Re: listview: infoPtr might be invalid after WM_NOTIFY

[Dimi Paun]

> Dimi, if you think this is ugly, or if you are working on a better
> solution,
> please do protest.

Well, in part it's a matter of style, and IMO this will clutter the code.
Moreover, the patch as it is now works by accident. For example:

   /* send NM_RELEASEDCAPTURE notification */
-  notify(infoPtr, NM_RELEASEDCAPTURE);
+  notify(infoPtr->hwndSelf, NM_RELEASEDCAPTURE);

   if (!infoPtr->bFocus) SetFocus(infoPtr->hwndSelf);

See, after the notify() the infoPtr may be invalid. This means
that if we assume the control can be deleted at any point we
send out a notification, we have to reget and recheck infoPtr
after every function call. There's got to be a better way.

I personally think an exception-based solution would be better.
This is what exceptions where invented. I know they look alien
in C, but I use them every day in Java for good effect.
It's true, we have to be careful to release resources along the
way, but we have only 6 such allocations that need protecting,
and they are localized. And there we already have a try/catch
simulated with goto's.

Another approach may be to ref count the structure pointed to
by infoPtr, and release it at exit from WinProc when the count
is 0. Sort of a poor man's garbage collection. I'm cool with
this too, and in fact it may be cleaner then the exception-based
solution.

-- 
Dimi Paun <dimi(a)lattica.com>
Lattica, Inc.

listview: infoPtr might be invalid after WM_NOTIFY

[Lionel Ulmer]

On Tue, Sep 20, 2005 at 11:51:00AM -0400, Dimi Paun wrote:
> I personally think an exception-based solution would be better.
> This is what exceptions where invented.
> (...)

Correct me if I am wrong (I know absolutely nothing about how the listview
code works) but a flaw of the 'exception based' solution would be if the
application allocated memory that would re-use the just freed memory pointed
by 'infoPtr'.

This would mean that no exception would be triggered while the code would
still be wrong as it would write / read something that is clearly not what
it expects.

Now one could say that knowing the heap allocation algorithms this case
should never happen, but well, better safe than sorry.

       Lionel

-- 
		 Lionel Ulmer - http://www.bbrox.org/

listview: infoPtr might be invalid after WM_NOTIFY

[Dimi Paun]

On Wed, 2005-09-21 at 00:11 +0200, Lionel Ulmer wrote:
> Correct me if I am wrong (I know absolutely nothing about how the
> listview code works) but a flaw of the 'exception based' solution
> would be if the application allocated memory that would re-use the
> just freed memory pointed by 'infoPtr'.

This is true only if we rely on the access violation exception
(which is a possibility, I admit). But the test patch that I sent
checked the hwnd after each notify message with IsWindow(), and
if invalid it was throwing a custom exception.

So no, it does not suffer from the flaw that you mentioned.

-- 
Dimi Paun <dimi(a)lattica.com>
Lattica, Inc.

listview: infoPtr might be invalid after WM_NOTIFY

[Lionel Ulmer]

On Tue, Sep 20, 2005 at 11:32:38PM -0400, Dimi Paun wrote:
> This is true only if we rely on the access violation exception
> (which is a possibility, I admit). But the test patch that I sent
> checked the hwnd after each notify message with IsWindow(), and
> if invalid it was throwing a custom exception.

OK, so next time I will read the patch before saying stupid things :-)

        Lionel

-- 
		 Lionel Ulmer - http://www.bbrox.org/