ReentrantReadWriteLock的使用

ReentrantReadWriteLock的使用很简单，它其实是ReentrantLock的升级版，在并发读写的时候应用广泛。

它提供了获取读锁和写锁的方法，在调用读写锁的时候，读锁可以并发同时调用，但是写锁只能一个线程调用其他线程等待。

import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;

public class UseReentrantReadWriteLock {
	//读写锁对象
	private ReentrantReadWriteLock rwLock = new ReentrantReadWriteLock();
	//获得读锁
	private ReadLock readLock = rwLock.readLock();
	//获得写锁
	private WriteLock writeLock = rwLock.writeLock();
	
	public void read() {
		readLock.lock();
		try {
			System.err.println("线程 " + Thread.currentThread().getName() + " 进入了读方法。。。");
			Thread.sleep(3000);
			System.err.println("线程 " + Thread.currentThread().getName() + " 推出了读方法。。。");
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			readLock.unlock();
		}
	}
	
	public void write() {
		readLock.lock();
		try {
			System.err.println("线程 " + Thread.currentThread().getName() + " 进入了写方法。。。");
			Thread.sleep(3000);
			System.err.println("线程 " + Thread.currentThread().getName() + " 执行了写方法。。。");
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			readLock.unlock();
		}
	}
	
	public static void main(String[] args) {
		UseReentrantReadWriteLock urwLock = new UseReentrantReadWriteLock();
		
		Thread t1 = new Thread(new Runnable() {
			@Override
			public void run() {
				urwLock.read();
			}
		}, "t1");
		
		Thread t2 = new Thread(new Runnable() {
			@Override
			public void run() {
				urwLock.read();
			}
		}, "t2");
		
		Thread t3 = new Thread(new Runnable() {
			@Override
			public void run() {
				urwLock.write();
			}
		}, "t3");
		
		t1.start();
		t2.start();
		t3.start();
	}
}

测试：

1、注释t3.start();，只测试读结果如下：

2、注释t1.start();，测试读写结果如下：只有线程3执行完了之后线程2才能获取到锁执行