<AWT Dev> EventQueue changes

[Artem Ananiev]

Oleg Sukhodolsky wrote:
> 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?

I'm currently aware of at least 3 requests for this functionality: from 
NetBeans team, from JWebPane team and from JavaWebStart/deploment team. 
In general, in every application with multiple AppContexts controllable 
event pump is required to implement cross-AppContext synchronous calls 
(like COM).

Thanks,

Artem

> 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.