利用多线程技术实现机器人的运动序列

Question

我有一段代码，我想使用wait()和notify()来确保机器人腿的移动顺序。代码如下：

public class Leg implements Runnable {

    private final Object monitor = new Object();
    private final String name;

    public Leg(String name) {
        this.name = name;
    }
    @Override
    public void run() {
        while (true) {
            synchronized (monitor) {
                move();
                monitor.notify();
                try {
                    monitor.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }

        }

    }
    private void move() {
        System.out.println(name);
    }


    public static void main(String[] args) {
        CompletableFuture.allOf(
                CompletableFuture.runAsync(new Leg("left")),
                CompletableFuture.runAsync(new Leg("right"))
        ).join();
    }
}

现在的输出如下：

left 
right
// and then it stops moving.

我希望代码继续移动(不只移动一次)。这就是为什么我感兴趣的原因是我做错了什么？

Answer 1

你有两个Leg对象和两个线程要处理，每个线程都有一个monitor对象，所以当你使用notify和wait时，它只影响一个线程(当前正在运行的线程)：

synchronized (monitor) {
    move();
    monitor.notify(); // notify current thread, it's no meaning
    try {
        monitor.wait(); // current thread will block here and there is no thread wake up it
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

也许这就是你需要的：

import java.util.concurrent.CompletableFuture;

public class Leg implements Runnable {

    private final String name;
    private Leg nextLeg;
    private volatile boolean active;

    public Leg(String name) {
        this.name = name;
    }

    public void setNextLeg(Leg nextLeg) {
        this.nextLeg = nextLeg;
    }

    public void active() {
        synchronized (this) {
            this.active = true;
            notify();
        }
    }

    @Override
    public void run() {
        while (true) {
            try {
                synchronized (this) {
                    while (!active) {
                        wait();
                    }
                    move();
                    active = false;
                    nextLeg.active();
                }
            }
            catch (Exception e) {
                e.printStackTrace();
            }
        }

    }
    private void move() {
        System.out.println(name);
    }


    public static void main(String[] args) {
        Leg left = new Leg("left");
        Leg right = new Leg("right");
        left.setNextLeg(right);
        right.setNextLeg(left);
        left.active();
        CompletableFuture.allOf(
                CompletableFuture.runAsync(left),
                CompletableFuture.runAsync(right)
        ).join();
    }
}