pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex);

分析：

  •  函数作用：阻塞等待一个条件变量
  • 阻塞等待条件变量cond(参数1)满足
  • 释放已掌握的互斥锁(解锁互斥量)，相当于pthread_mutex_unlock(&mutex); {1、2两步为一个原子操作}
  • 当被唤醒，pthread_cond_wait函数返回，解除阻塞并重新获取互斥锁pthread_mutex_lock(&mutex);

 1. 示例

 1 #include <pthread.h> 
 2 #include <unistd.h>
 3 #include <stdlib.h>
 4 #include <stdio.h>
 5  
 6 struct msg
 7 {
 8     struct msg *next;
 9     int num;
10 };
11  
12 struct msg *head;
13 struct msg *mp;
14  
15 pthread_cond_t has_product = PTHREAD_COND_INITIALIZER;  //静态初始化：一个条件变量和一个互斥量 
16 pthread_mutex_t lock = PTHREAD_MUTEX_INITIALIZER;
17  
18 void *consumer(void *p)
19 {
20     for (; ;)
21     {
22         pthread_mutex_lock(&lock);
23         while (head == NULL)                           //头指针为空，说明没有节点 可以为if吗 
24             pthread_cond_wait(&has_product, &lock);
25         mp = head;
26         head = mp->next;                               //模拟消费掉一个产品
27         pthread_mutex_unlock(&lock);
28         printf("-consume-----%d\n", mp->num);
29         free(mp);
30         sleep(rand() % 5);
31     }
32 }
33  
34 void *producer(void *p)
35 {
36     for (; ;) 
37     {
38         mp = malloc(sizeof(struct msg));
39         mp->num = rand() % 1000 + 1;                  //模拟生产一个产品
40         printf("-Produce----%d\n", mp->num);
41  
42         pthread_mutex_lock(&lock);
43         mp->next = head;
44         head = mp;
45         pthread_mutex_unlock(&lock);
46  
47         pthread_cond_signal(&has_product);          //将等待在该条件变量上的一个线程唤醒
48         sleep(rand() % 5);
49     }
50 }
51  
52 int main()
53 {
54     pthread_t pid, cid;
55     srand(time(NULL));
56     pthread_create(&pid, NULL, producer, NULL);
57     pthread_create(&cid, NULL, consumer, NULL);
58     pthread_join(pid, NULL);
59     pthread_join(cid, NULL);
60     return 0;
61 }