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

[Mark Roden]

Hi David,

Unfortunately,  the current vtk master branch is seriously broken in
its java wrappings.  I'm putting together a bug report now...

Thanks,
Mark

On Fri, Feb 11, 2011 at 10:09 AM, David Gobbi <david.gobbi at gmail.com> wrote:
> 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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>>>>
>>>
>>
>