sem_post(3) - Linux man page

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.

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).

Referenced By

sem_close(3), sem_destroy(3), sem_init(3), sem_open(3), sem_unlink(3)