Re: [perl-win32-gui-hackers] DoEvents() bug.

[Glenn L. <pe...@ne...>]

On approximately 12/9/2003 2:59 AM, came the following characters from
the keyboard of Stephen Pick:

> Hi all.
> 
> When I do this:
> 
> Win32::GUI::Dialog()
> 
> I receive all my events like WM_LBUTTONDOWN (-onMouseDown) once, as
> should happen.
> 
> When I do this:
> 
> while(1) {
> 	Win32::GUI::DoEvents()
> 	print "Loop!\n";
> }
> 
> I get endless calls to my event handler so long as the mouse button is
> down. I have NO idea why. Must be some kind of windows internal thing.

Certain Windows messages are "queued and combined" if you are not 
looking, but the more often you look, the more often you get them....  I 
could say if MouseDown is one of those, off hand.

I have noticed that a difference between Dialog() and DoEvents() is that 
if used to process a dialog box containing a text box, that the former 
responds normally, but the latter generally doubles the characters 
received by the text box.  One difference in my situation is that I was 
  calling DoEvents() from an event, and that might cause some sort of 
reentrancy problem, but I couldn't understand what it would be if it is 
such.  I gave up and restructured my code to use Dialog() only.

> Additionally, since the code for DoEvents() and Dialog() is practically
> identical except that DoEvents uses PeekMessage and Dialog uses
> GetMessage, I copied both into seperate files and took a look at them in
> WinMerge. Interesting. Dialog does ENTER; SAVETMPS; before doing
> GetMessage and FREETMPS; LEAVE; at the end of it's while() loop.
> DoEvents() doesn't do this. 

This is because Dialog is "long-running" and needs to be sure to do Perl 
temporary variable management, and DoEvents returns to Perl more often, 
so can let Perl do the temporary variable management.  I think.

> Also, DoEvents has the line "acc =
> perlud->hAcc;", and Dialog() DOESNT have that. Dialog() does a
> comparison on acc (acc != NULL) in the next few lines just like DoEvents
> does, but this comparison will always yield false in Dialog().

I think that was one of the lines I "fixed" in making accelerator keys 
work.  If not, it should have been.  What version of source are you 
looking at?

> So. I don't have a compiler here but this is weird. Surely these
> functions should be identical but for the change from GetMessage to
> PeekMessage. Moreover, if these functions should be identical then why
> write the same code for both when a simple function that does either
> PeekMessage or GetMessage depending on an argument would remove a lot of
> redundant code, for example the new function checkEvents(hwnd,
> peekmessage) would do the current Dialog() code with PeekMessage if
> peekmessage was set to 1, otherwise it'd do GetMessage, and the Dialog()
> and DoEvents() methods could be truncated to:

Well, the exit condition is different too, not just the call to 
GetMessage vs PeekMessage.  But that also could be based on the 
"argument".  I agree there is much redundant code there, also see DoModal.

> 
> DWORD
> Dialog(hwnd=NULL)
> 	HWND hwnd
> CODE:
> 	RETVAL = checkEvents(hwnd,0);
> OUTPUT:
> 	RETVAL
> 
> DWORD
> DoEvents(hwnd=NULL)
> 	HWND hwnd
> CODE:
> 	RETVAL = checkEvents(hwnd,1);
> OUTPUT:
> 	RETVAL
> 
> 
> 
> Steve
> 
> 
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-- 
Glenn -- http://nevcal.com/
===========================
Like almost everyone, I receive a lot of spam every day, much of it
offering to help me get out of debt or get rich quick.  It's ridiculous.
-- Bill Gates

And here is why it is ridiculous:
  The division that includes Windows posted an operating profit of $2.26 
  billion on revenue of $2.81 billion.
  --from Reuters via 
http://biz.yahoo.com/rc/031113/tech_microsoft_msn_1.html

So that's profit of over 400% of investment... with a bit more 
investment in Windows technology, particularly in the area of 
reliability, the profit percentage might go down, but so might the bugs 
and security problems?  Seems like it would be a reasonable tradeoff. 
WalMart earnings are 3.4% of investment.