1

在方法上使用 synchronized 关键字一次只允许一个线程执行该方法，但 EDT 可以处理将在该方法中同时运行的多个“事件”。请参阅下面的示例代码进行演示。单击测试按钮时，输出为：

0 before dialog, EDT=true
1 before dialog, EDT=true
(click OK button for 1 here)
1 after dialog, EDT=true
(click OK button for 0 here)
0 after dialog, EDT=true

我正在寻找的是一种方法，一次只允许一个 EDT 事件在 test() 方法中处于活动状态，以便输出为

0 before dialog, EDT=true
(click OK button for 0 here)
0 after dialog, EDT=true
1 before dialog, EDT=true
(click OK button for 1 here)
1 after dialog, EDT=true

好像以前一定有人解决过这个问题。我认为可以在方法的开头编写某种锁定对象来使用，或者将方法包装起来，但是懒惰，宁愿不重新发明轮子。

我的测试用例：

package test1;

import javax.swing.JDialog;
import javax.swing.JOptionPane;
import javax.swing.SwingUtilities;
import javax.swing.SwingWorker;

public class EDTSyncTest extends javax.swing.JFrame {
  private static final Object locker = new Object();

  private int counter;

  public EDTSyncTest() {
    initComponents();
  }

  private synchronized void test() {
    int l_id = counter++;
    logit("" + l_id + " before dialog, EDT=" + SwingUtilities.isEventDispatchThread());

    JOptionPane l_pane = new JOptionPane("test id " + l_id);
    JDialog l_diag = l_pane.createDialog(this, "test");
    l_diag.setModal(true);
    l_diag.setVisible(true);

    logit("" + l_id + " after dialog, EDT=" + SwingUtilities.isEventDispatchThread());
  }

  private void startTest() {
     new Delayer().execute();
     test();
  }

  private static void logit(String a_msg) {
    System.out.println(a_msg);
  }

  private class Delayer extends SwingWorker<Object, Object> {
    @Override
    protected Object doInBackground() throws Exception {
      Thread.sleep(2000);
      return null;
    }
    @Override
    protected void done() {
      test();
    }
  }

  private void initComponents() {

    jButton1 = new javax.swing.JButton();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    getContentPane().setLayout(new java.awt.FlowLayout());

    jButton1.setText("Test");
    jButton1.setName("jButton1"); // NOI18N
    jButton1.addActionListener(new java.awt.event.ActionListener() {
      public void actionPerformed(java.awt.event.ActionEvent evt) {
        jButton1ActionPerformed(evt);
      }
    });
    getContentPane().add(jButton1);

    pack();
  }

  private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    startTest();
  }                                        

  public static void main(String args[]) {

    java.awt.EventQueue.invokeLater(new Runnable() {
      public void run() {
        new EDTSyncTest().setVisible(true);
      }
    });
  }
  protected javax.swing.JButton jButton1;
}
4

2 回答 2

5

好的，这是我在millimoose的支持下给出的答案：D

让我们从这些观察开始：

  • 只有一个EDT 线程
  • 一个线程只有一个执行上下文
  • 模态对话框阻塞当前执行上下文
  • SwingWorker.done 总是在 EDT 上调用

因此，模态对话框不能阻止摆动事件，否则会导致整个 UI 变得无响应；那么，它如何在不阻塞摇摆事件的情况下进行阻塞呢？

模态对话框运行它自己的事件调度循环。然后，代码执行调用图（在 SwingWorker 完成后完全在 EDT 线程上运行）如下所示：

-> done (process FIRST done)
  -> 0/before
    -> modal dialog event loop (process NEXT done)
      -> 1/before
        -> modal dialog event loop (TOP DIALOG)
        <- OK PRESSED
      <- 1/after
    <- OK PRESSED
  <- 0/after 
<- back to normal EDT event loop

因此，模态对话框在运行时仍然处理摆动事件，但是以“递归”方式。

于 2013-05-28T23:56:29.360 回答
1

我刚刚弄清楚自己，但正如@millimoose 评论的那样：

该test()方法不是被同时调用的，它只是被递归调用。

稍微修改一下你的代码，你会看到：

logit("" + l_id + " before dialog, EDT="
    + SwingUtilities.isEventDispatchThread());
new Throwable().printStackTrace(System.out);

输出：

0 before dialog, EDT=true
java.lang.Throwable
    at EDTSyncTest.test(EDTSyncTest.java:22)
    at EDTSyncTest.startTest(EDTSyncTest.java:35)
    at EDTSyncTest.jButton1ActionPerformed(EDTSyncTest.java:75)
    at EDTSyncTest.access$1(EDTSyncTest.java:74)
    at EDTSyncTest$1.actionPerformed(EDTSyncTest.java:66)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    /* ... */
    at java.awt.EventDispatchThread.run(Unknown Source)
1 before dialog, EDT=true
java.lang.Throwable
    at EDTSyncTest.test(EDTSyncTest.java:22)
    at EDTSyncTest.access$0(EDTSyncTest.java:17)
    at EDTSyncTest$Delayer.done(EDTSyncTest.java:51)
    at javax.swing.SwingWorker$5.run(Unknown Source)
    /* ... */
    at java.awt.Dialog.setVisible(Unknown Source)
    at EDTSyncTest.test(EDTSyncTest.java:27)
    at EDTSyncTest.startTest(EDTSyncTest.java:35)
    at EDTSyncTest.jButton1ActionPerformed(EDTSyncTest.java:75)
    at EDTSyncTest.access$1(EDTSyncTest.java:74)
    at EDTSyncTest$1.actionPerformed(EDTSyncTest.java:66)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    /* ... */
    at java.awt.EventDispatchThread.run(Unknown Source)
1 after dialog, EDT=true
0 after dialog, EDT=true
于 2013-05-28T23:53:12.833 回答