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Eliminate global mutex by using pthread_once's state field as

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a semaphore.
This commit is contained in:
davidxu 2008-05-30 00:02:59 +00:00
parent 6d8aba47d8
commit 8951bcd14c
1 changed files with 29 additions and 33 deletions
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62
lib/libthr/thread/thr_once.c
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@ -38,10 +38,7 @@ __weak_reference(_pthread_once, pthread_once);
#define ONCE_NEVER_DONE PTHREAD_NEEDS_INIT
#define ONCE_DONE PTHREAD_DONE_INIT
#define ONCE_IN_PROGRESS 0x02
#define ONCE_MASK 0x03
static pthread_mutex_t _thr_once_lock = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t _thr_once_cv = PTHREAD_COND_INITIALIZER;
#define ONCE_WAIT 0x03
/*
* POSIX:
@ -55,47 +52,46 @@ once_cancel_handler(void *arg)
{
pthread_once_t *once_control = arg;
_pthread_mutex_lock(&_thr_once_lock);
once_control->state = ONCE_NEVER_DONE;
_pthread_mutex_unlock(&_thr_once_lock);
_pthread_cond_broadcast(&_thr_once_cv);
if (atomic_cmpset_rel_int(&once_control->state, ONCE_IN_PROGRESS, ONCE_NEVER_DONE))
return;
atomic_store_rel_int(&once_control->state, ONCE_NEVER_DONE);
_thr_umtx_wake(&once_control->state, INT_MAX, 0);
}
int
_pthread_once(pthread_once_t *once_control, void (*init_routine) (void))
{
struct pthread *curthread;
int wakeup = 0;
int state;
if (once_control->state == ONCE_DONE)
for (;;) {
state = once_control->state;
if (state == ONCE_DONE)
return (0);
if (state == ONCE_NEVER_DONE) {
if (atomic_cmpset_acq_int(&once_control->state, state, ONCE_IN_PROGRESS))
break;
} else if (state == ONCE_IN_PROGRESS) {
if (atomic_cmpset_acq_int(&once_control->state, state, ONCE_WAIT))
_thr_umtx_wait_uint(&once_control->state, ONCE_WAIT, NULL, 0);
} else if (state == ONCE_WAIT) {
_thr_umtx_wait_uint(&once_control->state, state, NULL, 0);
} else
return (EINVAL);
}
curthread = _get_curthread();
THR_CLEANUP_PUSH(curthread, once_cancel_handler, once_control);
init_routine();
THR_CLEANUP_POP(curthread, 0);
if (atomic_cmpset_rel_int(&once_control->state, ONCE_IN_PROGRESS, ONCE_DONE))
return (0);
_pthread_mutex_lock(&_thr_once_lock);
while (*(volatile int *)&(once_control->state) == ONCE_IN_PROGRESS)
_pthread_cond_wait(&_thr_once_cv, &_thr_once_lock);
/*
* If previous thread was canceled, then the state still
* could be ONCE_NEVER_DONE, we need to check it again.
*/
if (*(volatile int *)&(once_control->state) == ONCE_NEVER_DONE) {
once_control->state = ONCE_IN_PROGRESS;
_pthread_mutex_unlock(&_thr_once_lock);
curthread = _get_curthread();
THR_CLEANUP_PUSH(curthread, once_cancel_handler, once_control);
init_routine();
THR_CLEANUP_POP(curthread, 0);
_pthread_mutex_lock(&_thr_once_lock);
once_control->state = ONCE_DONE;
wakeup = 1;
}
_pthread_mutex_unlock(&_thr_once_lock);
if (wakeup)
_pthread_cond_broadcast(&_thr_once_cv);
atomic_store_rel_int(&once_control->state, ONCE_DONE);
_thr_umtx_wake(&once_control->state, INT_MAX, 0);
return (0);
}
void
_thr_once_init()
{
_thr_once_lock = PTHREAD_MUTEX_INITIALIZER;
_thr_once_cv = PTHREAD_COND_INITIALIZER;
}