如何在Java中使用wait（）和notify（）？ [英] How to use wait() and notify() in Java?

问题描述

据我所知，我想在互斥锁上调用wait（），当我希望当前线程停止工作，直到另一个线程在同一个互斥对象上调用notify（）。这似乎没有用。

As I understand, I am suppose to call wait() on the mutex, when I want the current thread to stop working until another thread calls notify() on the same mutex object. That doesn't seem to be working.

我正在尝试将线程打印为1-10。然后等待另一个线程打印11-20。然后第一个线程将再次打印21-30

I'm trying to make a thread print 1-10. Then wait for another thread to print 11-20. And then the first thread would again print 21-30

Main.java

public class Main {
    public static void main(String[] args) throws InterruptedException {
        Object mutex = 1;

        Thread child1 = new Thread(new Child1(mutex));
        Thread child2 = new Thread(new Child2(mutex));

        child1.start();
        child2.start();

    }

}

Child1.java

public class Child1 implements Runnable {
    Object mutex;

    public Child1(Object mutex){
        this.mutex = mutex;
    }

    public void run() {
        synchronized (mutex) {
            for(int c = 0; c < 10; c++){
                System.out.println(c+1);
            }

            try {
                wait();
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }


        for(int c = 20; c < 31; c++){
            System.out.println(c+1);
        }
    }
}

Child2.java

public class Child2 implements Runnable {
    Object mutex;

    public Child2(Object mutex) {
        this.mutex = mutex;
    }

    public void run() {
        synchronized (mutex) {
            for (int c = 11; c < 21; c++) {
                System.out.println(c);
            }
            notify();
        }

    }
}

输出

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17Exception in thread "Thread-0" 
18
19
20
Exception in thread "Thread-1" java.lang.IllegalMonitorStateException
    at java.lang.Object.wait(Native Method)
    at java.lang.Object.wait(Object.java:502)
    at task42.Child1.run(Child1.java:18)
    at java.lang.Thread.run(Thread.java:745)
java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at task42.Child2.run(Child2.java:15)
    at java.lang.Thread.run(Thread.java:745)

我缺少什么？

推荐答案

你必须添加 mutex 引用 wait（）和 notify（）;也就是说，将 wait（）更改为 mutex.wait（）和 notify（）到 mutex.notify（）。

You must add the mutex reference to wait() and notify(); that is, change wait() to mutex.wait() and notify() to mutex.notify().

如果没有这个，你打算等待/通知此（方法（）相当于 this.method（））

Without this, you are calling to wait/notify on this (method() is equivalent to this.method())

这是您的代码，并进行了相应的更改：

Here is your code with the appropriate changes made:

Child1.java

Child1.java

public class Child1 implements Runnable {
    Object mutex;

    public Child1(Object mutex){
        this.mutex = mutex;
    }

    public void run() {
        synchronized (mutex) {
            for(int c = 0; c < 10; c++){
                System.out.println(c+1);
            }

            try {
                mutex.wait(); // Changed here
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }


        for(int c = 20; c < 31; c++){
            System.out.println(c+1);
        }
    }
}

Child2.java

Child2.java

public class Child2 implements Runnable {
    Object mutex;

    public Child2(Object mutex) {
        this.mutex = mutex;
    }

    public void run() {
        synchronized (mutex) {
            for (int c = 11; c < 21; c++) {
                System.out.println(c);
            }
            mutex.notify(); // Changed here
        }

    }
}

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