Re: [perl-win32-gui-hackers] User Object leak for combobox

[Robert M. <rm...@po...>]

A long time ago Jeremy White wrote:
> When the code below is run, it leaks User objects in the task manager. This 
> is with the latest codeline running under XP.

And under Win98 and Win2k, all versions of perl that I have.

> Both -dropdown and -dropdownlist options highlight the leak. I've have a 
> quick glance through the code but can't seem to find anything that could 
> cause this - a windows bug perhaps?

I'm on a roll today!  I've just committed a change that fixes this.  I 
may fix all sorts of other memory leaks for dynamically 
created/destroyed child windows.

When you call DestroyWindow on a window, Windows automatically calls 
DestroyWindow on all it's children.  However, the drop-down listview dox 
is not a child of the combobox window (it's a top-level window, so that 
it can draw outside the main window's client area).

When DestroyWindow is called on a ComboBox, the ComboBox itself takes 
responsibility for tidying up the drop-down window, which it does in 
it's WM_NCDESTROY handler.

However, we tidy-up our PERLUD structure in our WM_DESTROY handler, and 
we never removed our sub-class proc, restoring the original windows 
prodedure for the controls.  Hence, the WM_NCDESTROY messages were being 
delivered to our subclass proc, and because PERLUD has been freed we no 
longer knew where to send the WM_NCDESTROY, and so passed it to 
DefWindProc. Oops, no longer tidying up the Combo-box drop-down.

I've added a couple of lines to to our perud_free() routine to restore 
the original window proc (if there was one), so the WM_NCDESTORY 
messages go to the control's handler.  This fixes this problem, and 
potentially many others where controls may have tidied-up in their 
WM_NCDESTROY handlers.

Regards,
Rob.

> 
> It's only a minor problem, and again only an issue if dynamic controls are 
> repeatedly created/destroyed. Saying that, there is only a 10K limit on 
> objects before things go boom - and win32-gui does seem to create a lot of 
> objects - my app - before it's done anything has 650+, so it might be 
> highlighting some other problem.
> 
> Cheers,
> 
> jez.
> 
> 
> use strict;
> use warnings;
> $|=1;
> use Win32::GUI();
> 
> my $main = new Win32::GUI::Window (
> 	-size => [400,400],
> );
> 
> for (1..100) {
> my $box=$main->AddCombobox(
>     -name => 'combo',
>     #-dropdownlist => 1,
>     -dropdown => 1,
>     -left => 100,
>     -top  =>4,
>     -width => 100,
>     -height => 100,
> );
> print "$box \n";
> sleep(1);
> }
> 
> 
> 
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