We have determined that the cause of the crash in regression test
test/java/awt/Component/ComponentLeakTest is a Motif bug. Since a Motif fix
may not be available for sometime, we need to work-around this bug in our code.


Date: Fri, 2 Feb 2001 21:41:19 +0300
From: "Danila A. Sinopalnikov" <###@###.###>
To: David Mendenhall <###@###.###>
Cc: ###@###.###
Subject: Re: ComponentLeakTest crash
Mime-Version: 1.0
Content-Disposition: inline
User-Agent: Mutt/1.2.5i

Hi Dave,

i reproduced this bug once with the ComponentLeakTest. The stack trace
was exactly the same as the one you sent to me. It looks like this
problem is specific for FileDialog with an associated drop target. On
Solaris we use Motif XmFileSelectionDialog which is a compound objects
which contains several child widgets with Motif preregistered drop
sites - XmTextField widgets and scrollbars of XmScrolledWindow
widgets. When the FileDialog is disposed we remove a drop target. When
the drop target is removed the corresponding Motif drop site of the
dialog is unregistered. Then we proceed with disposal and destroy
XmFileSelectionDialog. It destroys all its children which unregister
their drop sites in corresponding destroy callbacks.
The test crashes when the drop site of a vertical scrollbar of a
scrolled window of a list is unregistered. It attempts to access a
parent drop site which is the dialog drop site which was previously
unregistered and its structures are destroyed. The crash happens when
we access the destroyed structure via dangling pointers.

I wrote a simple Motif test case (filedialog.c) which simulates the
ComponentLeakTest: it creates a file dialog and registers a drop site
on it, then unregisters a drop site and destroys the dialog.
The test crashes in exactly the same way. To reproduce run the test
case and press "Ok".

The test issues a warning:
Warning:
    Name:
    Class: XmFileSelectionBox
    Registering a widget as a drop site out of sequence.
    Ancestors must be registered before any of their
    descendants are registered.

But this warning is not the cause of the crash.

It looks like this is a Motif bug: if we register a composite drop
site on a parent widget, then register a drop site on its child, then
unregister the parent drop site, the test will crash if we try to
unregister a child drop site.

I checked it with another test case (checkbox.c). To reproduce the
crash, run the test and click 3 times on the checkbox. It will
demonstrate the same crash.

It is unclear why the java test case doesn't crash every time.

Currently the best solution i see is to unregister drop targets
registered on the file dialog children before we register a drop site
on a file dialog. I have to test it before sending.

Thanks,
Danila.