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Re: Re: Adding a new thread model to GCC

Currently, --enable-threads=win32 map to gthr-win32.{h|c}, could we map

--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 ?


On Thu, Apr 14, 2016 at 10:24 AM, lh_mouse <> 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
> -------------------------------------------------------------
> åääïTorvald Riegel <>
> åéææï2016-04-14 01:40
> æääïlh_mouse
> æéïgcc,mingw-w64-public
> äéïRe: 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:
> 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:
> 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.

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