python采用pika库使用rabbitmq（六）公平调度（Fair dispatch）

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)

带消息持久化+公平分发的完整代码

 1 import pika
 2 import sys
 3  
 4 connection = pika.BlockingConnection(pika.ConnectionParameters(
 5         host='localhost'))
 6 channel = connection.channel()
 7  
 8 channel.queue_declare(queue='task_queue', durable=True)
 9  
10 message = ' '.join(sys.argv[1:]) or "Hello World!"
11 channel.basic_publish(exchange='',
12                       routing_key='task_queue',
13                       body=message,
14                       properties=pika.BasicProperties(
15                          delivery_mode = 2, # make message persistent
16                       ))
17 print(" [x] Sent %r" % message)
18 connection.close()

cend.py

 1 import pika
 2 import time
 3  
 4 connection = pika.BlockingConnection(pika.ConnectionParameters(
 5         host='localhost'))
 6 channel = connection.channel()
 7  
 8 channel.queue_declare(queue='task_queue', durable=True)
 9 print(' [*] Waiting for messages. To exit press CTRL+C')
10  
11 def callback(ch, method, properties, body):
12     print(" [x] Received %r" % body)
13     time.sleep(body.count(b'.'))
14     print(" [x] Done")
15     ch.basic_ack(delivery_tag = method.delivery_tag)
16  
17 channel.basic_qos(prefetch_count=1)
18 channel.basic_consume(callback,
19                       queue='task_queue')
20  
21 channel.start_consuming()

receive.py