NAME¶
sem_post - unlock a semaphore
SYNOPSIS¶
#include <semaphore.h>
int sem_post(sem_t *sem);
Link with
-pthread.
DESCRIPTION¶
sem_post() increments (unlocks) the semaphore pointed to by
sem.
If the semaphore's value consequently becomes greater than zero, then another
process or thread blocked in a
sem_wait(3) call will be woken up and
proceed to lock the semaphore.
RETURN VALUE¶
sem_post() returns 0 on success; on error, the value of the semaphore is
left unchanged, -1 is returned, and
errno is set to indicate the error.
ERRORS¶
- EINVAL
- sem is not a valid semaphore.
- EOVERFLOW
- The maximum allowable value for a semaphore would be exceeded.
ATTRIBUTES¶
Multithreading (see pthreads(7))¶
The
sem_post() function is thread-safe.
POSIX.1-2001.
NOTES¶
sem_post() is async-signal-safe: it may be safely called within a signal
handler.
EXAMPLE¶
See
sem_wait(3).
SEE ALSO¶
sem_getvalue(3),
sem_wait(3),
sem_overview(7)
COLOPHON¶
This page is part of release 3.74 of the Linux
man-pages project. A
description of the project, information about reporting bugs, and the latest
version of this page, can be found at
http://www.kernel.org/doc/man-pages/.
