Hi Przemek,
Okay, I now get what's happening. I didn't count with the
fact that this problem can be exploited by EXIT PROC and
not just rogue error handler, but yeah, EXIT will trigger
these just if they were part of the handler.
This is pretty grave...
Now I've simply removed this dbCloseAll() from this EXIT PROC,
since it's not crucial anyway.
Brgds,
Viktor
On 2008.11.03., at 13:10, Przemyslaw Czerpak wrote:
On Mon, 03 Nov 2008, Szak�ts Viktor wrote:
Hi Viktor,
This code will consistently GPF (tried in 1.0.1 BCC 5.5,
current 1.0.1dev with MSVC 2005, and a bit older 1.1.0dev with BCC
5.8)
---
PROC Main()
USE nothere // This file should not exist, and a QUIT should be
selected in the RTE alert.
RETURN
EXIT PROCEDURE App_Exit()
dbCloseAll()
RETURN
---
Exactly and it's an example of the problem I was talking about when
user code closes open WA when some other code still operates on it.
EXIT procedures in ST mode are executed just after QUIT in RT error
before control returns to RDD. It's Clipper compatible behavior.
In MT mode I change it to execute EXIT procedures after leaving all
functions by all threads so this code will not exploit the problem
but it does not fix it. Such situation can be created also in other
ways too, f.e. custom error handler can close WA on which someone
operates. To resolve it we will need similar mechanism to the one I
added to GT code and each time WA pointer is accessed then it should
be later freed. In GT it's done by hb_gt_Base()/hb_gt_BaseFree() and
it will force many modifications in existing RDD code.
We can also try to create some partial solution but it will only
reduce the problem.
The effect of the above code depends on memory context. After
dbCloseAll() the RDD code will operate on freed memory where
WA were located. It may cause GPF or not but of course it serious
bug.
best regards,
Przemek
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