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13 lines
249 B

#include <semaphore.h>
#include "pthread_impl.h"
int sem_trywait(sem_t *sem)
{
int val = sem->__val[0];
if (val>0) {
int new = val-1-(val==1 && sem->__val[1]);
if (a_cas(sem->__val, val, new)==val) return 0;
}
errno = EAGAIN;
return -1;
}