[Insight-users] Cannot abort properlly multithreaded filters

[Didier Rajon]

Hi,
I'm having problem trying to abort an itk filter which is multi-threaded (such as itkResampleImageFilter).
I'm using itk (v. 1.8), vtk (v.4.2) for the rendering, and Qt (v. 3.3.3) for the user interface on Linux red-hat . In my user interface, I have a dialog window that shows the progress of the filters and allows the user to stop the process by clicking an "abort" button.
If I run my program on a single processor machine, everything works fine, I see the progression of the filter on  the progress bar (for this I set an observer on the ProgressEvent), I can abort the filter (By calling the AbortGenerateDataOn() member of the filter), and I can re-execute the filter as I wish.  On the other hand, if I run my program on a 2-processor machine, each time I abort a multi-threaded filter and try to re-execute the filter right after the abort, a "segmentation fault" is produced.
I think this has to do with itkProgressReporter. I went to look at the code of itkProgressReporter and it seems to me, that the abort only affects the threadId 0, which means that the second thread (and probably all other threads if I had more than 2 processors) is still running after I abort the filter. If I re-execute the process just after the abort, I get the "segmentation fault". On the other hand, if I wait long enough before I re-execute the filter so that the second thread has time to complete, everything works fine.
I also checked the CPU consumption of my system (using the "top" command) and my process is still using CPU time after I abort the filter.  If I re-execute the filter before the CPU time of my process is down to 0, the "segmentation fault" occurs.  If I wait until the CPU time is finally down to 0, then I can re-execute the filter without problem.
Do I need to do something special in order to be able to abort my multithreaded filters, or is this a problem that should be handled by itkProgressReporter?

I also noticed that filters that use itkProgressAccumulator (such as itkDiscreteGaussianFilter) are not abortable (what ever the number of processors).  I went to look at the code of itkProgressAccumulator and I found that there is nothing done in this class (nor in itkDiscreteGaussianImageFilter) to propagate the AbortGenerateData flag to the sub-filters of the mini pipe-line.
Is this also a problem that I can solve be doing some special things in order to propagate the AbortGenerateData flag, or is this a problem that should be handled by itkProgressAccumulator?

Thanks for helping me solving these two problems.

Didier.



Didier A. Rajon
University of Florida
Department of Neurological Surgery
MBI L2100, PO Box 100265
GAINESVILLE, FL, 32610-0265
Tel: (352) 294 0144
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