Java语言ReadWriteLock特性实例测试

Java语言ReadWriteLock特性实例测试

本文研究的主要是ReadWriteLock特性，具体如下。

ReadWriteLock几点特性

readLock 与 readLock 不互斥

readLock 与 writeLock 互斥

writeLock 与 readLock 互斥

writeLock 与 writeLock 互斥

举例来说:

线程1, 先拿到readLock, 线程2试图拿readLock, 可以拿到

线程1, 先拿到readLock, 线程2试图拿writeLock, 阻塞等待,直到线程1释放锁之后才可以拿到

线程1, 先拿到writeLock,线程2试图拿readLock, 阻塞等待,直到线程1释放锁之后才可以拿到

线程1, 先拿到writeLock,线程2试图拿writeLock, 阻塞等待,直到线程1释放锁之后才可以拿到

测试代码

package com.alioo.lock;

import java.text.SimpleDateFormat;

import java.util.Date;

import java.util.concurrent.locks.Lock;

import java.util.concurrent.locks.ReadWriteLock;

import java.util.concurrent.locks.ReentrantReadWriteLock;

/**

*

*/

public class ReadWriteLockDemo {

static SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss.SSS");

public static void main(String[] args) {

Data data = new Data();

Worker t1 = new Worker(data, false);

//写

Worker t2 = new Worker(data, true);

//读

Worker t3 = new Worker(data, true);

//读

t1.start();

t2.start();

t3.start();

}

static class Worker extends Thread {

Data data;

Boolean read;

public Worker(Data data, Boolean read) {

this.data = data;

this.read = read;

}

public void run() {

if (read)

data.read(); else

data.write();

}

}

static class Data {

ReadWriteLock lock = new ReentrantReadWriteLock();

Lock read = fkFOwuVAplock.readLock();

Lock write = lock.writeLock();

public void write() {

try {

Thread.sleep(2000);

//

}

catch (Exception e) {

}

write.lock();

System.out.println(Thread.currentThread() + " write:begin "

+ sdf.format(new Date()));

try {

Thread.sleep(5000);

//

}

catch (Exception e) {

}

finally {

System.out.println(Thread.currentThread() + " write:end "

+ sdf.format(new Date()));

write.unlock();

}

}

public int read() {fkFOwuVAp

read.lock();

System.out.println(Thread.currentThread()+ " read :begin "

+ sdf.format(new Date()));

try {

Thread.sleep(5000);

//

}

catch (Exception e) {

}

finally {

System.out.println(Thread.currentThread() + " read :end "

+ sdf.format(new Date()));

read.unlock();

}

return 1;

}

}

}

测试结果:

Thread[Thread-2,5,main] read :begin 2018-01-22 13:54:16.794

Thread[Thread-1,5,main] read :begin 2018-01-22 13:54:16.794

Thread[Thread-2,5,main] read :end 2018-01-22 13:54:21.795

Thread[Thread-1,5,main] read :end 2018-01-22 13:54:21.795

Thread[Thread-0,5,main] write:begin 2018-01-22 13:54:21.79fkFOwuVAp5

Thread[Thread-0,5,main] write:end 2018-01-22 13:54:26.795

测试结果解读:

同时启动了3个线程,其中1号线程Thread[Thread-0,5,main],执行fkFOwuVApwrite时先休眠了2秒.那么 2,3号线程Thread[Thread-1,5,main],Thread[Thread-2,5,main]将会优先执行代码

read.lock();

由于read.lock();是不互斥的(即可重入的),所以他们同时拿到了锁,通过日志可以看出来

Thread[Thread-2,5,main] read :begin 2018-01-22 13:54:16.794

Thread[Thread-1,5,main] read :begin 2018-01-22 13:54:16.794

而且他们执行的时间开销是相同的(测试代码中都是休眠5秒),所以也将同时执行结束

Thread[Thread-2,5,main] read :end 2018-01-22 13:54:21.795

Thread[Thread-1,5,main] read :end 2018-01-22 13:54:21.795

只有当所有的readLock被释放掉之后,writeLock才能拿到锁,而这个时候Thread[Thread-1,5,main],Thread[Thread-2,5,main]执行结束后就会释放锁readLock

所以Thread[Thread-0,5,main]这个时候拿到了writeLock并执行自己的业务代码

Thread[Thread-0,5,main] write:begin 2018-01-22 13:54:21.795

Thread[Thread-0,5,main] write:end 2018-01-22 13:54:26.795

总结

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