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

[Bradley Lowekamp]

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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