Pythonrabbitmq的使用（二）

上一篇介绍了rabbitmq的安装和经典的hello world！实例。这里将对工作队列（Work Queues）做一个了解。因为是接上一篇说明的，所以如果没看过上一篇，看这篇可能会比较难理解。上一篇的地址是：ubuntu安装rabbitmq和python的使用实现

修改send.py，从命令行参数里接收信息，并发送

import sys
message= ' '.join(sys.argv[1:])or "Hello World!"
channel.basic_publish(exchange='',
routing_key='hello',
body=message)
print " [x] Sent %r" % (message,) 

修改receive.py的回调函数。

import time
def callback(ch, method, properties, body):
print " [x] Received %r" % (body,)
time.sleep( body.count('.') )
print " [x] Done" 

这边先打开两个终端，都运行worker.py，处于监听状态，这边就相当于两个工作者。打开第三个终端，运行new_task.py

$ python new_task.py First message.
$ python new_task.py Second message..
$ python new_task.py Third message...
$ python new_task.py Fourth message....
$ python new_task.py Fifth message..... 

观察worker.py接收到任务，其中一个工作者接收到3个任务 ：

$ python worker.py
[*] Waiting for messages. To exit press CTRL+C
[x] Received 'First message.'
[x] Received 'Third message...'
[x] Received 'Fifth message.....' 

另外一个工作者接收到2个任务 ：

$ python worker.py
[*] Waiting for messages. To exit press CTRL+C
[x] Received 'Second message..'
[x] Received 'Fourth message....' 

消息确认就是当工作者完成任务后，会反馈给rabbitmq。修改worker.py中的回调函数：

def callback(ch, method, properties, body):
print " [x] Received %r" % (body,)
time.sleep(5)
print " [x] Done"
ch.basic_ack(delivery_tag= method.delivery_tag) 

channel.basic_publish(exchange='',
routing_key="task_queue",
body=message,
properties=pika.BasicProperties(
delivery_mode= 2,# make message persistent
)) 

上面实例中，虽然每个工作者是依次分配到任务，但是每个任务不一定一样。可能有的任务比较重，执行时间比较久；有的任务比较轻，执行时间比较短。如果能公平调度就最好了，使用basic_qos设置prefetch_count=1，使得rabbitmq不会在同一时间给工作者分配多个任务，即只有工作者完成任务之后，才会再次接收到任务。

channel.basic_qos(prefetch_count=1) 

new_task.py完整代码

#!/usr/bin/env python
import pika
import sys
connection= pika.BlockingConnection(pika.ConnectionParameters(
host='localhost'))
channel= connection.channel()
channel.queue_declare(queue='task_queue', durable=True)
message= ' '.join(sys.argv[1:])or "Hello World!"
channel.basic_publish(exchange='',
routing_key='task_queue',
body=message,
properties=pika.BasicProperties(
delivery_mode= 2,# make message persistent
))
print " [x] Sent %r" % (message,)
connection.close() 

worker.py完整代码

#!/usr/bin/env python
import pika
import time
connection= pika.BlockingConnection(pika.ConnectionParameters(
host='localhost'))
channel= connection.channel()
channel.queue_declare(queue='task_queue', durable=True)
print ' [*] Waiting for messages. To exit press CTRL+C'
def callback(ch, method, properties, body):
print " [x] Received %r" % (body,)
time.sleep( body.count('.') )
print " [x] Done"
ch.basic_ack(delivery_tag= method.delivery_tag)
channel.basic_qos(prefetch_count=1)
channel.basic_consume(callback,
queue='task_queue')
channel.start_consuming() 

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