sem_post - unlock a semaphore
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.
For an explanation of the terms used in this section, see attributes(7).
- sem is not a valid semaphore.
- The maximum allowable value for a semaphore would be exceeded.
sem_post() is async-signal-safe: it may be safely called within a signal
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