Red Hat Summit Red Hat SummitSuporteConsoleDesenvolvedoresComeçar um testeContato

Este conteúdo não está disponível no idioma selecionado.

6.7.4. Priority Queue Demonstration

The following program demonstrates the use and behavior of a priority queue.
Python
#!/usr/bin/python

import sys
from qpid.messaging import *

connection = Connection("localhost:5672")
connection.open()
try:
  ssn = connection.session()
  
  x = 0
  print "\n"
  while True:
    print "Create queue with 2 or 10 priority levels?"
    x = raw_input()
    if (x == "2") or (x == "10"):
      break

  tx = ssn.sender("nonpriority-demo-queue; {create: always, node: {type: 'queue'}}")
  print "Creating a priority queue with " + x + " priority levels:"
  address =  "priority-demo-queue; {create: always, "
  address = address + "node:{x-declare: {auto-delete:True, "
  address = address + "arguments: {'qpid.priorities': "
  address = address + x + "}}}}"
  print address
  txpriority = ssn.sender(address)

  rx = ssn.receiver('nonpriority-demo-queue')
  rxpriority = ssn.receiver("priority-demo-queue")
  rxbrowse = ssn.receiver("priority-demo-queue; {mode: browse}")

  print "\nPress Enter to continue\n"
  x = raw_input()

  print "First message sent:"
  msg = Message("priority 1")
  msg.priority = 1
  tx.send(msg)
  txpriority.send(msg)
  print msg

  print "Second message sent:"
  msg = Message('priority 4')
  msg.priority = 4
  tx.send(msg)
  txpriority.send(msg)
  print msg

  print "\nPress Enter to continue\n"
  x = raw_input()
  print "BROWSE PRIORITY QUEUE"
  print "First browse in priority queue:"
  print rxbrowse.fetch()

  print "Second browse in priority queue:"
  print rxbrowse.fetch()

  print "\nPress Enter to continue\n"
  x = raw_input()

  print "ACQUIRE PRIORITY QUEUE"
  print "First message in priority queue:"
  print rxpriority.fetch()

  print "Second message in priority queue:"
  print rxpriority.fetch()

  print "\nPress Enter to continue\n"
  x = raw_input()

  print "ACQUIRE NON-PRIORITY QUEUE"
  print "First message in non-priority queue:"
  print rx.fetch()

  print "Second message in non-priority queue:"
  print rx.fetch()

  ssn.acknowledge()
finally:
  connection.close()
Copy to Clipboard Toggle word wrap
When run, this program allows you to create a priority queue with 2 or 10 priority levels. It then sends two messages to this queue, with priorities 1 and 4. It then demonstrates the behavior of browsing and acquiring from the priority queue, and contrasts this with acquiring from a non-priority queue.
Here is the output when the program is run and a priority queue with 10 distinct priority levels is created: 
Create queue with 2 or 10 priority levels?
10
Creating a priority queue with 10 priority levels:
priority-demo-queue; {create: always, node:{x-declare: {auto-delete:True, arguments: {'qpid.priorities': 10}}}}
Copy to Clipboard Toggle word wrap
The queue is declared as auto-delete: True to allow the program to be run multiple times with different values for qpid.priorities. If the queue already exists when the sender is created, the value given for qpid.priorities has no effect. This value only has an effect when the queue is created. 
First message sent:
Message(priority=1, content='priority 1')
Second message sent:
Message(priority=4, content='priority 4')
Copy to Clipboard Toggle word wrap
Two messages are sent, one with priority 1 (the lowest priority), and one with priority 4 (a higher priority).
The first examination is of a browsing receiver. Priority queuing has no effect for browsers, only acquiring consumers, so we see our messages in the order they were sent - FIFO First In, First Out: 
BROWSE PRIORITY QUEUE
First browse in priority queue:
Message(priority=1, properties={'x-amqp-0-10.routing-key': u'priority-demo-queue'}, content='priority 1')
Second browse in priority queue:
Message(priority=4, properties={'x-amqp-0-10.routing-key': u'priority-demo-queue'}, content='priority 4')
Copy to Clipboard Toggle word wrap
However, when we acquire the messages from the priority queue, we see that they are dequeued in order of descending priority - our priority 4 message is delivered before the priority 1 message, even though it was sent later: 
ACQUIRE PRIORITY QUEUE
First message in priority queue:
Message(priority=4, properties={'x-amqp-0-10.routing-key': u'priority-demo-queue'}, content='priority 4')
Second message in priority queue:
Message(priority=1, properties={'x-amqp-0-10.routing-key': u'priority-demo-queue'}, content='priority 1')
Copy to Clipboard Toggle word wrap
Finally, for contrast, the messages are dequeued from a non-priority queue, where they are delivered in the order they were received by the broker: 
ACQUIRE NON-PRIORITY QUEUE
First message in non-priority queue:
Message(priority=1, properties={'x-amqp-0-10.routing-key': u'nonpriority-demo-queue'}, content='priority 1')
Second message in non-priority queue:
Message(priority=4, properties={'x-amqp-0-10.routing-key': u'nonpriority-demo-queue'}, content='priority 4')
Copy to Clipboard Toggle word wrap
When the demonstration is run and a priority queue with only 2 distinct levels is select, you will observe that the priority queue delivers the message in the same order they were delivered: 
Create queue with 2 or 10 priority levels?
2
Creating a priority queue with 2 priority levels:
priority-demo-queue; {create: always, node:{x-declare: {auto-delete:True, arguments: {'qpid.priorities': 2}}}}

....

ACQUIRE PRIORITY QUEUE
First message in priority queue:
Message(priority=1, properties={'x-amqp-0-10.routing-key': u'priority-demo-queue'}, content='priority 1')
Second message in priority queue:
Message(priority=4, properties={'x-amqp-0-10.routing-key': u'priority-demo-queue'}, content='priority 4')
Copy to Clipboard Toggle word wrap
When a queue has only two distinct priority levels, those levels are the message priority bands 1-5 and 6-10. Since our messages both have priorities in the band 1-5, they are considered to have the same priority, and are delivered based on the order they were received by the broker.
Report a bug
Voltar ao topo
Red Hat logoGithubredditYoutubeTwitter

Aprender

Experimente, compre e venda

Comunidades

Sobre a documentação da Red Hat

Ajudamos os usuários da Red Hat a inovar e atingir seus objetivos com nossos produtos e serviços com conteúdo em que podem confiar. Explore nossas atualizações recentes.

Tornando o open source mais inclusivo

A Red Hat está comprometida em substituir a linguagem problemática em nosso código, documentação e propriedades da web. Para mais detalhes veja o Blog da Red Hat.

Sobre a Red Hat

Fornecemos soluções robustas que facilitam o trabalho das empresas em plataformas e ambientes, desde o data center principal até a borda da rede.

Theme

© 2025 Red Hat