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major semaphore improvements (performance and correctness)

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1. make sem_[timed]wait interruptible by signals, per POSIX
2. keep a waiter count in order to avoid unnecessary futex wake syscalls
This commit is contained in:
Rich Felker
2011-04-06 12:24:34 -04:00
parent cd3bb38412
commit a113434cd6
5 changed files with 37 additions and 21 deletions
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45
src/thread/sem_timedwait.c
View File

@ -1,26 +1,41 @@
#include <semaphore.h>
#include "pthread_impl.h"
static void cleanup(void *p)
{
a_dec(p);
}
int sem_timedwait(sem_t *sem, const struct timespec *at)
{
int val;
int r;
if (a_fetch_add(sem->__val, -1) > 0) return 0;
a_inc(sem->__val);
if (at && at->tv_nsec >= 1000000000UL) {
errno = EINVAL;
return -1;
}
a_inc(sem->__val+1);
pthread_cleanup_push(cleanup, sem->__val+1)
CANCELPT_BEGIN;
for (;;) {
if (a_fetch_add(sem->__val, -1) > 0) return 0;
val = a_fetch_add(sem->__val, 1)+1;
if (val==1) __wake(sem->__val, 1, 0);
if (at && at->tv_nsec >= 1000000000UL) {
errno = EINVAL;
return -1;
}
CANCELPT_BEGIN;
if (val <= 0 && __timedwait(sem->__val, val, CLOCK_REALTIME, at, 0) == ETIMEDOUT) {
errno = ETIMEDOUT;
CANCELPT_TRY;
CANCELPT_END;
return -1;
r = 0;
if (!sem_trywait(sem)) break;
r = __timedwait(sem->__val, 0, CLOCK_REALTIME, at, 0);
if (r) {
errno = r;
r = -1;
break;
}
CANCELPT_TRY;
CANCELPT_END;
}
CANCELPT_END;
pthread_cleanup_pop(1);
return r;
}