[vtk-developers] Shared ownership of an array of pointers

[David Gobbi]

Hi Phillippe,

A vtkVariant is 64 bits, it should be no larger than a pointer.  There
is a function call overhead in ToVTKObject(), which might be a concern to you.

The vtkSmartPointer is exactly the same size as a pointer, so there is no size
overhead.  It has no computational overhead, either, except for the "operator=",
the copy constructor, and the destructor (I wouldn't even count the overhead in
the destructor, because you have to call ->Delete() eventually anyway).  So do
not avoid smart pointers because you are worried about efficiency.  The VTK
smart pointers are very efficient because vtkObjectBase already has a built-in
reference count.

 - David


On Tue, Nov 20, 2012 at 9:35 AM, Philippe Pébay
<philippe.pebay at kitware.com> wrote:
> Hello David
>
> Thanks for the suggestion: I am concerned by the overhead that comes with
> variants. Wouldn't it be more lightweight to use a vtkVoidArray instead? The
> array can potentially contain O(10⁶) pointers. By the way this is for the
> same reason that I have, so far, refrained from using vtkSmartPointers as
> opposed to raw pointers, by fear of the overhead involved. Is this extra
> caution excessive?
>
> Thanks
> Philippe
>
> On Tue, Nov 20, 2012 at 5:31 PM, David Gobbi <david.gobbi at gmail.com> wrote:
>>
>> Hi Philippe,
>>
>> If the pointers are pointers to VTK objects, then you can use
>> vtkVariantArray.
>>
>>  - David
>>
>>
>> On Tue, Nov 20, 2012 at 9:29 AM, Philippe Pébay
>> <philippe.pebay at kitware.com> wrote:
>> > Just an idea: couldn't a vtkVoidArray be used (or abused) as container
>> > of
>> > raw pointers, that would be appropriately downcasted internally to the
>> > concrete type to which they are supposed to point? For instance, instead
>> > of
>> > having a
>> >  vtkMyInternalObject** obj
>> > instance variable, couldn't I use a
>> >  vtkVoidArray* obj
>> > instead, where each entry in obj would be the raw pointer to a
>> > vtkSmartPointer<vtkMyInternalObject>?
>> >
>> > Thanks
>> > Philippe
>> >
>> >
>> > On Tue, Nov 20, 2012 at 5:14 PM, Philippe Pébay
>> > <philippe.pebay at kitware.com>
>> > wrote:
>> >>
>> >> Hello Kyle
>> >>
>> >> Yes, I would want to avoid a dependency on Boost. But this is basically
>> >> what I am tried to reproduce (the Boost shared array of pointers).
>> >>
>> >> Thanks
>> >> P
>> >>
>> >>
>> >> On Tue, Nov 20, 2012 at 5:13 PM, Kyle Lutz <kyle.lutz at kitware.com>
>> >> wrote:
>> >>>
>> >>> Would using boost suffice? Or do you want a solution using just VTK?
>> >>>
>> >>> -kyle
>> >>>
>> >>> On Tue, Nov 20, 2012 at 7:58 AM, Philippe Pébay
>> >>> <philippe.pebay at kitware.com> wrote:
>> >>> > Hello all,
>> >>> >
>> >>> > I need to keep track of shared ownership of an array of pointers.
>> >>> > Can
>> >>> > someone point me towards an example of code that already does this?
>> >>> > This
>> >>> > should amount to a small helper class that contains the array of
>> >>> > pointers
>> >>> > along with a reference count.
>> >>> >
>> >>> > Thank you!
>> >>> > Philippe
>> >>> >
>> >>> >
>> >>> > --
>> >>> > Philippe Pébay, PhD
>> >>> > Director of Visualization and High Performance Computing /
>> >>> > Directeur de la Visualisation et du Calcul Haute Performance
>> >>> > Kitware SAS
>> >>> > 26 rue Louis Guérin, 69100 Villeurbanne, France
>> >>> > +33 (0) 6.83.61.55.70 / 4.37.45.04.15
>> >>> > http://www.kitware.fr