The future implementation of boost.thread uses boost.mutex, condition and condition_any. What about renaming future to future_base or put it into namespace boost::detail and pass the sync. primitves (mutex, condition) as template args? This would provide the way that other libs could use the future impl with their own sync. primitives. namespace boost { namespace detail { template< typename MutexT, typename ConditionT > future {...}; }} namespace boost { typedef detail::future< mutex, condition > future; namespace fibers { class mutex {}; class condition {}; typedef detail::future< mutex, condition > future; }} boost::future -> uses pthreads/Win32 threads boost::fibers::future -> used for fibers Oliver