sem_post3
Increment (unlock) a semaphore
Usage
#include <semaphore.h>
int
sem_post(sem_t *sem);
Library
Standard C Library (libc, -lc)
Overview
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.
Return values
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.
Errors
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.
Releases
70 releases since FreeBSD 4.0-RELEASE; the text changed 43 times.