On Nov 1, 2009, at 10:33 AM, Jean-Denis Muys wrote:
>
>> Followup on my memory corruption bug:
>>
>> I got a few suggestions (thanks everybody):
>>
>> - a memory watch point: I may be able to use that idea, but so far, I
>> could not clearly identify a fixed location that's corrupted.
>> - Guard Malloc: I have a machine that I started about 12 hours ago
>> with Guard Malloc enabled. The host app hasn't finished launching
>> yet.
>> - Valgrind: I still have 10.5 running on a Mac mini, so I started the
>> host app under Valgrind. It's veryyyy slow. Still running.
>> - static analyzer: it doesn't detect anything wrong (but of course,
>> my
>> code is C++).
>>
>> I also wanted to report that I made some significant progress on how
>> to call malloc heap checking facility at will.
>
> I managed to "fix" the memory corruption bug I had. Actually, I
> still don't understand why it used to crash and not anymore. This is
> a rather peculiar situation, that you might find interesting.
>
> The following idiom corrupted memory:
>
> long bad()
> {
> [...]
>
> sql::ResultSet *results = preparedStmt->executeQuery();
>
> [...]
>
> delete results;
> zoneCheck();
>
> return result;
> }
>
> While this one runs fine and nice:
>
> long good()
> {
> [...]
>
> std::auto_ptr<sql::ResultSet>results(preparedStmt->executeQuery());
>
> [...]
>
> zoneCheck();
>
> return result;
> }
>
>
> Since all std::auto_ptr does is to call delete on its internal
> pointer when it goes out of scope (even in case of an exception), I
> am still totally puzzled by this behaviour.
>
> As an aside, the library behind all this is mySQL's C++/Connector.
>
> I'd be interested by a possible explanation: my C++ is not sharp (no
> pun, really) enough to grasp all the subtleties.
Well, in the first case delete is called *before* zoneCheck, and in
the second, it is called *after*.
To me, that suggests that looking at the destructor for sql::ResultSet.
-- Marshall
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