2015-03-08 12:20 GMT+01:00 Marco Costalba <[email protected]>:
> I am one of the developer of a chess engine called Stockfish:
>
> https://github.com/official-stockfish/Stockfish
>
> A chess engine is a high performance piece of multi-thread software, where
> even a small sub-optimal code path immediately translates in a sensible
> slow down.
>
> The master version is written in C++03 and uses some low level wrappers to
> get thread functionality on supported platforms:
>
> https://github.com/official-stockfish/Stockfish/blob/master/src/platform.h
>
> Recently we started to switch to C++11 for various reasons, but especially
> due to library support for std::thread and friends. This allows us to
> greatly simplify the code and getting rid of all the platform specific
> wrappers.
>
> While on Linux and on MSVC 2013 we have similar performance between C++11
> and C++03 versions, under Windows with mingw there is a huge performance
> gap when run in SMP mode (around 30% slower), when we run in single thread
> mode speed is similar. This is particularly unfortunate because our release
> version is compiled with gcc for all the platforms because currently gcc
> gives the best speed.
>
> After some analysis we realized the speed difference is all due to thread
> library implementation on mingw that is based on POSIX instead of native
> Win32 threads.
>
> We have goggled around for some specific version of mingw that used win32
> _and_ supports std::thread, but we have found nothing so far.
>
> So I would like to ask:
>
> 1. There exists somewhere a mingw-w64 build supporting native win32
> std::thread?
>
No, and the reason is that currently, GCC (and libstdc++) only has a fully
implemented internal threading library (inside libgcc) based on pthreads,
not win32 threads. The MinGW-w64 project provides the winpthreads library
which allows GCC to build its C++11 threading libraries.
> 2. There is some plan to develop it?
>
Yes, and no. So far, no one has submitted the patches that would make this
possible (i.e. extend the GCC win32 threading implemenation and lat
libstdc++ use that). An alternative path would be to create a separate
implementation of the relevant functionality in libstdc++, written directly
on top of the Win32 API.
Fortunately for you though, I recently (well, a couple months ago) learned
about an implementation of the second option available here:
https://github.com/meganz/mingw-std-threads
The author so kindly relicensed the files under the MinGW-w64 runtime
license, which is essentially public domain or Zlib license where public
domain doesn't exist.
I'm curious as to how good that implementation would perform for you!
Ruben
>
>
> Thanks for your help and support
>
> Marco
>
>
>
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