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 <[email protected]> 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. ------------------------------------------------------------------------------ Find and fix application performance issues faster with Applications Manager Applications Manager provides deep performance insights into multiple tiers of your business applications. It resolves application problems quickly and reduces your MTTR. Get your free trial! https://ad.doubleclick.net/ddm/clk/302982198;130105516;z _______________________________________________ Mingw-w64-public mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/mingw-w64-public
