[ITK-dev] [ITK] Thread-unsafety of transform classes FOLLUWUP

[Matt McCormick]

Thanks for the further investigations.

I think it should default to zero fixed parameters.  Here's a patch:

  http://review.source.kitware.com/#/c/17789/

Thanks,
Matt

On Tue, Oct 28, 2014 at 1:41 PM, Bradley Lowekamp
<blowekamp at mail.nih.gov> wrote:
> Perhaps the constructor needs another argument name numberOfFixedParameters,
> which defaults to the prior argument?
>
> Brad
>
> On Oct 28, 2014, at 1:21 PM, Williams, Norman K
> <norman-k-williams at uiowa.edu> wrote:
>
> This is mostly for Bradley Lowenkamp and Matt McCormick, but at some point
> the wider developer community will be affected and input solicited.
>
> The MatrixOffsetTransformBase has 3 values in its FixedParameters, which is
> the values of the center of rotation.
>
> There was a mystery as to why MatrixOffsetTransformBase starts out with 12
> fixed parameters, when it only really has 3.
>
> The reason is in the constructor for Transform, which initializes the
> FixedParameters to have the same number of values as the Parameters.
>
> This is a design flaw; it represents the Anti-Pattern “Initialize a
> member/variable to a default that is almost always wrong.”
>
> This leads to most Transform classes resizing the FixedParameters when
> GetFixedParameters is called, and assigning their value based on the actual
> fixed parameters for that Transform class.
>
> This is thread-unsafe, since resizing m_FixedParameters involves  a
> free/allocate pair.
>
> template <typename TScalar,
>           unsigned int NInputDimensions,
>           unsigned int NOutputDimensions>
> Transform<TScalar, NInputDimensions, NOutputDimensions>
> ::Transform(NumberOfParametersType numberOfParameters) :
>   m_Parameters(numberOfParameters),
>   m_FixedParameters(numberOfParameters)
> #ifdef ITKV3_COMPATIBILITY
>   , m_SharedLocalJacobian(NOutputDimensions, numberOfParameters)
> #endif
> {
> }
>
>
>
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