Manual Pages  — SEM_POST

sem_post – increment (unlock) a semaphore

LIBRARY SYNOPSIS DESCRIPTION RETURN VALUES ERRORS SEE ALSO STANDARDS

Standard C Library (libc, -lc)

#include <semaphore.h>

int
sem_post(sem_t *sem);

The sem_post() function increments (unlocks) the semaphore pointed to by sem. If there are threads blocked on the semaphore when sem_post() is called, then the highest priority thread that has been blocked the longest on the semaphore will be allowed to return from sem_wait().

The sem_post() function is signal-reentrant and may be called within signal handlers.

The sem_post function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The sem_post() function will fail if:

[EINVAL]
	The sem argument points to an invalid semaphore.
[EOVERFLOW]
	The semaphore value would exceed SEM_VALUE_MAX.

The sem_post() function conforms to IEEE Std 1003.1-96 ("POSIX.1").