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;
}
}
}
}
// Possible lock states are MUTEX_UNLOCKED, MUTEX_LOCKED and MUTEX_SLEEPING.
// MUTEX_SLEEPING means that there is presumably at least one sleeping thread.
// Note that there can be spinning threads during all states - they do not
// affect mutex's state.
void
runtime_lock(Lock *l)
{
uint32 i, v, wait, spin;
if(runtime_m()->locks++ < 0)
runtime_throw("runtime_lock: lock count");
// Speculative grab for lock.
v = runtime_xchg(&l->key, MUTEX_LOCKED);
if(v == MUTEX_UNLOCKED)
return;
// wait is either MUTEX_LOCKED or MUTEX_SLEEPING
// depending on whether there is a thread sleeping
// on this mutex. If we ever change l->key from
// MUTEX_SLEEPING to some other value, we must be
// careful to change it back to MUTEX_SLEEPING before
// returning, to ensure that the sleeping thread gets
// its wakeup call.
wait = v;
// On uniprocessor's, no point spinning.
// On multiprocessors, spin for ACTIVE_SPIN attempts.
spin = 0;
if(runtime_ncpu > 1)
spin = ACTIVE_SPIN;
for(;;) {
// Try for lock, spinning.
for(i = 0; i < spin; i++) {
while(l->key == MUTEX_UNLOCKED)
if(runtime_cas(&l->key, MUTEX_UNLOCKED, wait))
return;
runtime_procyield(ACTIVE_SPIN_CNT);
}
// Try for lock, rescheduling.
for(i=0; i < PASSIVE_SPIN; i++) {
while(l->key == MUTEX_UNLOCKED)
if(runtime_cas(&l->key, MUTEX_UNLOCKED, wait))
return;
runtime_osyield();
}
// Sleep.
v = runtime_xchg(&l->key, MUTEX_SLEEPING);
if(v == MUTEX_UNLOCKED)
return;
wait = MUTEX_SLEEPING;
runtime_futexsleep(&l->key, MUTEX_SLEEPING, -1);
}
}
