Linux系统编程_课时86_读写锁练习

课时86_读写锁练习

1、要求

3个线程不定时写同一个全局资源，5个线程不定时读同一个全局资源。

2、不加锁

2.1、不加锁代码

#include <stdio.h> //printf对应的头文件
#include <unistd.h> //usleep对应的头文件
#include <pthread.h> //线程对应的头文件

//全局变量
int number;

void* write_func(void* arg)
{
	//循环写
	while(1)
	{
		number++;
		printf("==write:%lu,%d\n",pthread_self(),number);
		usleep(500);
	}
	return NULL;
}

void* read_func(void* arg)
{
	while(1)
	{
		printf("&&read:%lu,%d\n",pthread_self(),number);
		usleep(500);
	}
	return NULL;
}

//主函数
int main()
{
	//子线程ID
	pthread_t	pthid[8];
	
	//创建3个写线程
	for(int i = 0; i < 3; ++i)
	{
		pthread_create(&pthid[i],NULL,write_func,NULL);
	}
	//创建5个读线程
	for(int i = 3; i < 8; ++i)
	{
		pthread_create(&pthid[i],NULL,read_func,NULL);
	}	
	
	//阻塞，资源回收
	for(int i = 0; i < 8; ++i)
	{
		pthread_join(pthid[i],NULL);
	}
	return 0;
}

2.2、不加锁代码执行结果

&&read:140000195254016,15932
==write:140000228824832,15931

结果分析：
打印number顺序应该从小到大，写操作number=15931后，没有及时打印printf("==write:%lu,%d\n",pthread_self(),number);然后读read到的是写入后的数值15931。如果在printf("==write:%lu,%d\n",pthread_self(),number);代码后解锁，就不会出现打印不及时的情况。

3、加读写锁

3.1、加读写锁代码

#include <stdio.h> //printf对应的头文件
#include <unistd.h> //usleep对应的头文件
#include <pthread.h> //线程对应的头文件

//全局变量
int number;

//创建读写锁
pthread_rwlock_t lock;

void* write_func(void* arg)
{
	//循环写
	while(1)
	{
		//加写锁
		pthread_rwlock_wrlock(&lock);
		number++;
		printf("==write:%lu,%d\n",pthread_self(),number);
		//解锁
		pthread_rwlock_unlock(&lock);
		usleep(50);
	}
	return NULL;
}

void* read_func(void* arg)
{
	while(1)
	{
		//加读锁
		pthread_rwlock_rdlock(&lock);
		printf("&&read:%lu,%d\n",pthread_self(),number);
		//解锁
		pthread_rwlock_unlock(&lock);
		usleep(50);
	}
	return NULL;
}

//主函数
int main()
{
	//子线程ID
	pthread_t	pthid[8];
	
	//初始化读写锁
	pthread_rwlock_init(&lock,NULL);
	//创建3个写线程
	for(int i = 0; i < 3; ++i)
	{
		pthread_create(&pthid[i],NULL,write_func,NULL);
	}
	//创建5个读线程
	for(int i = 3; i < 8; ++i)
	{
		pthread_create(&pthid[i],NULL,read_func,NULL);
	}	
	
	//阻塞，资源回收
	for(int i = 0; i < 8; ++i)
	{
		pthread_join(pthid[i],NULL);
	}
	
	//释放读写锁资源
	pthread_rwlock_destroy(&lock);
	return 0;
}

3.2、加读写锁代码执行结果

没有出现，打印的number先大后小的现象。

==write:140429330933504,9235
==write:140429347718912,9236
&&read:140429314148096,9236
&&read:140429305755392,9236
&&read:140429288969984,9236
&&read:140429322540800,9236
&&read:140429297362688,9236
==write:140429339326208,9237
==write:140429330933504,9238
==write:140429347718912,9239