[源码解析] 并行分布式任务队列 Celery 之 Task是什么

[源码解析] 并行分布式任务队列 Celery 之 Task是什么

0x00 摘要

Celery是一个简单、灵活且可靠的，处理大量消息的分布式系统，专注于实时处理的异步任务队列，同时也支持任务调度。本文目的是看看 Celery 的 task 究竟是什么，以及如果我们想从无到有实现一个 task 机制，有哪些地方需要注意，应该如何处理。

因为 task 和 Consumer 消费密切相关，为了更好的说明，故本文与上文有部分重复，请谅解。

0x01 思考出发点

我们可以大致想想需要一些问题，也就是我们下面剖析的出发点和留意点。

task 究竟是什么？
task 有什么分类？
有没有内置的 task？
task 如何注册到系统中？
用户自定义的 task 如何注册到系统中？

我们在下面会逐一回答这些问题。

0x02 示例代码

示例代码服务端如下，这里使用了装饰器来包装待执行任务。

Task就是用户自定义的业务代码，这里的 task 就是一个加法功能。

from celery import Celery
app = Celery('myTest', broker='redis://localhost:6379')
@app.task
def add(x,y):
    print(x+y)
    return x+y
if __name__ == '__main__':
    app.worker_main(argv=['worker'])

发送代码如下：

from myTest import add
re = add.apply_async((2,17))

0x03 任务是什么

为了了解 task 是什么，我们首先打印出运行变量看看，这里选取了主要成员变量：

self = {add} <@task: myTest.add of myTest at 0x7faf35f0a208>
 Request = {str} 'celery.worker.request:Request'
 Strategy = {str} 'celery.worker.strategy:default'
 app = {Celery} <Celery myTest at 0x7faf35f0a208>
 backend = {DisabledBackend} <celery.backends.base.DisabledBackend object at 0x7faf364aea20>
 from_config = {tuple: 9} (('serializer', 'task_serializer'), ('rate_limit', 'task_default_rate_limit'), ('priority', 'task_default_priority'), ('track_started', 'task_track_started'), ('acks_late', 'task_acks_late'), ('acks_on_failure_or_timeout', 'task_acks_on_failure_or_timeout'), ('reject_on_worker_lost', 'task_reject_on_worker_lost'), ('ignore_result', 'task_ignore_result'), ('store_errors_even_if_ignored', 'task_store_errors_even_if_ignored'))
 name = {str} 'myTest.add'
 priority = {NoneType} None
 request = {Context} <Context: {}>
 request_stack = {_LocalStack: 0} <celery.utils.threads._LocalStack object at 0x7faf36405e48>
 serializer = {str} 'json'

可以看出来，'myTest.add' 是一个Task变量。

于是我们需要看看Task 是什么。Task 的实现在 Celery 中你会发现有两处，

一处位于 celery/app/task.py；
第二个位于 celery/task/base.py 中；

他们之间是有关系的，你可以认为第一个是对外暴露的接口，而第二个是具体的实现。

0x04 Celery应用与任务

任务是 Celery 里不可缺少的一部分，它可以是任何可调用对象。每一个任务通过一个唯一的名称进行标识， worker 通过这个名称对任务进行检索。任务可以通过 app.task 装饰器进行注册，需要注意的一点是，当函数有多个装饰器时，为了保证 Celery 的正常运行，app.task 装饰器需要在最外层。

Task 承载的功能就是在 Celery 应用中，启动对应的消息消费者。

任务最基本的形式就是函数，任务发布最直接的想法就是client将要执行的相关函数代码打包，发布到broker。分布式计算框架 spark 就是使用这种方式（Spark的思想比较简单：挪计算不挪数据）。2.0之前的celery也支持这种任务发布的方式。

这种方式显而易见的一个坏处是传递给broker的数据量可能会比较大。解决的办法也很容易想到，就是把要发布的任务相关的代码，提前告诉worker。这就是全局集合和注解注册的作用。

当采用 "提前告诉 worker 我们自定义的 task" 时候，定义 task 的方法如下：

@app.task(name='hello_task')
def hello():
  print('hello')

其中的app是worker中的application，通过装饰器的方式，对任务函数注册。

app会维护一个字典，key是任务的名字，也就是这里的hello_task，value是这个函数的内存地址。任务名必须唯一，但是任务名这个参数不是必须的，如果没有给这个参数，celery会自动根据包的路径和函数名生成一个任务名。

通过上面这种方式，client发布任务只需要提供任务名以及相关参数，不必提供任务相关代码：

# client端
app.send_task('hello_task')

这里需要注意：client发布任务后，任务会以一个消息的形式写入broker队列，带有任务名称等相关参数，等待worker获取。这里任务的发布，是完全独立于worker端的，即使worker没有启动，消息也会被写入队列。

这种方式也有显而易见的坏处，所有要执行的任务代码都需要提前在worker端注册好，client端和worker端的耦合变强了。

因此，我们需要从 Celery 应用启动时候开始看。

4.1 全局回调集合和内置任务

Celery 启动首先就是来到 celery/_state.py

这里建立了一个全局 set，用来收集所有的任务 tasks。

#: Global set of functions to call whenever a new app is finalized.
#: Shared tasks, and built-in tasks are created by adding callbacks here.
_on_app_finalizers = set()

在启动时候，系统通过调用如下函数来添加任务。

def connect_on_app_finalize(callback):
    """Connect callback to be called when any app is finalized."""
    _on_app_finalizers.add(callback)
    return callback

首先，celery/app/builtins.py 就定义了很多内置任务，需要一一添加到全局回调集合中。

@connect_on_app_finalize
def add_map_task(app):
    from celery.canvas import signature
    @app.task(name='celery.map', shared=False, lazy=False)
    def xmap(task, it):
        task = signature(task, app=app).type
        return [task(item) for item in it]
    return xmap

其次，系统流程会来到我们的自定义task，把这个 task 注册到全局回调集合中。

即，可以这么理解：Celery 启动之后，会查找代码中，哪些类或者函数使用了 @task注解，然后就把这些类或者函数注册到全局回调集合中。

@app.task
def add(x,y):
    print(x+y)
    return x+y

4.2 装饰器@app.task

我们顺着 @app.task 来到了 Celery 应用本身。

代码位于：celery/app/base.py。

@app.task 的作用是返回 _create_task_cls 来构建一个task proxy，然后加入应用待处理队列 pending，并且利用connect_on_app_finalize(cons) 加入全局回调集合。

_create_task_cls = {function} <function Celery.task.<locals>.inner_create_task_cls.<locals>._create_task_cls at 0x7ff1a7b118c8>

具体代码如下：

def task(self, *args, **opts):
    if USING_EXECV and opts.get('lazy', True):
        from . import shared_task
        return shared_task(*args, lazy=False, **opts)
    def inner_create_task_cls(shared=True, filter=None, lazy=True, **opts):
        _filt = filter
        def _create_task_cls(fun):
            if shared:
                def cons(app):
                    return app._task_from_fun(fun, **opts)
                cons.__name__ = fun.__name__
                connect_on_app_finalize(cons)   # 这里是重点，加入全局回调集合
            if not lazy or self.finalized:
                ret = self._task_from_fun(fun, **opts)
            else:
                # return a proxy object that evaluates on first use
                ret = PromiseProxy(self._task_from_fun, (fun,), opts,
                                   __doc__=fun.__doc__)
                self._pending.append(ret) # 加入应用pending
            if _filt:
                return _filt(ret)
            return ret
        return _create_task_cls
    if len(args) == 1:
        if callable(args[0]):
            return inner_create_task_cls(**opts)(*args)
    return inner_create_task_cls(**opts)

4.2.1 建立 Proxy 实例

按照示例中的调用，Celery 返回了Proxy的实例，传入参数就是task_by_cons。

此时查看一下Proxy类的实现，该类位于celery/local.py中。

class Proxy(object):
    """Proxy to another object."""
    # Code stolen from werkzeug.local.Proxy.
    __slots__ = ('__local', '__args', '__kwargs', '__dict__')
    def __init__(self, local,
                 args=None, kwargs=None, name=None, __doc__=None):
        object.__setattr__(self, '_Proxy__local', local)            # 将传入参数local设置到_Proxy__local属性中
        object.__setattr__(self, '_Proxy__args', args or ())        # 设置列表属性
        object.__setattr__(self, '_Proxy__kwargs', kwargs or {})    # 设置键值属性
        if name is not None:
            object.__setattr__(self, '__custom_name__', name)
        if __doc__ is not None:
            object.__setattr__(self, '__doc__', __doc__)
    ...
    def _get_current_object(self):
        """Get current object.
        This is useful if you want the real
        object behind the proxy at a time for performance reasons or because
        you want to pass the object into a different context.
        """
        loc = object.__getattribute__(self, '_Proxy__local')        # 获取初始化传入的local
        if not hasattr(loc, '__release_local__'):                   # 如果没有__release_local__属性
            return loc(*self.__args, **self.__kwargs)               # 函数调用，将初始化的值传入调用该函数
        try:  # pragma: no cover
            # not sure what this is about
            return getattr(loc, self.__name__)                      # 获取当前__name__属性值
        except AttributeError:  # pragma: no cover
            raise RuntimeError('no object bound to {0.__name__}'.format(self))
    ...
    def __getattr__(self, name):
        if name == '__members__':
            return dir(self._get_current_object())
        return getattr(self._get_current_object(), name)            # 获取obj的属性
    def __setitem__(self, key, value):
        self._get_current_object()[key] = value                     # 设置key val
    def __delitem__(self, key):
        del self._get_current_object()[key]                         # 删除对应key
    def __setslice__(self, i, j, seq):
        self._get_current_object()[i:j] = seq                       # 列表操作
    def __delslice__(self, i, j):
        del self._get_current_object()[i:j]
    def __setattr__(self, name, value):
        setattr(self._get_current_object(), name, value)            # 设置属性
    def __delattr__(self, name):
        delattr(self._get_current_object(), name)                   # 删除对应属性

我们只展示了部分属性，分析如上，主要是根据传入的是否local是否是函数，或者包含release_local来判断是否是调用函数，或是获取属性来处理。

4.2.2 添加待处理

上面代码中，如下会把 task 添加到 Celery 应用的 pending queue。

self._pending.append(ret)

_pending定义如下，就是一个 deque：

class Celery:
    """Celery application.
    """
    def __init__(self, main=None, loader=None, backend=None,
                 amqp=None, events=None, log=None, control=None,
                 set_as_current=True, tasks=None, broker=None, include=None,
                 changes=None, config_source=None, fixups=None, task_cls=None,
                 autofinalize=True, namespace=None, strict_typing=True,
                 **kwargs):
        self._pending = deque()

此时全局集合如下：

_on_app_finalizers = {set: 10}
 {function} <function add_chunk_task at 0x7fc200a81400>
 {function} <function add_backend_cleanup_task at 0x7fc200a81048>
 {function} <function add_starmap_task at 0x7fc200a81488>
 {function} <function add_group_task at 0x7fc200a812f0>
 {function} <function add_map_task at 0x7fc200a81510>
 {function} <function Celery.task.<locals>.inner_create_task_cls.<locals>._create_task_cls.<locals>.cons at 0x7fc200af4510>
 {function} <function add_accumulate_task at 0x7fc200aa0158>
 {function} <function add_chain_task at 0x7fc200a81378>
 {function} <function add_unlock_chord_task at 0x7fc200a81598>
 {function} <function add_chord_task at 0x7fc200aa01e0>

具体逻辑如图：

                           +------------------------------+
                           |  _on_app_finalizers = set()  |
                           |                              |
                           +--------------+---------------+
                                          |
                 connect_on_app_finalize  |
 +------------+                           |
 | builtins.py| +-----------------------> |
 +------------+                           |
                                          |
                 connect_on_app_finalize  |
+-------------+                           |
|User Function| +---------------------->  |
+-------------+                           |
                                          v
             +----------------------------------------------------------------------------------------------------+
             |                                        _on_app_finalizers                                          |
             |                                                                                                    |
             |                                                                                                    |
             |    ^function add_chunk_task>                                                                       |
             |    <function add_backend_cleanup_task>                                                             |
             |    <function add_starmap_task>                                                                     |
             |    <function add_group_task>                                                                       |
             |    <function add_map_task^                                                                         |
             |    <function Celery.task.vlocals^.inner_create_task_cls.<locals>._create_task_cls.<locals>.cons>   |
             |    <function add_accumulate_taskv                                                                  |
             |    <function add_chain_task>                                                                       |
             |    <function add_unlock_chord_task>                                                                |
             |    vfunction add_chord_task>                                                                       |
             |                                                                                                    |
             +----------------------------------------------------------------------------------------------------+

至此，得倒了一个全局 set ：_on_app_finalizers，用来收集所有的任务 tasks。

手机上如图：

4.3 Celery Worker 启动

目前 Celery 知道了有哪些 task，并且把它们收集起来，但是还不知道它们的逻辑意义。或者可以这么认为，Celery 只是知道有哪些类，但是没有这些类的实例。

因为消费 task 是 Celery 的核心功能，所以我们不可避免的要再回顾下 Worker 的启动，但是这里我们注重 worker 之中与 task 相关的部分。

其实就是处理上面的全局 set ：_on_app_finalizers。把这些暂时没有意义的 task 与 Celery 应用关联起来。

具体来说，就是：

根据 task 的具体类生成 task 的实例；
把这些具体task 实例与 Celery 联系起来，比如用 task 名字就可以找到具体实例；
配合实例的各种属性；

4.3.1 Worker 示例

这里的Worker 就是 Celery 用来消费的 worker 实例。

所以，我们直接来到 worker 看看。

代码位于：celery/bin/worker.py

@click.pass_context
@handle_preload_options
def worker(ctx, hostname=None, pool_cls=None, app=None, uid=None, gid=None,
           loglevel=None, logfile=None, pidfile=None, statedb=None,
           **kwargs):
    """Start worker instance."""
    app = ctx.obj.app
    worker = app.Worker(
        hostname=hostname, pool_cls=pool_cls, loglevel=loglevel,
        logfile=logfile,  # node format handled by celery.app.log.setup
        pidfile=node_format(pidfile, hostname),
        statedb=node_format(statedb, hostname),
        no_color=ctx.obj.no_color,
        **kwargs)  # 运行到这里
    worker.start()
    return worker.exitcode

4.3.2 WorkController

在 worker = app.Worker 之中，我们会发现，间接调用到了 WorkerController。

代码运行到这里，位于：celery/worker/worker.py。

这里做了一些初始化工作，我们继续探究。

class WorkController:
    """Unmanaged worker instance."""
    def __init__(self, app=None, hostname=None, **kwargs):
        self.app = app or self.app
        self.hostname = default_nodename(hostname)
        self.startup_time = datetime.utcnow()
        self.app.loader.init_worker()
        self.on_before_init(**kwargs) # 运行到这里

4.3.3 Worker(WorkController)

代码运行到这里，位于：celery/apps/worker.py

这里调用到了 trace.setup_worker_optimizations，这样马上就看到 task 了。

class Worker(WorkController):
    """Worker as a program."""
    def on_before_init(self, quiet=False, **kwargs):
        self.quiet = quiet
        trace.setup_worker_optimizations(self.app, self.hostname)

4.3.4 trace 进入任务联系

代码运行到这里，位于：celery/app/trace.py。

调用到 app.finalize()，目的是启动之前，搞定所有任务。

def setup_worker_optimizations(app, hostname=None):
    """Setup worker related optimizations."""
    global trace_task_ret
    hostname = hostname or gethostname()
    # make sure custom Task.__call__ methods that calls super
    # won't mess up the request/task stack.
    _install_stack_protection()
    app.set_default()
    # evaluate all task classes by finalizing the app.
    app.finalize()

4.3.5 把任务和应用关联起来

费了半天劲，我们才来到了关键逻辑。

app.finalize() 会添加任务到 Celery 应用。

即：之前系统把所有的task都收集起来了，得倒了一个全局 set ：_on_app_finalizers。但是这个 set 中的task 目前没有逻辑意义，需要和 Celery 应用联系起来才行，所以这里就是要建立关联。

堆栈如下：

_task_from_fun, base.py:450
_create_task_cls, base.py:425
add_chunk_task, builtins.py:128
_announce_app_finalized, _state.py:52
finalize, base.py:511
setup_worker_optimizations, trace.py:643
on_before_init, worker.py:90
__init__, worker.py:95
worker, worker.py:326
caller, base.py:132
new_func, decorators.py:21
invoke, core.py:610
invoke, core.py:1066
invoke, core.py:1259
main, core.py:782
start, base.py:358
worker_main, base.py:374

代码如下：

def finalize(self, auto=False):
    """Finalize the app.
    This loads built-in tasks, evaluates pending task decorators,
    reads configuration, etc.
    """
    with self._finalize_mutex:
        if not self.finalized:
            if auto and not self.autofinalize:
                raise RuntimeError('Contract breach: app not finalized')
            self.finalized = True
            _announce_app_finalized(self) # 这里是关键，建立关联
            pending = self._pending
            while pending:
                maybe_evaluate(pending.popleft()) 
            for task in self._tasks.values():
                task.bind(self)
            self.on_after_finalize.send(sender=self)

4.3.5.1 添加任务

_announce_app_finalized(self) 函数是为了 : 把全局回调集合 _on_app_finalizers 中的回调函数运行，得到任务的实例，然后就把它们加入到 Celery 的任务列表，用户可以通过 task 名字得到对应的 task 实例。

def _announce_app_finalized(app):
    callbacks = set(_on_app_finalizers)
    for callback in callbacks:
        callback(app)

对于我们的用户自定义任务，callback 就是 _create_task_cls，因此就是运行 _create_task_cls 进行添加。

def inner_create_task_cls(shared=True, filter=None, lazy=True, **opts):
    _filt = filter
    def _create_task_cls(fun):
        if shared:
            def cons(app):
                return app._task_from_fun(fun, **opts)
            cons.__name__ = fun.__name__
            connect_on_app_finalize(cons)
        if not lazy or self.finalized:
            ret = self._task_from_fun(fun, **opts) # 这里

于是，在初始化过程中，为每个 app 添加该任务时，会调用到 app._task_from_fun(fun, **options)。

_task_from_fun 之中，使用如下代码把任务添加到 celery 之中。这样就关联起来。

self._tasks[task.name] = task

于是 self._tasks就为：

_tasks = {TaskRegistry: 10}
 NotRegistered = {type} <class 'celery.exceptions.NotRegistered'>
 'celery.starmap' = {xstarmap} <@task: celery.starmap of myTest at 0x25da0ca0d88>
 'celery.chord' = {chord} <@task: celery.chord of myTest at 0x25da0ca0d88>
 'celery.accumulate' = {accumulate} <@task: celery.accumulate of myTest at 0x25da0ca0d88>
 'celery.chunks' = {chunks} <@task: celery.chunks of myTest at 0x25da0ca0d88>
 'celery.chord_unlock' = {unlock_chord} <@task: celery.chord_unlock of myTest at 0x25da0ca0d88>
 'celery.group' = {group} <@task: celery.group of myTest at 0x25da0ca0d88>
 'celery.map' = {xmap} <@task: celery.map of myTest at 0x25da0ca0d88>
 'myTest.add' = {add} <@task: myTest.add of myTest at 0x25da0ca0d88>
 'celery.backend_cleanup' = {backend_cleanup} <@task: celery.backend_cleanup of myTest at 0x25da0ca0d88>
 'celery.chain' = {chain} <@task: celery.chain of myTest at 0x25da0ca0d88>
 __len__ = {int} 10

具体代码如下：

def _task_from_fun(self, fun, name=None, base=None, bind=False, **options):
    if not self.finalized and not self.autofinalize:
        raise RuntimeError('Contract breach: app not finalized')
    name = name or self.gen_task_name(fun.__name__, fun.__module__)
    base = base or self.Task
    if name not in self._tasks:
        run = fun if bind else staticmethod(fun)
        task = type(fun.__name__, (base,), dict({
            'app': self,
            'name': name,
            'run': run,
            '_decorated': True,
            '__doc__': fun.__doc__,
            '__module__': fun.__module__,
            '__annotations__': fun.__annotations__,
            '__header__': staticmethod(head_from_fun(fun, bound=bind)),
            '__wrapped__': run}, **options))()
        self._tasks[task.name] = task
        task.bind(self)  # connects task to this app
        add_autoretry_behaviour(task, **options)
    else:
        task = self._tasks[name]
    return task

4.3.5.2 bind

其中task在默认情况下是celery.app.task:Task，在动态生成该实例后，调用了task.bind(self)方法，这里就是设置 app 各种属性。

@classmethod
def bind(cls, app):
    was_bound, cls.__bound__ = cls.__bound__, True
    cls._app = app                                          # 设置类的_app属性
    conf = app.conf                                         # 获取app的配置信息
    cls._exec_options = None  # clear option cache
    if cls.typing is None:
        cls.typing = app.strict_typing
    for attr_name, config_name in cls.from_config:          # 设置类中的默认值
        if getattr(cls, attr_name, None) is None:           # 如果获取该属性为空
            setattr(cls, attr_name, conf[config_name])      # 使用app配置中的默认值
    # decorate with annotations from config.
    if not was_bound:
        cls.annotate()
        from celery.utils.threads import LocalStack
        cls.request_stack = LocalStack()                    # 使用线程栈保存数据
    # PeriodicTask uses this to add itself to the PeriodicTask schedule.
    cls.on_bound(app)
    return app

4.3.5.3 处理 "待处理"

运行回到 Celery，此时代码位于：celery/app/base.py

变量如下：

pending = {deque: 1} deque([<@task: myTest.add of myTest at 0x7fd907623550>])
self = {Celery} <Celery myTest at 0x7fd907623550>

从pending 中提取任务之后，会进行处理。前面我们提到，有一些 task 的待处理工作，就是在这里执行。

代码位于：celery/local.py

def __maybe_evaluate__(self):
    return self._get_current_object()
def _get_current_object(self):
    try:
        return object.__getattribute__(self, '__thing')

此时self如下，就是任务本身：

self = {add} <@task: myTest.add of myTest at 0x7fa09ee1e320>

返回就是 myTest.add 任务本身。

4.3.6 多进程 VS Task

目前已经得到了所有的 task，并且每一个task都有自己的实例，可以进行调用。

因为任务消费需要用到多进程，所以我们需要先大致看看多进程如何启动的。

让我们继续看看 Celery Worker 的启动。

在 Celery Worker 启动过程中，会启动不同的bootsteps，在 Worker 启动过程中，对应的 steps 为：[<step: Hub>, <step: Pool>, <step: Consumer>]。

start, bootsteps.py:116
start, worker.py:204
worker, worker.py:327
caller, base.py:132
new_func, decorators.py:21
invoke, core.py:610
invoke, core.py:1066
invoke, core.py:1259
main, core.py:782
start, base.py:358
worker_main, base.py:374

代码位于：celery/bootsteps.py

def start(self, parent):
    self.state = RUN
    if self.on_start:
        self.on_start()
    for i, step in enumerate(s for s in parent.steps if s is not None):
        self.started = i + 1
        step.start(parent)

变量为：

parent.steps = {list: 3}
 0 = {Hub} <step: Hub>
 1 = {Pool} <step: Pool>
 2 = {Consumer} <step: Consumer>
 __len__ = {int} 3

具体 任务处理的逻辑 启动就在 Pool 之中。

在 Pool(bootsteps.StartStopStep) 中，如下代码 w.process_task = w._process_task 给具体的 pool 配置了回调方法。即当 pool 接到通知，有运行机会时候，他知道用什么回调函数来获取/执行具体的task。

class Pool(bootsteps.StartStopStep):
    """Bootstep managing the worker pool.
    Describes how to initialize the worker pool, and starts and stops
    the pool during worker start-up/shutdown.
    Adds attributes:
        * autoscale
        * pool
        * max_concurrency
        * min_concurrency
    """
    def create(self, w):
        procs = w.min_concurrency
        w.process_task = w._process_task # 这里配置回调函数

方法如下，可以预计，未来会通过 req.execute_using_pool(self.pool) 这里调用到多进程：

def _process_task(self, req):
    """Process task by sending it to the pool of workers."""
        req.execute_using_pool(self.pool)

此时变量为：

self = {Pool} <step: Pool>
semaphore = {NoneType} None
threaded = {bool} False
w = {Worker} celery

4.3.7 总结

最后得到如下逻辑，这个TaskRegistry 在执行任务会用到：

self._tasks = {TaskRegistry: 10}
 NotRegistered = {type} <class 'celery.exceptions.NotRegistered'>
 'celery.chunks' = {chunks} <@task: celery.chunks of myTest at 0x7fb652da5fd0>
 'celery.backend_cleanup' = {backend_cleanup} <@task: celery.backend_cleanup of myTest at 0x7fb652da5fd0>
 'celery.chord_unlock' = {unlock_chord} <@task: celery.chord_unlock of myTest at 0x7fb652da5fd0>
 'celery.group' = {group} <@task: celery.group of myTest at 0x7fb652da5fd0>
 'celery.map' = {xmap} <@task: celery.map of myTest at 0x7fb652da5fd0>
 'celery.chain' = {chain} <@task: celery.chain of myTest at 0x7fb652da5fd0>
 'celery.starmap' = {xstarmap} <@task: celery.starmap of myTest at 0x7fb652da5fd0>
 'celery.chord' = {chord} <@task: celery.chord of myTest at 0x7fb652da5fd0>
 'myTest.add' = {add} <@task: myTest.add of myTest at 0x7fb652da5fd0>
 'celery.accumulate' = {accumulate} <@task: celery.accumulate of myTest at 0x7fb652da5fd0>
 __len__ = {int} 10

图例如下：

                           +------------------------------+
                           |  _on_app_finalizers = set()  |
                           |                              |
                           +--------------+---------------+
                                          |
                 connect_on_app_finalize  |
 +------------+                           |
 | builtins.py| +-----------------------> |
 +------------+                           |
                                          |
                 connect_on_app_finalize  |
+-------------+                           |
|User Function| +---------------------->  |
+-------------+                           |
                                          v
             +----------------------------------------------------------------------------------------------------+
             |                                        _on_app_finalizers                                          |
             |                                                                                                    |
             |                                                                                                    |
             |    ^function add_chunk_task>                                                                       |
             |    <function add_backend_cleanup_task>                                                             |
             |    <function add_starmap_task>                                                                     |
             |    <function add_group_task>                                                                       |
             |    <function add_map_task^                                                                         |
             |    <function Celery.task.vlocals^.inner_create_task_cls.<locals>._create_task_cls.<locals>.cons>   |
             |    <function add_accumulate_taskv                                                                  |
             |    <function add_chain_task>                                                                       |
             |    <function add_unlock_chord_task>                                                                |
             |    vfunction add_chord_task>                                                                       |
             |                                                                                                    |
             +----------------------------+-----------------------------------------------------------------------+
                                          |
                                          |
                                          |                           +--------------------------------------------------------------------------------------------+
                              finalize    v                           |                                                                                            |
                                                                      |                          TaskRegistry                                                      |
                           +---------------------------+              |                                                                                            |
                           |                           |              |                                                                                            |
                           |           Celery          |              |                                                                                            |
                           |                           |              |   NotRegistered = {type} <class 'celery.exceptions.NotRegistered'>                         |
    _process_task   <-------------------+  process_task|              |   'celery.chunks' = {chunks} <@task: celery.chunks of myTest>                              |
                           |                           |              |   'celery.backend_cleanup' = {backend_cleanup} <@task: celery.backend_cleanup of myTest >  |
                           |                           |              |   'celery.chord_unlock' = {unlock_chord} <@task: celery.chord_unlock of myTest>            |
                           |                _tasks  +------------->   |   'celery.group' = {group} <@task: celery.group of myTest>                                 |
                           |                           |              |   'celery.map' = {xmap} <@task: celery.map of myTest>                                      |
                           |                           |              |   'celery.chain' = {chain} <@task: celery.chain of myTest>                                 |
                           +---------------------------+              |   'celery.starmap' = {xstarmap} <@task: celery.starmap of myTest>                          |
                                                                      |   'celery.chord' = {chord} <@task: celery.chord of myTest>                                 |
                                                                      |   'myTest.add' = {add} <@task: myTest.add of myTest>                                       |
                                                                      |   'celery.accumulate' = {accumulate} <@task: celery.accumulate of myTest>                  |
                                                                      |                                                                                            |
                                                                      +--------------------------------------------------------------------------------------------+

手机如下：

或者我们调整图结构，从另一个角度看看。

            +------------------------------+
            |  _on_app_finalizers = set()  |
            |                              |
            +--------------+---------------+
                           |
                           |
                           |       connect_on_app_finalize     +------------+
                           |   <----------------------------+  | builtins.py|
                           |                                   +------------+
                           |
                           |       connect_on_app_finalize
                           |                                  +-------------+
 +                         |   <---------------------------+  |User Function|
                           |                                  +-------------+
                           v
+------------------------------------------------------------------------------------------------+
|                                      _on_app_finalizers                                        |
|                                                                                                |
|                                                                                                |
|  ^function add_chunk_task>                                                                     |
|  <function add_backend_cleanup_task>                                                           |
|  <function add_starmap_task>                                                                   |
|  <function add_group_task>                                                                     |
|  <function add_map_task^                                                                       |
|  <function Celery.task.vlocals^.inner_create_task_cls.<locals>._create_task_cls.<locals>.cons> |
|  <function add_accumulate_taskv                                                                |
|  <function add_chain_task>                                                                     |
|  <function add_unlock_chord_task>                                                              |
|  vfunction add_chord_task>                                                                     |
|                                                                                                |
+--------------------------+---------------------------------------------------------------------+
                           |
                           |
               finalize    |
                           |
                           |
                           v
             +-------------+-------------+
             |                           |
             |           Celery          |
             |                           |
             |                 _tasks    |
             |                    +      |
             |                    |      |
             +---------------------------+
                                  |
                                  |
                                  |
                                  v
  +--------------------------------------------------------------------------------------------+
  |                                                                                            |
  |                          TaskRegistry                                                      |
  |                                                                                            |
  |   NotRegistered = {type} <class 'celery.exceptions.NotRegistered'>                         |
  |   'celery.chunks' = {chunks} <@task: celery.chunks of myTest>                              |
  |   'celery.backend_cleanup' = {backend_cleanup} <@task: celery.backend_cleanup of myTest >  |
  |   'celery.chord_unlock' = {unlock_chord} <@task: celery.chord_unlock of myTest>            |
  |   'celery.group' = {group} <@task: celery.group of myTest>                                 |
  |   'celery.map' = {xmap} <@task: celery.map of myTest>                                      |
  |   'celery.chain' = {chain} <@task: celery.chain of myTest>                                 |
  |   'celery.starmap' = {xstarmap} <@task: celery.starmap of myTest>                          |
  |   'celery.chord' = {chord} <@task: celery.chord of myTest>                                 |
  |   'myTest.add' = {add} <@task: myTest.add of myTest>                                       |
  |   'celery.accumulate' = {accumulate} <@task: celery.accumulate of myTest>                  |
  |                                                                                            |
  +--------------------------------------------------------------------------------------------+

手机如下：

0x05 Task定义

Task 定义的代码位于：celery/app/task.py。

从其成员变量可以清楚的看到大致功能分类如下：

基础信息，比如：

对应的Celery应用；
task 名字；
功能类信息；

错误处理信息，比如：

速率控制；
最大重试次数；
重试间隔时间；
重试时候的错误处理；

业务控制，比如：

是否ack late；
ack错误处理；
自动注册；
后端存储信息；
worker 出错如何处理；

任务控制，比如：

请求stack；
缺省request；
优先级；
失效时间；
执行option；

具体定义如下：

@abstract.CallableTask.register
class Task:
    __trace__ = None
    __v2_compat__ = False  # set by old base in celery.task.base
    MaxRetriesExceededError = MaxRetriesExceededError
    OperationalError = OperationalError
    Strategy = 'celery.worker.strategy:default'
    Request = 'celery.worker.request:Request'
    _app = None
    name = None
    typing = None
    max_retries = 3
    default_retry_delay = 3 * 60
    rate_limit = None
    ignore_result = None
    trail = True
    send_events = True
    store_errors_even_if_ignored = None
    serializer = None
    time_limit = None
    soft_time_limit = None
    backend = None
    autoregister = True
    track_started = None
    acks_late = None
    acks_on_failure_or_timeout = None
    reject_on_worker_lost = None
    throws = ()
    expires = None
    priority = None
    resultrepr_maxsize = 1024
    request_stack = None
    _default_request = None
    abstract = True
    _exec_options = None
    __bound__ = False
    from_config = (
        ('serializer', 'task_serializer'),
        ('rate_limit', 'task_default_rate_limit'),
        ('priority', 'task_default_priority'),
        ('track_started', 'task_track_started'),
        ('acks_late', 'task_acks_late'),
        ('acks_on_failure_or_timeout', 'task_acks_on_failure_or_timeout'),
        ('reject_on_worker_lost', 'task_reject_on_worker_lost'),
        ('ignore_result', 'task_ignore_result'),
        ('store_errors_even_if_ignored', 'task_store_errors_even_if_ignored'),
    )
    _backend = None  # set by backend property.

0x06 consumer

因为 task 是通过 Consumer 来调用，所以我们要看看 Consumer 中关于 task 的部分，就是把 task 和 consumer 联系起来，这样才能够让 Consumer 具体调用到 task。

6.1 Consumer steps

Consumer启动时候，也是要运行多个 steps。

parent.steps = {list: 8}
 0 = {Connection} <step: Connection>
 1 = {Events} <step: Events>
 2 = {Heart} <step: Heart>
 3 = {Mingle} <step: Mingle>
 4 = {Gossip} <step: Gossip>
 5 = {Tasks} <step: Tasks>
 6 = {Control} <step: Control>
 7 = {Evloop} <step: event loop>
 __len__ = {int} 8

6.2 Tasks steps

consumer 会启动 Tasks 这个bootsteps，这里会：

update_strategies ：配置每个任务的回调方法，比如：'celery.chunks' = {function} <function default.<locals>.task_message_handler at 0x7fc5a47d5a60>。
task_consumer = c.app.amqp.TaskConsumer ：这样 task 就和 amqp.Consumer 联系起来。
设置 QoS；
设置预取；

因此，task 的回调就和 amqp.Consumer 联系，消息通路就构建完成。

代码位于：celery/worker/consumer/tasks.py

class Tasks(bootsteps.StartStopStep):
    """Bootstep starting the task message consumer."""
    requires = (Mingle,)
    def __init__(self, c, **kwargs):
        c.task_consumer = c.qos = None
        super().__init__(c, **kwargs)
    def start(self, c):
        """Start task consumer."""
        c.update_strategies() # 配置每个任务的回调方法
        # - RabbitMQ 3.3 completely redefines how basic_qos works..
        # This will detect if the new qos smenatics is in effect,
        # and if so make sure the 'apply_global' flag is set on qos updates.
        qos_global = not c.connection.qos_semantics_matches_spec
        # set initial prefetch count
        c.connection.default_channel.basic_qos(
            0, c.initial_prefetch_count, qos_global,
        )
        c.task_consumer = c.app.amqp.TaskConsumer(
            c.connection, on_decode_error=c.on_decode_error,
        ) # task 就和 amqp.Consumer 联系起来
        def set_prefetch_count(prefetch_count):
            return c.task_consumer.qos(
                prefetch_count=prefetch_count,
                apply_global=qos_global,
            )
        c.qos = QoS(set_prefetch_count, c.initial_prefetch_count)

5.2.1 策略

关于 task 运行其实是需要一定策略的，这也可以认为是一种负载均衡。其策略如下:

SCHED_STRATEGY_FCFS = 1
SCHED_STRATEGY_FAIR = 4
SCHED_STRATEGIES = {
    None: SCHED_STRATEGY_FAIR,
    'default': SCHED_STRATEGY_FAIR,
    'fast': SCHED_STRATEGY_FCFS,
    'fcfs': SCHED_STRATEGY_FCFS,
    'fair': SCHED_STRATEGY_FAIR,
}

5.2.2 更新策略

update_strategies 会配置每个任务的回调策略以及回调方法，比如：'celery.chunks' = {function} <function default.<locals>.task_message_handler at 0x7fc5a47d5a60>。

堆栈如下：

update_strategies, consumer.py:523
start, tasks.py:26
start, bootsteps.py:116
start, consumer.py:311
start, bootsteps.py:365
start, bootsteps.py:116
start, worker.py:204
worker, worker.py:327
caller, base.py:132
new_func, decorators.py:21
invoke, core.py:610
invoke, core.py:1066
invoke, core.py:1259
main, core.py:782
start, base.py:358
worker_main, base.py:374

代码位于：celery/worker/consumer/consumer.py

def update_strategies(self):
        loader = self.app.loader                                                # app的加载器
        for name, task in items(self.app.tasks):                                # 遍历所有的任务
            self.strategies[name] = task.start_strategy(self.app, self)         # 将task的name设为key 将task start_strategy调用的返回值作为 value
            task.__trace__ = build_tracer(name, task, loader, self.hostname,
                                          app=self.app)                         # 处理相关执行结果的函数

app.tasks变量如下，这就是目前 Celery 注册的所有 tasks：

self.app.tasks = {TaskRegistry: 10}
 NotRegistered = {type} <class 'celery.exceptions.NotRegistered'>
 'celery.chunks' = {chunks} <@task: celery.chunks of myTest at 0x7fc5a36e8160>
 'celery.backend_cleanup' = {backend_cleanup} <@task: celery.backend_cleanup of myTest at 0x7fc5a36e8160>
 'celery.chord_unlock' = {unlock_chord} <@task: celery.chord_unlock of myTest at 0x7fc5a36e8160>
 'celery.group' = {group} <@task: celery.group of myTest at 0x7fc5a36e8160>
 'celery.map' = {xmap} <@task: celery.map of myTest at 0x7fc5a36e8160>
 'celery.chain' = {chain} <@task: celery.chain of myTest at 0x7fc5a36e8160>
 'celery.starmap' = {xstarmap} <@task: celery.starmap of myTest at 0x7fc5a36e8160>
 'celery.chord' = {chord} <@task: celery.chord of myTest at 0x7fc5a36e8160>
 'myTest.add' = {add} <@task: myTest.add of myTest at 0x7fc5a36e8160>
 'celery.accumulate' = {accumulate} <@task: celery.accumulate of myTest at 0x7fc5a36e8160>
 __len__ = {int} 10

此时我们继续查看task.start_strategy函数，

def start_strategy(self, app, consumer, **kwargs):
    return instantiate(self.Strategy, self, app, consumer, **kwargs)    # 生成task实例

此时self.Strategy的默认值是celery.worker.strategy:default，

def default(task, app, consumer,
        info=logger.info, error=logger.error, task_reserved=task_reserved,
        to_system_tz=timezone.to_system, bytes=bytes, buffer_t=buffer_t,
        proto1_to_proto2=proto1_to_proto2):
    """Default task execution strategy.
    Note:
        Strategies are here as an optimization, so sadly
        it's not very easy to override.
    """
    hostname = consumer.hostname                                # 设置相关的消费者信息
    connection_errors = consumer.connection_errors              # 设置错误值
    _does_info = logger.isEnabledFor(logging.INFO)
    # task event related
    # (optimized to avoid calling request.send_event)
    eventer = consumer.event_dispatcher
    events = eventer and eventer.enabled
    send_event = eventer.send
    task_sends_events = events and task.send_events
    call_at = consumer.timer.call_at
    apply_eta_task = consumer.apply_eta_task
    rate_limits_enabled = not consumer.disable_rate_limits
    get_bucket = consumer.task_buckets.__getitem__
    handle = consumer.on_task_request
    limit_task = consumer._limit_task
    body_can_be_buffer = consumer.pool.body_can_be_buffer
    Req = create_request_cls(Request, task, consumer.pool, hostname, eventer)       # 返回一个请求类
    revoked_tasks = consumer.controller.state.revoked
    def task_message_handler(message, body, ack, reject, callbacks,
                             to_timestamp=to_timestamp):
        if body is None:
            body, headers, decoded, utc = (
                message.body, message.headers, False, True,
            )
            if not body_can_be_buffer:
                body = bytes(body) if isinstance(body, buffer_t) else body
        else:
            body, headers, decoded, utc = proto1_to_proto2(message, body)           # 解析接受的数据
        req = Req(
            message,
            on_ack=ack, on_reject=reject, app=app, hostname=hostname,
            eventer=eventer, task=task, connection_errors=connection_errors,
            body=body, headers=headers, decoded=decoded, utc=utc,
        )                                                                           # 实例化请求
        if (req.expires or req.id in revoked_tasks) and req.revoked():
            return
        if task_sends_events:
            send_event(
                'task-received',
                uuid=req.id, name=req.name,
                args=req.argsrepr, kwargs=req.kwargsrepr,
                root_id=req.root_id, parent_id=req.parent_id,
                retries=req.request_dict.get('retries', 0),
                eta=req.eta and req.eta.isoformat(),
                expires=req.expires and req.expires.isoformat(),
            )                                                                       # 如果需要发送接受请求则发送
        if req.eta:                                                                 # 时间相关处理
            try:
                if req.utc:
                    eta = to_timestamp(to_system_tz(req.eta))
                else:
                    eta = to_timestamp(req.eta, timezone.local)
            else:
                consumer.qos.increment_eventually()
                call_at(eta, apply_eta_task, (req,), priority=6)
        else:
            if rate_limits_enabled:                                                 # 速率限制
                bucket = get_bucket(task.name)
                if bucket:
                    return limit_task(req, bucket, 1)
            task_reserved(req)                                                      #
            if callbacks:
                [callback(req) for callback in callbacks]
            handle(req)                                                             # 处理接受的请求
    return task_message_handler

此时处理的 handler 就是在 consumer 初始化的时候传入的 w.process_task，

def _process_task(self, req):
    """Process task by sending it to the pool of workers."""
        req.execute_using_pool(self.pool)

操作之后，得到了每个task的回调策略，这样当多进程调用时候，就知道如何调用task了，即对于我们目前的各个 task，当从broker 拿到任务消息之后，我们都调用 task_message_handler。

strategies = {dict: 10}
 'celery.chunks' = {function} <function default.<locals>.task_message_handler at 0x7fc5a47d5a60>
 'celery.backend_cleanup' = {function} <function default.<locals>.task_message_handler at 0x7fc5a4878400>
 'celery.chord_unlock' = {function} <function default.<locals>.task_message_handler at 0x7fc5a4878598>
 'celery.group' = {function} <function default.<locals>.task_message_handler at 0x7fc5a4878840>
 'celery.map' = {function} <function default.<locals>.task_message_handler at 0x7fc5a4878ae8>
 'celery.chain' = {function} <function default.<locals>.task_message_handler at 0x7fc5a4878d90>
 'celery.starmap' = {function} <function default.<locals>.task_message_handler at 0x7fc5a487b0d0>
 'celery.chord' = {function} <function default.<locals>.task_message_handler at 0x7fc5a487b378>
 'myTest.add' = {function} <function default.<locals>.task_message_handler at 0x7fc5a487b620>
 'celery.accumulate' = {function} <function default.<locals>.task_message_handler at 0x7fc5a487b8c8>
 __len__ = {int} 10

5.2.3 Request

celery.worker.strategy:default 之中，这部分代码需要看看：

Req = create_request_cls(Request, task, consumer.pool, hostname, eventer)  # 返回一个请求类

Strategy 中，以下目的是为了根据 task 实例构建一个 Request，从而把 broker 消息，consumer，多进程都联系起来。

具体可以看到 Request. execute_using_pool 这里就会和多进程处理开始关联，比如和 comsumer 的 pool 进程池联系起来。

Req = create_request_cls(Request, task, consumer.pool, hostname, eventer)

task 实例为：

myTest.add[863cf9b2-8440-4ea2-8ac4-06b3dcd2fd1f]

获得Requst代码为：

def create_request_cls(base, task, pool, hostname, eventer,
                       ref=ref, revoked_tasks=revoked_tasks,
                       task_ready=task_ready, trace=trace_task_ret):
    default_time_limit = task.time_limit
    default_soft_time_limit = task.soft_time_limit
    apply_async = pool.apply_async
    acks_late = task.acks_late
    events = eventer and eventer.enabled
    class Request(base):
        def execute_using_pool(self, pool, **kwargs):
            task_id = self.task_id
            if (self.expires or task_id in revoked_tasks) and self.revoked():
                raise TaskRevokedError(task_id)
            time_limit, soft_time_limit = self.time_limits
            result = apply_async(
                trace,
                args=(self.type, task_id, self.request_dict, self.body,
                      self.content_type, self.content_encoding),
                accept_callback=self.on_accepted,
                timeout_callback=self.on_timeout,
                callback=self.on_success,
                error_callback=self.on_failure,
                soft_timeout=soft_time_limit or default_soft_time_limit,
                timeout=time_limit or default_time_limit,
                correlation_id=task_id,
            )
            # cannot create weakref to None
            # pylint: disable=attribute-defined-outside-init
            self._apply_result = maybe(ref, result)
            return result
        def on_success(self, failed__retval__runtime, **kwargs):
            failed, retval, runtime = failed__retval__runtime
            if failed:
                if isinstance(retval.exception, (
                        SystemExit, KeyboardInterrupt)):
                    raise retval.exception
                return self.on_failure(retval, return_ok=True)
            task_ready(self)
            if acks_late:
                self.acknowledge()
            if events:
                self.send_event(
                    'task-succeeded', result=retval, runtime=runtime,
                )
    return Request

5.2.4 如何调用到多进程

前面回调函数 task_message_handler中有 req = Req(...)，这就涉及到了如何调用多进程，即 Request 类处理。

def task_message_handler(message, body, ack, reject, callbacks,
                         to_timestamp=to_timestamp):
    req = Req(
        message,
        on_ack=ack, on_reject=reject, app=app, hostname=hostname,
        eventer=eventer, task=task, connection_errors=connection_errors,
        body=body, headers=headers, decoded=decoded, utc=utc,
    )                                                                     # 实例化请求
    if req.eta:                                                           # 时间相关
    else:
        task_reserved(req)                                                #
        if callbacks:
            [callback(req) for callback in callbacks]
        handle(req)                                                       # 处理接受的请求
return task_message_handler

注意：

此时处理的 handle(req) 的 handle函数就是在 consumer 初始化的时候传入的 w.process_task，

def _process_task(self, req):
    """Process task by sending it to the pool of workers."""
        req.execute_using_pool(self.pool)

所以，handle(req) 实际上就是调用 Request 的 execute_using_pool 函数，就来到了多进程。

代码为：

class Request(base):
    def execute_using_pool(self, pool, **kwargs):
        task_id = self.task_id# 获取任务id
        if (self.expires or task_id in revoked_tasks) and self.revoked():# 检查是否过期或者是否已经执行过
            raise TaskRevokedError(task_id)
        time_limit, soft_time_limit = self.time_limits# 获取时间
        result = apply_async(# 执行对应的func并返回结果
            trace,
            args=(self.type, task_id, self.request_dict, self.body,
                  self.content_type, self.content_encoding),
            accept_callback=self.on_accepted,
            timeout_callback=self.on_timeout,
            callback=self.on_success,
            error_callback=self.on_failure,
            soft_timeout=soft_time_limit or default_soft_time_limit,
            timeout=time_limit or default_time_limit,
            correlation_id=task_id,
        )
        # cannot create weakref to None
        # pylint: disable=attribute-defined-outside-init
        self._apply_result = maybe(ref, result)
        return result

5.3 总结

因为信息量太大，所以分为三个图展示。

5.3.1 Strategy

strategy 逻辑为：

                                      +-----------------------+                      +---------------------------+
                                      | Celery                |                      | Consumer                  |
                                      |                       |                      |                           |
                                      |            consumer +--------------------->  |                           |            +---------------+
                                      |                       |                      |        task_consumer +---------------> | amqp.Consumer |
                                      |             _tasks    |                      |                           |            +---------------+
                                      |                +      |                      |                           |
                                      |                |      |                      |        strategies +----------------+
                                      +-----------------------+                      |                           |        |
                                                       |                             |                           |        |
                                                       |                             +---------------------------+        |
                                                       |                                                                  v
                                                       v
+------------------------------------------------------+-------------------------------------+  +-----------------------------------------------------------------------------+
|                                                                                            |  | strategies = {dict: 10}                                                     |
|                          TaskRegistry                                                      |  |  'celery.chunks' = function default.<locals>.task_message_handler           |
|                                                                                            |  |  'celery.backend_cleanup' = function default.<locals>.task_message_handler  |
|   NotRegistered = {type} <class 'celery.exceptions.NotRegistered'>                         |  |  'celery.chord_unlock' = function default.^locals>.task_message_handler     |
|   'celery.chunks' = {chunks} <@task: celery.chunks of myTest>                              |  |  'celery.group' = function default.<localsv.task_message_handler            |
|   'celery.backend_cleanup' = {backend_cleanup} <@task: celery.backend_cleanup of myTest >  |  |  'celery.map' = function default.<locals>.task_message_handler              |
|   'celery.chord_unlock' = {unlock_chord} <@task: celery.chord_unlock of myTest>            |  |  'celery.chain' = function default.<locals>.task_message_handler            |
|   'celery.group' = {group} <@task: celery.group of myTest>                                 |  |  'celery.starmap' = function default.<locals>.task_message_handler          |
|   'celery.map' = {xmap} <@task: celery.map of myTest>                                      |  |  'celery.chord' = function default.<locals>.task_message_handler            |
|   'celery.chain' = {chain} <@task: celery.chain of myTest>                                 |  |  'myTest.add' = function default.<locals^.task_message_handler              |
|   'celery.starmap' = {xstarmap} <@task: celery.starmap of myTest>                          |  |  'celery.accumulate' = function default.vlocals>.task_message_handler       |
|   'celery.chord' = {chord} <@task: celery.chord of myTest>                                 |  |                                                                             |
|   'myTest.add' = {add} <@task: myTest.add of myTest>                                       |  +-----------------------------------------------------------------------------+
|   'celery.accumulate' = {accumulate} <@task: celery.accumulate of myTest>                  |
|                                                                                            |
+--------------------------------------------------------------------------------------------+

手机如下

5.3.2 注册 task 逻辑

Celery 应用中注册的task 逻辑为

                           +------------------------------+
                           |  _on_app_finalizers = set()  |
                           |                              |
                           +--------------+---------------+
                                          |
                 connect_on_app_finalize  |
 +------------+                           |
 | builtins.py| +-----------------------> |
 +------------+                           |
                                          |
                 connect_on_app_finalize  |
+-------------+                           |
|User Function| +---------------------->  |
+-------------+                           |
                                          v
             +----------------------------------------------------------------------------------------------------+
             |                                        _on_app_finalizers                                          |
             |                                                                                                    |
             |                                                                                                    |
             |    ^function add_chunk_task>                                                                       |
             |    <function add_backend_cleanup_task>                                                             |
             |    <function add_starmap_task>                                                                     |
             |    <function add_group_task>                                                                       |
             |    <function add_map_task^                                                                         |
             |    <function Celery.task.vlocals^.inner_create_task_cls.<locals>._create_task_cls.<locals>.cons>   |
             |    <function add_accumulate_taskv                                                                  |
             |    <function add_chain_task>                                                                       |
             |    <function add_unlock_chord_task>                                                                |
             |    vfunction add_chord_task>                                                                       |
             |                                                                                                    |
             +----------------------------+-----------------------------------------------------------------------+
                                          |
                                          |
                                          |                           +--------------------------------------------------------------------------------------------+
                              finalize    v                           |                                                                                            |
                                                                      |                          TaskRegistry                                                      |
                           +---------------------------+              |                                                                                            |
                           |                           |              |                                                                                            |
                           |           Celery          |              |                                                                                            |
                           |                           |              |   NotRegistered = {type} <class 'celery.exceptions.NotRegistered'>                         |
    _process_task   <-------------------+  process_task|              |   'celery.chunks' = {chunks} <@task: celery.chunks of myTest>                              |
                           |                           |              |   'celery.backend_cleanup' = {backend_cleanup} <@task: celery.backend_cleanup of myTest >  |
                           |                           |              |   'celery.chord_unlock' = {unlock_chord} <@task: celery.chord_unlock of myTest>            |
                           |                _tasks  +------------->   |   'celery.group' = {group} <@task: celery.group of myTest>                                 |
 +---------------+         |                           |              |   'celery.map' = {xmap} <@task: celery.map of myTest>                                      |
 | amqp.Consumer |  <--------+  task_consumer          |              |   'celery.chain' = {chain} <@task: celery.chain of myTest>                                 |
 +---------------+         |                           |              |   'celery.starmap' = {xstarmap} <@task: celery.starmap of myTest>                          |
                           +---------------------------+              |   'celery.chord' = {chord} <@task: celery.chord of myTest>                                 |
                                                                      |   'myTest.add' = {add} <@task: myTest.add of myTest>                                       |
                                                                      |   'celery.accumulate' = {accumulate} <@task: celery.accumulate of myTest>                  |
                                                                      |                                                                                            |
                                                                      +--------------------------------------------------------------------------------------------+

手机如下：

5.3.3 处理任务逻辑

当从broker获取消息之后，处理任务时候逻辑为：

                         +
  Consumer               |
                 message |
                         v         strategy  +------------------------------------+
            +------------+------+            | strategies                         |
            | on_task_received  | <--------+ |                                    |
            |                   |            |[myTest.add : task_message_handler] |
            +------------+------+            +------------------------------------+
                         |
                         |
 +------------------------------------------------------------------------------------+
 strategy                |
                         |
                         |
                         v                Request [myTest.add]
            +------------+-------------+                       +---------------------+
            | task_message_handler     | <-------------------+ | create_request_cls  |
            |                          |                       |                     |
            +------------+-------------+                       +---------------------+
                         | _process_task_sem
                         |
+--------------------------------------------------------------------------------------+
 Worker                  | req[{Request} myTest.add]
                         v
                +--------+-----------+
                | WorkController     |
                |                    |
                |            pool +-------------------------+
                +--------+-----------+                      |
                         |                                  |
                         |               apply_async        v
             +-----------+----------+                   +---+-------+
             |{Request} myTest.add  | +---------------> | TaskPool  |
             +----------------------+                   +-----------+
                                        myTest.add

手机如下图：

至此，Celery启动全部分析结束，我们下一步看看一个完整的例子，即消息如何从发送到被消费的流程。

0xFF 参考

celery源码分析-Task的初始化与发送任务

Celery 源码解析三： Task 对象的实现

Celery-4.1 用户指南: Application(应用)