[cfe-dev] Which version of libc++ provides C++14 shared_mutex header

[Edward Diener]

I asked this question about libc++ on the LLVM developers mailing list 
but since no one had any informatory answer there they suggested I come 
here.

I want to determine, for a given _LIBCPP_VERSION of libc++, whether the 
C++14 header file shared_mutex is supported/provided at compile time 
through some sort of predefined macro or combination of macros.

Since libc++ appears to be independent of clang, gcc, or whatever 
compiler might want to use it as its C++ standard library, I would have 
expected that the optimum way of doing this was to find libc++ 
documentation that explained that for a particular _LIBCPP_VERSION a 
particular set of header files were supported. Or, at the very least, 
for a particular _LIBCPP_VERSION C++03 header files only were supported, 
for another particular _LIBCPP_VERSION C++03 and C++11 header files were 
supported, for another particular _LIBCPP_VERSION C++03, C++11, and 
C++14 header files were supported etc. Or something like that.

I do know about the clang include file checking macros but I don't know 
with what version of clang I can expect this to work. But given that the 
include file checking macros were introduced in gcc with version 5.1, 
and given that other compilers could potentially be using libc++, I am 
hoping that there is a strictly libc++ solution to my problem.

If there is not I would like to recommed to the libc++ developers that 
there should be.

I am working to potentially add support in Boost.config to shared_mutex 
header file detection, and libc++ is one of the standard libraries 
supported by Boost.config. Unfortunately the detection of standard 
header files for Boost.config in libc++ is pretty primitive. Is there 
any documentation about the predefined macros in libc++ which could help 
us at Boost come up with a much better way to determine what libc++ 
supports and does not support for any given release of the library ? If 
I have missed a discussion or discussions about this regarding libc++ 
please feel free to point me in the right direction. My google search 
regarding libc++ and how to tell what is supports for any given release 
yields almost nothing of value and its documentation page at 
http://libcxx.llvm.org/ does not tell me anything like what I want to 
know either.