[Insight-developers] Static initialization in itkImageSource causes early registration of ITKIOFactory

[Bradley Lowekamp]

Hello JC,

This is quite an interesting side-effect of the changes I introduced.

I am glad that you were able to figure this out. For a variety of reasons, it's likely a very bad thing for all that to occur during static initialization in ITK. So it certainly needs to be fixed.

I agree that lazy initialization is the way to go. Unfortunately it needs to be thread safe so its a little more completed.

ITKv4 performs the factory initialization when the user creates the first ITK object.  And that changed with this patch, and need to be fixed.

CONCLUSION:

Inside ITK, we can not use statically initialized ITK object.

Brad

On Apr 3, 2013, at 10:54 AM, Jean-Christophe Fillion-Robin <jchris.fillionr at kitware.com> wrote:

> Hi Brad, 
> 
> Following commit 4c47e7d [1] of February 19th and commit defb9c1 [2] of March 1st, due to static initialization, the initialization of ObjectFactory  now happens when ITK shared library are loaded [3][4].
> 
> This caused a regression in Slicer where the ObjectFactory were expected to be loaded while attempting to load an image for the first time. 
> 
> In Slicer case, the environment variable ITK_AUTOLOAD_PATH was set during the initialization of the qSlicerCoreApplication, which is now too late.
> 
> By commenting line where a new ImageRegionSplitterSlowDimension is instantiated [5][6] and updating the method "GetImageRegionSplitter / GetGlobalDefaultSplitter" to return 0 [7][8], the initialization can happen on demand instead of when ITK libraries are loaded.
> 
> An easy solution for us would be to ensure the "ITK_AUTOLOAD_PATH" environment variable is set in the application launcher for Windows and Linux application and set in Info.plist file associated with the application bundle on MacOSX [9]
> 
> To provide more details, within Slicer we set the CMake variable ITK_NO_IO_FACTORY_REGISTER_MANAGER before doing an "include(${ITK_USE_FILE}) so that IOFactory are loaded only by calling the method "itkFactoryRegistration" associated with a shared library we named ITKFactoryRegistration. This approach allowed us to disable the automatic registration of factory in selected part of the code. More details here [10]
> 
> It seems the new ITK commits 4c47e7d and defb9c1 prevent from completely leveraging the use of ITK_NO_IO_FACTORY_REGISTER_MANAGER variable, the code should probably be updated to consider this.
> 
> 
> Let me know what you think.
> 
> Thanks
> Jc
> 
> 
> [1] https://github.com/Kitware/ITK/commit/4c47e7d
> [2] https://github.com/Kitware/ITK/commit/defb9c1
> [3] https://github.com/Kitware/ITK/blob/4c47e7d672bad5d83b92c2df5f293cca618e2740/Modules/Core/Common/src/itkImageSource.cxx#L27
> [4] https://github.com/Kitware/ITK/blob/4c47e7d672bad5d83b92c2df5f293cca618e2740/Modules/Core/Common/src/itkObjectFactoryBase.cxx#L142-144
> [5] https://github.com/Kitware/ITK/blob/defb9c1d084c8d55df61947587427839f9968ecf/Modules/IO/ImageBase/src/itkImageIOBase.cxx#L760
> [6] https://github.com/Kitware/ITK/blob/4c47e7d672bad5d83b92c2df5f293cca618e2740/Modules/Core/Common/src/itkImageSource.cxx#L27
> [7] https://github.com/Kitware/ITK/blob/defb9c1d084c8d55df61947587427839f9968ecf/Modules/IO/ImageBase/src/itkImageIOBase.cxx#L765
> [8] https://github.com/Kitware/ITK/blob/4c47e7d672bad5d83b92c2df5f293cca618e2740/Modules/Core/Common/src/itkImageSource.cxx#L32
> [9] http://www.herzbube.ch/blog/2009/01/how-set-environment-variables-mac-os-x-applications
> [10] https://github.com/Slicer/Slicer/commit/03b8961
> 
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