NAME
sem_post - unlock a semaphore
SYNOPSIS
#include <semaphore.h>
int sem_post(sem_t *sem);
Link with -lrt or -pthread.
DESCRIPTION
sem_post() increments (unlocks) the semaphore pointed to by sem. If the semaphores 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).
SEE ALSO
sem_getvalue(3), sem_wait(3), sem_overview(7)
COLOPHON
This page is part of release 3.23 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.