<AWT Dev> [7u8] Review request for 7177040: Deadlock between PostEventQueue.noEvents, EventQueue.isDispatchThread and SwingUtilities.invokeLater

[Peter Levart]

Ok, now to get rid of flushLock in SunToolkit so that flushPendingEvents is
written as plain:

    public static void flushPendingEvents()  {
        AppContext appContext = AppContext.getAppContext();
        PostEventQueue postEventQueue =
            (PostEventQueue)appContext.get(POST_EVENT_QUEUE_KEY);
        if (postEventQueue != null) {
            postEventQueue.flush();
        }
    }

... you could merge the recursion prevention functionality into the
PostEventQueue in a manner similar to this:

class PostEventQueue {
    private EventQueueItem queueHead = null;
    private EventQueueItem queueTail = null;
    private final EventQueue eventQueue;

    // For the recursion prevention and noEvents() status
    private Thread flushingThread = null;

    PostEventQueue(EventQueue eq) {
        eventQueue = eq;
    }

    public synchronized boolean noEvents() {
        return queueHead == null && flushingThread == null;
    }

    public void flush() {
        EventQueueItem tempQueue;
        synchronized (this) {
            while (flushingThread != null && flushingThread !=
Thread.currentThread()) try {
                wait();
            }
            catch (InterruptedException e) { // what can we do?
                Thread.currentThread().interrupt();
                return;
            }

            // prevent recursion
            if (flushingThread == Thread.currentThread()) return;

            tempQueue = queueHead;
            queueHead = queueTail = null;

            // queue was empty
            if (tempQueue == null) return;

            flushingThread = Thread.currentThread();
            notify();
        }
        try {
            while (tempQueue != null) {
                eventQueue.postEvent(tempQueue.event);
                tempQueue = tempQueue.next;
            }
        }
        finally {
            synchronized (this) {
                flushingThread = null;
                notify();
            }
        }
    }

    /*
     * Enqueue an AWTEvent to be posted to the Java EventQueue.
     */
    void postEvent(AWTEvent event) {
        EventQueueItem item = new EventQueueItem(event);

        synchronized (this) {
            if (queueHead == null) {
                queueHead = queueTail = item;
            } else {
                queueTail.next = item;
                queueTail = item;
            }
        }
        SunToolkit.wakeupEventQueue(eventQueue, event.getSource() ==
AWTAutoShutdown.getInstance());
    }
} // class PostEventQueue


What do you think?

Regards, Peter


2012/7/24 Oleg Pekhovskiy <oleg.pekhovskiy at oracle.com>

> Hi Peter,
>
> so obvious, thank you!
>
> Oleg.
>
>
> 7/24/2012 3:42 PM, Peter Levart wrote:
>
>> Hi Oleg,
>>
>> This is just cosmetics, but:
>>
>> SunToolkit:
>> public synchronized boolean noEvents() {
>>         return queueHead == null && !isFlushing;
>>     }
>>
>> ... a thread calling noEvents could see occasional "spikes" of false
>> return even though there is no flushing being performed (when other thread
>> is calling flush on an empty PostEventQueue).
>>
>> Improved flush method would look like this:
>>
>>      public void flush() {
>>          EventQueueItem tempQueue;
>>          synchronized (this) {
>>              tempQueue = queueHead;
>>              queueHead = queueTail = null;
>>              isFlushing =*/(tempQueue != null)/*;
>>
>>          }
>>          try {
>>              while (tempQueue != null) {
>>                  eventQueue.postEvent(**tempQueue.event);
>>                  tempQueue = tempQueue.next;
>>              }
>>          }
>>          finally {
>>              isFlushing = false;
>>          }
>>      }
>>
>> Regards, Peter
>>
>> 2012/7/23 Oleg Pekhovskiy <oleg.pekhovskiy at oracle.com <mailto:
>> oleg.pekhovskiy@**oracle.com <oleg.pekhovskiy at oracle.com>>>
>>
>>
>>     Hi!
>>
>>     Please review this back-port being already pushed to jdk8 but
>>     deferred for 7u6.
>>
>>     Bug:
>>     http://bugs.sun.com/view_bug.**do?bug_id=7177040<http://bugs.sun.com/view_bug.do?bug_id=7177040>
>>
>>     Webrev:
>>     http://cr.openjdk.java.net/~**bagiras/7u8/7177040.1<http://cr.openjdk.java.net/~bagiras/7u8/7177040.1>
>>     <http://cr.openjdk.java.net/%**7Ebagiras/7u8/7177040.1<http://cr.openjdk.java.net/%7Ebagiras/7u8/7177040.1>
>> >
>>
>>
>>     Review thread for 7u6:
>>     http://mail.openjdk.java.net/**pipermail/awt-dev/2012-July/**
>> 003106.html<http://mail.openjdk.java.net/pipermail/awt-dev/2012-July/003106.html>
>>
>>     Reviewers 7u6 & 8:
>>     Anthony Petrov, Anton Tarasov
>>
>>     Thanks,
>>     Oleg
>>
>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mail.openjdk.java.net/pipermail/awt-dev/attachments/20120724/335cc090/attachment.html