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