[源码分析] 消息队列 Kombu 之 启动过程
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 是如何启动，以及如何搭建一个基本的架子。
因为之前有一个综述，所以大家会发现，一些概念讲解文字会同时出现在后续文章和综述之中。
0x01 示例
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 启动
让我们顺着程序流程看看Kombu都做了些什么，也可以对 Kombu 内部有所了解。
本文关注的重点是：Connection，Channel 和 Hub 是如何联系在一起的。
2.1 Hub
在程序开始，我们建立了Hub。
Hub的作用是建立消息Loop，但是此时尚未建立，因此只是一个静态实例。
hub = Hub()
其定义如下：
class Hub:
"""Event loop object.
Arguments:
timer (kombu.asynchronous.Timer): Specify custom timer instance.
"""
def __init__(self, timer=None):
self.timer = timer if timer is not None else Timer()
self.readers = {}
self.writers = {}
self.on_tick = set()
self.on_close = set()
self._ready = set()
self._running = False
self._loop = None
self.consolidate = set()
self.consolidate_callback = None
self.propagate_errors = ()
self._create_poller()
因为此时没有建立loop，所以目前重要的步骤是建立Poll，其Stack如下：
_get_poller, eventio.py:321
poll, eventio.py:328
_create_poller, hub.py:113
__init__, hub.py:96
main, testUb.py:22
<module>, testUb.py:55
在eventio.py中有如下，我们可以看到Kombu可以使用多种模型来进行内核消息处理：
def _get_poller():
if detect_environment() != 'default':
# greenlet
return _select
elif epoll:
# Py2.6+ Linux
return _epoll
elif kqueue and 'netbsd' in sys.platform:
return _kqueue
elif xpoll:
return _poll
else:
return _select
因为本机情况，这里选择的是：_poll。
+------------------+
| Hub |
| |
| | +-------------+
| poller +---------------> | _poll |
| | | | +-------+
| | | _poller+---------> | poll |
+------------------+ | | +-------+
+-------------+
2.2 Exchange与Queue
其次建立了Exchange与Queue。
- Exchange：交换机，消息发送者将消息发至 Exchange，Exchange 负责将消息分发至 Queue；
- Queue：消息队列，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；
因为此时也没有具体消息，所以我们暂且无法探究Exchange机制。
exchange = Exchange('asynt')
queue = Queue('asynt', exchange, 'asynt')
此时将把Exchange与Queue联系起来。图示如下：
+------------------+
| Hub |
| |
| | +-------------+
| poller +---------------> | _poll |
| | | | +-------+
| | | _poller+---------> | poll |
+------------------+ | | +-------+
+-------------+
+----------------+ +-------------------+
| Exchange | | Queue |
| | | |
| | | |
| channel | <------------+ exchange |
| | | |
| | | |
+----------------+ +-------------------+
2.3 Connection
第三步就是建立Connection。
Connection是对 MQ 连接的抽象，一个 Connection 就对应一个 MQ 的连接。现在就是对'redis://localhost:6379'连接进行抽象。
conn = Connection('redis://localhost:6379')
2.3.1 定义
由定义注释可知，Connection是到broker的连接。从具体代码可以看出，Connection更接近是一个逻辑概念，具体功能都委托给别人完成。
消息从来不直接发送给队列，甚至 Producers 都可能不知道队列的存在。 Producer如何才能将消息发送给Consumer呢？这中间需要经过 Message Broker 的处理和传递。
AMQP中，承担 Message Broker 功能的就是 AMQP Server。也正是从这个角度讲，AMQP 的 Producer 和Consumer 都是 AMQP Client。
在Kombu 体系中，用 transport 对所有的 broker 进行了抽象，为不同的 broker 提供了一致的解决方案。通过Kombu，开发者可以根据实际需求灵活的选择或更换broker。
Connection主要成员变量是，但是此时没有赋值：
- _connection：
- _transport：就是上面提到的对 broker 的抽象。
- cycle：与broker交互的调度策略。
- failover_strategy：在连接失效时，选取其他hosts的策略。
- heartbeat：用来实施心跳。
代码如下：
class Connection:
"""A connection to the broker"""
port = None
virtual_host = '/'
connect_timeout = 5
_connection = None
_default_channel = None
_transport = None
uri_prefix = None
#: The cache of declared entities is per connection,
#: in case the server loses data.
declared_entities = None
#: Iterator returning the next broker URL to try in the event
#: of connection failure (initialized by :attr:`failover_strategy`).
cycle = None
#: Additional transport specific options,
#: passed on to the transport instance.
transport_options = None
#: Strategy used to select new hosts when reconnecting after connection
#: failure. One of "round-robin", "shuffle" or any custom iterator
#: constantly yielding new URLs to try.
failover_strategy = 'round-robin'
#: Heartbeat value, currently only supported by the py-amqp transport.
heartbeat = None
resolve_aliases = resolve_aliases
failover_strategies = failover_strategies
hostname = userid = password = ssl = login_method = None
2.3.2 init 与 transport
Connection内部主要任务是建立了transport。
Stack大致如下：
Transport, redis.py:1039
<module>, redis.py:1031
import_module, __init__.py:126
symbol_by_name, imports.py:56
resolve_transport, __init__.py:70
get_transport_cls, __init__.py:85
__init__, connection.py:183
main, testUb.py:40
<module>, testUb.py:55
2.4 Transport
在Kombu体系中，用transport对所有的broker进行了抽象，为不同的broker提供了一致的解决方案。通过Kombu，开发者可以根据实际需求灵活的选择或更换broker。
Transport：真实的 MQ 连接，也是真正连接到 MQ(redis/rabbitmq) 的实例。就是存储和发送消息的实体，用来区分底层消息队列是用amqp、Redis还是其它实现的。
Transport负责具体操作，但是很多操作移交给 loop 与 MultiChannelPoller 进行。
2.4.1 定义
其主要成员变量为：
- 本transport的驱动类型，名字；
- 对应的 Channel；
- cycle：MultiChannelPoller，具体下文提到；
定义如下：
class Transport(virtual.Transport):
"""Redis Transport."""
Channel = Channel
polling_interval = None # disable sleep between unsuccessful polls.
default_port = DEFAULT_PORT
driver_type = 'redis'
driver_name = 'redis'
implements = virtual.Transport.implements.extend(
asynchronous=True,
exchange_type=frozenset(['direct', 'topic', 'fanout'])
)
def __init__(self, *args, **kwargs):
if redis is None:
raise ImportError('Missing redis library (pip install redis)')
super().__init__(*args, **kwargs)
# Get redis-py exceptions.
self.connection_errors, self.channel_errors = self._get_errors()
# All channels share the same poller.
self.cycle = MultiChannelPoller()
2.4.2 移交操作
Transport负责具体操作，但是很多操作移交给 loop 与 MultiChannelPoller 进行，具体从下面代码可见。
def register_with_event_loop(self, connection, loop):
cycle = self.cycle
cycle.on_poll_init(loop.poller)
cycle_poll_start = cycle.on_poll_start
add_reader = loop.add_reader
on_readable = self.on_readable
def _on_disconnect(connection):
if connection._sock:
loop.remove(connection._sock)
cycle._on_connection_disconnect = _on_disconnect
def on_poll_start():
cycle_poll_start()
[add_reader(fd, on_readable, fd) for fd in cycle.fds]
loop.on_tick.add(on_poll_start)
loop.call_repeatedly(10, cycle.maybe_restore_messages)
health_check_interval = connection.client.transport_options.get(
'health_check_interval',
DEFAULT_HEALTH_CHECK_INTERVAL
)
loop.call_repeatedly(
health_check_interval,
cycle.maybe_check_subclient_health
)
其中重点是MultiChannelPoller。一个Connection有一个Transport， 一个Transport有一个MultiChannelPoller，对poll操作都是由MultiChannelPoller完成，redis操作由channel完成。
2.4.3 MultiChannelPoller
定义如下，可以理解为执行engine，主要作用是：
- 收集channel；
- 建立fd到channel的映射；
- 建立channel到socks的映射；
- 使用poll；
class MultiChannelPoller:
"""Async I/O poller for Redis transport."""
eventflags = READ | ERR
def __init__(self):
# active channels
self._channels = set()
# file descriptor -> channel map.
self._fd_to_chan = {}
# channel -> socket map
self._chan_to_sock = {}
# poll implementation (epoll/kqueue/select)
self.poller = poll()
# one-shot callbacks called after reading from socket.
self.after_read = set()
2.4.4 获取
Transport是预先生成的，若需要，则依据名字取得。
TRANSPORT_ALIASES = {
'amqp': 'kombu.transport.pyamqp:Transport',
'amqps': 'kombu.transport.pyamqp:SSLTransport',
'pyamqp': 'kombu.transport.pyamqp:Transport',
'librabbitmq': 'kombu.transport.librabbitmq:Transport',
'memory': 'kombu.transport.memory:Transport',
'redis': 'kombu.transport.redis:Transport',
......
'pyro': 'kombu.transport.pyro:Transport'
}
_transport_cache = {}
def resolve_transport(transport=None):
"""Get transport by name. """
if isinstance(transport, str):
try:
transport = TRANSPORT_ALIASES[transport]
except KeyError:
if '.' not in transport and ':' not in transport:
from kombu.utils.text import fmatch_best
alt = fmatch_best(transport, TRANSPORT_ALIASES)
else:
if callable(transport):
transport = transport()
return symbol_by_name(transport)
return transport
def get_transport_cls(transport=None):
"""Get transport class by name.
"""
if transport not in _transport_cache:
_transport_cache[transport] = resolve_transport(transport)
return _transport_cache[transport]
此时Connection数据如下，注意其部分成员变量尚且没有意义：
conn = {Connection} <Connection: redis://localhost:6379// at 0x7faa910cbd68>
alt = {list: 0} []
connect_timeout = {int} 5
connection = {Transport} <kombu.transport.redis.Transport object at 0x7faa91277710>
cycle = {NoneType} None
declared_entities = {set: 0} set()
default_channel = {Channel} <kombu.transport.redis.Channel object at 0x7faa912700b8>
failover_strategies = {dict: 2} {'round-robin': <class 'itertools.cycle'>, 'shuffle': <function shufflecycle at 0x7faa9109a0d0>}
failover_strategy = {type} <class 'itertools.cycle'>
heartbeat = {int} 0
host = {str} 'localhost:6379'
hostname = {str} 'localhost'
manager = {Management} <kombu.transport.virtual.base.Management object at 0x7faa91270160>
port = {int} 6379
recoverable_channel_errors = {tuple: 0} ()
resolve_aliases = {dict: 2} {'pyamqp': 'amqp', 'librabbitmq': 'amqp'}
transport = {Transport} <kombu.transport.redis.Transport object at 0x7faa91277710>
transport_cls = {str} 'redis'
uri_prefix = {NoneType} None
userid = {NoneType} None
virtual_host = {str} '/'
至此，Kombu的基本就建立完成，但是彼此之间没有建立逻辑联系。
所以此时示例如下，注意此时三者没有联系：
+-------------------+ +---------------------+ +--------------------+
| Connection | | redis.Transport | | MultiChannelPoller |
| | | | | |
| | | | | _channels |
| | | cycle +------------> | _fd_to_chan |
| transport +---------> | | | _chan_to_sock |
| | | | | poller |
+-------------------+ +---------------------+ | after_read |
| |
+--------------------+
+------------------+
| Hub |
| |
| | +-------------+
| poller +---------------> | _poll |
| | | | +-------+
| | | _poller+---------> | poll |
+------------------+ | | +-------+
+-------------+
+----------------+ +-------------------+
| Exchange | | Queue |
| | | |
| | | |
| channel | <------------+ exchange |
| | | |
| | | |
+----------------+ +-------------------+
0x03 Connection注册hub
之前我们提到，基本架子已经建立起来，但是各个模块之间彼此没有联系，下面我们就看看如何建立联系。
示例代码来到：
conn.register_with_event_loop(hub)
这里进行了注册，此时作用是把hub与Connection联系起来。随之调用到：
def register_with_event_loop(self, loop):
self.transport.register_with_event_loop(self.connection, loop)
进而调用到transport类：<kombu.transport.redis.Transport object at 0x7fd23e962dd8>
具体代码如下：
def register_with_event_loop(self, connection, loop):
cycle = self.cycle
cycle.on_poll_init(loop.poller)# 这里建立联系，loop就是hub
cycle_poll_start = cycle.on_poll_start
add_reader = loop.add_reader
on_readable = self.on_readable
def _on_disconnect(connection):
if connection._sock:
loop.remove(connection._sock)
cycle._on_connection_disconnect = _on_disconnect
def on_poll_start():
cycle_poll_start()
[add_reader(fd, on_readable, fd) for fd in cycle.fds]
loop.on_tick.add(on_poll_start)
loop.call_repeatedly(10, cycle.maybe_restore_messages)
health_check_interval = connection.client.transport_options.get(
'health_check_interval',
DEFAULT_HEALTH_CHECK_INTERVAL
)
loop.call_repeatedly(
health_check_interval,
cycle.maybe_check_subclient_health
)
3.1 建立Channel
注册最初是建立Channel。这里有一个连接的动作，就是在这里，建立了Channel。
@property
def connection(self):
"""The underlying connection object"""
if not self._closed:
if not self.connected:
return self._ensure_connection(
max_retries=1, reraise_as_library_errors=False
)
return self._connection
具体建立是在 base.py 中完成，这是 Transport 基类。Stack 如下：
create_channel, base.py:920
establish_connection, base.py:938
_establish_connection, connection.py:801
_connection_factory, connection.py:866
retry_over_time, functional.py:325
_ensure_connection, connection.py:439
connection, connection.py:859
register_with_event_loop, connection.py:266
main, testUb.py:41
<module>, testUb.py:55
3.2 Channel
Channel：与AMQP中概念类似，可以理解成共享一个Connection的多个轻量化连接。就是真正的连接。
可以认为是 redis 操作和连接的封装。每个 Channel 都可以与 redis 建立一个连接，在此连接之上对 redis 进行操作，每个连接都有一个 socket，每个 socket 都有一个 file，从这个 file 可以进行 poll。
为了更好的说明，我们提前给出这个通讯流程大约如下：
+---------------------------------------------------------------------------------------------------------------------------------------+
| +--------------+ 6 parse_response |
| +--> | Linux Kernel | +---+ |
| | +--------------+ | |
| | | |
| | | event |
| | 1 | |
| | | 2 |
| | | |
+-------+---+ socket + | |
| redis | <------------> port +--> fd +--->+ v |
| | | +------+--------+ |
| | socket | | Hub | |
| | <------------> port +--> fd +--->----------> | | |
| port=6379 | | | | |
| | socket | | readers +-----> Transport.on_readable |
| | <------------> port +--> fd +--->+ | | + |
+-----------+ +---------------+ | |
| |
3 | |
+----------------------------------------------------------------------------------------+ |
| v
| _receive_callback
| 5 +-------------+ +-----------+
+------------+------+ +-------------------------+ 'BRPOP' = Channel._brpop_read +-----> | Channel | +------------------> | Consumer |
| Transport | | MultiChannelPoller | +------> channel . handlers 'LISTEN' = Channel._receive +-------------+ +---+-------+
| | | | | 8 |
| | on_readable(fileno) | | | ^ |
| cycle +---------------------> | _fd_to_chan +----------------> channel . handlers 'BRPOP' = Channel._brpop_read | |
| | 4 | | | 'LISTEN' = Channel._receive | |
| _callbacks[queue]| | | | | on_m | 9
| + | +-------------------------+ +------> channel . handlers 'BRPOP' = Channel._brpop_read | |
+-------------------+ 'LISTEN' = Channel._receive | |
| | v
| 7 _callback |
+-----------------------------------------------------------------------------------------------------------------------------------------+ User Function
手机上如下：
3.2.1 定义
Channel 主要成员是：
- async_pool ：redis异步连接池；
- pool ：redis连接池；
- channel_id ：Channel ID；
- client ：就是StrictRedis之类的driver；
- connection ：对应的Transport；
- cycle = {FairCycle} <FairCycle: 0/0 []>
- queue_order_strategy ：获取queue的策略；
- state ：BrokerState状态；
- subclient ：PubSub所用的client；
keyprefix_queue = '{p}_kombu.binding.%s'.format(p=KEY_PREFIX) ：bing用到的key；
比如_get_client可以看出来client。
def _get_client(self):
if redis.VERSION < (3, 2, 0):
raise VersionMismatch(
'Redis transport requires redis-py versions 3.2.0 or later. '
'You have {0.__version__}'.format(redis))
return redis.StrictRedis
简化版定义如下：
class Channel(virtual.Channel):
"""Redis Channel."""
QoS = QoS
_client = None
_subclient = None
keyprefix_queue = '{p}_kombu.binding.%s'.format(p=KEY_PREFIX)
keyprefix_fanout = '/{db}.'
sep = 'x06x16'
_fanout_queues = {}
unacked_key = '{p}unacked'.format(p=KEY_PREFIX)
unacked_index_key = '{p}unacked_index'.format(p=KEY_PREFIX)
unacked_mutex_key = '{p}unacked_mutex'.format(p=KEY_PREFIX)
unacked_mutex_expire = 300 # 5 minutes
unacked_restore_limit = None
visibility_timeout = 3600 # 1 hour
max_connections = 10
queue_order_strategy = 'round_robin'
_async_pool = None
_pool = None
from_transport_options = (
virtual.Channel.from_transport_options +
('sep',
'ack_emulation',
'unacked_key',
......
'max_connections',
'health_check_interval',
'retry_on_timeout',
'priority_steps') # <-- do not add comma here!
)
connection_class = redis.Connection if redis else None
3.2.2 基类
基类定义如下：
class Channel(AbstractChannel, base.StdChannel):
"""Virtual channel.
Arguments:
connection (ConnectionT): The transport instance this
channel is part of.
"""
#: message class used.
Message = Message
#: QoS class used.
QoS = QoS
#: flag to restore unacked messages when channel
#: goes out of scope.
do_restore = True
#: mapping of exchange types and corresponding classes.
exchange_types = dict(STANDARD_EXCHANGE_TYPES)
#: flag set if the channel supports fanout exchanges.
supports_fanout = False
#: Binary <-> ASCII codecs.
codecs = {'base64': Base64()}
#: Default body encoding.
#: NOTE: ``transport_options['body_encoding']`` will override this value.
body_encoding = 'base64'
#: counter used to generate delivery tags for this channel.
_delivery_tags = count(1)
#: Optional queue where messages with no route is delivered.
#: Set by ``transport_options['deadletter_queue']``.
deadletter_queue = None
# List of options to transfer from :attr:`transport_options`.
from_transport_options = ('body_encoding', 'deadletter_queue')
# Priority defaults
default_priority = 0
min_priority = 0
max_priority = 9
最终具体举例如下：
self = {Channel} <kombu.transport.redis.Channel object at 0x7fe61aa88cc0>
Client = {type} <class 'redis.client.Redis'>
Message = {type} <class 'kombu.transport.virtual.base.Message'>
QoS = {type} <class 'kombu.transport.redis.QoS'>
active_fanout_queues = {set: 0} set()
active_queues = {set: 0} set()
async_pool = {ConnectionPool} ConnectionPool<Connection<host=localhost,port=6379,db=0>>
auto_delete_queues = {set: 0} set()
channel_id = {int} 1
client = {Redis} Redis<ConnectionPool<Connection<host=localhost,port=6379,db=0>>>
codecs = {dict: 1} {'base64': <kombu.transport.virtual.base.Base64 object at 0x7fe61a987668>}
connection = {Transport} <kombu.transport.redis.Transport object at 0x7fe61aa399b0>
connection_class = {type} <class 'redis.connection.Connection'>
cycle = {FairCycle} <FairCycle: 0/0 []>
deadletter_queue = {NoneType} None
exchange_types = {dict: 3} {'direct': <kombu.transport.virtual.exchange.DirectExchange object at 0x7fe61aa53588>, 'topic': <kombu.transport.virtual.exchange.TopicExchange object at 0x7fe61aa53550>,
handlers = {dict: 2} {'BRPOP': <bound method Channel._brpop_read of <kombu.transport.redis.Channel object at 0x7fe61aa88cc0>>, 'LISTEN': <bound method Channel._receive of <kombu.transport.redis.Channel object at 0x7fe61aa88cc0>>}
pool = {ConnectionPool} ConnectionPool<Connection<host=localhost,port=6379,db=0>>
qos = {QoS} <kombu.transport.redis.QoS object at 0x7fe61aa88e48>
queue_order_strategy = {str} 'round_robin'
state = {BrokerState} <kombu.transport.virtual.base.BrokerState object at 0x7fe61a987748>
subclient = {PubSub} <redis.client.PubSub object at 0x7fe61aa39cc0>
3.2.3 redis消息回调函数
关于上面成员变量，这里需要说明的是
handlers = {dict: 2}
{
'BRPOP': <bound method Channel._brpop_read of <kombu.transport.redis.Channel object at 0x7fe61aa88cc0>>,
'LISTEN': <bound method Channel._receive of <kombu.transport.redis.Channel object at 0x7fe61aa88cc0>>
}
这是redis有消息时的回调函数，即：
- BPROP 有消息时候，调用 Channel._brpop_read；
- LISTEN 有消息时候，调用 Channel._receive；
3.2.4 Redis 直接相关的主要成员
与Redis 直接相关的成员定义在：redis/client.py。
与 Redis 直接相关的主要成员是如下，会利用如下变量进行具体 redis操作：
- async_pool ：redis异步连接池；
- pool ：redis连接池；
- client ：就是StrictRedis之类的driver；
- subclient ：PubSub所用的client；
分别对应如下类型：
channel = {Channel} <kombu.transport.redis.Channel object at 0x7fabeea23b00>
Client = {type} <class 'redis.client.Redis'>
async_pool = {ConnectionPool} ConnectionPool<Connection<host=localhost,port=6379,db=0>>
client = {Redis} Redis<ConnectionPool<Connection<host=localhost,port=6379,db=0>>>
connection = {Transport} <kombu.transport.redis.Transport object at 0x7fabeea23940>
connection_class = {type} <class 'redis.connection.Connection'>
connection_class_ssl = {type} <class 'redis.connection.SSLConnection'>
pool = {ConnectionPool} ConnectionPool<Connection<host=localhost,port=6379,db=0>>
subclient = {PubSub} <redis.client.PubSub object at 0x7fabeea97198>
具体代码如下：
def _create_client(self, asynchronous=False):
if asynchronous:
return self.Client(connection_pool=self.async_pool)
return self.Client(connection_pool=self.pool)
def _get_pool(self, asynchronous=False):
params = self._connparams(asynchronous=asynchronous)
self.keyprefix_fanout = self.keyprefix_fanout.format(db=params['db'])
return redis.ConnectionPool(**params)
def _get_client(self):
if redis.VERSION < (3, 2, 0):
raise VersionMismatch(
'Redis transport requires redis-py versions 3.2.0 or later. '
'You have {0.__version__}'.format(redis))
return redis.StrictRedis
@property
def pool(self):
if self._pool is None:
self._pool = self._get_pool()
return self._pool
@property
def async_pool(self):
if self._async_pool is None:
self._async_pool = self._get_pool(asynchronous=True)
return self._async_pool
@cached_property
def client(self):
"""Client used to publish messages, BRPOP etc."""
return self._create_client(asynchronous=True)
@cached_property
def subclient(self):
"""Pub/Sub connection used to consume fanout queues."""
client = self._create_client(asynchronous=True)
return client.pubsub()
因为添加了Channel，所以此时如下：
+-----------------+
| Channel |
| | +-----------------------------------------------------------+
| client +---------> | Redis<ConnectionPool<Connection<host=localhost,port=6379> |
| | +-----------------------------------------------------------+
| |
| | +---------------------------------------------------+-+
| pool +----------> |ConnectionPool<Connection<host=localhost,port=6379 > |
| | +---------------------------------------------------+-+
| |
| |
| |
| connection |
| |
+-----------------+
+-------------------+ +---------------------+ +--------------------+
| Connection | | redis.Transport | | MultiChannelPoller |
| | | | | |
| | | | | _channels |
| | | cycle +------------> | _fd_to_chan |
| transport +---------> | | | _chan_to_sock |
| | | | | poller |
+-------------------+ +---------------------+ | after_read |
| |
+------------------+ +--------------------+
| Hub |
| |
| | +-------------+
| poller +---------------> | _poll |
| | | | +-------+
| | | _poller+---------> | poll |
+------------------+ | | +-------+
+-------------+
+----------------+ +-------------------+
| Exchange | | Queue |
| | | |
| | | |
| channel | <------------+ exchange |
| | | |
| | | |
+----------------+ +-------------------+
3.3 channel 与 Connection 联系
讲到这里，基本道理大家都懂，但是具体两者之间如何联系，我们需要再剖析下。
3.3.1 从Connection得到channel
在Connection定义中有如下，原来 Connection 是通过 transport 来得到 channel：
def channel(self):
"""Create and return a new channel."""
self._debug('create channel')
chan = self.transport.create_channel(self.connection)
return chan
3.3.2 Transport具体创建
在Transport之中有：
def create_channel(self, connection):
try:
return self._avail_channels.pop()
except IndexError:
channel = self.Channel(connection)
self.channels.append(channel)
return channel
原来在 Transport 有两个channels 列表：
self._avail_channels
self.channels
如果_avail_channels 有内容则直接获取，否则生成一个新的Channel。
在真正连接时候，会调用 establish_connection 放入self._avail_channels。
def establish_connection(self):
# creates channel to verify connection.
# this channel is then used as the next requested channel.
# (returned by ``create_channel``).
self._avail_channels.append(self.create_channel(self))
return self # for drain events
其堆栈如下：
__init__, redis.py:557
create_channel, base.py:921
establish_connection, base.py:939
_establish_connection, connection.py:801
_connection_factory, connection.py:866
retry_over_time, functional.py:313
_ensure_connection, connection.py:439
connection, connection.py:859
channel, connection.py:283
<module>, node.py:11
3.3.3 建立联系
在init中有：
def __init__(self, *args, **kwargs):
super().__init__(*args, **kwargs)
if not self.ack_emulation: # disable visibility timeout
self.QoS = virtual.QoS
self._queue_cycle = cycle_by_name(self.queue_order_strategy)()
self.Client = self._get_client()
self.ResponseError = self._get_response_error()
self.active_fanout_queues = set()
self.auto_delete_queues = set()
self._fanout_to_queue = {}
self.handlers = {'BRPOP': self._brpop_read, 'LISTEN': self._receive}
......
self.connection.cycle.add(self) # add to channel poller.
if register_after_fork is not None:
register_after_fork(self, _after_fork_cleanup_channel)
重点是：
self.connection.cycle.add(self) # add to channel poller.
这就是把 Channel与Transport 中的 poller 联系起来，这样Transport可以利用Channel去与真实的redis进行交互。
堆栈如下：
add, redis.py:277
__init__, redis.py:531
create_channel, base.py:920
establish_connection, base.py:938
_establish_connection, connection.py:801
_connection_factory, connection.py:866
retry_over_time, functional.py:325
_ensure_connection, connection.py:439
connection, connection.py:859
register_with_event_loop, connection.py:266
main, testUb.py:41
因为已经联系起来，所以此时如下：
+-----------------+
| Channel |
| | +-----------------------------------------------------------+
| client +---------> | Redis<ConnectionPool<Connection<host=localhost,port=6379> |
| | +-----------------------------------------------------------+
| |
| | +---------------------------------------------------+-+
| pool +----------> |ConnectionPool<Connection<host=localhost,port=6379 > |
| | +---------------------------------------------------+-+
| |
| | <------------------------------------------------------------+
| | |
| connection +---------------+ |
| | | |
+-----------------+ | |
v |
+-------------------+ +---+-----------------+ +--------------------+ |
| Connection | | redis.Transport | | MultiChannelPoller | |
| | | | | | |
| | | | | _channels +--------+
| | | cycle +------------> | _fd_to_chan |
| transport +---------> | | | _chan_to_sock |
| | | | | poller |
+-------------------+ +---------------------+ | after_read |
| |
+------------------+ +--------------------+
| Hub |
| |
| | +-------------+
| poller +---------------> | _poll |
| | | | +-------+
| | | _poller+---------> | poll |
+------------------+ | | +-------+
+-------------+
+----------------+ +-------------------+
| Exchange | | Queue |
| | | |
| | | |
| channel | <------------+ exchange |
| | | |
| | | |
+----------------+ +-------------------+
3.3 Transport 与 Hub 联系
on_poll_init 这里就是把 kombu.transport.redis.Transport 与 Hub 联系起来。
用self.poller = poller把Transport与Hub的poll联系起来。这样 Transport 就可以利用 poll。
def on_poll_init(self, poller):
self.poller = poller
for channel in self._channels:
return channel.qos.restore_visible(
num=channel.unacked_restore_limit,
)
此时变量如下：
poller = {_poll} <kombu.utils.eventio._poll object at 0x7fb9bcd87240>
self = {MultiChannelPoller} <kombu.transport.redis.MultiChannelPoller object at 0x7fb9bcdd6a90>
after_read = {set: 0} set()
eventflags = {int} 25
fds = {dict: 0} {}
poller = {_poll} <kombu.utils.eventio._poll object at 0x7fb9bcd87240>
因此，我们最终如下：
+-----------------+
| Channel |
| | +-----------------------------------------------------------+
| client +---------> | Redis<ConnectionPool<Connection<host=localhost,port=6379> |
| | +-----------------------------------------------------------+
| |
| | +---------------------------------------------------+-+
| pool +----------> |ConnectionPool<Connection<host=localhost,port=6379 > |
| | +---------------------------------------------------+-+
| |
| | <------------------------------------------------------------+
| | |
| connection +---------------+ |
| | | |
+-----------------+ | |
v |
+-------------------+ +---+-----------------+ +--------------------+ |
| Connection | | redis.Transport | | MultiChannelPoller | |
| | | | | | |
| | | | | _channels +--------+
| | | cycle +------------> | _fd_to_chan |
| transport +---------> | | | _chan_to_sock |
| | | | +<----+ poller |
+-------------------+ +---------------------+ | | after_read |
| | |
+------------------+ +--------------+ +--------------------+
| Hub | |
| | v
| | +-------+-----+
| poller +---------------> | _poll |
| | | | +-------+
| | | _poller+---------> | poll |
+------------------+ | | +-------+
+-------------+
+----------------+ +-------------------+
| Exchange | | Queue |
| | | |
| | | |
| channel | <------------+ exchange |
| | | |
| | | |
+----------------+ +-------------------+
0x04 总结
具体如图，可以看出来，上面三个基本模块已经联系到了一起。
可以看到，
- 目前是以Transport为中心，把 Channel代表的真实 redis 与 Hub其中的poll联系起来，但是具体如何使用则尚未得知。
- 用户是通过Connection来作为API入口，connection可以得到Transport。
既然基本架构已经搭好，所以从下文开始，我们看看 Consumer 是如何运作的。