OpenEuphoria

Re: Win32Lib doEvents()

• Posted by Matt Lewis <matthewwalkerlewis at gmail.com> Jul 08, 2005
• 582 views

Larry Miller wrote:
> 
> I have found doEvents to be very useful but there is a potential problem in
> it's use.
> The problem occurs when PeekMessage in doEvents receives a WM_QUIT message.
> GetMessage
> in the event loop tests for this and terminates the loop and the application.
> But in
> doEvents there is no such test and this will cause a serious problem.
> 
> The following code illustrates the problem. Yes, it is contrived and not the
> way an
> application would normally do things, but it does illustrate the basic
> problem.
> 

<snip>

> If you click on the windows close button the window will close, but Task
> Manager shows
> that the process is still very much alive - and with very high CPU usage. 
> 
> The problem does not appear to be unique to Win32Lib. I have examined the code
> of ARWEN
> and it's doEvents() function appears to work in a similar maner, and subject
> to the
> same problem. (I have not actually confirmed the problem in ARWEN).
> 
> In my case I have replaced doEvents() with a procedure that does test for
> WM_QUIT and
> then shuts down the application. But I am not certain that this is the best
> solution
> to the problem. 
> 
> In any case this issue should be resolved in Win32Lib.
> 

Yes, this is definitely a problem.  It's interesting that this has never
been caught before.  The solution is probably to catch the WM_QUIT, but
not to act on it until getting back to event_loop.

Here are some changes you can make to solve this problem (though of course
it won't get you out of your infinite loop, which win32lib can't help.  First,
here's a modified test app:

include win32lib.ew
without warning

atom Win

procedure handler(integer id,atom event,sequence param)
	atom t
	if event=w32HActivate then
		t = time()
		while time() < t + 5 do
			doEvents(0)
		end while
	end if
end procedure

	Win=create(Window,"Test",0,100,100,600,400,0)
	setHandler(Win,w32HActivate,routine_id("handler"))
	WinMain(Win,Normal)

Now, here is how you need to change win32lib:

-- begin mwl 7/8/05 (right above eventLoop()):
integer vWmQuit
vWmQuit = 0
-- end mwl 7/8/05

-- then, inside eventLoop():
    -- message loop
    while ActiveEL[el] = 0
      and vWinMainState = kStarted 
      -- begin mwl 7/8/05
      and vWmQuit = 0 do
	  -- end mwl 7/8/05

-- and finally, inside of doEvents():
    if w32Func( xPeekMessage, { msg, hWnd, 0, 0, PM_REMOVE } ) then
    	-- begin mwl 7/8/05
     	if peek4u(msg+4) = WM_QUIT  then
     		vWmQuit = 1
     	end if
     	-- end mwl 7/8/05

Matt Lewis