Error “unknown delivery tag” occurs when i try ack messages to RabbitMQ using pika (python)

Question

I want process messages in few threads but i\'m getting error during execute this code:

from __future__ import with_statement
import pika
import sys
from pika.ad         


        

Answer 1

There is a bug with your code. You share a channel across threads. This is not supported by pika (see FAQ). You have 2 options:

1. Define the no_ack=True flag in basic_get(...) and do not use the channel object in thread's function doWork(...)

2. If you need to ACK message only after you have finished your work, then let the main thread (the while True: loop) handle the message ack (and not the worker thread). Below is a modified version of your code that does that.

   from __future__ import with_statement
   import pika
   import sys
   from pika.adapters.blocking_connection import BlockingConnection
   from pika import connection, credentials
   import time
   import threading
   import random
   from pika.adapters.select_connection import SelectConnection
   from pika.connection import Connection
   import traceback
   from Queue import Queue, Empty
   
   def doWork(body, args, channel, ack_queue):
       time.sleep(random.random())
       ack_queue.put(args.delivery_tag)
   
   def doAck(channel):
       while True:
           try:
               r = ack_queue.get_nowait()
           except Empty:
               r = None
           if r is None:
               break
           try:
               channel.basic_ack(delivery_tag=r)
           except:
               traceback.print_exc()
   
   auth = credentials.PlainCredentials(username="guest", password="guest")
   params = connection.ConnectionParameters(host="localhost", credentials=auth)
   conn = BlockingConnection(params)
   channel = conn.channel()
   # Create a queue for the messages that should be ACKed by main thread
   ack_queue = Queue()
   
   while True:
       time.sleep(0.03)    
       try:
           doAck(channel)
           method_frame, header_frame, body = channel.basic_get(queue="test_queue")
           if method_frame.NAME == 'Basic.GetEmpty':
               continue        
           t = threading.Thread(target=doWork, args=[body, method_frame, channel, ack_queue])
           t.setDaemon(True)
           t.start()
       except Exception, e:
           traceback.print_exc()
           continue