will undo the runtime_sched.mcpu++ above.
	runtime_gosched();

	// Gosched 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.
#ifdef USING_SPLIT_STACK
	gp->gcstack = nil;
#endif
	gp->gcnext_sp = nil;
	runtime_memclr(&gp->gcregs, sizeof gp->gcregs);
}
Exemple #4
0
// Try to increment mcpu.  Report whether succeeded.
static bool
canaddmcpu(void)
{
	uint32 v;

	for(;;) {
		v = runtime·sched.atomic;
		if(atomic_mcpu(v) >= atomic_mcpumax(v))
			return 0;
		if(runtime·cas(&runtime·sched.atomic, v, v+(1<<mcpuShift)))
			return 1;
	}
}
Exemple #5
0
// 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.
void
runtime·exitsyscall(void)
{
	uint32 v;

	// Fast path.
	// If we can do the mcpu++ bookkeeping and
	// find that we still have mcpu <= mcpumax, then we can
	// start executing Go code immediately, without having to
	// schedlock/schedunlock.
	v = runtime·xadd(&runtime·sched.atomic, (1<<mcpuShift));
	if(m->profilehz == runtime·sched.profilehz && atomic_mcpu(v) <= atomic_mcpumax(v)) {
		// There's a cpu for us, so we can run.
		g->status = Grunning;
		// Garbage collector isn't running (since we are),
		// so okay to clear gcstack.
		g->gcstack = nil;

		if(m->profilehz > 0)
			runtime·setprof(true);
		return;
	}

	// Tell scheduler to put g back on the run queue:
	// mostly equivalent to g->status = Grunning,
	// but keeps the garbage collector from thinking
	// that g is running right now, which it's not.
	g->readyonstop = 1;

	// All the cpus are taken.
	// The scheduler will ready g and put this m to sleep.
	// When the scheduler takes g away from m,
	// it will undo the runtime·sched.mcpu++ above.
	runtime·gosched();

	// Gosched 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->gcstack = nil;
}
Exemple #6
0
// Implementation of runtime.GOMAXPROCS.
// delete when scheduler is stronger
int32
runtime·gomaxprocsfunc(int32 n)
{
	int32 ret;
	uint32 v;

	schedlock();
	ret = runtime·gomaxprocs;
	if(n <= 0)
		n = ret;
	if(n > maxgomaxprocs)
		n = maxgomaxprocs;
	runtime·gomaxprocs = n;
	if(runtime·gomaxprocs > 1)
		runtime·singleproc = false;
 	if(runtime·gcwaiting != 0) {
 		if(atomic_mcpumax(runtime·sched.atomic) != 1)
 			runtime·throw("invalid mcpumax during gc");
		schedunlock();
		return ret;
	}

	setmcpumax(n);

	// If there are now fewer allowed procs
	// than procs running, stop.
	v = runtime·atomicload(&runtime·sched.atomic);
	if(atomic_mcpu(v) > n) {
		schedunlock();
		runtime·gosched();
		return ret;
	}
	// handle more procs
	matchmg();
	schedunlock();
	return ret;
}
Exemple #7
0
// 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;
}
Exemple #8
0
// 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;
}