转自：https://blog.csdn.net/wangzhiyu1980/article/details/44227913
参考:
https://blog.csdn.net/YEYUANGEN/article/details/37593533
https://www.cnblogs.com/secondtonone1/p/5580203.html
一个简单的实例程序，说明pthread_cond_wait 和 pthread_cond_broadcast 的使用方式。
函数定义：
int pthread_cond_wait(pthread_cond_t *cond, pthread_mutex_t *mutex)
int pthread_cond_broadcast(pthread_cond_t *cond)
函数说明：
pthread_cond_wait ：有两个输入参数，一个是pthread_cond_t，是函数将要等待的信号，另一个是 pthread_mutex_t，一个互斥锁。用于对信号量进行保护，防止多个线程同时对其进行操作。在线程开始等待信号量前，必须由本线程对互斥锁进行锁定，然后pthread_cond_wait会更新条件等待队列，并且释放互斥量，允许其他线程进行访问；当cond 满足条件允许线程继续执行时，wait_cond也会先对mutex 进行锁定，对cond进行处理，然后再允许线程继续运行。所以pthread_cond_wait() 后的pthread_mutex_unlock()还是必要的。
实例程序：
#include <pthread.h>
#include <iostream>
#include <unistd.h>
using namespace std;
static pthread_mutex_t mtx=PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t cond=PTHREAD_COND_INITIALIZER;
static void* func_1(void* arg)
{
cout << "func_1 start" << endl;
pthread_mutex_lock(&mtx);
cout << "func_1 lock mtx" << endl;
cout << "func_1 wait cond" << endl;
pthread_cond_wait(&cond, &mtx);
cout << "func_1 unlock mtx" << endl;
pthread_mutex_unlock(&mtx);
cout << "func_1 end" << endl;
sleep(5);
return NULL;
}
static void* func_2(void* arg)
{
cout << "func_2 start" << endl;
pthread_mutex_lock(&mtx);
cout << "func_2 lock mtx" << endl;
cout << "func_2 wait cond" << endl;
pthread_cond_wait(&cond, &mtx);
cout << "func_2 unlock mtx" << endl;
pthread_mutex_unlock(&mtx);
cout << "func_2 end" << endl;
sleep(5);
return NULL;
}
int main()
{
pthread_t tid1, tid2;
cout << "main create thread" << endl;
pthread_create(&tid1, NULL, func_1, NULL);
pthread_create(&tid2, NULL, func_2, NULL);
sleep(3);
cout << "main boradcast signal" << endl;
pthread_cond_broadcast(&cond);
cout << "main join thread" << endl;
pthread_join(tid1, NULL);
pthread_join(tid2, NULL);
cout << "main end" << endl;
return 0;
}
测试结果：
