[vtkusers] Reference counting in 6.3

[Weiguang guan]

Hi Dan,

Thank you very much for the reply.

I still use the old way (vtkABC *v= vtkABC::New()) rather than using VTK 
smart pointer. The reference counting mechanism of VTK must have changed 
although I don't know when (which version) that happened.

The reference count of a VTK object used to be 1 right after its 
creation. But now it is not always the case. I find source objects (like 
vtkCubeSource, vtkImageEllipsoidSource, etc) have reference count = 2 
right after being created while filter object have reference count = 1. 
I haven't checked every class to see if there is an exception to the 
above finding.

Here is a three-line code section together with running results:
vtkCubeSource* cube = vtkCubeSource::New();                    // 
ReferenceCount of cube = 2
vtkShrinkPolyData* shrink = vtkShrinkPolyData::New();     // 
ReferenceCount of cube = 2, ReferenceCount of shrink= 1
shrink->SetInputConnection(cube->GetOutputPort()); // ReferenceCount of 
cube = 2, ReferenceCount of shrink= 2
It can not be explained by the old VTK reference counting mechanism.

Best,
Weiguang

On 21/10/2015 3:11 PM, Dan Lipsa wrote:
> Hi Weiguang,
> Take a look at
> http://www.vtk.org/Wiki/VTK/Tutorials/SmartPointers
> This might clarify some of your questions. You have to remember that 
> the reference count is stored in the objects themselves unlike the c++ 
> shared_ptr where the reference count is stored in the shared pointer 
> object.
>
> For the first question: do you assign the object to a vtk smart 
> pointer? That would explain why the reference count is 2.
> For the rest of the questions: when you set up the pipeline there are 
> other objects involved besides the filter themselves, so it is harder 
> to understand of the reference count.
>
> Also you can set VTK_DEBUG_LEAKS when you build VTK if you are 
> concerned about leaks.
>
> Dan
>
>
> On Thu, Oct 15, 2015 at 4:13 PM, Weiguang guan 
> <guanw at rhpcs.mcmaster.ca <mailto:guanw at rhpcs.mcmaster.ca>> wrote:
>
>     Hello,
>
>     I find, in debug mode, that the ReferenceCount of a
>     vtkImageEllipsoidSource object becomes 2 right after being
>     initiated (vtkImageEllipsoidSourc::New()). It should be 1 not 2,
>     right? How could this happen?
>
>     My second question is --- when you make a connection
>     A->SetInputConnection(B->GetOutputPort()); Whose reference count
>     will be increased by 1, A or B? I think B's reference count should
>     be increased because it is used by A. But what I find is just the
>     opposite.
>
>     My third question is about setting up more than 1 connection for a
>     filter. Taking vtkImageMathematics as an example, I do
>     vtkImageMathematics* A = vtkImageMathematics::New();
>     A->SetInputConnection(0, B1->GetOutputPort();
>     A->SetInputConnection(0, B2->GetOutputPort();
>
>     I find that the reference count of A gets increased by the first
>     SetInputConnection() call only.
>
>     Can someone explain how reference counting works in VTK? Thanks.
>
>     Best,
>     Weiguang
>     _______________________________________________
>     Powered by www.kitware.com <http://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
>
>     Search the list archives at: http://markmail.org/search/?q=vtkusers
>
>     Follow this link to subscribe/unsubscribe:
>     http://public.kitware.com/mailman/listinfo/vtkusers
>
>

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://public.kitware.com/pipermail/vtkusers/attachments/20151023/9a803f83/attachment.html>