NAME
sem_post – increment (unlock) a semaphore
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <semaphore.h>
int
sem_post(sem_t *sem);
DESCRIPTION
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.
SEE ALSO
STANDARDS
The sem_post() function conforms to ISO/IEC 9945-1:1996 (“POSIX.1”).