Remove column major specialization.

[trivialfis]

As cuDF is actually dense data, removing all the specializations.

• Use shared pointer for inplace prediction. Using dmlc::any with ArrayInterface might lead to some subtle bugs as dmlc::any needs to copy the underlying value, while ArrayInterface contains stack allocated memory char type[3].

[RAMitchell]

Makes sense to change cudf to row major.

What if we want to add cupy csc? We would have to add all the column major stuff back.

[hcho3]

Do you need help with fixing build issue on Mac OSX?

[trivialfis]

@hcho3 Yes please ... Thanks!

@RAMitchell Do you want me to keep the code here? Honestly I have never used CSC as data matrix before.

[RAMitchell]

I don't think it's a big deal, we can always remove it and look up the code on version control later.

[hcho3]

So the issue is that the virtual destructor of dmlc::DataIter (parent class) is declared nothrow(false), so it can potentially throw at destruction. The C++ runtime in Mac OSX assumes that the type T in the expression std::make_shared<T> won't ever throw exceptions.

Why dmlc::DataIter has a throwing destructor? MXNet has a child class of dmlc::DataIter that allocates GPU memory, and GPU allocators may throw when de-allocating memory (e.g. double-free). References: apache/mxnet#14223 (comment), dmlc/dmlc-core#506

Solution is to not use std::make_shared<T>.

Related:

• https://stackoverflow.com/questions/43791221/stdmake-shared-with-throwing-dtor-and-libc-doesnt-compile
• throwing destructors cannot be used with smart pointers capnproto/capnproto#553

[hcho3]

Indeed removing std::make_shared<T> fixed the build. Shall we add a linter check to prohibit the use of std::make_shared<T> in CPU code?

[trivialfis]

@hcho3 Thanks a lot for fixing the issue! Also thanks for providing references for related issues.

Shall we add a linter check to prohibit the use of std::make_shared in CPU code?

One of the osx build was passing even using std::make_shared, I think for working around language implementation quirks we just have to do it case by case.

[hcho3]

Another alternative is to define a small utility function that does what std::make_shared<T> does but allows throwing destructors.

[codecov-commenter]

Codecov Report

Merging #5755 into master will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #5755      +/-   ##
==========================================
- Coverage   82.62%   82.61%   -0.02%     
==========================================
  Files          12       12              
  Lines        2728     2726       -2     
==========================================
- Hits         2254     2252       -2     
  Misses        474      474              

Impacted Files	Coverage Δ
python-package/xgboost/data.py	73.06% <0.00%> (-0.20%)	⬇️

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[trivialfis]

@hcho3 Let stay with the workaround for now. Implementing std::make_shared correctly is not trivial.