A线程读取，B线程打印-优快云博客

本文链接：https://blog.youkuaiyun.com/Orlaithe/article/details/129326663

该程序演示了一个使用POSIX线程（pthread）进行文件读写的同步示例。两个线程callBack1和callBack2分别负责读取文件和写入标准输出。它们通过互斥锁(mutex)和条件变量(cond)进行同步，确保在读写操作间正确切换。主函数创建并启动这两个线程，读取名为./copy.c的文件内容并显示在终端。

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#include "head.h"
ssize_t res,res_w;
int fd_r;
char buf[20]="";
int flag=0;
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t cond=PTHREAD_COND_INITIALIZER;
void* callBack1(void* arg)
{
	lseek(fd_r,0,SEEK_SET);
	while(1)
	{
		//设置flag开关选择
		pthread_mutex_lock(&mutex);
		if(flag!=0)
		{
			pthread_cond_wait(&cond,&mutex);
		}
		res=read(fd_r,buf,sizeof(buf));
		flag=1;
		pthread_cond_signal(&cond);
		pthread_mutex_unlock(&mutex);
		if(0==res)
			break;
	}
	pthread_exit(NULL);

}
void* callBack2(void* arg)
{
	while(1)
	{
		pthread_mutex_lock(&mutex);
		if(flag!=1)
		{
			pthread_cond_wait(&cond,&mutex);
		}
		res_w=write(1,buf,res);
		flag=0;
		pthread_cond_signal(&cond);
		pthread_mutex_unlock(&mutex);
		if(res_w==0)
			break;
	}
	pthread_exit(NULL);
}
int main(int argc, const char *argv[])
{
	fd_r=open("./copy.c",O_RDONLY);
//	size=lseek(fd_r,0,SEEK_END);
	pthread_mutex_init(&mutex,NULL);
	pthread_cond_init(&cond,NULL);
	pthread_t tid1;
	if(pthread_create(&tid1,NULL,callBack1,NULL)!=0)
	{
		fprintf(stderr,"pthread_create failed __%d__\n",__LINE__);
		return -1;
	}
	pthread_t tid2;
	if(pthread_create(&tid2,NULL,callBack2,NULL)!=0)
	{
		fprintf(stderr,"pthread_create failed __%d__\n",__LINE__);
		return -1;
	}
	pthread_join(tid1,NULL);
	pthread_cancel(tid2);
	close(fd_r);
	pthread_mutex_destroy(&mutex);
	pthread_cond_destroy(&cond);
	return 0;
}