#
# Licensed to the Apache Software Foundation (ASF) under one
# or more contributor license agreements.  See the NOTICE file
# distributed with this work for additional information
# regarding copyright ownership.  The ASF licenses this file
# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License.  You may obtain a copy of the License at
# 
#   http://www.apache.org/licenses/LICENSE-2.0
# 
# Unless required by applicable law or agreed to in writing,
# software distributed under the License is distributed on an
# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
# KIND, either express or implied.  See the License for the
# specific language governing permissions and limitations
# under the License.
#

"""
This module augments the standard python multithreaded Queue
implementation to add a close() method so that threads blocking on the
content of a queue can be notified if the queue is no longer in use.
"""

from Queue import Queue as BaseQueue, Empty, Full

class Closed(Exception): pass

class Queue(BaseQueue):

  END = object()

  def __init__(self, *args, **kwargs):
    BaseQueue.__init__(self, *args, **kwargs)
    self._real_put = self.put
    self.listener = self._real_put

  def close(self):
    self.put(Queue.END)

  def get(self, block = True, timeout = None):
    self.put = self._real_put
    try:
      result = BaseQueue.get(self, block, timeout)
      if result == Queue.END:
        # this guarantees that any other waiting threads or any future
        # calls to get will also result in a Closed exception
        self.put(Queue.END)
        raise Closed()
      else:
        return result
    finally:
      self.put = self.listener
      pass

  def listen(self, listener):
    self.listener = listener
    self.put = self.listener