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

[Peter Levart]

Hi Oleg,

Here's even better flush() method. It completes the flush even if
interrupted while waiting and then sets the interrupted status just before
exit...

    public void flush() {
        boolean interrupted = false;
        try {
            EventQueueItem tempQueue;

            synchronized (this) {
                while (flushingThread != null && flushingThread !=
Thread.currentThread()) {
                    try {
                        wait();
                    }
                    catch (InterruptedException e) {
                        interrupted = true;
                    }
                }

                // 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();
                }
            }
        }
        finally
        {
            if (interrupted) Thread.currentThread().interrupt();
        }
    }


Regards, Peter


2012/7/24 Peter Levart <peter.levart at gmail.com>

> 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
>>>
>>>
>>>
>>
>
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