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.
sem is not a valid semaphore.
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)
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