[Insight-developers] multithreading update w/example code

[Miller, James V (Research)]

I think I located the Win32OutputWindow problem.

Here is my current best guess.

When multiple threads are being used, we create N-1 new threads
and use the main thread as the Nth thread to split the job across.
The Win32OutputWindow calls SendMessage() which sends a message
to the "main" thread and waits for its response.

So on a 2 processor system, the second thread sends a debug message
to the output window and waits for it to return.  The main thread 
also sends a debug message to the output window and waits for it to 
return.  The problem is that the main thread is too busy waiting 
for it to handle the message to handle the message.

I think we might be able to use PostMessage instead of SendMessage
or I can change the threading code so it always starts N threads and
does not use the main thread.  The latter will require figuring out
how to get the multi-threader code to handle the event loop AND
wait for the threads to finish.


-----Original Message-----
From: Miller, James V (Research) 
Sent: Monday, April 22, 2002 3:33 PM
To: 'Damion Shelton'; insight-developers@public.kitware.com
Subject: RE: [Insight-developers] multithreading update w/example code


I was able to duplicate the problem on a dual processor
WinNT system.

Here's the rub: the Win32OutputWindow is deadlocking when
multiple threads write at the same time.  This is occuring
because you have DebugOn() on the GradientImageFilter.

Turning DebugOff() on the GradientImageFilter and the program
works fine for me.



-----Original Message-----
From: Damion Shelton [mailto:dmshelto@andrew.cmu.edu]
Sent: Monday, April 22, 2002 1:47 PM
To: insight-developers@public.kitware.com
Subject: [Insight-developers] multithreading update w/example code


Hi,

In our continuing efforts to track down the multithreading weirdness with a 
dual Athlon XP machine, we've narrowed our test code down to the following 
example, which does not include any of our own code.

Based on the debug output, it looks like it hangs in the gradient filter. 
By "hangs", we mean that the processor usage drops to 0% and the program 
never returns.

Any ideas, please let us know. We can check this in as 
"itkMultithreadingTest" or something similar if that would be a help in 
diagnosing the problem.

Thanks,
Damion and Wilson

------

#include <stdio.h>

// Basic ITK stuff
#include "itkSize.h"
#include "itkIndex.h"
#include "itkImage.h"
#include "itkImageRegionIterator.h"
#include "itkPoint.h"
#include "itkShrinkImageFilter.h"
#include "itkGradientImageFilter.h"

// Image file reading
#include "itkImageFileReader.h"
#include "itkMetaImageIOFactory.h"

// Main for testing BloxImage/BloxPixel storage
void main()
{
  const unsigned int dim = 3;

  // Image typedef
  typedef itk::Image< unsigned char, dim > TImageType;
  typedef itk::ImageFileReader<TImageType> ImageFileReaderType;

  // The input file reader
  ImageFileReaderType::Pointer reader;

  //set up the reader and register the possible types
  reader = ImageFileReaderType::New();
  reader->DebugOn();
  itk::MetaImageIOFactory::RegisterOneFactory();
  reader->SetFileName("d:/brainweb/brainweb1.mha");
  reader->GetOutput()->SetRequestedRegionToLargestPossibleRegion();
  reader->Update();

  // Shrink by a factor of 2
  typedef itk::ShrinkImageFilter<TImageType, TImageType> ShrinkType;
  ShrinkType::Pointer pShrink = ShrinkType::New();
  pShrink->SetShrinkFactors(2);
  pShrink->SetInput( reader->GetOutput() );

  // Create a gradient filter
  typedef itk::GradientImageFilter<TImageType> TGradientFilter;
  TGradientFilter::Pointer gradFilter = TGradientFilter::New();
  gradFilter->DebugOn();
  gradFilter->SetInput( pShrink->GetOutput() );

  // Run the whole pipeline
  gradFilter->Update();

  // Get the output of the pipeline
  TGradientFilter::OutputImageType::Pointer gradOutput = 
gradFilter->GetOutput();
}
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