Name
sem_post - unlock a semaphoreLibrary
POSIX threads library ( libpthread ", " -lpthread )Synopsis
#include <semaphore.h> int sem_post(sem_t * sem );
Description
sem_post() increments (unlocks) the semaphore pointed to bysem. 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 |
| T} | Thread safety | MT-Safe |
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)