pthread_cond_broadcast与pthread_cond_signal的区别——linuxc

柔情只为你懂 2022-10-16 03:00 128阅读 0赞

转载：[https://blog.csdn.net/afootball/article/details/107937516][https_blog.csdn.net_afootball_article_details_107937516]

pthread\_cond\_signal——唤醒睡眠的线程，一次只能唤醒一个线程  
pthread\_cond\_broadcast——唤醒睡眠的线程，一次唤醒所有睡眠的线程

**理解:**

1.  pthread\_cond\_wait函数是**解锁等待**（即：函数被调用后，互斥锁是出于解锁状态的。）这也是为什么demon1中，两个线程都加锁了，但是进入睡眠的打印信息都打印出来了，因为线程1调用该函数后，将锁解开了。
2.  pthread\_cond\_wait函数是解锁等待，也就是说，在该函数调用前必须要加锁，否则就谈不上解锁。那么pthread\_cond\_signal函数的调用过程中是否必须加锁呢？？？
3.  以下示例的用法，未加任何判断条件的wait,阻塞，可以用作是线程间的通信，有点象Qt中的信号与槽的操作。
4.  pthread\_cond\_signal函数每次唤醒的线程未知，故此函数使用时，是针对一个生产者对应一个消费者的问题。
5.

demon1——pthread\_cond\_signal

#include <stdio.h>
    #include <pthread.h>
    
    static pthread_t thread1;
    static pthread_t thread2;
    
    //静态初始化
    static pthread_mutex_t lock=PTHREAD_MUTEX_INITIALIZER;
    static pthread_cond_t cond=PTHREAD_COND_INITIALIZER;
    
    void *function1()
    
    {
    	while(1)
    	{
    		pthread_mutex_lock(&lock);
    		printf("=====  线程1进入睡眠        ====\n");
    		pthread_cond_wait(&cond,&lock);
    		printf("====  线程1    唤醒    ====\n");
    		pthread_mutex_unlock(&lock);
    	}
    }
    
    void *function2()
    
    {
    	while(1)
    	{
    		pthread_mutex_lock(&lock);
    		printf("=====  线程2进入睡眠        ====\n");
    		pthread_cond_wait(&cond,&lock);
    		printf("====  线程2    唤醒    ====\n");
    		pthread_mutex_unlock(&lock);
    	}
    }
    
    
    int main()
    {
    	int i=0;
    	if(-1==pthread_create(&thread1,NULL,function1,NULL))
    	{
    		printf("thread_create1 fail!\n");
    		pthread_detach(thread1);
    	}
    
    	if(-1==pthread_create(&thread2,NULL,function2,NULL))
    	{
    		printf("thread_create fail!\n");
    		pthread_detach(thread1);
    	}
    
    	while(1)
    	{
    		sleep(2);
    		i++;
    		printf("\n 第%d次唤醒\n",i);
    		pthread_mutex_lock(&lock);
    		if(-1==pthread_cond_signal(&cond))
    		{
    			printf("pthread_cond_broadcast error!\n");
    		}
    		pthread_mutex_unlock(&lock);
    	}
    	return 0;
    }

运行结果：

![å¨è¿éæå¥å¾çæè¿°][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Fmb290YmFsbA_size_16_color_FFFFFF_t_70]

demon2——pthread\_cond\_broadcast

#include <stdio.h>
    #include <pthread.h>
    
    static pthread_t thread1;
    static pthread_t thread2;
    
    //静态初始化
    static pthread_mutex_t lock=PTHREAD_MUTEX_INITIALIZER;
    static pthread_cond_t cond=PTHREAD_COND_INITIALIZER;
    
    void *function1()
    
    {
    	while(1)
    	{
    		pthread_mutex_lock(&lock);
    		printf("=====  线程1进入睡眠        ====\n");
    		pthread_cond_wait(&cond,&lock);
    		printf("====  线程1    唤醒    ====\n");
    		pthread_mutex_unlock(&lock);
    	}
    }
    
    void *function2()
    
    {
    	while(1)
    	{
    		pthread_mutex_lock(&lock);
    		printf("=====  线程2进入睡眠        ====\n");
    		pthread_cond_wait(&cond,&lock);
    		printf("====  线程2    唤醒    ====\n");
    		pthread_mutex_unlock(&lock);
    	}
    }
    
    
    int main()
    {
    	int i=0;
    	if(-1==pthread_create(&thread1,NULL,function1,NULL))
    	{
    		printf("thread_create1 fail!\n");
    		pthread_detach(thread1);
    	}
    
    	if(-1==pthread_create(&thread2,NULL,function2,NULL))
    	{
    		printf("thread_create fail!\n");
    		pthread_detach(thread1);
    	}
    
    	while(1)
    	{
    		sleep(2);
    		i++;
    		printf("\n 第%d次唤醒\n",i);
    		pthread_mutex_lock(&lock);
    		if(-1==pthread_cond_broadcast(&cond))
    		{
    			printf("pthread_cond_broadcast error!\n");
    		}
    		pthread_mutex_unlock(&lock);
    	}
    	return 0;
    }

运行结果：  
![å¨è¿éæå¥å¾çæè¿°][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Fmb290YmFsbA_size_16_color_FFFFFF_t_70 1]

对比运行结果，清楚的可以发现pthread\_cond\_broadcast可以唤醒所有睡眠的线程

[https_blog.csdn.net_afootball_article_details_107937516]: https://blog.csdn.net/afootball/article/details/107937516
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Fmb290YmFsbA_size_16_color_FFFFFF_t_70]: /images/20221014/7e8dcc7359034e77a5878eaaffca3fb8.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2Fmb290YmFsbA_size_16_color_FFFFFF_t_70 1]: /images/20221014/c3152deb16aa43ca98aca42b18fe4fdf.png