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

David Cole david.cole at kitware.com
Tue Nov 20 17:34:22 EST 2012 

Its implementation is just a linked list. It will be as fast as you
can possibly be for:

  - iterating the whole collection and doing something on each element
  - adding a new element to the end of the list

For all else, including finding or removing specific items (by index
or identity), it will be as ridiculously slow as you'd expect a linked
list to be...

After just a glance at the implementation, I'm not surprised it doesn't "scale".

If you need scalability, perhaps a better implementation could be
dropped in to the same API.


On Tue, Nov 20, 2012 at 5:25 PM, Philippe Pébay
<philippe.pebay at kitware.com> wrote:
> 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
>
> _______________________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
>
> Follow this link to subscribe/unsubscribe:
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