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// Copyright 2011 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.
// +build darwin netbsd openbsd plan9 windows
#include "runtime.h"
// This implementation depends on OS-specific implementations of
//
// uintptr runtime_semacreate(void)
// Create a semaphore, which will be assigned to m->waitsema.
// The zero value is treated as absence of any semaphore,
// so be sure to return a non-zero value.
//
// int32 runtime_semasleep(int64 ns)
// If ns < 0, acquire m->waitsema and return 0.
// If ns >= 0, try to acquire m->waitsema for at most ns nanoseconds.
// Return 0 if the semaphore was acquired, -1 if interrupted or timed out.
//
// int32 runtime_semawakeup(M *mp)
// Wake up mp, which is or will soon be sleeping on mp->waitsema.
//
enum
{
LOCKED = 1,
ACTIVE_SPIN = 4,
ACTIVE_SPIN_CNT = 30,
PASSIVE_SPIN = 1,
};
void
runtime_lock(Lock *l)
{
M *m;
uintptr v;
uint32 i, spin;
m = runtime_m();
if(m->locks++ < 0)
runtime_throw("runtime_lock: lock count");
// Speculative grab for lock.
if(runtime_casp((void**)&l->key, nil, (void*)LOCKED))
return;
if(m->waitsema == 0)
m->waitsema = runtime_semacreate();
// On uniprocessor's, no point spinning.
// On multiprocessors, spin for ACTIVE_SPIN attempts.
spin = 0;
if(runtime_ncpu > 1)
spin = ACTIVE_SPIN;
for(i=0;; i++) {
v = (uintptr)runtime_atomicloadp((void**)&l->key);
if((v&LOCKED) == 0) {
unlocked:
if(runtime_casp((void**)&l->key, (void*)v, (void*)(v|LOCKED)))
return;
i = 0;
}
if(i<spin)
runtime_procyield(ACTIVE_SPIN_CNT);
else if(i<spin+PASSIVE_SPIN)
runtime_osyield();
else {
// Someone else has it.
// l->waitm points to a linked list of M's waiting
// for this lock, chained through m->nextwaitm.
// Queue this M.
for(;;) {
m->nextwaitm = (void*)(v&~LOCKED);
if(runtime_casp((void**)&l->key, (void*)v, (void*)((uintptr)m|LOCKED)))
break;
v = (uintptr)runtime_atomicloadp((void**)&l->key);
if((v&LOCKED) == 0)
goto unlocked;
}
if(v&LOCKED) {
// Queued. Wait.
runtime_semasleep(-1);
i = 0;
}
}
}
}
void
runtime_unlock(Lock *l)
{
uintptr v;
M *mp;
if(--runtime_m()->locks < 0)
runtime_throw("runtime_unlock: lock count");
for(;;) {
v = (uintptr)runtime_atomicloadp((void**)&l->key);
if(v == LOCKED) {
if(runtime_casp((void**)&l->key, (void*)LOCKED, nil))
break;
} else {
// Other M's are waiting for the lock.
// Dequeue an M.
mp = (void*)(v&~LOCKED);
if(runtime_casp((void**)&l->key, (void*)v, mp->nextwaitm)) {
// Dequeued an M. Wake it.
runtime_semawakeup(mp);
break;
}
}
}
}
// One-time notifications.
void
runtime_noteclear(Note *n)
{
n->key = 0;
}
void
runtime_notewakeup(Note *n)
{
M *mp;
do
mp = runtime_atomicloadp((void**)&n->key);
while(!runtime_casp((void**)&n->key, mp, (void*)LOCKED));
// Successfully set waitm to LOCKED.
// What was it before?
if(mp == nil) {
// Nothing was waiting. Done.
} else if(mp == (M*)LOCKED) {
// Two notewakeups! Not allowed.
runtime_throw("notewakeup - double wakeup");
} else {
// Must be the waiting m. Wake it up.
runtime_semawakeup(mp);
}
}
void
runtime_notesleep(Note *n)
{
M *m;
m = runtime_m();
if(m->waitsema == 0)
m->waitsema = runtime_semacreate();
if(!runtime_casp((void**)&n->key, nil, m)) { // must be LOCKED (got wakeup)
if(n->key != LOCKED)
runtime_throw("notesleep - waitm out of sync");
return;
}
// Queued. Sleep.
if(m->profilehz > 0)
runtime_setprof(false);
runtime_semasleep(-1);
if(m->profilehz > 0)
runtime_setprof(true);
}
void
runtime_notetsleep(Note *n, int64 ns)
{
M *m;
M *mp;
int64 deadline, now;
if(ns < 0) {
runtime_notesleep(n);
return;
}
m = runtime_m();
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");
}
}
}
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