2011-11-22 21:24:44 +01:00
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// Copyright 2011 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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2014-06-07 00:37:27 +02:00
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// +build darwin netbsd openbsd plan9 solaris windows
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2012-01-13 06:11:45 +01:00
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2011-11-22 21:24:44 +01:00
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#include "runtime.h"
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// This implementation depends on OS-specific implementations of
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//
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2012-01-13 06:11:45 +01:00
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// uintptr runtime_semacreate(void)
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2011-11-22 21:24:44 +01:00
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// Create a semaphore, which will be assigned to m->waitsema.
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// The zero value is treated as absence of any semaphore,
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// so be sure to return a non-zero value.
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//
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2012-01-13 06:11:45 +01:00
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// int32 runtime_semasleep(int64 ns)
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2011-11-22 21:24:44 +01:00
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// If ns < 0, acquire m->waitsema and return 0.
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// If ns >= 0, try to acquire m->waitsema for at most ns nanoseconds.
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// Return 0 if the semaphore was acquired, -1 if interrupted or timed out.
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//
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2012-01-13 06:11:45 +01:00
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// int32 runtime_semawakeup(M *mp)
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2011-11-22 21:24:44 +01:00
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// Wake up mp, which is or will soon be sleeping on mp->waitsema.
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//
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enum
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{
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LOCKED = 1,
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ACTIVE_SPIN = 4,
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ACTIVE_SPIN_CNT = 30,
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PASSIVE_SPIN = 1,
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};
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void
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runtime_lock(Lock *l)
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{
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2011-11-29 22:58:48 +01:00
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M *m;
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2011-11-22 21:24:44 +01:00
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uintptr v;
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uint32 i, spin;
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2011-11-29 22:58:48 +01:00
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m = runtime_m();
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2011-11-22 21:24:44 +01:00
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if(m->locks++ < 0)
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runtime_throw("runtime_lock: lock count");
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// Speculative grab for lock.
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2013-07-16 08:54:42 +02:00
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if(runtime_casp((void**)&l->key, nil, (void*)LOCKED))
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2011-11-22 21:24:44 +01:00
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return;
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if(m->waitsema == 0)
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m->waitsema = runtime_semacreate();
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// On uniprocessor's, no point spinning.
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// On multiprocessors, spin for ACTIVE_SPIN attempts.
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spin = 0;
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if(runtime_ncpu > 1)
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spin = ACTIVE_SPIN;
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for(i=0;; i++) {
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2013-07-16 08:54:42 +02:00
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v = (uintptr)runtime_atomicloadp((void**)&l->key);
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2011-11-22 21:24:44 +01:00
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if((v&LOCKED) == 0) {
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unlocked:
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2013-07-16 08:54:42 +02:00
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if(runtime_casp((void**)&l->key, (void*)v, (void*)(v|LOCKED)))
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2011-11-22 21:24:44 +01:00
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return;
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i = 0;
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}
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if(i<spin)
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runtime_procyield(ACTIVE_SPIN_CNT);
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else if(i<spin+PASSIVE_SPIN)
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runtime_osyield();
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else {
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// Someone else has it.
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// l->waitm points to a linked list of M's waiting
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// for this lock, chained through m->nextwaitm.
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// Queue this M.
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for(;;) {
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m->nextwaitm = (void*)(v&~LOCKED);
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2013-07-16 08:54:42 +02:00
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if(runtime_casp((void**)&l->key, (void*)v, (void*)((uintptr)m|LOCKED)))
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2011-11-22 21:24:44 +01:00
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break;
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2013-07-16 08:54:42 +02:00
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v = (uintptr)runtime_atomicloadp((void**)&l->key);
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2011-11-22 21:24:44 +01:00
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if((v&LOCKED) == 0)
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goto unlocked;
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}
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if(v&LOCKED) {
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// Queued. Wait.
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runtime_semasleep(-1);
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i = 0;
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}
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}
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}
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}
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void
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runtime_unlock(Lock *l)
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{
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uintptr v;
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M *mp;
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for(;;) {
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2013-07-16 08:54:42 +02:00
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v = (uintptr)runtime_atomicloadp((void**)&l->key);
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2011-11-22 21:24:44 +01:00
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if(v == LOCKED) {
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2013-07-16 08:54:42 +02:00
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if(runtime_casp((void**)&l->key, (void*)LOCKED, nil))
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2011-11-22 21:24:44 +01:00
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break;
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} else {
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// Other M's are waiting for the lock.
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// Dequeue an M.
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mp = (void*)(v&~LOCKED);
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2013-07-16 08:54:42 +02:00
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if(runtime_casp((void**)&l->key, (void*)v, mp->nextwaitm)) {
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2011-11-22 21:24:44 +01:00
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// Dequeued an M. Wake it.
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runtime_semawakeup(mp);
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break;
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}
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}
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}
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2013-11-06 20:49:01 +01:00
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if(--runtime_m()->locks < 0)
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runtime_throw("runtime_unlock: lock count");
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2011-11-22 21:24:44 +01:00
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}
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// One-time notifications.
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void
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runtime_noteclear(Note *n)
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{
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2013-07-16 08:54:42 +02:00
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n->key = 0;
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2011-11-22 21:24:44 +01:00
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}
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void
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runtime_notewakeup(Note *n)
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{
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M *mp;
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do
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2013-07-16 08:54:42 +02:00
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mp = runtime_atomicloadp((void**)&n->key);
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while(!runtime_casp((void**)&n->key, mp, (void*)LOCKED));
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2011-11-22 21:24:44 +01:00
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// Successfully set waitm to LOCKED.
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// What was it before?
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if(mp == nil) {
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// Nothing was waiting. Done.
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} else if(mp == (M*)LOCKED) {
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// Two notewakeups! Not allowed.
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runtime_throw("notewakeup - double wakeup");
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} else {
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// Must be the waiting m. Wake it up.
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runtime_semawakeup(mp);
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}
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}
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void
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runtime_notesleep(Note *n)
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{
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2011-11-29 22:58:48 +01:00
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M *m;
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m = runtime_m();
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2013-11-06 20:49:01 +01:00
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2013-12-06 19:26:27 +01:00
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/* For gccgo it's OK to sleep in non-g0, and it happens in
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stoptheworld because we have not implemented preemption.
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2013-11-06 20:49:01 +01:00
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if(runtime_g() != m->g0)
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runtime_throw("notesleep not on g0");
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2013-12-06 19:26:27 +01:00
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*/
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2013-11-06 20:49:01 +01:00
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2011-11-22 21:24:44 +01:00
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if(m->waitsema == 0)
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m->waitsema = runtime_semacreate();
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2013-07-16 08:54:42 +02:00
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if(!runtime_casp((void**)&n->key, nil, m)) { // must be LOCKED (got wakeup)
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if(n->key != LOCKED)
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2011-11-22 21:24:44 +01:00
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runtime_throw("notesleep - waitm out of sync");
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return;
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}
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// Queued. Sleep.
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2014-06-07 00:37:27 +02:00
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m->blocked = true;
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2011-11-22 21:24:44 +01:00
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runtime_semasleep(-1);
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2014-06-07 00:37:27 +02:00
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m->blocked = false;
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2011-11-22 21:24:44 +01:00
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}
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2013-11-06 20:49:01 +01:00
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static bool
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notetsleep(Note *n, int64 ns, int64 deadline, M *mp)
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2011-11-22 21:24:44 +01:00
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{
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2011-11-29 22:58:48 +01:00
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M *m;
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2011-11-22 21:24:44 +01:00
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2011-11-29 22:58:48 +01:00
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m = runtime_m();
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2013-11-06 20:49:01 +01:00
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// Conceptually, deadline and mp are local variables.
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// They are passed as arguments so that the space for them
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// does not count against our nosplit stack sequence.
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2011-11-22 21:24:44 +01:00
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// Register for wakeup on n->waitm.
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2013-07-16 08:54:42 +02:00
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if(!runtime_casp((void**)&n->key, nil, m)) { // must be LOCKED (got wakeup already)
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if(n->key != LOCKED)
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2011-11-22 21:24:44 +01:00
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runtime_throw("notetsleep - waitm out of sync");
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2013-11-06 20:49:01 +01:00
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return true;
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}
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if(ns < 0) {
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// Queued. Sleep.
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2014-06-07 00:37:27 +02:00
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m->blocked = true;
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2013-11-06 20:49:01 +01:00
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runtime_semasleep(-1);
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2014-06-07 00:37:27 +02:00
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m->blocked = false;
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2013-11-06 20:49:01 +01:00
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return true;
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2011-11-22 21:24:44 +01:00
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}
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deadline = runtime_nanotime() + ns;
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for(;;) {
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// Registered. Sleep.
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2014-06-07 00:37:27 +02:00
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m->blocked = true;
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2011-11-22 21:24:44 +01:00
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if(runtime_semasleep(ns) >= 0) {
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2014-06-07 00:37:27 +02:00
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m->blocked = false;
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2011-11-22 21:24:44 +01:00
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// Acquired semaphore, semawakeup unregistered us.
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// Done.
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2013-11-06 20:49:01 +01:00
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return true;
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2011-11-22 21:24:44 +01:00
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}
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2014-06-07 00:37:27 +02:00
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m->blocked = false;
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2011-11-22 21:24:44 +01:00
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// Interrupted or timed out. Still registered. Semaphore not acquired.
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2013-11-06 20:49:01 +01:00
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ns = deadline - runtime_nanotime();
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if(ns <= 0)
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2011-11-22 21:24:44 +01:00
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break;
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// Deadline hasn't arrived. Keep sleeping.
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}
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// Deadline arrived. Still registered. Semaphore not acquired.
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// Want to give up and return, but have to unregister first,
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// so that any notewakeup racing with the return does not
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// try to grant us the semaphore when we don't expect it.
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for(;;) {
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2013-07-16 08:54:42 +02:00
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mp = runtime_atomicloadp((void**)&n->key);
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2011-11-22 21:24:44 +01:00
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if(mp == m) {
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// No wakeup yet; unregister if possible.
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2013-07-16 08:54:42 +02:00
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if(runtime_casp((void**)&n->key, mp, nil))
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2013-11-06 20:49:01 +01:00
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return false;
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2011-11-22 21:24:44 +01:00
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} else if(mp == (M*)LOCKED) {
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// Wakeup happened so semaphore is available.
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// Grab it to avoid getting out of sync.
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2014-06-07 00:37:27 +02:00
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m->blocked = true;
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2011-11-22 21:24:44 +01:00
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if(runtime_semasleep(-1) < 0)
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runtime_throw("runtime: unable to acquire - semaphore out of sync");
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2014-06-07 00:37:27 +02:00
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m->blocked = false;
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2013-11-06 20:49:01 +01:00
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return true;
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} else
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2011-11-22 21:24:44 +01:00
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runtime_throw("runtime: unexpected waitm - semaphore out of sync");
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}
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}
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2013-11-06 20:49:01 +01:00
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bool
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runtime_notetsleep(Note *n, int64 ns)
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{
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M *m;
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bool res;
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m = runtime_m();
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if(runtime_g() != m->g0 && !m->gcing)
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runtime_throw("notetsleep not on g0");
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if(m->waitsema == 0)
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m->waitsema = runtime_semacreate();
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res = notetsleep(n, ns, 0, nil);
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return res;
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}
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// same as runtime_notetsleep, but called on user g (not g0)
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// calls only nosplit functions between entersyscallblock/exitsyscall
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bool
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runtime_notetsleepg(Note *n, int64 ns)
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{
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M *m;
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bool res;
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m = runtime_m();
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if(runtime_g() == m->g0)
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runtime_throw("notetsleepg on g0");
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if(m->waitsema == 0)
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m->waitsema = runtime_semacreate();
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runtime_entersyscallblock();
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res = notetsleep(n, ns, 0, nil);
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runtime_exitsyscall();
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return res;
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}
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