[ITK-dev] MatrixOffsetTransformBase::GetFixedParameters not ThreadSafe -- regression test?

[Williams, Norman K]

If the API says

const bool GetInverse(Self *inverse) const;

If that changes the internal state of the class, isn’t that false advertising?

Actually, I tried just fixing that one problem in MatrixOffsetTransformBase, and it just kicked the problem slightly down the road.

ImageMaskSpatialObject::IsInside also advertises as being a const method; yet it calls SetInternalInverseTransformToWorldToIndexTransform() which is ALSO marked as const, and yet modifies an instance variable.



From: Bradley Lowekamp <blowekamp at mail.nih.gov<mailto:blowekamp at mail.nih.gov>>
Date: Friday, October 24, 2014 at 12:25 PM
To: Mushly McMushmaster <norman-k-williams at uiowa.edu<mailto:norman-k-williams at uiowa.edu>>
Cc: ITK <insight-developers at itk.org<mailto:insight-developers at itk.org>>
Subject: Re: [ITK-dev] MatrixOffsetTransformBase::GetFixedParameters not ThreadSafe -- regression test?

Kent,

Mutable member are evil.

Would it be possible to have the m_Center and the m_FixedArray point to the same block of data?

Brad

On Oct 24, 2014, at 12:59 PM, Williams, Norman K <norman-k-williams at uiowa.edu<mailto:norman-k-williams at uiowa.edu>> wrote:

The problem is worse than I thought.

CompositeTransform::GetFixedParameters() dynamically resizes the FixedParameters array, and then does a bunch of std::copy to copy fixed parameters out of its list of sub-transforms.

The only way to make that thread safe is to use a Mutex lock to guard where it changes the member variable.

From: <Williams>, Mushly McMushmaster <norman-k-williams at uiowa.edu<mailto:norman-k-williams at uiowa.edu>>
Date: Friday, October 24, 2014 at 11:45 AM
To: ITK <insight-developers at itk.org<mailto:insight-developers at itk.org>>
Subject: [ITK-dev] MatrixOffsetTransformBase::GetFixedParameters not ThreadSafe -- regression test?

I was going to address this bug that I just logged:

https://issues.itk.org/jira/browse/ITK-3324

Basically, if GetFixedParameters is called from multiple threads, it introduces a race to resize the internal fixed parameter array.

This was never  a problem before Hans Johnson’s recent patch to propagate fixed parameters int Transform::GetInverse() methods.  He added:

inverse->SetFixedParameters(this->GetFixedParameters());

which makes perfect sense.

I have a decent idea of how to make this better:  Set the fixed parameters’ size in the constructor for MatrixOffsetTransformBase, and set the fixed parameters in SetCenter.  I will review the other instances of GetFixedParameters and GetParameters to see if they’re similarly thread-unsafe.

But how do you write a regression test for this?




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