[Rcpp-devel] mixing R's and C++'s RNGs and distributions

[Matt D.]

On 6/22/2015 12:31, Ramon Diaz-Uriarte wrote:
> Actually, I just noticed that things will not work if you need your package
> to run on Windoze: Rtools uses gcc 4.6.3 there, and this will not work with
> gcc 4.6 (neither in Linux nor Windows) with flag -std=c++0x or
> -std=gnu++0x. I guess this should be fixable, but I do not know enough to
> do it.
Hi again!

I've just tried with the work-in-progress, _experimental_ version 
available at the following location:
https://rawgit.com/kevinushey/RToolsToolchainUpdate/master/mingwnotes.html

// In particular, I've used "Windows native compiler for 64 bit Windows 
output mingw32mingw64_gcc-4.9.2.toolchain.tar.gz".

This works better -- the only missing part is <thread> support :-( 
However, it is not exactly essential here, in that it's used solely in 
one place -- to get some extra entropy; that's all.
After temporarily removing dependence on `std::this_thread::get_id()`, 
the example -- available at 
http://www.pcg-random.org/posts/ease-of-use-without-loss-of-power.html 
-- compiles and runs successfully.

Incidentally,  one can get threads support for MinGW using MSYS2, which 
gives:
Thread model: posix
gcc version 4.9.2 (Rev5, Built by MSYS2 project)

However, the MinGW that comes with Rtools uses the following:
Thread model: win32
gcc version 4.9.2 (GCC)

I presume there must be a reason for that. There are certainly 
trade-offs present: 
https://wiki.qt.io/MinGW-64-bit#GCC_Threading_model_.28posix_vs_win32.29
What hits us here is the "no C++11 <thread>, <mutex>, or <future> " 
("C11" appears to be a typo) part for the win32 choice.
// See also: 
https://stackoverflow.com/questions/17242516/mingw-w64-threads-posix-vs-win32

Note that there's nothing multithreading-specific about the library, so 
even though I've also tested it with 
https://github.com/meganz/mingw-std-threads (warning: just something 
I've ran across while searching for multithreading support for MinGW 
built w/ win32 threading model, quality and license unknown) and also 
made it compile & work after a small patch (adding the std::hash 
specialization), it's probably possible to use another source of entropy 
here.

I presume another idea would be to use a different GCC version, but 
that's rather tedious -- 
https://stackoverflow.com/questions/25455829/using-a-different-gcc-version-from-that-included-with-rtools-with-rcpp-on-window
Other than the above, I'm wondering myself what's the "official" 
recommendation for the C++11 threading support w/ Rcpp on Windows.

Best,

Matt