[Qt-interest] On overriding qMalloc in QVector

[Benoit Jacob]

2009/10/22 Thiago Macieira <thiago at kde.org>:
> Em Quinta-feira 22 Outubro 2009, às 16:40:07, você escreveu:
>> We need to pass the alignment requirements from the compiler to the
>>  allocator  function. So we need a qMallocAligned function.
>
> Unfortunately, that won't work.
>
> I managed to get an aligned QVector data, but the change is not data-
> compatible.

ah ok.

>
> If I put this change in Qt 4.6, then we could have newly-compiled code
> allocating aligned buffers passing a QVector to code that wasn't recompiled. If
> that older code tried to free the vector, the application would most likely
> crash.
>
> I think I can safely make the change for QMap and QHash though. QList isn't
> affected by this issue, while QLinkedList cannot be solved properly (it uses
> new on QLinkedListNode<T>).

hm, since this can't be done for QVector, i'd say don't bother. it
would only make things more complicated.
Somehow the trick of redefining Q_DECL_IMPORT fixes the crash we're
experiencing so we'll just cross fingers and go with that.

Just please consider
 - either adding custom allocator support in Qt 5
 - or make sure to honor the alignment settings when compiling in
c++1x (new keyword alignof, not yet supported by any compiler that i
know). (Of course you won't be able to require c++1x for another 10
years but you might take advantage of it when it is enabled).

Either solution would satisfy me though the former is more general.

Cheers,
Benoit

>
> --
> Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
>  Senior Product Manager - Nokia, Qt Development Frameworks
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