Example for semaphore in C

semaphore.c

#include <stdio.h>
#include <pthread.h>
#include <stdlib.h>     /* for exit() */
#include <semaphore.h>  /* for sem_xxxx() */

sem_t semp;
int val;

static void *wait_fun(void *arg)
{
    while(1) {
        sem_wait(&semp);
        sem_getvalue(&semp, &val);
        fprintf(stderr, "thread==> count : %d \n", val);
    }
}

int main(void)
{
    pthread_t pthread_tid = 0;

    sem_post(&semp);
    sem_post(&semp);

    sem_getvalue(&semp, &val);
    fprintf(stderr, "main==> count : %d \n", val);
#if 0
    sem_post(&semp);
    sem_post(&semp);
    sem_post(&semp);
#endif

    if (pthread_create(&pthread_tid, NULL, wait_fun, NULL) != 0 ) {
        printf("failed : wait_fun create \n");
        exit(EXIT_FAILURE);
    }

    pthread_join(pthread_tid, NULL);

    exit(EXIT_SUCCESS);
}