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[源码分析] 消息队列 Kombu 之 Producer
0x00 摘要
本系列我们介绍消息队列 Kombu。Kombu 的定位是一个兼容 AMQP 协议的消息队列抽象。通过本文，大家可以了解 Kombu 中的 Producer 概念。
0x01 示例代码
下面使用如下代码来进行说明。
本示例来自https://liqiang.io/post/kombu-source-code-analysis-part-5系列，特此深表感谢。
def main(arguments): hub = Hub() exchange = Exchange('asynt_exchange') queue = Queue('asynt_queue', exchange, 'asynt_routing_key') def send_message(conn): producer = Producer(conn) producer.publish('hello world', exchange=exchange, routing_key='asynt_routing_key') print('message sent') def on_message(message): print('received: {0!r}'.format(message.body)) message.ack() # hub.stop() # <-- exit after one message conn = Connection('redis://localhost:6379') conn.register_with_event_loop(hub) def p_message(): print(' kombu ') with Consumer(conn, [queue], on_message=on_message): send_message(conn) hub.timer.call_repeatedly(3, p_message) hub.run_forever()if __name__ == '__main__': sys.exit(main(sys.argv[1:])) 0x02 来由
前文已经完成了构建部分，Consumer部分，下面来到了Producer部分，即如下代码：
def send_message(conn): producer = Producer(conn) producer.publish('hello world', exchange=exchange, routing_key='asynt') print('message sent') 我们知道，Transport需要把Channel与文件信息联系起来，但是此时Transport信息如下，文件信息依然没有，这是我们以后需要留意的：
transport = {Transport} Channel = {type} Cycle = {type} Management = {type} channel_max = {int} 65535 channels = {list: 2} [ , ] client = {Connection} cycle = {MultiChannelPoller} after_read = {set: 0} set() eventflags = {int} 25 fds = {dict: 0} {} poller = {_poll} default_connection_params = {dict: 2} {'port': 6379, 'hostname': 'localhost'} default_port = {int} 6379 driver_name = {str} 'redis' driver_type = {str} 'redis' implements = {Implements: 3} {'asynchronous': True, 'exchange_type': frozenset({'direct', 'topic', 'fanout'}), 'heartbeats': False} manager = {Management} polling_interval = {NoneType} None state = {BrokerState} 0x03 建立
3.1 定义
Producer中，主要变量是：
- _channel ：就是channel；
- exchange ：exchange；
但是本文示例没有传入exchange，这就有些奇怪，我们需要继续看看。
class Producer: """Message Producer. Arguments: channel (kombu.Connection, ChannelT): Connection or channel. exchange (kombu.entity.Exchange, str): Optional default exchange. routing_key (str): Optional default routing key. """ #: Default exchange exchange = None #: Default routing key. routing_key = '' #: Default serializer to use. Default is JSON. serializer = None #: Default compression method. Disabled by default. compression = None #: By default, if a defualt exchange is set, #: that exchange will be declare when publishing a message. auto_declare = True #: Basic return callback. on_return = None #: Set if channel argument was a Connection instance (using #: default_channel). __connection__ = None
3.2 init
init代码如下。
def __init__(self, channel, exchange=None, routing_key=None, serializer=None, auto_declare=None, compression=None, on_return=None): self._channel = channel self.exchange = exchange self.routing_key = routing_key or self.routing_key self.serializer = serializer or self.serializer self.compression = compression or self.compression self.on_return = on_return or self.on_return self._channel_promise = None if self.exchange is None: self.exchange = Exchange('') if auto_declare is not None: self.auto_declare = auto_declare if self._channel: self.revive(self._channel) 3.2.1 转换channel
这里有个重要转换。
- 最开始是把输入参数 Connection 赋值到 self._channel。
- 然后 revive 方法做了转换为 channel，即 self._channel 最终是 channel 类型。
但是 exchange 依然没有意义，是 direct 类型。
代码如下：
def revive(self, channel): """Revive the producer after connection loss.""" if is_connection(channel): connection = channel self.__connection__ = connection channel = ChannelPromise(lambda: connection.default_channel) if isinstance(channel, ChannelPromise): self._channel = channel self.exchange = self.exchange(channel) else: # Channel already concrete self._channel = channel if self.on_return: self._channel.events['basic_return'].add(self.on_return) self.exchange = self.exchange(channel)
此时变量为：
producer = {Producer} auto_declare = {bool} True channel = {Channel} compression = {NoneType} None connection = {Connection} exchange = {Exchange} Exchange ''(direct) on_return = {NoneType} None routing_key = {str} '' serializer = {NoneType} None 逻辑如图：
+----------------------+ +-------------------+| Producer | | Channel || | | | +-----------------------------------------------------------+| | | client +-------------> | Redis || channel +------------------> | | +-----------------------------------------------------------+| | | pool || exchange | +---------> | | <------------------------------------------------------------+| | | | | || connection | | +----> | connection +---------------+ || + | | | | | | |+--+-------------------+ | | +-------------------+ | | | | | | v | | | | | +-------------------+ +---+-----------------+ +--------------------+ | | | | | | Connection | | redis.Transport | | MultiChannelPoller | | | +----------------------> | | | | | | | | | | | | | | | _channels +--------+ | | | | | | cycle +------------> | _fd_to_chan | | | | | transport +---------> | | | _chan_to_sock | | +-------->+ | | | | | +------+ poller | | | | +-------------------+ +---------------------+ | | after_read | | | | | | | | | | | +--------------------+ | | | +------------------+ +---------------+ | | | | Hub | | | | | | | v | | | | | +------+------+ | | | | poller +---------------> | _poll | | publish | | | | | | +-------+ +--------------------------------+ | | | _poller+---------> | poll | | | | +------------------+ | | +-------+ | | | +-------------+ +-------------------+ | +-----> +----------------+ | Queue | | | | Exchange | | _channel | +---------+ | | | | | | | exchange +--------------------> | channel | | | | | | | | | +-------------------+ +----------------+
手机如图：
0x04 发送
发送消息是通过producer.publish完成。
def send_message(conn): producer = Producer(conn) producer.publish('hello world', exchange=exchange, routing_key='asynt') print('message sent') 此时传入exchange作为参数。原来如果没有 Exchange，是可以在这里进行补救。
producer.publish继续调用到如下，可以看到分为两步：
- 调用channel的组装消息函数
prepare_message； - 调用channel的发送消息
basic_publish；
因此，最终发送消息还是通过channel完成。
def _publish(self, body, priority, content_type, content_encoding, headers, properties, routing_key, mandatory, immediate, exchange, declare): channel = self.channel message = channel.prepare_message( body, priority, content_type, content_encoding, headers, properties, ) if declare: maybe_declare = self.maybe_declare [maybe_declare(entity) for entity in declare] # handle autogenerated queue names for reply_to reply_to = properties.get('reply_to') if isinstance(reply_to, Queue): properties['reply_to'] = reply_to.name return channel.basic_publish( message, exchange=exchange, routing_key=routing_key, mandatory=mandatory, immediate=immediate, ) 4.1 组装消息 in channel
channel 的组装消息函数prepare_message完成组装功能，基本上是为消息添加各种属性。
def prepare_message(self, body, priority=None, content_type=None, content_encoding=None, headers=None, properties=None): """Prepare message data.""" properties = properties or {} properties.setdefault('delivery_info', {}) properties.setdefault('priority', priority or self.default_priority) return {'body': body, 'content-encoding': content_encoding, 'content-type': content_type, 'headers': headers or {}, 'properties': properties or {}} 消息如下：
message = {dict: 5} 'body' = {str} 'aGVsbG8gd29ybGQ=' 'content-encoding' = {str} 'utf-8' 'content-type' = {str} 'text/plain' 'headers' = {dict: 0} {} __len__ = {int} 0 'properties' = {dict: 5} 'delivery_mode' = {int} 2 'delivery_info' = {dict: 2} {'exchange': 'asynt_exchange', 'routing_key': 'asynt_routing_key'} 'priority' = {int} 0 'body_encoding' = {str} 'base64' 'delivery_tag' = {str} '1b03590e-501c-471f-a5f9-f4fdcbe3379a' __len__ = {int} 5 4.2 发送消息 in channel
channel的发送消息basic_publish完成发送功能。此时使用了传入的参数exchange。
发送消息basic_publish方法是调用_put方法：
def basic_publish(self, message, exchange, routing_key, **kwargs): """Publish message.""" self._inplace_augment_message(message, exchange, routing_key) if exchange: return self.typeof(exchange).deliver( message, exchange, routing_key, **kwargs ) # anon exchange: routing_key is the destination queue return self._put(routing_key, message, **kwargs)
4.3 deliver in exchange
self.typeof(exchange).deliver代码接着来到exchange。本文是DirectExchange。
注意，这里用到了self.channel._put。就是Exchange的成员变量channel。
class DirectExchange(ExchangeType): """Direct exchange. The `direct` exchange routes based on exact routing keys. """ type = 'direct' def lookup(self, table, exchange, routing_key, default): return { queue for rkey, _, queue in table if rkey == routing_key } def deliver(self, message, exchange, routing_key, **kwargs): _lookup = self.channel._lookup _put = self.channel._put for queue in _lookup(exchange, routing_key): _put(queue, message, **kwargs) 4.4 binding 转换
我们知道，Exchange的作用只是将发送的 routing_key 转化为 queue 的名字。这样发送就知道发到哪个 queue 。
因此依据_lookup方法得到对应的queue 。
def _lookup(self, exchange, routing_key, default=None): """Find all queues matching `routing_key` for the given `exchange`. Returns: str: queue name -- must return the string `default` if no queues matched. """ if default is None: default = self.deadletter_queue if not exchange: # anon exchange return [routing_key or default] try: R = self.typeof(exchange).lookup( self.get_table(exchange), exchange, routing_key, default, ) except KeyError: R = [] if not R and default is not None: warnings.warn(UndeliverableWarning(UNDELIVERABLE_FMT.format( exchange=exchange, routing_key=routing_key)), ) self._new_queue(default) R = [default] return R
此处具体逻辑为：
第一，调用到channel的方法。这里的 exchange 名字为 asynt_exchange。
def get_table(self, exchange): key = self.keyprefix_queue % exchange with self.conn_or_acquire() as client: values = client.smembers(key) if not values: raise InconsistencyError(NO_ROUTE_ERROR.format(exchange, key)) return [tuple(bytes_to_str(val).split(self.sep)) for val in values]
我们看看Redis内容，发现集合内容如下：
127.0.0.1:6379> smembers _kombu.binding.asynt_exchange1) "asynt_routing_key\x06\x16\x06\x16asynt_queue"
第二，因此得到对应binding为：
{b'asynt_routing_key\x06\x16\x06\x16asynt_queue'}
即从 exchange 得到 routing_key ---> queue 的规则，然后再依据 routing_key 得到 queue。就知道 Consumer 和 Producer 需要依据哪个 queue 交换消息。
逻辑如下：
+---------------------------------+ | exchange | | | 1 routing_key x | |+----------+ | | +------------+| Producer | +-----------------> | routing_key x ---> queue x | | Consumer |+--------+-+ | | +------------+ | | routing_key y ---> queue y | | | | ^ | | routing_key z ---> queue z | | | | | | | +---------------------------------+ | | | | | | | | | | | | | | | | | | +-----------+ | | 2 message | | 3 message | +-------------------------------> | queue X | +--------------------+ | | +-----------+
4.5 _put in channel
channel的_put 方法被用来继续处理，可以看到其最终调用到了client.lpush。
client为：
Redis >>
代码为：
def _put(self, queue, message, **kwargs): """Deliver message.""" pri = self._get_message_priority(message, reverse=False) with self.conn_or_acquire() as client: client.lpush(self._q_for_pri(queue, pri), dumps(message))
redis怎么区别不同的queue？
实际是每个 queue 被赋予一个字符串 name，这个 name 就是 redis 对应的 list 的 key。知道应该向哪个 list 放消息，后续就是向此 list 中 lpush 消息。
如下方法完成转换功能。
def _q_for_pri(self, queue, pri): pri = self.priority(pri) if pri: return f"{queue}{self.sep}{pri}" return queue 现在发消息之后，redis内容如下，我们可以看出来，消息作为list 的item，放入到之中。
127.0.0.1:6379> lrange asynt_queue 0 -11) "{\"body\": \"aGVsbG8gd29ybGQ=\", \"content-encoding\": \"utf-8\", \"content-type\": \"text/plain\", \"headers\": {}, \"properties\": {\"delivery_mode\": 2, \"delivery_info\": {\"exchange\": \"asynt_exchange\", \"routing_key\": \"asynt_routing_key\"}, \"priority\": 0, \"body_encoding\": \"base64\", \"delivery_tag\": \"df7af424-e1ab-4c08-84b5-1cd5c97ed25d\"}}"127.0.0.1:6379> 0x05 总结
现在我们总结如下：
- Producers: 发送消息的抽象类；
- Consumers：接受消息的抽象类，consumer需要声明一个queue，并将queue与指定的exchange绑定，然后从queue里面接收消息；
- Exchange：MQ 路由，消息发送者将消息发至Exchange，Exchange负责将消息分发至队列；
- Queue：对应的 queue 抽象，存储着即将被应用消费掉的消息，Exchange负责将消息分发Queue，消费者从Queue接收消息；
- Channel：与AMQP中概念类似，可以理解成共享一个Connection的多个轻量化连，就是真实redis连接；
于是逻辑链已经形成，大约是这样的：
- Producer的publish方法接受参数Exchange，于是就发送消息到此Exchange；
- Producer调用channel的组装消息函数
prepare_message为消息添加各种属性； - Producer调用channel的发送消息basic_publish发送消息，此时使用了传入的参数exchange。
- basic_publish方法调用exchange.deliver(exchange, routing_key)来发送消息；
- Exchange中有成员变量Channel，也有成员变量Queues，每个queue对应一个routing_key；
- deliver使用_lookup方法依据key得到对应的queue；
- deliver使用Exchange成员变量Channel的_put方法来向queue中投放消息；
- Channel拿到自己的redis连接池，即client为
Redis<ConnectionPool<Connection<host=localhost,port=6379,db=0>>>；于是可以基于此进行redis操作； - redis怎么区别不同的queue，实际是每个queue被赋予一个字符串name，这就是redis对应的list的key;
- 既然得到了名字为queue的list，则向此list中lpush消息。
- Consumer去Queue取消息；
动态逻辑如下：
+------------+ +------------+ +------------+ +-----------------------+ | producer | | channel | | exchange | | Redis | +---+--------+ +----+-------+ +-------+----+ +----------+------------+ | | | | | | | |publish('', exchange, routing_key) | | | | | | | | prepare_message | | | | | | | | +----------------------------------> | | | | | | | | basic_publish (exchange, routing_key)| | | | | | | | +----------------------------------> | | | | | | | | | deliver(exchange, routing_key)| | | | | | | +-----------------------------> | | | | | | | | | | | | _lookup(exchange, routing_key) | | | | | | | | | | | _put(queue, message) | | | v | | | | <---------------------------+ | | | | | | | _q_for_pri(queue, pri) | | | + | | v | | | | | client.lpush | | | | +--------------------------------------------------> | | | | | v v v v
手机如下：
0xFF 参考
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