Currently, --enable-threads=win32 map to gthr-win32.{h|c}, could we map
--enable-threads=win32-vista
--enable-threads=win32-win7 // Windows 7 and Windows Server 2008 R2
--enable-threads=win32-win8 // Windows 8 and Windows Server 2012
--enable-threads=win32-win8.1 // Windows 8.1 and Windows Server 2012 R2
--enable-threads=win32-win10 // Windows 10 and Windows Server 2016
to gthr-windows.{h|c} with the corresponding _WIN32_WINNT macros ?
Regards,
Dongsheng
On Thu, Apr 14, 2016 at 10:24 AM, lh_mouse <lh_mo...@126.com> wrote:
> Yes I learnt those *ByAddress* functions a few months ago and was shocked
> that Microsoft had plagiarized futex from Linux.
> As you have pointed out already, those APIs are only available on Windows 8
> and later.
>
> If we need fuex semantics on Windows 7 and earlier, we must simulate it.
> However, since futexes and keyed events work differently, simulation of
> futexes using keyed events would:
> 0) require a lot of work, and
> 1) suffer from performance penalty just like if we simulate keyed events on
> Windows 2000.
>
> The major difference is that, the FUTEX_WAIT syscall is an atomic
> compare-and-sleep operation, while the NtWaitForKeyedEvent syscall provides
> no comparison.
> Instead, the NtReleasedKeyedEvent syscall blocks the current thread until one
> thread is woken up, while FUTEX_WAKE does nothing and returns immediately.
>
> So here is my condition: in no event shall portability harm either efficiency
> or maintainability.
> Linux and Windows work differently. I consider it 'harmful' to make one look
> like the other.
>
>
> ------------------
> Best regards,
> lh_mouse
> 2016-04-14
>
> -------------------------------------------------------------
> 发件人：Torvald Riegel <trie...@redhat.com>
> 发送日期：2016-04-14 01:40
> 收件人：lh_mouse
> 抄送：gcc,mingw-w64-public
> 主题：Re: Adding a new thread model to GCC
>
> 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.
>
>
>
