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Reuse nwaiter member field to record number of waiters, in sem_post(),

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this should reduce the chance having to do a syscall when there is no
waiter in the semaphore.
This commit is contained in:
David Xu 2007-11-21 06:01:02 +00:00
parent d618552420
commit 4877aaebc1
1 changed files with 31 additions and 7 deletions
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38
lib/libthr/thread/thr_sem.c
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@ -172,6 +172,14 @@ _sem_trywait(sem_t *sem)
return (-1);
}
static void
sem_cancel_handler(void *arg)
{
sem_t *sem = arg;
atomic_add_int(&(*sem)->nwaiters, -1);
}
int
_sem_wait(sem_t *sem)
{
@ -191,13 +199,19 @@ _sem_wait(sem_t *sem)
_pthread_testcancel();
do {
atomic_add_int(&(*sem)->nwaiters, 1);
while ((val = (*sem)->count) > 0) {
if (atomic_cmpset_acq_int(&(*sem)->count, val, val - 1))
if (atomic_cmpset_acq_int(&(*sem)->count, val, val - 1)) {
atomic_add_int(&(*sem)->nwaiters, -1);
return (0);
}
}
THR_CLEANUP_PUSH(curthread, sem_cancel_handler, sem);
_thr_cancel_enter(curthread);
retval = _thr_umtx_wait_uint(&(*sem)->count, 0, NULL);
atomic_add_int(&(*sem)->nwaiters, -1);
_thr_cancel_leave(curthread);
THR_CLEANUP_POP(curthread, 0);
} while (retval == 0);
errno = retval;
return (-1);
@ -228,19 +242,26 @@ _sem_timedwait(sem_t * __restrict sem,
*/
_pthread_testcancel();
do {
atomic_add_int(&(*sem)->nwaiters, 1);
while ((val = (*sem)->count) > 0) {
if (atomic_cmpset_acq_int(&(*sem)->count, val, val - 1))
if (atomic_cmpset_acq_int(&(*sem)->count, val, val - 1)) {
atomic_add_int(&(*sem)->nwaiters, -1);
return (0);
}
}
if (abstime == NULL) {
atomic_add_int(&(*sem)->nwaiters, -1);
errno = EINVAL;
return (-1);
}
THR_CLEANUP_PUSH(curthread, sem_cancel_handler, sem);
clock_gettime(CLOCK_REALTIME, &ts);
TIMESPEC_SUB(&ts2, abstime, &ts);
_thr_cancel_enter(curthread);
retval = _thr_umtx_wait_uint(&(*sem)->count, 0, &ts2);
atomic_add_int(&(*sem)->nwaiters, -1);
_thr_cancel_leave(curthread);
THR_CLEANUP_POP(curthread, 0);
} while (retval == 0);
errno = retval;
return (-1);
@ -249,7 +270,7 @@ _sem_timedwait(sem_t * __restrict sem,
int
_sem_post(sem_t *sem)
{
int val, retval;
int val, retval = 0;
if (sem_check_validity(sem) != 0)
return (-1);
@ -263,9 +284,12 @@ _sem_post(sem_t *sem)
*/
do {
val = (*sem)->count;
} while (!atomic_cmpset_acq_int(&(*sem)->count, val, val + 1));
retval = _thr_umtx_wake(&(*sem)->count, val + 1);
if (retval > 0)
retval = 0;
} while (!atomic_cmpset_rel_int(&(*sem)->count, val, val + 1));
if ((*sem)->nwaiters) {
retval = _thr_umtx_wake(&(*sem)->count, val + 1);
if (retval > 0)
retval = 0;
}
return (retval);
}