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

[Philippe Pébay]

Hello David

Thanks for the summary about the absence of performance hit when using SPs
as opposed to RPs. I will remember it and use them more often as a result.

Regarding the variant array, yes, the conversion to vtkObject is a concern.
I think that the most efficient option would be to create a small helper
class that would internally store a raw array of pointers. That helper
would derive from vtkObjectBase. That should avoid any perfomance hit.

Philippe

On Tue, Nov 20, 2012 at 5:49 PM, David Gobbi <david.gobbi at gmail.com> wrote:

> 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
>



-- 
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 <http://www.kitware.fr/>
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