十五、读写锁ReentrantReadWriteLock

一、简介

有时候我们对资源的修改操作非常地少，但是读取的频率却很高。如果采用一般的互斥锁，那么大量的读取操作也需要做等待。基于读写分离的思想，我们可以使用JDK的读写锁来处理这种情况。

1）读读不互斥；

2）读写互斥。

3）写写互斥

JDK文档地址：http://tool.oschina.net/uploads/apidocs/jdk-zh/java/util/concurrent/locks/ReentrantReadWriteLock.html

二、代码示例

import java.util.concurrent.locks.ReentrantReadWriteLock;

public class ReadWriteLockDemo {
    private static ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
    private static ReentrantReadWriteLock.ReadLock readLock = lock.readLock();
    private static ReentrantReadWriteLock.WriteLock writeLock = lock.writeLock();

    private static void read() {
        for (int i = 0; i < 2; i++) {
            int finalI = i;
            new Thread(() -> {
                readLock.lock();
                try {
                    System.out.println("get read lock i=" + finalI);
                    Thread.sleep(1000);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                readLock.unlock();
            }).start();
        }
    }

    public static void write() {
        new Thread(() -> {
            writeLock.lock();
            System.out.println("get write lock");
            try {
                Thread.sleep(2000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            writeLock.unlock();
        }).start();
    }

    public static void main(String[] args) throws InterruptedException {
        write();
        read();
    }
}