man:sem_post
SEM_POST(3) Linux Programmer's Manual SEM_POST(3)
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 sig- nal handler.
EXAMPLE
See sem_wait(3).
SEE ALSO
sem_getvalue(3), sem_wait(3), sem_overview(7), signal-safety(7)
COLOPHON
This page is part of release 4.16 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/.
Linux 2017-03-13 SEM_POST(3)
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