<AWT Dev> EventQueue changes
Artem.Ananiev at Sun.COM
Thu Sep 11 01:10:01 PDT 2008
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
>> 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
>> 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
>> 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.
> With best regards, Oleg.
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