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Getting the value of a semaphore

#include <pthread.h> #include <stdio.h> #include <stdlib.h> #include <unistd.h> #include <string.h> #include <semaphore.h> #define THREAD_NUM 4 sem_t sem; void* routine(void* args) { int index = *(int*)args; int semVal; sem_wait(&sem); sleep(index + 1); sem_getvalue(&sem, &semVal); printf("(%d) Current semaphore value after wait is %d\n", index, semVal); sem_post(&sem); sem_getvalue(&sem, &semVal); printf("(%d) Current semaphore value after post is %d\n", index, semVal); free(args); } int main(int argc, char *argv[]) { pthread_t th[THREAD_NUM]; sem_init(&sem, 0, 4); int i; for (i = 0; i < THREAD_NUM; i++) { int* a = malloc(sizeof(int)); *a = i; if (pthread_create(&th[i], NULL, &routine, a) != 0) { perror("Failed to create thread"); } } for (i = 0; i < THREAD_NUM; i++) { if (pthread_join(th[i], NULL) != 0) { perror("Failed to join thread"); } } sem_destroy(&sem); return 0; }