如何从另一个线程暂停和恢复Java中的线程

Z时代
2024-01-10
分类：问答

我正在用Java Swing编写应用程序。我需要的是一个可以使用图形界面中的按钮停止“阐述”线程的过程。

这里有一个简单的项目专注于我的需求

import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JTextArea;
/*
 * To change this template, choose Tools | Templates
 * and open the template in the editor.
 */
/**
 *
 * @author Nikola
 */
public class Main extends javax.swing.JFrame
{
    private MyThread THREAD;
    public Main()
    {
        initComponents();
    }
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">
    private void initComponents() {
        jButton1 = new javax.swing.JButton();
        jScrollPane1 = new javax.swing.JScrollPane();
        jTextArea1 = new javax.swing.JTextArea();
        jButton2 = new javax.swing.JButton();
        jButton3 = new javax.swing.JButton();
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        jButton1.setText("Pause Thread");
        jButton1.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton1ActionPerformed(evt);
            }
        });
        jTextArea1.setColumns(20);
        jTextArea1.setRows(5);
        jScrollPane1.setViewportView(jTextArea1);
        jButton2.setText("Resume Thread");
        jButton2.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton2ActionPerformed(evt);
            }
        });
        jButton3.setText("Start Thread");
        jButton3.addActionListener(new java.awt.event.ActionListener() {
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                jButton3ActionPerformed(evt);
            }
        });
        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                        .addComponent(jButton3)
                        .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.RELATED, 63, Short.MAX_VALUE)
                        .addComponent(jButton2)
                        .addGap(18, 18, 18)
                        .addComponent(jButton1))
                    .addComponent(jScrollPane1))
                .addContainerGap())
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(javax.swing.GroupLayout.Alignment.TRAILING, layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(jScrollPane1, javax.swing.GroupLayout.DEFAULT_SIZE, 244, Short.MAX_VALUE)
                .addPreferredGap(javax.swing.LayoutStyle.ComponentPlacement.UNRELATED)
                .addGroup(layout.createParallelGroup(javax.swing.GroupLayout.Alignment.BASELINE)
                    .addComponent(jButton1)
                    .addComponent(jButton2)
                    .addComponent(jButton3))
                .addContainerGap())
        );
        pack();
    }// </editor-fold>
    private void jButton3ActionPerformed(java.awt.event.ActionEvent evt)
    {
        THREAD = new MyThread(jTextArea1);
        THREAD.start();
    }
    private void jButton1ActionPerformed(java.awt.event.ActionEvent evt)
    {
        try
        {
            THREAD.pauseThread();
        }
        catch (InterruptedException ex)
        {
            ex.printStackTrace();
        }
    }
    private void jButton2ActionPerformed(java.awt.event.ActionEvent evt)
    {
        THREAD.resumeThread();
    }
    public static void main(String args[])
    {
        /*
         * Set the Nimbus look and feel
         */
        //<editor-fold defaultstate="collapsed" desc=" Look and feel setting code (optional) ">
        /*
         * If Nimbus (introduced in Java SE 6) is not available, stay with the
         * default look and feel. For details see
         * http://download.oracle.com/javase/tutorial/uiswing/lookandfeel/plaf.html
         */
        try
        {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels())
            {
                if ("Nimbus".equals(info.getName()))
                {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        }
        catch (ClassNotFoundException ex)
        {
            java.util.logging.Logger.getLogger(Main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        catch (InstantiationException ex)
        {
            java.util.logging.Logger.getLogger(Main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        catch (IllegalAccessException ex)
        {
            java.util.logging.Logger.getLogger(Main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        catch (javax.swing.UnsupportedLookAndFeelException ex)
        {
            java.util.logging.Logger.getLogger(Main.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }
        //</editor-fold>
        /*
         * Create and display the form
         */
        java.awt.EventQueue.invokeLater(new Runnable()
        {
            public void run()
            {
                new Main().setVisible(true);
            }
        });
    }
    // Variables declaration - do not modify
    private javax.swing.JButton jButton1;
    private javax.swing.JButton jButton2;
    private javax.swing.JButton jButton3;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JTextArea jTextArea1;
    // End of variables declaration
}
class MyThread extends Thread
{
    JTextArea area;
    private final Object lock = new Object();
    public MyThread(JTextArea area)
    {
        super();
        this.area = area;
    }
    @Override
    public void run()
    {
        for(int i=0 ; ; i++)
            area.setText(i+"");
    }
    public void pauseThread() throws InterruptedException
    {
        synchronized(lock)
        {
            lock.wait();
        }
    }
    public void resumeThread()
    {
        synchronized(lock)
        {
            lock.notify();
        }
    }
}

问题很简单：在实际的应用程序中，用户设置一些选项，然后启动线程，对选定的数据进行详细说明。

我想提供一个“暂停”按钮，以便用户可以暂时停止详细说明并进行必要的检查，然后可以恢复操作。

我编码的方式是停止的图形线程，而不是“精化”线程。

如果运行示例代码并按“开始”，则文本区域开始计数。我需要的最终结果是，当我按下“暂停”按钮时，线程进入“睡眠”状态，计数停止；当我按下“恢复”按钮时，线程“唤醒”，文本区域中的计数开始再数一次。

回答：

您无法按照您想要的方式最终从另一个线程中暂停一个线程。

您需要做的是通过设置某种标志来通知另一个线程应该停止。有问题的线程必须具有检查该标志并在发生这种情况时暂停其工作的逻辑。

因此，在这种特殊情况下，可能MyThread如下更改：

class MyThread extends Thread {
    private volatile boolean running = true; // Run unless told to pause
    ...
    @Override
    public void run()
    {
        for(int i=0 ; ; i++)
        {
            // Only keep painting while "running" is true
            // This is a crude implementation of pausing the thread
            while (!running)
                yield;
            area.setText(i+"");
    }
    public void pauseThread() throws InterruptedException
    {
        running = false;
    }
    public void resumeThread()
    {
        running = true;
    }
}