// User-level semaphore implementation:
// try to do the operations in user space on u,
// but when it's time to block, fall back on the kernel semaphore k.
// This is the same algorithm used in Plan 9.
void
usemacquire(Usema *s)
{
if((int32)xadd(&s->u, -1) < 0) {
if(s->k == 0)
initsema(&s->k);
mach_semacquire(s->k);
}
}
int32
runtime·semasleep(int64 ns)
{
int32 v;
if(m->profilehz > 0)
runtime·setprof(false);
v = runtime·mach_semacquire(m->waitsema, ns);
if(m->profilehz > 0)
runtime·setprof(true);
return v;
}
void
lock(Lock *l)
{
if(m->locks < 0)
throw("lock count");
m->locks++;
if(xadd(&l->key, 1) > 1) { // someone else has it; wait
// Allocate semaphore if needed.
if(l->sema == 0)
initsema(&l->sema);
mach_semacquire(l->sema);
}
}
