modified semtest.c

semtest.c (text/plain), 1.76 KB, created by Don Hatch on 2011-04-13 07:05:08 UTC

/* Compile and run with something like:
 * gcc -Wall -g semtest.c -lpthread -o semtest
 * valgrind --tool=memcheck ./semtest
 */

#include <stdio.h>
#include <stdlib.h>
#include <sched.h>
#include <pthread.h>
#include <semaphore.h>
#include <string.h>

/* we show output every N loops to show we're still alive */
#define N 500000

/* sem is used to coordinate the waiter and the poster */
sem_t sem;

/* varsem is the semaphore created and destroyed */
sem_t *varsem;


/* thread 2 */
void *waiter(void *unused) {
	unsigned int count = 0;
	for (;;) {
		/* create a semaphore */
		varsem = malloc(sizeof(sem_t));
		sem_init(varsem, 0, 0);

		/* let the poster know he can post */
		sem_post(&sem);

		/* wait for poster's post */
		while (sem_wait(varsem) != 0)
			perror("sem_wait() in waiter");

		/* destroy the semaphore */
		if (sem_destroy(varsem) != 0) {
			perror("destroy failed");
		}

		/* trash the semaphore memory before freeing it */
		memset(varsem, '\1', sizeof(sem_t));

		free(varsem);

		count++;
		if ((count % N) == 0) {
			printf("waiter\t%u\n", count);
			fflush(stdout);
		}
	}
}

/* thread 3 */
void *poster(void *unused) {
	unsigned int count = 0;
	for (;;) {
		/* wait for waiter's notification that we can post varsem */
		while (sem_wait(&sem) != 0)
			perror("sem_wait() in poster");

		/* post varsem */
		if (sem_post(varsem) != 0) {
			perror("sem_post() in poster");
			exit(1);
		}

		count++;
		if ((count % N) == 0) {
			printf("poster\t%u\n", count);
			fflush(stdout);
		}

	}
}


int main(void) {
	pthread_t t1, t2;

	sem_init(&sem, 0, 0);
	printf("sem: %p\n", &sem);
	fflush(stdout);

	pthread_create(&t1, NULL, &waiter, NULL);
	pthread_create(&t2, NULL, &poster, NULL);

	pthread_join(t1, NULL);
	pthread_join(t2, NULL);

	sem_destroy(&sem);
	return 0;
}