user32: After handling an internal message give a chance to real message to arrive.

[Dmitry Timoshkov]

Alexandre Julliard <julliard at winehq.org> wrote:

> >> I may have one, once I understand what you are trying to fix. What is
> >> the actual problem that prompted you to write the tests and the fix?
> >
> > The problem is described in the first test for sending inter-thread
> > messages: https://www.winehq.org/pipermail/wine-patches/2015-April/138750.html
> > My original guess was that the problem is caused by internal message
> > handling in Wine, and the tests I created confirmed that there is a problem
> > in that area. The patch we are discussing fixes the problem discovered
> > by these tests.
> 
> I still don't understand why internal messages would be different. Is
> that because you get only one inter-thread message instead of several?

The problem is that once Get/PeekMessage handles an internal message it
doesn't yield control to another thread and checks the message queue
immediately, this misses a sent message from another thread and instead
returns a previously posted one. I admit that this is a pure artificial
thing that I stumbled upon, but it reveals a real bug in Wine with internal
message handling.

> I think it would be better to try to write a test that replicates the
> problem you are seeing.

I tried to simplify the tests since calling EndDialog+GetMessage+DestroyMessage
from different threads may create pretty complicated scenarios, and most
obvious (to me) things to test are SendMessage+Get/PeekMessage and SetWindowPos+
Get/PeekMessage from different threads are two cases that should cover things
that I think may lead to the observed bug(s).

I can sertainly add more tests, but only when already sent ones are accepted
to avoid creating conflicts and resending them again.

> In particular, testing GetQueueStatus instead of
> message sequences is not very convincing to me, since it doesn't
> properly show what's going on.

I tried to test both as much as possible, did I miss some cases where one of
GetQueueStatus or a message sequence is not tested?

-- 
Dmitry.