notyfy()和notifyAll()区别

2019-11-09 17:18:56

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wait()方法表示，放弃当前对资源的占有权，等啊等啊，一直等到有人通知我，我才会运行后面的代码。 notify()方法表示，当前的线程已经放弃对资源的占有，通知等待的线程来获得对资源的占有权，但是只有一个线程能够从wait状态中恢复，然后继续运行wait()后面的语句； notifyAll()方法表示，当前的线程已经放弃对资源的占有，通知所有的等待线程从wait()方法后的语句开始运行。读出什么区别没有？上例子，先是一个nofiyAll()的例子：

java代码

package com.thread.wait; public class Wait { PRivate int counter = 0; private String name = null; public Wait(int counter,String name){ this.counter = counter; this.name = name; } public synchronized void doSomthing(){ int tempCounter = --counter; if(tempCounter <= 0){ customizedNotifyAll(); } else { while(tempCounter > 0){ try { System.out.println(Thread.currentThread().getName()+"-<"+name+tempCounter+">"+"will invoke WAIT()"); --tempCounter; wait(); } catch (InterruptedException e) { e.printStackTrace(); notifyAll(); } System.out.println(Thread.currentThread().getName()+"-<"+name+tempCounter+">"+"has been ACTIVED"); } customizedNotifyAll(); } } public void customizedNotifyAll(){ notifyAll(); System.out.println(Thread.currentThread().getName()+"-<"+name+counter+">"+"::"+"INVOKED NOTIFYALL() AND FINISHED"); } } Java代码

package com.thread.wait; public class TestThread implements Runnable { private Wait wait; public TestThread(Wait wait){ this.wait = wait; } public void run() { wait.doSomthing(); } public static void main(String [] args){ Wait wait = new Wait(4,"DAVID"); Thread t1 = new Thread(new TestThread(wait)); Thread t2 = new Thread(new TestThread(wait)); Thread t3 = new Thread(new TestThread(wait)); Thread t4 = new Thread(new TestThread(wait)); t1.start(); t2.start(); t3.start(); t4.start(); } } 运行的结果： Thread-0-<DAVID3>will invoke WAIT() Thread-1-<DAVID2>will invoke WAIT() Thread-2-<DAVID1>will invoke WAIT() Thread-3-<DAVID0>::INVOKED NOTIFYALL() AND FINISHED Thread-0-<DAVID2>has been ACTIVED Thread-0-<DAVID2>will invoke WAIT() Thread-1-<DAVID1>has been ACTIVED Thread-1-<DAVID1>will invoke WAIT() Thread-2-<DAVID0>has been ACTIVED Thread-2-<DAVID0>::INVOKED NOTIFYALL() AND FINISHED Thread-0-<DAVID1>has been ACTIVED Thread-0-<DAVID1>will invoke WAIT() Thread-1-<DAVID0>has been ACTIVED Thread-1-<DAVID0>::INVOKED NOTIFYALL() AND FINISHED Thread-0-<DAVID0>has been ACTIVED Thread-0-<DAVID0>::INVOKED NOTIFYALL() AND FINISHED 看到了吧，一旦调用notifyAll（）方法，所有的等待线程都会从调用wait()方法的地方继续运行起来。这个运行结果可能每次都不一样，有时候只有两个线程运行完成而其余两个线程在等待其它线程调用notifyAll()方法，有时候只有三个线程运行完成，而另一个还在等待中。由于本文是讲解notify以及notifyAll方法，所以对上面的原因不多加以解释。然后是notify()方法的例子：就是将wait类中的customizedNotifyAll()方法中的notifyAll()方法换成notify()方法运行结果： Thread-1-<DAVID3>will invoke WAIT() Thread-0-<DAVID2>will invoke WAIT() Thread-2-<DAVID1>will invoke WAIT() Thread-3-<DAVID0>::INVOKED NOTIFYALL() AND FINISHED Thread-1-<DAVID2>has been ACTIVED Thread-1-<DAVID2>will invoke WAIT() Did you see that?所有的等待线程中，只有一个线程运行完成了，而其它的线程还在傻傻地等待，poor guys! 每次运行的结果会不一样，但是始终只有一个线程能够运行完成。 Summary： notify()方法只是让一个线程从wait中恢复过来，至于具体是哪个，那就得看那些线程的运气了(不设置优先级的情况下)，继续执行后面的语句； notifyAll()方法是让所有的线程从wait中恢复过来，继续执行后面的语句。

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