读写锁ReentrantReadWriteLock的使用

package com.thread.test.Lock;

import java.util.Random;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class ReadWriteLockDemo {

    private int value;

    public Object handleRead(Lock lock) throws InterruptedException {
        try {
            lock.lock();// 模拟读操作
            Thread.sleep(1000);// 假设单个读操作耗时1s,读操作的耗时越多，读写锁的优势越明显
            return value;
        } finally {
            lock.unlock();
        }
    }

    public void handleWrite(Lock lock, int index) throws InterruptedException {
        try {
            lock.lock();// 模拟写操作
            Thread.sleep(1000);// 假设单个写操作耗时1s
            value = index;
        } finally {
            lock.unlock();
        }
    }

    private static Lock lock = new ReentrantLock();// 普通的重入锁
    private static ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();// 读写锁
    private static Lock readLock = readWriteLock.readLock();// 读锁
    private static Lock writeLock = readWriteLock.writeLock();// 写锁
    // 读写锁中：允许多个线程读，所以18个读线程是完全并行的；
    // 读写锁中：读-写互斥，及读阻塞写，写阻塞读；写写互斥，写写阻塞。所以两个写线程实际是串行的
    // 所以用读写锁，整个操作耗时大概2s就结束了
    // 如果用普通的重入锁，那么这20个线程都是串行执行的，耗时大概20s

    public static void main(String[] args) {
        final ReadWriteLockDemo demo = new ReadWriteLockDemo();
        Runnable readRunnable = new Runnable() {
            public void run() {
                try {
                    demo.handleRead(readLock);// 读锁
                    // demo.handleRead(lock);//普通的重入锁
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };

        Runnable writeRunnable = new Runnable() {
            public void run() {
                try {
                    demo.handleWrite(writeLock, new Random().nextInt());// 写锁
                    // demo.handleWrite(lock, new Random().nextInt());//普通的重入锁
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        };
        for (int i = 0; i < 18; i++) {
            new Thread(readRunnable).start();// 开启18个读线程
        }
        for (int j = 18; j < 20; j++) {
            new Thread(writeRunnable).start();// 开启2个写线程
        }
    }
}