java - 如何暂停所有正在运行的线程？然后恢复？

Question

我已经看过这个问题:How pause and then resume a thread?

我在 stackoverflow 中看到了很多与我的问题相关的问题，但我无法理解它们，因为它们很抽象，对我的情况不够具体。

有 2 个倒计时标签。单击 Start Button 时，将执行倒计时。同样，当你点击Pause Button时，它应该被暂停。但是，我收到一个错误:Exception in thread "AWT-EventQueue-0"java.lang.IllegalMonitorStateException

2 线程已启动，但我无法使用 wait() 方法停止它。请让我知道如何停止线程，并实现 resume 按钮。谢谢。下面的简单示例

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.*;

class FirstCountDown extends SwingWorker<Integer, Integer> {

public Integer doInBackground() {
    for(int i=0; i<1000; i++){
    CountDown.count1.setText(String.valueOf(1000-i));
    try {
        Thread.sleep(100);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    } 
    return null;
}
}

class SecondCountDown extends SwingWorker<Integer, Integer> {

public Integer doInBackground(){
    for(int i=0; i<1000; i++){
        CountDown.count2.setText(String.valueOf(1000-i));
    try {
        Thread.sleep(50);
    } catch (InterruptedException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    }
    return null;
}
}

class CountDown extends JFrame  {

static JLabel count1;
static JLabel count2; 
static JButton startButton;
static JButton pauseButton;
static JButton resumeButton;
FirstCountDown first = new FirstCountDown();
SecondCountDown second = new SecondCountDown();

public CountDown(){
count1 = new JLabel("1000");
count2 = new JLabel("1000");
startButton = new JButton("start");
startButton.addActionListener(new ActionListener()  {
    public void actionPerformed(ActionEvent e){
        first.execute();
        second.execute();
    }
});
pauseButton = new JButton("pause");
pauseButton.addActionListener(new ActionListener()  {
    public void actionPerformed(ActionEvent e){
        try {
            first.wait();
            second.wait();
        } catch (InterruptedException e1) {
            // TODO Auto-generated catch block
            e1.printStackTrace();
        }
    }
});

resumeButton = new JButton("resume");

setSize(300,100);
setLayout(new FlowLayout());
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
add(count1);
add(count2);
add(startButton);
add(pauseButton);
add(resumeButton);
setVisible(true);

        }

public static void main(String args[]) {

    CountDown g = new CountDown();

}
}

Answer 1

您不能通过调用 wait() 来暂停线程执行。 wait() 挂起当前 线程，直到另一个线程调用同一对象上的notify() 或notifyAll()上一个线程调用了 wait()。此外，为了在对象上调用 wait()、notify() 或 notifyAll()，调用线程必须持有 对象的监视器通过做

synchronized(object) {
    object.wait();
}

为了暂停计数，您需要一个标志并提供两种方法来暂停和恢复计数。像这样的东西:

class FirstCountDown extends SwingWorker<Integer, Integer> {

    private _suspended = false;

    public synchronized void suspend() { _suspended = true; notify(); }
    public synchronized void resume() { _suspended = false; notify(); }

    public Integer doInBackground() {
        for(int i=0; i<1000; i++) {
            synchronized(this) {
                while (_suspended) {
                    wait(); // The current thread will block until some else calls notify()
                            // Then if _suspended is false, it keeps looping the for
                }
            }
            CountDown.count1.setText(String.valueOf(1000-i));
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        } 
        return null;
    }
}