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

[Jean-Christophe Fillion-Robin]

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

<https://github.com/Kitware/ITK/blob/4c47e7d672bad5d83b92c2df5f293cca618e2740/Modules/Core/Common/src/itkImageSource.cxx#L27>
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