PERF: Remove SystemInformation data from ResourceProbe, fix issue #350

[N-Dekker]

ITK 4.9 added system info to itk::ResourceProbe (the base class of
itk::TimeProbe and itk::MemoryProbe), by calling GetSystemInformation()
in its constructor. This function call appeared very time consuming.
Using Visual Studio 2017 (Release configuration), it was observed that a single
GetSystemInformation() function call took more than 0.1 second.

This commit removes the this->GetSystemInformation() function call from
ResourceProbe, deprecates the member function, removes the related data
members, and only retrieves the system info when and where it is actually being
used: in PrintSystemInformation and PrintJSONSystemInformation.

Fixes issue #350, "Major performance issue TimeProbe, ResourceProbe
constructor", which was based on the analysis of an elastix example
case by Theo van Walsum (@tvanwalsum).

[dzenanz]

This generally looks good to me. I don't know whether anyone used GetSystemInformation via this class instead of directly, but even if they did the remedy would not be hard. It should be documented in ITK5 MigrationGuide document.

Interestingly, Mac build fails with this incomprehensible message:

Undefined symbols for architecture x86_64:
   "___cxa_deleted_virtual", referenced from:
      vtable for itk::MemoryProbe in itkMemoryProbe.cxx.o
      vtable for itk::ResourceProbe<unsigned long, double> in itkMemoryProbe.cxx.o
      vtable for itk::TimeProbe in itkTimeProbe.cxx.o
      vtable for itk::ResourceProbe<double, double> in itkTimeProbe.cxx.o
ld: symbol(s) not found for architecture x86_64

The other build have not finished as of now.

[N-Dekker]

@dzenanz Thanks! It looks like Mac doesn't like the way I "deleted" GetSystemInformation():

  virtual void GetSystemInformation() final = delete;

It could be a compiler bug, because I think my code is fine :-) However, I could also simply just remove the member function declaration. Would that be OK to you as well?

P.S. Note that GetSystemInformation() already was a protected member function of ResourceProbe, so it was probably never called outside ResourceProbe.

[dzenanz]

I think it would be better if you properly deprecated it.

[N-Dekker]

I think it would be better if you properly deprecated it.

Thanks @dzenanz I'll make it a deprecated member function that does completely nothing. (It did not return anything anyway.)

PS I hope it will then eventually be removed with ITK 5.1. (It does not seem useful to keep a protected member function that just does nothing in there for very long.) OK?

[hjmjohnson]

Thanks! This is a great cleanup.