pika详解 (一)

pika

pika处理消息可以简单分为以下几个步骤：

1. 我们首先创建连接对象，然后启动事件循环。
2. 当有连接时，调用on_connected方法。在该方法中创建channel
3. channel创建完成，将调用on_channel_open方法。在该方法中，声明了一个queue。
4. queue声明成功后，将调用on_queue_declared。在该方法中，调用channel.basic_consume，为RabbitMQ传递的每条消息调用handle_delivery。
5. 当RabbitMQ有发送消息，将调用handle_delivery方法传递AMQP Method框架，Header框架和Body

官方给出的示例如下：

import pika

# Create a global channel variable to hold our channel object in
channel = None

# Step #2
def on_connected(connection):
    """Called when we are fully connected to RabbitMQ"""
    # Open a channel
    connection.channel(on_channel_open)

# Step #3
def on_channel_open(new_channel):
    """Called when our channel has opened"""
    global channel
    channel = new_channel
    channel.queue_declare(queue="test", durable=True, exclusive=False, auto_delete=False, callback=on_queue_declared)

# Step #4
def on_queue_declared(frame):
    """Called when RabbitMQ has told us our Queue has been declared, frame is the response from RabbitMQ"""
    channel.basic_consume('test', handle_delivery)

# Step #5
def handle_delivery(channel, method, header, body):
    """Called when we receive a message from RabbitMQ"""
    print(body)

# Step #1: Connect to RabbitMQ using the default parameters
parameters = pika.ConnectionParameters()
connection = pika.SelectConnection(parameters, on_connected)

try:
    # Loop so we can communicate with RabbitMQ
    connection.ioloop.start()
except KeyboardInterrupt:
    # Gracefully close the connection
    connection.close()
    # Loop until we're fully closed, will stop on its own
    connection.ioloop.start()

认证：

认证使用PlainCredentials ，传递给credentials参数

import pika
credentials = pika.PlainCredentials('username', 'password')
parameters = pika.ConnectionParameters(credentials=credentials)

连接器的参数传递：

有两种方式：ConnectionParameters 和 URLParameters

TCP Backpressure

TCP背压， 流控机制的一种， 在rabbitmq 2.0 channel.flow移除，使用tcp backpresssure进行限流。 参数backpressure_detection。 如果pika发现有太多消息积压， 将调用通过add_backpressure_callback注册的回调函数。

默认超过平常10倍的积压将会调用，这个参数也可以设置， 设置方法为set_backpressure_multiplier 值为整数

例如：

import pika

parameters = pika.URLParameters('amqp://guest:guest@rabbit-server1:5672/%2F?backpressure_detection=t')

pika扩展时， 需要启动监听，使用connection.ioloop.start()方法

import pika

def on_open(connection):
    # Invoked when the connection is open
    pass

# Create our connection object, passing in the on_open method
connection = pika.SelectConnection(on_open_callback=on_open)

try:
    # Loop so we can communicate with RabbitMQ
    connection.ioloop.start()
except KeyboardInterrupt:
    # Gracefully close the connection
    connection.close()
    # Loop until we're fully closed, will stop on its own
    connection.ioloop.start()

拥有4种连接器

1. pika.BlockingConnection - 同步模式， 简单易用
2. pika.SelectConnection - 没有第三方依赖包的异步模式
3. pika.adapters.tornado_connection.TornadoConnection - 基于Tornado 的异步IO请求模式
4. pika.adapters.twisted_connection.TwistedProtocolConnection - 基于Twisted’的异步IO请求模式