<AWT Dev> EventQueue changes

[Oleg Sukhodolsky]

On Mon, Sep 15, 2008 at 11:05 AM, Oleg Sukhodolsky <son.two at gmail.com> wrote:
> Hi Artem,
>
> I believe that three problems you want to fix are rather independent
> so, I will write one message for every problem (also this way we will
> have shorter messages ;)
>
>> 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().
>
> here is a question: what "as much as possible" means?  If it means one
> EDT for one EQ than it looks reasonable,
> and the only issue is correct implemtation of this idea.  If you meant
> something else, please clarify this.
>
> BTW, as a side note: do not forget that we can not guarantee that
> thread which is used as EDT will be the same all the time,
> because of AWT autoshutdown.

also the same EDT for different EQs will not work for the following code:

--- executed on EDT --
pushd(newEQ);
//do something
pop()

Oleg.
>
> 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.
>>
>