SEM_WAIT(3) BSD Programmer's Manual SEM_WAIT(3)
sem_wait, sem_trywait - decrement (lock) a semaphore
#include <semaphore.h> int sem_wait(sem_t *sem); int sem_trywait(sem_t *sem);
The sem_wait() function decrements (locks) the semaphore pointed to by sem, but blocks if the value of sem is zero, until the value is non-zero and the value can be decremented. The sem_trywait() function decrements (locks) the semaphore pointed to by sem only if the value is non-zero. Otherwise, the semaphore is not decre- mented and an error is returned.
The sem_wait() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
sem_wait() and sem_trywait() will fail if: [EINVAL] sem points to an invalid semaphore. Additionally, sem_trywait() will fail if: [EAGAIN] The semaphore value was zero, and thus could not be decre- mented.
sem_destroy(3), sem_getvalue(3), sem_init(3), sem_open(3), sem_post(3)
sem_wait() and sem_trywait() conform to ISO/IEC 9945-1:1996 ("POSIX.1"). MirBSD #10-current February 15, 2000 1