【Linux多线程编程-自学记录】09.Linux多线程之读写锁

Linux多线程编程学习代码（代码已上传gitee，还请各位兄弟点个Star哦！）

https://gitee.com/chenshao777/linux_thread.git

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笔记：
1.读写锁可以避免同一时刻只有一个线程对变量有使用权
phread_rwlock_init()

2.读写锁有三种状态，读加锁、写加锁、不加锁

3.读加锁时，其他线程都可以占用读模式的读写锁
如果此时有线程以写模式对其进行加锁，则会阻塞，而且后来的读模式加锁也会阻塞，防止写锁请求失败

4.写加锁时，线程独占读写锁，其他线程的读写锁请求都会阻塞

5.读加锁模式下，若线程希望写加锁，则会阻塞，直到所有线程释放锁为止

6.读写锁非常适合经常需要读动作的程序

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读模式加锁
int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock);
int pthread_rwlock_tryrdlock(pthread_rwlock_t "rwlock); //尝试加读模式锁，失败则不阻塞
写模式加锁
int pthread_rwlock_wrlock(pthread_rwlock_t "rwlock);
int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);
解锁
int pthread_rwlock_unlock(pthread_rwlock_t *rwlock);
销毁
pthread_rwlock_destroy(pthread_rwlock_t *rwlock);
成功返回0

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spu.h文件

#ifndef _SPU_H_
#define _SPU_H_

#include<stdio.h>
#include<pthread.h>
#include<stdlib.h>
#include<string.h>
#include<unistd.h>
#include<sys/types.h>
#include<signal.h>
#include<errno.h>

#endif

09.thread_rwlock.c文件

/*
  1.创建三个线程，都对 money 全局变量进行操作
  2.线程1每次对 money 加10
  3.线程2每次对 money 加0.01
  4.线程3读取 money 的值
*/

#include "spu.h"

float money;
//定义读写锁
pthread_rwlock_t rwlock;

void *thread_fun1(void *arg)
{
    
    
    while(1)
    {
    
    
        pthread_rwlock_wrlock(&rwlock);  //加写锁
        money += 10;
        printf("01: money = %.2f\n",money);
        pthread_rwlock_unlock(&rwlock);  //解锁
        usleep(500000);  //500ms延时
    }
    return (void*)1;
}

void *thread_fun2(void *arg)
{
    
    
    while(1)
    {
    
    
        pthread_rwlock_wrlock(&rwlock);  //加写锁
        money += 0.01;
        printf("02: money = %.2f\n",money);
        pthread_rwlock_unlock(&rwlock);  //解锁
        usleep(500000); 
    }
	return (void*)2;
}

void *thread_fun3(void *arg)
{
    
    
    while(1)
    {
    
    
        pthread_rwlock_rdlock(&rwlock);  //加读锁
        printf("03: reade money = %.2f\n",money);
        pthread_rwlock_unlock(&rwlock);  //解锁
        usleep(500000);  //500ms延时
    }
	return (void*)3;
}

int main(int argc, char *argv[])
{
    
    	
	int err1, err2, err3;
	pthread_t thread_id1, thread_id2, thread_id3; 

    void *__retval;
    
    //首先初始化读写锁
    pthread_rwlock_init(&rwlock, NULL);

	err1 = pthread_create(&thread_id1, NULL, thread_fun1, NULL);
	if(err1 != 0)
		printf("create thread01 failed!\n");

    err2 = pthread_create(&thread_id2, NULL, thread_fun2, NULL);
	if(err2 != 0)
		printf("create thread02 failed!\n"); 

    err3 = pthread_create(&thread_id3, NULL, thread_fun3, NULL);
	if(err3 != 0)
		printf("create thread03 failed!\n"); 

    sleep(1);
    pthread_exit(__retval);
}