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eliminate global waiters count in pthread_once

This commit is contained in:
Rich Felker 2014-10-13 18:26:28 -04:00
parent df37d3960a
commit 0054840839
1 changed files with 13 additions and 9 deletions
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22
src/thread/pthread_once.c
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@ -2,14 +2,14 @@
static void undo(void *control) static void undo(void *control)
{ {
a_store(control, 0); /* Wake all waiters, since the waiter status is lost when
__wake(control, 1, 1); * resetting control to the initial state. */
if (a_swap(control, 0) == 3)
__wake(control, -1, 1);
} }
int __pthread_once(pthread_once_t *control, void (*init)(void)) int __pthread_once(pthread_once_t *control, void (*init)(void))
{ {
static int waiters;
/* Return immediately if init finished before, but ensure that /* Return immediately if init finished before, but ensure that
* effects of the init routine are visible to the caller. */ * effects of the init routine are visible to the caller. */
if (*control == 2) { if (*control == 2) {
@ -17,10 +17,11 @@ int __pthread_once(pthread_once_t *control, void (*init)(void))
return 0; return 0;
} }
/* Try to enter initializing state. Three possibilities: /* Try to enter initializing state. Four possibilities:
* 0 - we're the first or the other cancelled; run init * 0 - we're the first or the other cancelled; run init
* 1 - another thread is running init; wait * 1 - another thread is running init; wait
* 2 - another thread finished running init; just return */ * 2 - another thread finished running init; just return
* 3 - another thread is running init, waiters present; wait */
for (;;) switch (a_cas(control, 0, 1)) { for (;;) switch (a_cas(control, 0, 1)) {
case 0: case 0:
@ -28,11 +29,14 @@ int __pthread_once(pthread_once_t *control, void (*init)(void))
init(); init();
pthread_cleanup_pop(0); pthread_cleanup_pop(0);
a_store(control, 2); if (a_swap(control, 2) == 3)
if (waiters) __wake(control, -1, 1); __wake(control, -1, 1);
return 0; return 0;
case 1: case 1:
__wait(control, &waiters, 1, 1); /* If this fails, so will __wait. */
a_cas(control, 1, 3);
case 3:
__wait(control, 0, 3, 1);
continue; continue;
case 2: case 2:
return 0; return 0;