Adding a new thread model to GCC

[Torvald Riegel]

On Wed, 2016-04-13 at 17:17 +0800, lh_mouse wrote:
> Hi all,
> 
> The 'win32' thread model of gcc has been there since long long ago, being compatible with very old Windows versions, also having a number of drawbacks:
>   0) its implementation is very inefficient, and
>   1) its mutexes and condition variables require dynamic initialization and are unusable in C++11 as std::mutex requires a `constexpr` constructor, and
>   2) allocating a number of rarely used mutexes or condition variables would eventually make the system run out of kernel objects.
> 
> As a solution for 1) and 2), Microsoft introduced keyed events, details of which can be found here:
> http://joeduffyblog.com/2006/11/28/windows-keyed-events-critical-sections-and-new-vista-synchronization-features/

Have you looked at WaitOnAddress and WakeByAddressSingle /
WakeByAddressAll too?  AFAIK this is new in Windows 8, and seems similar
to futexes.

I think it might be better to get a std::synchronic (or similar)
implementation into GCC, and then use these to implement at least the
mutexes:
https://github.com/ogiroux/synchronic/blob/master/include/synchronic

One benefit would be that we then have one place where we have optimized
spinning/blocking in libstdc++ on Windows, and less platform-specific
code.