[lazarus] New Bug Entered

[Michael Van Canneyt]

On Mon, 14 Jul 2003, Mattias Gaertner wrote:

> On Sun, 13 Jul 2003 18:28:08 -0400
> bugtracker at miraclec.com wrote:
>
> >
> > Title: Datamodule generates AV on Lazarus exit
> >
> > Entered by: Tom Lisjac
> >
> > When a datamodule is renamed, OldCreateOrder is set and OnCreate and
> > OnDestroy events exist, Lazarus will AV upon exit with 1.0.10. Here are
> > the steps to reproduce:
> >
> > Bring up Lazarus in a new project.
> > Add a datamodule with File | New | Datamodule
> > With Property editor:
> >    Rename the datamodule to dmt
> >    Set OldCreationOrder to True
> >    Create empty OnCreate and OnDestroy event handlers
> > Exiting Lazarus (saving or not) generates an AV
> >
> > This problem appeared after upgrading to 1.0.10 in a datamodule that had
> > been working fine with 1.0.7.
>
> Now, there you found a difficult thing. I always wonder, when it will
> appear. The IDE creates datamodule/forms descendents on the fly. That means,
> it really creates new classes and procedures at runtime. These procedures
> are empty and do nothing. The current trick is to copy an empty procedure. I
> was always sure, that this will give us trouble, as soon as the caller
> checks the stack or uses some special calling convention. Now you find an
> example:
>
> try
>   AnEvent(Self);
> except
> end;
>
> When the 'except' frees the exception frame, it runs into trouble (internal
> error).
> I have commented the try..except in the LCL, so this error is hidden.
> One correct solution is to create better "empty procedures". This means an
> empty procedure, with the right length of parameters. I'm not sure how to do
> this for all kinds of calling conventions and processors.

You can't.

> Another solution is to simulate procedures. That means the procedures are
> not really set. But this requires changing TReader/TWriter to handle fake
> events and the RTTI will be incomplete.
> I prefer the first solution.
>
> Maybe a fpc guru can give me a hint.

Before destroying your instances, all methods should simply be set to nil.
This is OK as long as it happens after the form file was written.

Michael.