SEM_POST(3) |
Library Functions Manual |
SEM_POST(3) |
NAME
sem_post — increment (unlock) a semaphore
LIBRARY
POSIX Real-time Library (librt, -lrt)
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().
sem_post() 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
sem_post() will fail if:
-
[EINVAL]
-
sem points to an invalid semaphore.
STANDARDS
sem_post() conforms to ISO/IEC 9945-1:1996 (“POSIX.1”).