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2017-03-13

manpages-dev

Manual pages about using GNU/Linux for development

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Linux kernel and C library user-space interface documentation

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
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.

EXAMPLE

COLOPHON

This page is part of release 5.00 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/.
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