Block on a Semaphore Count

sem_wait(3RT)

Prototype:
int	sem_wait(sem_t *sem);

#include <semaphore.h>

sem_t sem;
int ret;

ret = sem_wait(&sem); /* wait for semaphore */

Use sema_wait(3THR) to block the calling thread until the count in the semaphore pointed to by sem becomes greater than zero, then atomically decrement it.

Return Values

sem_wait() returns zero after completing successfully. Any other return value indicates that an error occurred. When any of the following conditions occurs, the function fails and returns the corresponding value.

EINVAL

sem points to an illegal address.

EINTR

A signal interrupted this function.