pthread_cond_wait 和 pthread_cond_signal 用法

#include <pthread.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>

#define err(msg) perror(msg)

static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;

static int running = 1;

static void * wait_thread(void *arg)
{
        pthread_mutex_lock(&mutex);
        while (running)
                pthread_cond_wait(&cond, &mutex);
        pthread_mutex_unlock(&mutex);

        printf("receive signal.\n");
}

static void * signal_thread(void *arg)
{
        sleep(3);

        pthread_mutex_lock(&mutex);
        running = 0;
        pthread_cond_signal(&cond);
        pthread_mutex_unlock(&mutex);
}

int main(void)
{
        pthread_t t1, t2;

        if (pthread_create(&t1, NULL, wait_thread, NULL) != 0) {
                err("pthread_create");
                goto err;
        }

        if (pthread_create(&t2, NULL, signal_thread, NULL) != 0) {
                err("pthread_create");
                goto err;
        }

        while (running)
                sleep(1);

        return 0;
err:
        return -1;
}