synchronization primitive.  To create a lock,
call threading.Lock().  Methods are:

acquire() -- lock the lock, possibly blocking until it can be obtained
release() -- unlock of the lock
locked() -- test whether the lock is currently locked

A lock is not owned by the thread that locked it; another thread may
unlock it.  A thread attempting to lock a lock that it has already locked
will block until another thread unlocks it.  Deadlocks may ensue.