Java 多线程高并发 3.5 — ReadWriteLock 读写锁使用

ReadWriteLock 又称为共享锁，的读写分离锁，内部分为读锁和写锁

关于 A 和 B 线程，读和写的关系

A 读 — B 读：不互斥、不阻塞
A 读 — B 写：互斥，互相阻塞
A 写 — B 写：互斥，互相阻塞

用法：非常简单，和 ReentrantLock 一样

public class TestReadWriteLock {
	
	// 实例化读写锁
	private static final ReadWriteLock readWriteLock = new ReentrantReadWriteLock();	
	private static final Lock readLock = readWriteLock.readLock();	
	private static final Lock writeLock = readWriteLock.writeLock();	
	private static int count = 0;
	
	static class ReadThread implements Runnable {
		@Override
		public void run() {
			readLock.lock();
			try {
				System.out.println(System.currentTimeMillis() + " : " + Thread.currentThread().getName() + " 进来了: count = " + count);
				Thread.sleep(2000);
			} catch (Exception e) {
			} finally {
				readLock.unlock();
			}
		}
	}
	
	static class WriteThread implements Runnable {
		@Override
		public void run() {
			writeLock.lock();
			try {
				System.out.println(System.currentTimeMillis() + " : " + Thread.currentThread().getName() + " 进来了: count = " + (++count));
				Thread.sleep(2000);
			} catch (Exception e) {
			} finally {
				writeLock.unlock();
			}
		}
	}
	
	public static void main(String[] args) throws InterruptedException {
		System.out.println("======开始测试写锁======");
		Thread[] threads = new Thread[10];
		ReadThread read = new ReadThread();
		for (int i = 0; i < threads.length; i++) threads[i] = new Thread(read, "线程 " + i);
		for (int i = 0; i < threads.length; i++) threads[i].start();
		for (int i = 0; i < threads.length; i++) threads[i].join();
		
		System.out.println("\n======开始测试读锁======");
		WriteThread write = new WriteThread();
		for (int i = 0; i < threads.length; i++) threads[i] = new Thread(write, "线程 " + i);
		for (int i = 0; i < threads.length; i++) threads[i].start();
		for (int i = 0; i < threads.length; i++) threads[i].join();
	}
}

输出结果，读锁相当于没有锁
======开始测试写锁======
1537876265912 : 线程 0 进来了: count = 0
1537876265912 : 线程 1 进来了: count = 0
1537876265912 : 线程 2 进来了: count = 0
1537876265912 : 线程 3 进来了: count = 0
1537876265913 : 线程 5 进来了: count = 0
1537876265912 : 线程 4 进来了: count = 0
1537876265913 : 线程 7 进来了: count = 0
1537876265913 : 线程 8 进来了: count = 0
1537876265913 : 线程 6 进来了: count = 0
1537876265913 : 线程 9 进来了: count = 0


======开始测试读锁======
1537876267915 : 线程 0 进来了: count = 1
1537876269916 : 线程 2 进来了: count = 2
1537876271916 : 线程 1 进来了: count = 3
1537876273917 : 线程 4 进来了: count = 4
1537876275918 : 线程 3 进来了: count = 5
1537876277918 : 线程 5 进来了: count = 6
1537876279919 : 线程 6 进来了: count = 7
1537876281919 : 线程 7 进来了: count = 8
1537876283920 : 线程 8 进来了: count = 9
1537876285920 : 线程 9 进来了: count = 10