sem_post man page

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).

InterfaceAttributeValue
sem_post()Thread safetyMT-Safe

Conforming to

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

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Referenced By

sem_close(3), sem_destroy(3), sem_getvalue(3), sem_init(3), sem_open(3), sem_overview(7), sem_timedwait(3p), sem_unlink(3), sem_wait(3).

2015-03-02 Linux Linux Programmer's Manual