Which version of libc++ provides C++14 shared_mutex header

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.

There currently no useful versioning information provided by the
libc++ headers. I hope to change this before 3.7 so that
`_LIBCPP_VERSION` matches the major and minor release version numbers.

/Eric

There currently no useful versioning information provided by the
libc++ headers. I hope to change this before 3.7 so that
`_LIBCPP_VERSION` matches the major and minor release version numbers.

Please do. Having to guess what a C++ standard library implementation supports at compile time is not the way to do things. I am a bit surprised that none of the libc++ developers even thought of this unless the intention of libc++ is that it should always be coupled with clang and never used by any other compiler implementation.

Thanks !