NAME

sem_post - unlock a semaphore

LIBRARY

POSIX threads library (libpthread, -lpthread)

SYNOPSIS

#include <semaphore.h>

int sem_post(sem_t *sem);

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).

STANDARDS

POSIX.1-2008.

HISTORY

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)