[Boost-users] [thread] boost::thread automatically detached when thread terminates?

Is a boost::thread object automatically detached when a thread terminates? I read in the Boost.Thread 1.44 documentation: "If the thread of execution represented by the boost::thread object has already completed, or the boost::thread object represents Not-a-Thread, then join() returns immediately." Is it really required to call join() or timed_join()? Or can I also call joinable() which would return false then? Boris