java - 如何“同步”线程依次运行？

问题描述

我想让我的方法打印出 4 行“Hello world！”，但我的代码似乎无法按我的意愿工作。有没有办法保证它会按照我的意愿运行？有时我得到 2 行，有时单词顺序错误，等等。有时它会按我想要的方式打印单词，但大多数情况下不会。对于我的代码中可能伤害您的眼睛的任何错误，我深表歉意，我仍在学习，因此我在这里。感谢您的任何建议。

public class PrintHelloWorld {

final Lock lock = new ReentrantLock(true);
private volatile String state = "inactive";

public void printHelloWorld() {
    LocksManager manager = new LocksManager();

    Thread t1 = new Thread(() -> {
        synchronized (manager.getObject(0)) {
            for (int i = 0; i < 4; i++) {
                System.out.print("Hello ");
                try {
                    manager.notify(1);
                    state = "running t2";
                    while(!state.equals("running t1"))
                        manager.wait(0);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    });

    Thread t2 = new Thread(() -> {
        synchronized (manager.getObject(1)) {
            for (int i = 0; i < 4; i++) {
                System.out.print("world");
                try {
                    manager.notify(2);
                    state = "running t3";
                    while (!state.equals("running t2"))
                        manager.wait(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    });

    Thread t3 = new Thread(() -> {
        synchronized (manager.getObject(2)) {
            for (int i = 0; i < 4; i++) {
                System.out.println("!");
                try {
                    manager.notify(0);
                    state = "running t1";
                    while (!state.equals("running t3"))
                        manager.wait(2);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    });
    {
        t1.start();
        t2.start();
        t3.start();
        try {
            t1.join();
            t2.join();
            t3.join();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}

private class LocksManager {
    private volatile Object[] locks;

    public LocksManager() {
        locks = new Object[3];

        for (int i=0; i<3; i++)
            locks[i] = new Object();
    }

    public Object getObject(int number) {
        return locks[number];
    }

    public void wait(int number) throws InterruptedException {
        synchronized (locks[number]) {
            locks[number].wait();
        }
    }

    public void notify(int number) {
        synchronized (locks[number]) {
            locks[number].notify();
        }
    }

}
}

输出应如下所示：

Hello world!
Hello world!
Hello world!
Hello world!

但有时它看起来像这样：

Hello world!
Hello !
worldHello !
worldHello !
world

或这个：

Hello !
world

标签： javamultithreading

java - 如何“同步”线程依次运行？

问题描述

解决方案

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