[vtkusers] stenciling problem-- is this code thread safe?

[David Gobbi]

I should add: with the current VTK master and release branches,
vtkPolyDataToImageStencil no longer requires vtkLinearExtrusionFilter
to be used beforehand.  So you could try that.

 - David


On Fri, Feb 11, 2011 at 11:06 AM, David Gobbi <david.gobbi at gmail.com> wrote:
> I was doubtful about the global memory, but I looked through the
> filters just to be sure.  And guess what I found... here is some
> highly suspect code in vtkLinearExtrusionFilter:
>
> double *vtkLinearExtrusionFilter::ViaNormal(double x[3], vtkIdType id,
>                                           vtkDataArray *n)
> {
>  static double xNew[3], normal[3];
>  int i;
>
>  n->GetTuple(id, normal);
>  for (i=0; i<3; i++)
>    {
>    xNew[i] = x[i] + this->ScaleFactor*normal[i];
>    }
>
>  return xNew;
> }
>
> Code like the above is definitely going to cause thread problems.
> And this isn't the only place in that class where code like this appears.
>
> Yikes!
>
>  - David
>
>
> On Fri, Feb 11, 2011 at 10:46 AM, Mark Roden <mmroden at gmail.com> wrote:
>> What I mean is, I have a vtkPolyData that has been DeepCopied and a
>> vtkImageData that is binary and distinct from all other data.
>>
>> When I call the previously listed code with multiple threads (each
>> with their own polydata and binary image to fill in), the result is
>> generally a very garbled image.  If I call from a single thread in
>> series, one for each polydata/image pair, then everything works out
>> fine.
>>
>> So it seems to me that something in the above series isn't thread
>> safe.  Each thread is declaring its own local objects, but is there
>> some global memory that's being used or accessed here?
>>
>> On Fri, Feb 11, 2011 at 9:23 AM, David Gobbi <david.gobbi at gmail.com> wrote:
>>> Hi Mark,
>>>
>>> Explain in more detail what you mean by "call from multiple threads".
>>> VTK is, in general, not thread safe and you cannot call Update() on
>>> a filter from more than one thread.  Each thread needs to have its own
>>> set of filters.  And in general, you cannot feed a data object into more
>>> than one thread, because even simple methods like GetBounds() are
>>> not thread safe.
>>>
>>> When using VTK from multiple threads, it is necessary to apply
>>> extreme caution.
>>>
>>>  - David
>>>
>>>
>>> On Fri, Feb 11, 2011 at 10:00 AM, Mark Roden <mmroden at gmail.com> wrote:
>>>> Hi all,
>>>>
>>>> This code does not have threads enabled in vtk 5.6.1 (the code is in Java):
>>>>
>>>>        vtkLinearExtrusionFilter extruder = new vtkLinearExtrusionFilter();
>>>>        extruder.SetInput(data);
>>>>        extruder.SetVector(0, 0, spacing[2]);
>>>>        extruder.Update();
>>>>        vtkPolyData extruderOutput = extruder.GetOutput();
>>>>
>>>>        vtkPolyDataToImageStencil pol2Stenc = new vtkPolyDataToImageStencil();
>>>>        pol2Stenc.SetTolerance(0);
>>>>        pol2Stenc.SetInput(extruderOutput);
>>>>        pol2Stenc.SetInformationInput(binaryOrgan);
>>>>        pol2Stenc.Update();
>>>>        vtkImageStencilData pol2StencOutput = pol2Stenc.GetOutput();
>>>>
>>>>        // This is where the memory leak is!!!!
>>>>        vtkImageStencil stencil = new vtkImageStencil();
>>>>        stencil.SetInput(binaryOrgan);
>>>>        stencil.ReverseStencilOn();
>>>>        stencil.SetStencil(pol2StencOutput);
>>>>        stencil.Update();
>>>>
>>>>        // We're doing this because of an email to Mark
>>>>        // that says this will fix our memory issues
>>>>        final vtkImageData stencilOutput = stencil.GetOutput();
>>>>        final vtkImageData imageToKeep = new vtkImageData();
>>>>        imageToKeep.DeepCopy(stencilOutput);
>>>>        stencilOutput.Delete();
>>>>
>>>> When I try to call this code from multiple threads (ie, to create the
>>>> stencils for multiple organs), Bad Things happen, as in, the data are
>>>> entirely corrupted.  Is this code thread safe?
>>>>
>>>> Mark
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>>
>