[vtk-developers] More (fundamental) nastiness in vtkImageMultipleInputFilter

Charl P. Botha c.p.botha at ewi.tudelft.nl
Mon Mar 15 18:18:54 EST 2004

Dear developers,

When vtkImageMultipleInputFilter calls ThreadedExecute, it's called with 
"this->GetInputs()" as one of its parameters, the idea being that the 
child class will know how many inputs to use.

The fundamental problem with this is that the Inputs array is only valid 
for an index < GetNumberOfInputs(), but that the child's implementation 
of ThreadedExecute has no access to this call.  NumberOfInputs starts at 
0 and grows as new inputs are added.

To see this go wrong, instantiate for example a vtkImageMathematics, set 
its first input and then call its Update() method.  Watch your 
application segfault.

This is because this class's ThreadedExecute() checks for 
this->Inputs[1], which is past the end of the Inputs array!  It finds 
_some_ value and subsequently tries to dereference it.  BOOM.

My suggestion for a fix (workaround?) is that authors of 
vtkImageMultipleInputFilter child classes call SetNthInput(NULL) for as 
many inputs as they maximally are going to check for in ThreadedExecute. 
  Alternatively (and this is far more invasive), NumberOfInputs should 
be passed to the ThreadedExecute method.

Any other ideas?


charl p. botha http://cpbotha.net/ http://visualisation.tudelft.nl/

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