If one thread owns a 
timed_mutex object, attempts by another thread
to acquire ownership of that object will fail (for 
try_lock()) or block
(for 
lock(), 
try_lock_for(), and 
try_lock_until()) until
the owning thread has released ownership with a call to 
unlock() or the
call to 
try_lock_for() or 
try_lock_until() times out (having
failed to obtain ownership)
.