Linux
2017-03-13
manpages-dev
Manual pages about using GNU/Linux for development
man-pages
Linux kernel and C library user-space interface documentation
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 |
| 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.
EXAMPLE
See sem_wait(3).
