[PATCH] D17951: Implement is_always_lock_free

[Eric Fiselier via cfe-commits]

EricWF added inline comments.

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Comment at: include/atomic:859
@@ +858,3 @@
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<char32_t> = 2 == ATOMIC_CHAR32_T_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<wchar_t> = 2 == ATOMIC_WCHAR_T_LOCK_FREE;
+template <> _LIBCPP_CONSTEXPR bool __libcpp_always_lock_free<short> = 2 == ATOMIC_SHORT_LOCK_FREE;
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jfb wrote:
> bcraig wrote:
> > Do we need to support configurations were wchar_t is a typedef to an integer type, or is that an abomination too painful to deal with?
> > 
> > I have no idea if the rest of libcxx attempts to deal with wchar_t typedefs.
> Do you have examples of such platforms? The standard is pretty clear that they're wrong:
> 
> >  [basic.fundamental]
> >
> > Type `wchar_t` is a distinct type whose values can represent distinct codes for all members of the largest extended character set specified among the supported locales. Type `wchar_t` shall have the same size, signedness, and alignment requirements as one of the other integral types, called its *underlying type*.
> 
> I'll defer to @mclow.lists on whether we can about such implementations or not.
I don't think we have to deal with such typedefs for `wchar_t` but we do have to deal with non-sense typedefs (that we unfortunately supply) for `char16_t` and `char32_t` in C++03 mode with GCC. 

And our <atomic> implementation needs to compile in C++03 (Sorry, I did that).

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Comment at: include/atomic:898
@@ -834,1 +897,3 @@
 
+#if defined(__cpp_lib_atomic_is_always_lock_free)
+# if defined(_LIBCPP_LOCK_FREE_IS_SIZE_BASED)
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@mclow.lists I'm fine exposing this typedef retroactively in C++11 and earlier. Do you have any objections to that?


http://reviews.llvm.org/D17951