[PATCH v2] libstdc++: On Windows, retrieve thread-local variables via functions

[LIU Hao]

在 2025-12-8 22:03, Jonathan Wakely 写道:
> In C++14 I would declare it like this:
> 
> std::add_lvalue_reference_t<void (*)()>
> __get_once_call() noexcept;
> 
> But for C++11 we don't have add_lvalue_reference, so we need the
> slightly uglier form:
> 
> std::add_lvalue_reference<void (*)()>::type
> __get_once_call() noexcept;

Well, in my own code I have stuff like

    template<typename... _Args>
    using _Vfn = void (_Args...);

so this could be

    _Vfn<>*
    __get_once_call() noexcept;


If there's no such thing in libstdc++, I'm okay with this change.



> It occurs to me that we would only need the first #ifdef group if it
> did something like the errno trick:
> 
> #define __once_callable __get_once_callable()
> #define __once_call __get_once_call
> 
> (and #undef at the end of the file).
> 
> That way all the later code wouldn't need changes, it would continue
> to use __once_callable and __once_call but those would expand to calls
> to the getters. I don't love the use of macros with lowercase names,
> but it reduces the diffs between Windows and other targets to just
> that first #ifdef group.
> 
> What do you think?

Actually I thought about this a little, and right, I don't like these macros either. The first patch 
tried to avoid macros in a wrong way. If these names are available as macros, I'm fine with this change too.

Do I have to send a third patch?



-- 
Best regards,
LIU Hao
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