Use sem_post(3RT) to atomically increment the semaphore pointed to by sem.
int sem_post(sem_t *sem);
#include <semaphore.h> sem_t sem; int ret; ret = sem_post(&sem); /* semaphore is posted */
When any threads are blocked on the semaphore, one of the threads is unblocked.
sem_post() returns zero after completing successfully. Any other return value indicates that an error occurred. When the following condition occurs, the function fails and returns the corresponding value.
EINVAL
Description:sem points to an illegal address.