SEM_POST(3) |
FreeBSD Library Functions Manual |
SEM_POST(3) |
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.
STANDARDS
The
sem_post() function conforms to ISO/IEC 9945-1:1996 (“POSIX.1”).