Unresponsive threading involving Swing and AWT-EventQueue

Question

I have an application that is unresponsive and seems to be in a deadlock or something like a deadlock. See the two threads below. Notice that the My-Thread@101c thread blocks AWT-EventQueue-0@301. However, My-Thread has just called java.awt.EventQueue.invokeAndWait(). So AWT-EventQueue-0 blocks My-Thread (I believe).

My-Thread@101c, priority=5, in group 'main', status: 'WAIT'
     blocks AWT-EventQueue-0@301
      at java.lang.Object.wait(Object.java:-1)
      at java.lang.Object.wait(Object.java:485)
      at java.awt.EventQueue.invokeAndWait(Unknown Source:-1)
      at javax.swing.SwingUtilities.invokeAndWait(Unknown Source:-1)
      at com.acme.ui.ViewBuilder.renderOnEDT(ViewBuilder.java:157)
        .
        .
        .
      at com.acme.util.Job.run(Job.java:425)
      at java.lang.Thread.run(Unknown Source:-1)

AWT-EventQueue-0@301, priority=6, in group 'main', status: 'MONITOR'
     waiting for My-Thread@101c
      at com.acme.persistence.TransactionalSystemImpl.executeImpl(TransactionalSystemImpl.java:134)
        .
        .
        .
      at com.acme.ui.components.MyTextAreaComponent$MyDocumentListener.insertUpdate(MyTextAreaComponent.java:916)
      at javax.swing.text.AbstractDocument.fireInsertUpdate(Unknown Source:-1)
      at javax.swing.text.AbstractDocument.handleInsertString(Unknown Source:-1)
      at javax.swing.text.AbstractDocument$DefaultFilterBypass.replace(Unknown Source:-1)
      at javax.swing.text.DocumentFilter.replace(Unknown Source:-1)
      at com.acme.ui.components.FilteredDocument$InputDocumentFilter.replace(FilteredDocument.java:204)
      at javax.swing.text.AbstractDocument.replace(Unknown Source:-1)
      at javax.swing.text.JTextComponent.replaceSelection(Unknown Source:-1)
      at javax.swing.text.DefaultEditorKit$DefaultKeyTypedAction.actionPerformed(Unknown Source:-1)
      at javax.swing.SwingUtilities.notifyAction(Unknown Source:-1)
      at javax.swing.JComponent.processKeyBinding(Unknown Source:-1)
      at javax.swing.JComponent.processKeyBindings(Unknown Source:-1)
      at javax.swing.JComponent.processKeyEvent(Unknown Source:-1)
      at java.awt.Component.processEvent(Unknown Source:-1)
      at java.awt.Container.processEvent(Unknown Source:-1)
      at java.awt.Component.dispatchEventImpl(Unknown Source:-1)
      at java.awt.Container.dispatchEventImpl(Unknown Source:-1)
      at java.awt.Component.dispatchEvent(Unknown Source:-1)
      at java.awt.KeyboardFocusManager.redispatchEvent(Unknown Source:-1)
      at java.awt.DefaultKeyboardFocusManager.dispatchKeyEvent(Unknown Source:-1)
      at java.awt.DefaultKeyboardFocusManager.preDispatchKeyEvent(Unknown Source:-1)
      at java.awt.DefaultKeyboardFocusManager.typeAheadAssertions(Unknown Source:-1)
      at java.awt.DefaultKeyboardFocusManager.dispatchEvent(Unknown Source:-1)
      at java.awt.Component.dispatchEventImpl(Unknown Source:-1)
      at java.awt.Container.dispatchEventImpl(Unknown Source:-1)
      at java.awt.Window.dispatchEventImpl(Unknown Source:-1)
      at java.awt.Component.dispatchEvent(Unknown Source:-1)
      at java.awt.EventQueue.dispatchEvent(Unknown Source:-1)
      at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source:-1)
      at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source:-1)
      at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source:-1)
      at java.awt.EventDispatchThread.pumpEvents(Unknown Source:-1)
      at java.awt.EventDispatchThread.pumpEvents(Unknown Source:-1)
      at java.awt.EventDispatchThread.run(Unknown Source:-1)

Here is the TransactionalSystemImpl.executeImpl method:

private synchronized Object executeImpl(Transaction xact, boolean commit) {
    final Object result;

    try {
        if (commit) { // this is line 134
            clock.latch();
            synchronized(pendingEntries) {
                if (xactLatchCount > 0) {
                    pendingEntries.add(xact);
                } else {
                    xactLog.write(new TransactionEntry(xact, clock.time()));
                }
            }
        }

        final TransactionExecutor executor = transactionExecutorFactory.create(
                xact.getClass().getSimpleName()
        );

        if (executor == null) {
            throw new IllegalStateException("Failed to create transaction executor for transaction: " + xact.getClass().getName());
        }

        result = executor.execute(xact);

    } finally {
        if (commit) clock.unlatch();
    }

    return result;
}

Does anyone know what's going on here or how to fix it?

Answer 1

It's hard to tell without seeing the code, but from the stack trace, it looks like you're firing some sort of transactional code from the event dispatch thread. Does that code then kick off an instance of My-Thread? The EDT could be blocked waiting for My-Thread from within the transactional code, but My-Thread can't finish because it needs the EDT.

If this is the case, you can use SwingUtilities.invokeLater for your rendering so the EDT finishes the transactional code and then it will render the updates. Or, you can not perform the transactional code from the EDT. For actual work that's not related to rendering, you should use a SwingWorker to avoid doing any heavy processing on the EDT.