现在来看一段典型的应用:看注释即可。 - #include <pthread.h>
- #include <unistd.h>
-
- static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
- static pthread_cond_t cond = PTHREAD_COND_INITIALIZER;
-
- struct node {
- int n_number;
- struct node *n_next;
- } *head = NULL;
-
- /*[thread_func]*/
- static void cleanup_handler(void *arg)
- {
- printf("Cleanup handler of second thread./n");
- free(arg);
- (void)pthread_mutex_unlock(&mtx);
- }
- static void *thread_func(void *arg)
- {
- struct node *p = NULL;
-
- pthread_cleanup_push(cleanup_handler, p);
- while (1) {
- pthread_mutex_lock(&mtx); //这个mutex主要是用来保证pthread_cond_wait的并发性
- while (head == NULL) { //这个while要特别说明一下,单个pthread_cond_wait功能很完善,为何这里要有一个while (head == NULL)呢?因为pthread_cond_wait里的线程可能会被意外唤醒,如果这个时候head != NULL,则不是我们想要的情况。这个时候,应该让线程继续进入pthread_cond_wait
- pthread_cond_wait(&cond, &mtx); // pthread_cond_wait会先解除之前的pthread_mutex_lock锁定的mtx,然后阻塞在等待对列里休眠,直到再次被唤醒(大多数情况下是等待的条件成立而被唤醒,唤醒后,该进程会先锁定先pthread_mutex_lock(&mtx);,再读取资源
- //用这个流程是比较清楚的/*block-->unlock-->wait() return-->lock*/
- }
- p = head;
- head = head->n_next;
- printf("Got %d from front of queue/n", p->n_number);
- free(p);
- pthread_mutex_unlock(&mtx); //临界区数据操作完毕,释放互斥锁
- }
- pthread_cleanup_pop(0);
- return 0;
- }
-
- int main(void)
- {
- pthread_t tid;
- int i;
- struct node *p;
- pthread_create(&tid, NULL, thread_func, NULL); //子线程会一直等待资源,类似生产者和消费者,但是这里的消费者可以是多个消费者,而不仅仅支持普通的单个消费者,这个模型虽然简单,但是很强大
- /*[tx6-main]*/
- for (i = 0; i < 10; i++) {
- p = malloc(sizeof(struct node));
- p->n_number = i;
- pthread_mutex_lock(&mtx); //需要操作head这个临界资源,先加锁,
- p->n_next = head;
- head = p;
- pthread_cond_signal(&cond);
- pthread_mutex_unlock(&mtx); //解锁
- sleep(1);
- }
- printf("thread 1 wanna end the line.So cancel thread 2./n");
- pthread_cancel(tid); //关于pthread_cancel,有一点额外的说明,它是从外部终止子线程,子线程会在最近的取消点,退出线程,而在我们的代码里,最近的取消点肯定就是pthread_cond_wait()了。关于取消点的信息,有兴趣可以google,这里不多说了
- pthread_join(tid, NULL);
- printf("All done -- exiting/n");
- return 0;
- }
|