title: Upgrading read lock to write lock without releasing the first in C++11?
body: <p>I know it's possible using <a href="http://www.boost.org/doc/libs/1_57_0/doc/html/thread/synchronization.html#thread.synchronization.mutex_concepts.upgrade_lockable" rel="nofollow"><code>boost::UpgradeLockable</code></a> in C++14.<br>
  Is there anything similar for C++11?</p>