[vtkusers] Does vtkInformation::Set(DATA_OBJECT, ...) perform a deep copy?

Wed May 1 17:56:17 EDT 2013

The code with smartpointer should also work.
Assignment to smart pointer will increase the counter.
So output will not be deleted when filter goes out of scope.

( http://www.vtk.org/Wiki/VTK/Tutorials/SmartPointers )

But if you look in VTK api you would not find public functions which return
or pass smartpointer.
I think for a reason to avoid duplication of similar function. Returning
pointer is minimal and sufficient.

So people (at least me) are avoiding it, especially if you write piece of
code which later could be considered to be included in vtk.

Regards,
    Alex

On Wed, May 1, 2013 at 9:32 AM, Dominique Töpfer
<dominique at toepfer-web.de>wrote:

>  On 01.05.2013 16:50, Berk Geveci wrote:
>
> If you want the output of an algorithm to stick around after deleting it,
> you need to call Register() on the data object. Something like:
>
>      vtkSmartPointer<vtkReader1> Reader1 =
> vtkSmartPointer<vtkReader1>::New()
>     // set filename and update reader1
>     vtkDataSet * MyDataSet = Reader1->GetOutput();
>      MyDataSet->Register(0);
>
>
>
> Yes, but wouldn't you have to delete MyDataSet manually?
> Why not using SmartPointers also for MyDataSet? From what I understand
> after reading http://www.vtk.org/Wiki/VTK/Tutorials/SmartPointers , the
> following code should also work and memory is released automatically when
> the last pointer pointing to the data goes out of scope:
>
> vtkSmartPointer<vtkDataSet> MyFilter::GetMyDataSet( ... )
> {
>     vtkSmartPointer<vtkDataSet> MyDataSet;
>
>
>     if(SomeConditions)
>     {
>         vtkSmartPointer<vtkReader1> Reader1 =
> vtkSmartPointer<vtkReader1>::New()
>         // set filename and update reader1
>         MyDataSet = Reader1->GetOutput();
>     }
>     else
>     {
>         vtkSmartPointer<vtkReader2> Reader2 =
> vtkSmartPointer<vtkReader1>::New()
>         // set filename and update reader2
>         MyDataSet = Reader2->GetOutput();
>     }
>
>     return MyDataSet;
> }
>
> vtkSmartPointer<vtkDataSet> MyDataSet = GetMyDataSet( ... );
>
>
> Or did I miss something?
>
> Regards,
> Dominique
>
>
>
>  On Tue, Apr 30, 2013 at 5:14 PM, Sunrise <helios.corona at gmail.com> wrote:
>
>>  Thanks for the answer, Berk.
>>
>> I have a follow up question, which I guess I can solve it with strong
>> pointers. Assume the following
>>
>> vtkDataSet * MyFilter::GetMyDataSet(...)
>> {
>>
>> if(SomeConditions)
>> {
>>     vtkSmartPointer<vtkReader1> Reader1 =
>> vtkSmartPointer<vtkReader1>::New()
>>     // set filename and update reader1
>>     vtkDataSet * MyDataSet = Reader1->GetOutput();
>> }
>> else
>> {
>>     vtkSmartPointer<vtkReader2> Reader2 =
>> vtkSmartPointer<vtkReader1>::New()
>>      // set filename and update reader2
>>      vtkDataSet * MyDataSet = Reader2->GetOutput();
>> }
>>
>> // MyDataSet is out of scope here!
>> // Even if I remove if condition, they will be out of scope outside of
>> this function.
>>
>> return MyDataSet;
>>
>> }
>>
>> I want to make both reader1 and reader2 become SmartPointers. Otherwise
>> I have leak. At compile time I do not know how the code will end, only at
>> the run time it make the decision. So I do not know when to delete
>> reader1 and reader2.
>>
>> I do not want to use descrutor too. there are more readers than the
>> sample code that I put here, so at compile time the destructor do not know
>> how many reader1 and/or reader2 has been declared in order to delete
>> them manually. So, I prefer to declare all of them with Smart Pointers.
>>
>> But here is the problem: reader1 and reade2 are in clauses of If
>> condition, and they are in a function outside of RequestData. So they will
>> go out of scope.
>>
>> If using a strong pointer fix this problem, how can I apply a strong
>> pointer on MyDataSet in VTK?
>>
>> Again, thank you very much.
>>
>> -Sia
>>
>>
>>
>> On 04/29/2013 08:20 AM, Berk Geveci wrote:
>>
>> It does a shallow copy. The information object holds a strong reference
>> to the data object so
>>
>>  outputInfo->Set(vtkDataObject::DATA_OBJECT(),MyDataSet);
>>
>>  so it will increment the reference count of MyDataSet preventing it
>> from going out of scope.
>>
>>  -berk
>>
>>
>> On Sun, Apr 28, 2013 at 11:41 AM, Sunrise <helios.corona at gmail.com>wrote:
>>
>>>  I am wondering if the "Set" method in vtkInformation class performs a
>>> deep-copy or shallow-copy when I set a DATA_OBJECT into it?
>>>
>>> Suppose I have some vtkDataSet and I want to append them into outputInfoof a filter inside its
>>> RequestData method.
>>>
>>> int Filter1::RequestData(...)
>>> {
>>>     vtkSmartPointer<vtkSomeReader> myreader =
>>> vtkSmartPointer<vtkSomeReader>::New();
>>>     ...
>>>     vtkDataSet *MyDataSet = Reader->GetOutput();
>>>     outputInfo->Set(vtkDataObject::DATA_OBJECT(),MyDataSet);
>>>     ...
>>> }
>>>
>>> at the end of RequestData, both the pointer myreader and its data on
>>> the heap would be out of scope. Since I made them smart pointers, both
>>> pointer "myreader" and the data on the heap will be deleted (right?).
>>>
>>> But in the next filter of the pipeline (say Filter2 is connected to
>>> Filter1), I can receive the data in inputInfo
>>>
>>> int Filter2::RequestData(...)
>>> {
>>>     ...
>>>     ... inputInfo->Get(vtkDataObject::DATA_OBJECT());
>>> }
>>>
>>> I am wondering why still I can get the data, since data deferenced by
>>> MyDataSet in previous filter no longer exists?
>>>
>>> Does vtkInformation::Set perform a deep copy?
>>>
>>> Thank you.
>>>
>>> _______________________________________________
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>>
>>
>> _______________________________________________
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>>
>> Visit other Kitware open-source projects at
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>> Please keep messages on-topic and check the VTK FAQ at:
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>>
>
>
> _______________________________________________
> Powered by www.kitware.com
>
> Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html
>
> Please keep messages on-topic and check the VTK FAQ at: http://www.vtk.org/Wiki/VTK_FAQ
>
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>
>
> --
> Dominique Töpfer, Dipl.-Inform.
> Institute of Medical Physics
> University of Erlangen
>
>
> _______________________________________________
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>
> Visit other Kitware open-source projects at
> http://www.kitware.com/opensource/opensource.html
>
> Please keep messages on-topic and check the VTK FAQ at:
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>
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