Boost C++ Libraries: Ticket #12977: BOOST_NO_CXX11_HDR_MUTEX always defined when Clang is used https://svn.boost.org/trac10/ticket/12977 <p> Boost 1.63 boost/config/stdlib/libcpp.hpp has code </p> <pre class="wiki">#if __cplusplus &lt; 201103 ... # define BOOST_NO_CXX11_HDR_MUTEX ... </pre><p> So the macro is always defined despite of libc++ has std::mutex! Boost.Context - C++11 library never uses std::mutex as a consequence. </p> en-us Boost C++ Libraries /htdocs/site/boost.png https://svn.boost.org/trac10/ticket/12977 Trac 1.4.3 anonymous Mon, 17 Apr 2017 14:39:48 GMT <link>https://svn.boost.org/trac10/ticket/12977#comment:1 </link> <guid isPermaLink="false">https://svn.boost.org/trac10/ticket/12977#comment:1</guid> <description> <p> $ clang --version </p> <p> FreeBSD clang version 3.8.0 (tags/RELEASE_380/final 262564) (based on LLVM 3.8.0) Target: x86_64-unknown-freebsd11.0 Thread model: posix <a class="missing wiki">InstalledDir</a>: /usr/bin </p> </description> <category>Ticket</category> </item> <item> <dc:creator>John Maddock</dc:creator> <pubDate>Tue, 31 Jul 2018 18:41:50 GMT</pubDate> <title>status changed; resolution set https://svn.boost.org/trac10/ticket/12977#comment:2 https://svn.boost.org/trac10/ticket/12977#comment:2 <ul> <li><strong>status</strong> <span class="trac-field-old">new</span> → <span class="trac-field-new">closed</span> </li> <li><strong>resolution</strong> → <span class="trac-field-new">invalid</span> </li> </ul> <p> You need to compile in C++11 mode. </p> Ticket