Nov 15 2014

TryLock

《Java并发编程实战》这本书的缺点是有些例子给的不完整，所以想直接复制代码、运行看结果还是比较费力的，第13章显示锁的一个例子就是这样。在这种情况下，只能自己写或求助于互联网。下面用网上的一个小例子演示带有超时功能的tryLock的基本用法。关于Lock和同步代码块的区别以及更深入的研究，后续博文会有所涉及。

package com.freelemon.concurrency.chp13;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

/**
 * Created with IntelliJ IDEA.
 * User: hongbin
 * Date: 14-11-15
 * Time: 上午11:41
 * To change this template use File | Settings | File Templates.
 */
public class ReentrantLockingDemo {
    private final Lock lock = new ReentrantLock();

    public static void main(final String... args){
        new ReentrantLockingDemo().go();
    }

    private void go(){
        new Thread(newRunnable(), "Thread-1").start();
        new Thread(newRunnable(), "Thread-2").start();
    }

    private Runnable newRunnable(){
        return new Runnable(){

            @Override
            public void run() {
                do{
                    try{
                        if (lock.tryLock(500, TimeUnit.MILLISECONDS)){
                            try{
                                System.out.println("Locked thread " + Thread.currentThread().getName());
                                Thread.sleep(1000);
                            } finally {
                                lock.unlock();
                                    System.out.println("unlocked locked thread " + Thread.currentThread().getName());
                            }
                            break;
                        } else {
                            System.out.println("unable to lock thread " + Thread.currentThread().getName() + ", will try again.");
                        }
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                } while(true);
            }
        };
    }
}

运行结果如下：

Locked thread Thread-2
unable to lock thread Thread-1, will try again.
unlocked locked thread Thread-2
Locked thread Thread-1
unlocked locked thread Thread-1

参考资料

• Credit属于 http://robaustin.wikidot.com/reentrantlock

PS

• 上一篇谈到了CountDownLatch和CyclicBarrier，例子代码详见https://github.com/hongbinzuo/dojo/blob/master/src/com/freelemon/concurrency/countdownlatch/CountDownLatchTest.java 和 https://github.com/hongbinzuo/dojo/blob/master/src/com/freelemon/concurrency/cyclicbarrier/GameBarrier.java

Java, Concurrency