Java語(yǔ)言ReadWriteLock特性實(shí)例測(cè)試

更新時(shí)間：2018年02月11日 10:52:23 作者：Alioo-壞人

這篇文章主要介紹了Java語(yǔ)言ReadWriteLock特性實(shí)例測(cè)試，分享了相關(guān)代碼示例，小編覺(jué)得還是挺不錯(cuò)的，具有一定借鑒價(jià)值，需要的朋友可以參考下

本文研究的主要是ReadWriteLock特性，具體如下。

ReadWriteLock幾點(diǎn)特性

readLock 與 readLock 不互斥
readLock 與 writeLock 互斥
writeLock 與 readLock 互斥
writeLock 與 writeLock 互斥

舉例來(lái)說(shuō):

線程1, 先拿到readLock, 線程2試圖拿readLock, 可以拿到
線程1, 先拿到readLock, 線程2試圖拿writeLock, 阻塞等待,直到線程1釋放鎖之后才可以拿到
線程1, 先拿到writeLock,線程2試圖拿readLock, 阻塞等待,直到線程1釋放鎖之后才可以拿到
線程1, 先拿到writeLock,線程2試圖拿writeLock, 阻塞等待,直到線程1釋放鎖之后才可以拿到

測(cè)試代碼

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);
		//寫(xiě)
		Worker t2 = new Worker(data, true);
		//讀
		Worker t3 = new Worker(data, true);
		//讀
		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 = lock.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() {
			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;
		}
	}
}

測(cè)試結(jié)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 13:54:21.795
Thread[Thread-0,5,main] write:end 2018-01-22 13:54:26.795

測(cè)試結(jié)果解讀:

同時(shí)啟動(dòng)了3個(gè)線程,其中1號(hào)線程Thread[Thread-0,5,main],執(zhí)行write時(shí)先休眠了2秒.那么 2,3號(hào)線程Thread[Thread-1,5,main],Thread[Thread-2,5,main]將會(huì)優(yōu)先執(zhí)行代碼

read.lock();

由于read.lock();是不互斥的(即可重入的),所以他們同時(shí)拿到了鎖,通過(guò)日志可以看出來(lái)

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

而且他們執(zhí)行的時(shí)間開(kāi)銷(xiāo)是相同的(測(cè)試代碼中都是休眠5秒),所以也將同時(shí)執(zhí)行結(jié)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

只有當(dāng)所有的readLock被釋放掉之后,writeLock才能拿到鎖,而這個(gè)時(shí)候Thread[Thread-1,5,main],Thread[Thread-2,5,main]執(zhí)行結(jié)束后就會(huì)釋放鎖readLock

所以Thread[Thread-0,5,main]這個(gè)時(shí)候拿到了writeLock并執(zhí)行自己的業(yè)務(wù)代碼

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

總結(jié)

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