code: def start(self):
          
          # Delete any expired locks first
          self.delete_expired_locks()
          try:
              with transaction.atomic():
                  self.lock = DBMutex.objects.create(lock_id=self.lock_id)
          except IntegrityError:
              raise DBMutexError('Could not acquire lock: {0}'.format(self.lock_id))
docs: Acquires the db mutex lock. Takes the necessary steps to delete any stale locks.
          Throws a DBMutexError if it can't acquire the lock.