notify和notifyall的区别？

两个概念：

1、锁池EntryList

2、等待池 WaitSet

 

注意：锁池和等待池都是针对对象的

 

问题：notify和notifyall的区别？

-----》1、notifyAll会让所有处于等待池的线程全部进入锁池去竞争获取锁的机会

2、notify只会随机选取一个处于等待池的线程进入锁池去竞争获取锁的机会

 

public class NotificationDemo {
    private volatile boolean go = false;

    public static void main(String args[]) throws InterruptedException {
        final NotificationDemo test = new NotificationDemo();

        Runnable waitTask = new Runnable(){

            @Override
            public void run(){
                try {
                    test.shouldGo();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(Thread.currentThread().getName() + " finished Execution");
            }
        };

        Runnable notifyTask = new Runnable(){

            @Override
            public void run(){
                test.go();
                System.out.println(Thread.currentThread().getName() + " finished Execution");
            }
        };

        Thread t1 = new Thread(waitTask, "WT1"); //will wait
        Thread t2 = new Thread(waitTask, "WT2"); //will wait
        Thread t3 = new Thread(waitTask, "WT3"); //will wait
        Thread t4 = new Thread(notifyTask,"NT1"); //will notify

        //starting all waiting thread
        t1.start();
        t2.start();
        t3.start();

        //pause to ensure all waiting thread started successfully
        Thread.sleep(200);

        //starting notifying thread
        t4.start();

    }
    /*
     * wait and notify can only be called from synchronized method or bock
     */
    private synchronized void shouldGo() throws InterruptedException {
        while(go != true){
            System.out.println(Thread.currentThread()
                    + " is going to wait on this object");
            wait(); //release lock and reacquires on wakeup
            System.out.println(Thread.currentThread() + " is woken up");
        }
        go = false; //resetting condition
    }

    /*
     * both shouldGo() and go() are locked on current object referenced by "this" keyword
     */
    private synchronized void go() {
        while (go == false){
            System.out.println(Thread.currentThread()
                    + " is going to notify all or one thread waiting on this object");

            go = true; //making condition true for waiting thread
            //notify(); // only one out of three waiting thread WT1, WT2,WT3 will woke up
            notifyAll(); // all waiting thread  WT1, WT2,WT3 will woke up
        }

    }
}

----》屏蔽notifyAll()方法，打开notify（）方法，结果如下：

Thread[WT1,5,main] is going to wait on this object
Thread[WT2,5,main] is going to wait on this object
Thread[WT3,5,main] is going to wait on this object
Thread[NT1,5,main] is going to notify all or one thread waiting on this object
NT1 finished Execution
Thread[WT1,5,main] is woken up
WT1 finished Execution

 

 

-------》屏蔽notify方法，打开notifyAll()方法，结果如下：

Thread[WT1,5,main] is going to wait on this object
Thread[WT2,5,main] is going to wait on this object
Thread[WT3,5,main] is going to wait on this object
Thread[NT1,5,main] is going to notify all or one thread waiting on this object
Thread[WT3,5,main] is woken up
WT3 finished Execution
Thread[WT2,5,main] is woken up
Thread[WT2,5,main] is going to wait on this object
Thread[WT1,5,main] is woken up
Thread[WT1,5,main] is going to wait on this object
NT1 finished Execution