// 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);
}
}
void
runtime_notewakeup(Note *n)
{
if(runtime_xchg((uint32*)&n->key, 1))
runtime_throw("notewakeup - double wakeup");
runtime_futexwakeup((uint32*)&n->key, 1);
}
void
runtime_unlock(Lock *l)
{
uint32 v;
if(--runtime_m()->locks < 0)
runtime_throw("runtime_unlock: lock count");
v = runtime_xchg(&l->key, MUTEX_UNLOCKED);
if(v == MUTEX_UNLOCKED)
runtime_throw("unlock of unlocked lock");
if(v == MUTEX_SLEEPING)
runtime_futexwakeup(&l->key, 1);
}
void
runtime_notewakeup(Note *n)
{
runtime_xchg(&n->key, 1);
runtime_futexwakeup(&n->key, 1);
}
