Java notify() and notifyAll() test

最新推荐文章于 2024-01-06 16:00:03 发布

最新推荐文章于 2024-01-06 16:00:03 发布 · 98 阅读

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本文通过具体示例对比了Java中线程同步方法notify与notifyAll的区别。演示了如何使用这两种方法来唤醒等待中的线程，并解释了它们的工作原理及对线程调度的影响。

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程序会启动20个线程，20个线程都使用同一个sync的object（名字为SYNC）。线程启动代码如下：

final TC[] ts = new TC[20];
        for (int i = 0; i < ts.length; i++) {
            TC target = new TC("TC " + i, SYNC1);
            Thread thread = new Thread(target);
            ts[i] = target;
            thread.start();
}

------------------------------------------------------------
接下来马上启动另外一个线程用于做notify操作。


// 一个用于停止的Thread
        new Thread(new Runnable() {
            public void run() {
                synchronized (SYNC1) {
                    int i = 10;
                    while (i > 0) {
                        System.out.println("Now will notify the thread " + i);
                        ts[i].notifySelf();
                        try {
                            SYNC1.wait(10000);
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                        i--;
                    }
                }
            }
 }).start();

------------------------------------------------------------


启动的ＴＣ线程代码如下：

class TC implements Runnable {

    private final String name;

    private final Object sync;

    private boolean isRunning = false;

    public TC(String name, Object sync) {
        this.name = name;
        this.sync = sync;
    }

    public void run() {
        synchronized (sync) {
            while (true) {
                // 每个线程默认都加入线程池排队。这样有助于打乱线程在主线程中启动的顺序，方便后面的观测。
                if (!isRunning) {
                    try {
                        sync.wait(1000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    isRunning = true;
                }
                System.out.println(name + " Running .......");
                try {
                    sync.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }// Wait 1 second
            }
        }
    }

    public void notifySelf() {
        synchronized (sync) {
            System.out.println("Coming to notify the thread " + name);
            sync.notify();
        }

    }

}

---------------------------分割线---------------------------------

输出日志如下（//部分是我加的注释，不是实际输出）：

[color=darkred]Now will notify the thread 10 //首先试着notify第10个TC
Coming to notify the thread TC 10 // 也确实调用了SYNC的notify操作，但是因为当前还没有任何线程在wait，所以这个notify信号就被丢弃掉了。这个notify过去就过去了。不会影响后面的任何操作了。
TC 1 Running .......
TC 5 Running .......
TC 0 Running .......
TC 2 Running .......
TC 4 Running .......
TC 6 Running .......
TC 8 Running .......
TC 10 Running .......
TC 12 Running .......
TC 14 Running .......
TC 7 Running .......
TC 9 Running .......
TC 11 Running .......
TC 13 Running .......
TC 15 Running .......
TC 17 Running .......
TC 3 Running .......
TC 18 Running .......
TC 16 Running .......
TC 19 Running ....... //启动20线程，这20个线程启动的顺序已经被打乱了。不会从头到尾1-20的启动，而是如log显示1,5,0,2,4,6,8,10,12,14.........
//每个线程启动后会被wait(). wait的顺序是1,5,0,2,4,6,8,10,12,14.........
Now will notify the thread 9
Coming to notify the thread TC 9
TC 1 Running .......
Now will notify the thread 8
Coming to notify the thread TC 8
TC 5 Running .......
Now will notify the thread 7
Coming to notify the thread TC 7
TC 0 Running .......
Now will notify the thread 6
Coming to notify the thread TC 6
TC 2 Running .......
Now will notify the thread 5
Coming to notify the thread TC 5
TC 4 Running .......
Now will notify the thread 4
Coming to notify the thread TC 4
TC 6 Running .......
Now will notify the thread 3
Coming to notify the thread TC 3
TC 8 Running .......
Now will notify the thread 2
Coming to notify the thread TC 2
TC 10 Running .......
Now will notify the thread 1
Coming to notify the thread TC 1
TC 12 Running .......
//总共10个notify操作，但是因为启动的时候一个notify因为没有任何wait的线程给丢弃了，所以，这里只有9个notify起到了作用。他们是按照进入pool的顺序排队给notify。
//一个notify操作仅仅激活一个wait队列中的第一个线程。一对一操作。[/color]

-------------------------------分割线------------------------------
使用notifyAll代替notify。

日志输出：

[color=darkred]Now will notify the thread 10
Coming to notify the thread TC 10 //第一个notifyAll的操作还是被丢弃了
TC 0 Running .......
TC 1 Running .......
TC 3 Running .......
TC 5 Running .......
TC 7 Running .......
TC 9 Running .......
TC 11 Running .......
TC 13 Running .......
TC 15 Running .......
TC 17 Running .......
TC 19 Running .......
TC 2 Running .......
TC 4 Running .......
TC 6 Running .......
TC 8 Running .......
TC 10 Running .......
TC 12 Running .......
TC 14 Running .......
TC 16 Running .......
TC 18 Running .......
Now will notify the thread 9
Coming to notify the thread TC 9 //一个notifyAll的操作notify所以正在wait的线程。
TC 0 Running .......
TC 1 Running .......
TC 3 Running .......
TC 5 Running .......
TC 7 Running .......
TC 9 Running .......
TC 11 Running .......
TC 2 Running .......
TC 13 Running .......
TC 15 Running .......
TC 4 Running .......
TC 17 Running .......
TC 19 Running .......
TC 6 Running .......
TC 8 Running .......
TC 10 Running .......
TC 12 Running .......
TC 14 Running .......
TC 16 Running .......
TC 18 Running .......
[/color]