<AWT Dev> EventQueue changes

[Oleg Sukhodolsky]

On Tue, Sep 16, 2008 at 1:03 PM, Artem Ananiev <Artem.Ananiev at sun.com> wrote:
>
> Oleg Sukhodolsky wrote:
>>>
>>> 3. pumpEvents() API is made public, probably with some minor changes.
>>
>> what use cases you want to address by this new API?
>
> There are several tens of votes for all the related bugs. One more argument
> is that all the modern toolkits (Win32, GTK, SWT) have this API implemented,
> while AWT/Swing still misses it.
>
> I also constantly face with scenarios, when some developer needs to start a
> nested event pump and use a modal dialog for this, which looks quite ugly
> and unstable.

What kind of scenarios do you mean?

Thanks, Oleg.
>
> Thanks,
>
> Artem
>
>> Regards, Oleg.
>>
>> On Thu, Sep 11, 2008 at 12:10 PM, Artem Ananiev <Artem.Ananiev at sun.com>
>> wrote:
>>>
>>> Hi, Oleg,
>>>
>>> Oleg Sukhodolsky wrote:
>>>>
>>>> On Tue, Sep 9, 2008 at 3:55 PM, Artem Ananiev <Artem.Ananiev at sun.com>
>>>> wrote:
>>>>>
>>>>> Hi, AWT team,
>>>>>
>>>>> there are several issues related to EventQueue class with a long
>>>>> history.
>>>>> The number of user votes constantly grows, so I think it would be fine
>>>>> if
>>>>> we
>>>>> can get them fixed in some nearest future.
>>>>>
>>>>> The list of bugs include (but not limited to):
>>>>>
>>>>> 6424157: java.awt.EventQueue push/pop might cause threading issues
>>>>>
>>>>> 6542185: Threading issues with java.awt.EventQueue.push/pop
>>>>> (closed as not a defect, but some of described problems still exist)
>>>>>
>>>>> 4913324: Deadlock when using two event queues.
>>>>>
>>>>> 4516924: Request public access to pumpEvents(Conditional) type
>>>>> functionality.
>>>>>
>>>>> 6727884: Some Uncaught Exceptions are no longer getting sent to the
>>>>> Uncaught
>>>>> Exception Handlers
>>>>>
>>>>> Some of the described problems don't look related to each other,
>>>>> however
>>>>> after a closer look I found they really do. That's why I listed them
>>>>> here
>>>>> altogether, and would like to discuss some possible improvements:
>>>>>
>>>>> 1. Synchronization changes. Most of the problems with push/pop are
>>>>> caused
>>>>> by
>>>>> imperfect synchronization in EventQueue. Currently, all the actions
>>>>> like
>>>>> postEvent() or getNextEvent() are transferred back and forth in the
>>>>> stack
>>>>> of
>>>>> event queues, and each queue is accessed in its 'synchronized' block.
>>>>> Instead, a single lock looks more correct here.
>>>>>
>>>>> 2. EventDispatchThread lifecycle. It is a known fact, that event
>>>>> dispatch
>>>>> thread may die for some reason (for example, because of unhandled
>>>>> exception). When a new event comes, new EDT is created. Another case
>>>>> when
>>>>> EDT is switched is push/pop methods: when a new EQ is pushed/popped, a
>>>>> new
>>>>> EDT is created.
>>>>>
>>>>> I'm sure these changes of current dispatch thread is not what
>>>>> developers
>>>>> expect. Swing is considered as single-threaded toolkit, but it is
>>>>> really
>>>>> not...
>>>>>
>>>>> 3. Controllable event pump. This is what developers have been
>>>>> requesting
>>>>> for
>>>>> at least 8 years. With the current API this task cannot be solved, and
>>>>> all
>>>>> the external libs like Foxtrot are really just hacks and depend on JDK
>>>>> internals.
>>>>>
>>>>> From technical point of view, controllable event pump is just a several
>>>>> lines of code changes: we only need to make public the code which is
>>>>> used
>>>>> for modality event pumps.
>>>>>
>>>>> ----
>>>>>
>>>>> I have a prototype fix with all the three items implemented. Still, it
>>>>> would
>>>>> be fine to hear what all AWT developers think about proposed changes.
>>>>
>>>> I see list of problems, but do not see list of proposed changes :(
>>>> Did I miss something?
>>>
>>> You're right, the changes are not included, my fault... Here they are:
>>>
>>> 1. A single lock is introduced to handle all the EQ operations like push,
>>> pop, getNextEvent, etc. instead of locking all EQ objects one by one, if
>>> several.
>>>
>>> 2. EventDispatchThread is reused as much as possible. When a new EQ is
>>> pushed, it uses the old EDT instead of creating a new one. The same is
>>> true
>>> for pop().
>>>
>>> 3. pumpEvents() API is made public, probably with some minor changes.
>>>
>>> Thanks,
>>>
>>> Artem
>>>
>>>> With best regards, Oleg.
>