sem_post (3)

Table of Contents

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 5.09 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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Table of Contents

• Name
• Synopsis
• Description
• Return Value
• Errors
• Attributes
• Conforming to
• Notes
• Examples
• See Also
• Colophon