SEM_POST
Section: Linux Programmer's Manual (3)
Updated: 2020-08-13
Page Index
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
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
|
sem_post()
| Thread safety | MT-Safe
|
CONFORMING TO
POSIX.1-2001.
NOTES
sem_post()
is async-signal-safe:
it may be safely called within a signal handler.
EXAMPLES
See
sem_wait(3)
and
shm_open(3).
SEE ALSO
sem_getvalue(3),
sem_wait(3),
sem_overview(7),
signal-safety(7)
COLOPHON
This page is part of release 5.10 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
https://www.kernel.org/doc/man-pages/.