Wed, 31 Oct 2012 09:19:00 GMT

CountDownLatch如其所写，是一个倒计数的锁存器，当计数减�?时触发特定的事�g。利用这�U�特性，可以让主�U�程�{�待子线�E�的�l�束。下面以一个模拟运动员比赛的例子加以说明�?/div>

import java.util.concurrent.CountDownLatch;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Test {
    private static final int PLAYER_AMOUNT = 5;

    public static void main(String[] args) {
        //对于每位�q�动员，CountDownLatch�?后即�l�束比赛
        CountDownLatch begin = new CountDownLatch(1);
        //对于整个比赛�Q�所有运动员�l�束后才��结�?/span>
        CountDownLatch end = new CountDownLatch(PLAYER_AMOUNT);
        Player[] plays = new Player[PLAYER_AMOUNT];

        for (int i = 0; i < PLAYER_AMOUNT; i++)
            plays[i] = new Player(i + 1, begin, end);

        //讄��特定的线�E�池�Q�大��ؓ(f��)5
        ExecutorService exe = Executors.newFixedThreadPool(PLAYER_AMOUNT);
        for (Player p : plays)
            exe.execute(p); //分配�U�程
        begin.countDown();
        System.out.println("Race begins!");
        try {
            end.await(); //�{�待end状态变�?�Q�即为比赛结�?/span>
        } catch (InterruptedException e) {
            // TODO: handle exception
            e.printStackTrace();
        } finally {
            System.out.println("Race ends!");
        }
        exe.shutdown();
    }
}

class Player implements Runnable {

    private int id;
    private CountDownLatch begin;
    private CountDownLatch end;

    public Player(int i, CountDownLatch begin, CountDownLatch end) {
        // TODO Auto-generated constructor stub
        super();
        this.id = i;
        this.begin = begin;
        this.end = end;
    }

    public void run() {
        // TODO Auto-generated method stub
        try {
            begin.await(); //�{�待begin的状态�ؓ(f��)0
            Thread.sleep((long) (Math.random() * 100)); //随机分配旉��Q�即�q�动员完成时�?/span>
            System.out.println("Play" + id + " arrived.");
        } catch (InterruptedException e) {
            // TODO: handle exception
            e.printStackTrace();
        } finally {
            end.countDown(); //使end状态减1�Q�最�l�减�?
        }
    }
}

synchronized(this) 解释

Thu, 27 Sep 2012 08:03:00 GMT

public class DemoThread implements Runnable {
    public void run() {
        synchronized(this) {            //请问�q�里的this怎样理解�Q�t1和t2的地址不是不一样嘛�Q�怎么�?x��)只有一个线�E�运行？�Q�？
            for (int i = 0; i < 5; i++) {
                System.out.println(Thread.currentThread().getName() + " synchronized loop " + i);
            }
         }
    }

    public static void main(String[] args) {
        DemoThread t1 = new DemoThread();
        Thread ta = new Thread(t1, "A");
        Thread tb = new Thread(t1, "B");
        ta.start();
        tb.start();
    }
}

    解释�Q?br />    �q�里的this是指当前对象,也就是说不管ta�q�是tb,刚开始运行这�D�代码的时候会(x��)�l�这�D�代码加个锁,�q�样即�ɘq�行��C��间被替换�?
另一个线�E�也不会(x��)执行�q�段代码,因�ؓ(f��)�q�段代码加锁�?而钥匙在�l�代码加锁的那个�U�程手里,只有加锁的线�E�运行完�q�段代码,才会(x��)�l�代码解�?
然后其他�U�程才能执行�q�段代码..  加个synchronized(this)以后�q�行�l�果是这�? 
A synchronized loop 0 
A synchronized loop 1 
A synchronized loop 2 
A synchronized loop 3 
A synchronized loop 4 
B synchronized loop 0 
B synchronized loop 1 
B synchronized loop 2 
B synchronized loop 3 
B synchronized loop 4  

不加的话是这�?(��序�׃��,有好多种�l�果,�q�里只是其中一�U?.. 
A synchronized loop 0 
B synchronized loop 0 
A synchronized loop 1 
B synchronized loop 1 
A synchronized loop 2 
B synchronized loop 2 
A synchronized loop 3 
B synchronized loop 3 
B synchronized loop 4 
A synchronized loop 4

��一败涂�?/a> 2012-09-27 16:03 发表评论

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synchronized(this) 解释