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

[David Gobbi]

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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>>
>