sem_post - unlock a semaphore
#include <semaphore.h>
int sem_post(sem_t *sem);
Link with
-pthread.
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.
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.
- EINVAL
- sem is not a valid semaphore.
- EOVERFLOW
- The maximum allowable value for a semaphore would be exceeded.
For an explanation of the terms used in this section, see
attributes(7).
| Interface |
Attribute |
Value |
| sem_post () |
Thread safety |
MT-Safe |
POSIX.1-2001.
sem_post() is async-signal-safe: it may be safely called within a signal
handler.
See
sem_wait(3) and
shm_open(3).
sem_getvalue(3),
sem_wait(3),
sem_overview(7),
signal-safety(7)