code: def unlock(self, source_node, check_status=True):
          
          if self.status != self.S_LOCKED:
              raise RuntimeError("Trying to unlock a task with status %s" % self.status)
  
          self._status = self.S_READY
          if check_status: self.check_status()
          self.history.info("Unlocked by %s", source_node)
docs: Unlock the task, set its status to `S_READY` so that the scheduler can submit it.
          source_node is the :class:`Node` that removed the lock
          Call task.check_status if check_status is True.