摘要：
pthread_ cond_ wait（pthread_cond_t*秒，pthread_mutex_t*互斥）；分析：函数函数函数：块等待一个条件变量块等待条件变量cond（参数1）释放主互斥锁（解锁互斥锁），相当于pthread_互斥锁解锁（&mutex）；｛步骤1和2是一个原子操作｝当被唤醒时，pthread_cond_wait函数返回、解除锁定并重新获取互斥锁
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 ", 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 ", 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 }