Java notify() and notifyAll() test

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]