[Interest] QObject, PIMPL and overloading operator new

[Bo Thorsen]

Den 16-08-2013 15:04, Peter Koek skrev:
>
>  > Den 16-08-2013 11:34, Peter Koek skrev:
>  > > Suppose that I have objects deriving from QObject and want to control
>  > > their dynamic allocations for performance reasons. I would overload
>  > > operator new to allocate them, for example, into a pool. None of
> this is
>  > > implemented in any way yet.
>  > > The objects themselves would now be allocated in the pool. However,
>  > > since I didn't overload the operator new of QObjectPrivate it would not
>  > > be allocated into the pool which partly defeats the purpose, as I still
>  > > have a default allocation.
>  > > My question is: can I control the way the private parts of Qt
>  > > (specifically, QObjectPrivate) are allocated?
>  >
>  > Not without modifying the Qt sources. It's impossible.
>  >
>  > > I'd also like to verify the following statements in the context of an
>  > > LGPL license. I'd like to keep my source closed, so modifying the Qt
>  > > source directly is not possible. I'd also rather not derive my own
> PIMPL
>  > > object from QObjectPrivate to overload operator new, as it would
> destroy
>  > > binary compatibility with future versions of Qt5, even when not using
>  > > any of the QObjectPrivate members.
>  >
>  > As Konstantin already replied, it's not a problem to supply a modified
>  > Qt under LGPL. Only the modifications to Qt itself has to be supplied.
>
> That's why I wanted my statements verified (or falsified). Thanks for
> the info guys!
>
> Just for the record, has anyone ever reported noticeable performance
> degradation / heap segmentation when allocating/deallocating many
> (1000+) QObject derived types several times throughout the lifetime of
> an application?

I know it's dangerous to attempt guessing at optimizations, but I'll do 
it anyway: I'll bet you a nice bowl of tomate soup that the time spent 
on allocation of memory is completely dwarfed by the constructor chain 
of QObject. Forget it.

Bo.

-- 
Bo Thorsen, European Qt Manager, Integrated Computer Solutions
ICS - Delivering World-Class Applications for Embedded & Mobile Devices
http://ics.com/services