SwingWorker hangs at Unsafe.park()

问题:

I have a SwingWorker that communicates with a server in the background and then updates a JFrame. I was debugging my app and noticed that even after the SwingWorker finished its work, its thread still remained. It is hanging at Unsafe.park(java.lang.Object) which is a native method. I looked in to this further and found that all my other SwingWorkers in my app do the same thing after they finish. I can provide source code if someone wants it but I don't think it is necessary because the problem seems to be very general.

Update

I ran the app without the debugger and the problem is still happening. This is the dump of the SwingWorker thread:

"SwingWorker-pool-2-thread-1" daemon prio=6 tid=0x03219800 nid=0xd74 waiting on
condition [0x04b7f000]
   java.lang.Thread.State: WAITING (parking)
        at sun.misc.Unsafe.park(Native Method)
        - parking to wait for  <0x22ec63d8> (a java.util.concurrent.locks.Abstra
ctQueuedSynchronizer$ConditionObject)
        at java.util.concurrent.locks.LockSupport.park(Unknown Source)
        at java.util.concurrent.locks.AbstractQueuedSynchronizer$ConditionObject
.await(Unknown Source)
        at java.util.concurrent.LinkedBlockingQueue.take(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.getTask(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
        at java.lang.Thread.run(Unknown Source)

I made a sample program that uses SwingWorker the way it is normally used in a application. This program has the same problem. Here is the code:

package swingworkerlocktest;

import java.util.List;
import javax.swing.JFrame;
import javax.swing.JTextArea;
import javax.swing.SwingWorker;

public class SwingWorkerLockTest {

    public static void main(String[] args) {
        final JFrame frame = new JFrame("Frame");
        final JTextArea outputArea = new JTextArea(4, 20);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(outputArea);
        frame.pack();
        frame.setVisible(true);
        (new SwingWorker<Object, String>() {
            @Override
            protected Object doInBackground() throws Exception {
                publish("Background task.");
                return null;
            }

            @Override
            protected void process(List<String> chunks) {
                for (String str : chunks) {
                    outputArea.append(str + "\n");
                }
            }

            @Override
            protected void done() {
                outputArea.append("Background task finished.");
            }
        }).execute();
    }
}

回答1:

This is a normal behavior of SwingWorker, the Thread should terminate after 10 minutes if it is idle. It's explained here