6.8.7. Message Groups Demonstration

import sys
from qpid.messaging import *

def sendmsg(group, num):
# send the message to the broker and add it to our in-memory representation of the broker queue
  global memoryqueue
  global tx

  msg = Message(group + num)
  msg.properties = {'ourGroupID': group}

  tx.send(msg)
  memoryqueue.append(group + num)

def pullmsg(consumer):
# fetch a message from the broker and print it to the console  
  global counter
  global memoryqueue

  msg = consumers[consumer - 1].fetch(timeout = 1)
  
  print "\nQueued message: " + memoryqueue[counter]
  print "Consumer " + str(consumer) + " got: " + msg.content

  counter +=1
  return msg
  
# Two connections are used to simulate two distinct consumers  
connection = Connection("localhost:5672")
connection2 = Connection("localhost:5672")
connection.open()
connection2.open()

try:
  session = connection.session()
  session2 = connection2.session()
  
  x = raw_input('Enable message grouping [Y/n]?')

  if x == 'N' or x == 'n':
  
    # Create the queue without message groups
    tx = session.sender("test-nogroup-queue; {create: always, node:{x-declare:{auto-delete:True}}}")
    rx1 = session.receiver("test-nogroup-queue")
    rx2 = session2.receiver("test-nogroup-queue")
  
    print "\nMessage grouping is disabled"
    msggroup = False
  
  else:
  
    # Create the queue with message groups enabled
    tx = session.sender("test-group-queue; {create: always, node:{x-declare:{auto-delete: True, arguments: {'qpid.group_header_key': 'ourGroupID', 'qpid.shared_msg_group' : 1}}}}")
    rx1 = session.receiver("test-group-queue")
    rx2 = session2.receiver("test-group-queue")
  
    print "\nMessage grouping is enabled"
    msggroup = True

# Put the receivers in an array so we can use a function to fetch messages  
  consumers = []
  consumers.append(rx1)
  consumers.append(rx2)

  print "Sending interleaved messages from two different groups to the queue..."

# We create an in-memory picture of the queue, to see what order the messages are on the broker
  memoryqueue = []

  sendmsg('A', '1')
  sendmsg('B', '1')
  sendmsg('B', '2')
  sendmsg('A', '2')
  sendmsg('B', '3')
  sendmsg('A', '3')

  counter = 0 
  pullmsg(1)
  pullmsg(2)  
  
  if msggroup:
    print "\nConsumer 1 now owns message group A. Consumer 2 now owns message group B."  

  msgc1 = pullmsg(1)
  msgc2 = pullmsg(2)

  if msggroup:
    print "\nThe consumers will now acknowledge all the messages, or only the last one."
    resp = raw_input('Should they acknowlege all messages? [Y/n]')
  
    if resp == 'N' or resp == 'n':
      print "\nAcknowledging only part of the group. The consumers retain ownership of the group. This is an anti-pattern! See the source code comments for details."
  
      session.acknowledge(msgc1)
      session2.acknowledge(msgc2)
      antipattern = True
  
      # Acknowledging only part of a group is an anti-pattern. Messages are grouped to ensure that a single consumer can deal with the whole group. If this consumer now fails before completing the rest of the group, the unacknowledged messages in the group will be released and redelivered by the broker, but the acknowledged messages in the group are now missing in action!
  
    else:
      print "\nAcknowledging all fetched messages. The consumers will release ownership of the groups."
      session.acknowledge()
      session2.acknowledge()
      antipattern = False 
  
    print "\nPulling more messages from the queue:"

  pullmsg(1)
  pullmsg(2)
  if msggroup:
    if antipattern == False:
      print "\nConsumer 1 now owns message group B. Consumer 2 now owns message group A."
    print "\nSending some more messages to the queue..."
  
  sendmsg('B', '4')
  sendmsg('B', '5')
  sendmsg('A', '4')
  sendmsg('A', '5')
 
  pullmsg(1)
  pullmsg(2)
  pullmsg(1)
  pullmsg(2)

finally:
  connection.close()
  connection2.close()