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

[Philippe Pébay]

Hello David

Thanks for the suggestion. I looked into vtkCollection but the code was
running slow with large collections. But it is possible that I will not get
any better results with the vtkObjectArray. Are you surprised that the
vtkCollection did not scale well (my observation on only one platform)?

Thanks
Philippe


On Tue, Nov 20, 2012 at 6:41 PM, David Thompson
<david.thompson at kitware.com>wrote:

> Hi Philippe,
>
> I think the vtkObjectArray class sounds like a good idea, however be aware
> that vtkCollection already exists to fulfill a similar purpose.
>
>         David
>
> On Nov 20, 2012, at 12:28 PM, Philippe Pébay <philippe.pebay at kitware.com>
> wrote:
>
> > Hello David
> >
> > Yes, I think this is the best option. I am thinking that I could create
> this as a new concrete subclass of vtkAbstractArray available to all, and
> not only as a helper class internal to my hyper tree implementation. What
> do you think? Would this be useful?
> >
> > Thanks
> > Philippe
> >
> > On Tue, Nov 20, 2012 at 6:25 PM, David Gobbi <david.gobbi at gmail.com>
> wrote:
> > Hi Phillippe,
> >
> > Actually I was wrong about vtkVariant not having any size overhead.  It
> needs
> > to store the type along with the value.  So vtkVariantArray is no good
> for this.
> >
> > A helper class might be the best option.  You could make a vtkObjectArray
> > class which would be just like vtkVoidArray except that it would objects.
> >
> >  - David
> >
> >
> > On Tue, Nov 20, 2012 at 9:54 AM, Philippe Pébay
> > <philippe.pebay at kitware.com> wrote:
> > > 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
> >
> >
> >
> > --
> > 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
> > _______________________________________________
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>


-- 
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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