C++ pthread cond_wait 和 cond_broadcast的使用

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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。


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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:

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