This document describes the current stable version of Celery (5.2). For development docs, go here.
Source code for celery.canvas
"""Composing task work-flows.
.. seealso:
You should import these from :mod:`celery` and not this module.
"""
import itertools
import operator
from collections import deque
from collections.abc import MutableSequence
from copy import deepcopy
from functools import partial as _partial
from functools import reduce
from operator import itemgetter
from types import GeneratorType
from kombu.utils.functional import fxrange, reprcall
from kombu.utils.objects import cached_property
from kombu.utils.uuid import uuid
from vine import barrier
from celery._state import current_app
from celery.result import GroupResult, allow_join_result
from celery.utils import abstract
from celery.utils.collections import ChainMap
from celery.utils.functional import _regen
from celery.utils.functional import chunks as _chunks
from celery.utils.functional import (is_list, lookahead, maybe_list, regen,
seq_concat_item, seq_concat_seq)
from celery.utils.objects import getitem_property
from celery.utils.text import remove_repeating_from_task, truncate
__all__ = (
'Signature', 'chain', 'xmap', 'xstarmap', 'chunks',
'group', 'chord', 'signature', 'maybe_signature',
)
def maybe_unroll_group(group):
"""Unroll group with only one member."""
# Issue #1656
try:
size = len(group.tasks)
except TypeError:
try:
size = group.tasks.__length_hint__()
except (AttributeError, TypeError):
return group
else:
return list(group.tasks)[0] if size == 1 else group
else:
return group.tasks[0] if size == 1 else group
def task_name_from(task):
return getattr(task, 'name', task)
[docs]@abstract.CallableSignature.register
class Signature(dict):
"""Task Signature.
Class that wraps the arguments and execution options
for a single task invocation.
Used as the parts in a :class:`group` and other constructs,
or to pass tasks around as callbacks while being compatible
with serializers with a strict type subset.
Signatures can also be created from tasks:
- Using the ``.signature()`` method that has the same signature
as ``Task.apply_async``:
.. code-block:: pycon
>>> add.signature(args=(1,), kwargs={'kw': 2}, options={})
- or the ``.s()`` shortcut that works for star arguments:
.. code-block:: pycon
>>> add.s(1, kw=2)
- the ``.s()`` shortcut does not allow you to specify execution options
but there's a chaning `.set` method that returns the signature:
.. code-block:: pycon
>>> add.s(2, 2).set(countdown=10).set(expires=30).delay()
Note:
You should use :func:`~celery.signature` to create new signatures.
The ``Signature`` class is the type returned by that function and
should be used for ``isinstance`` checks for signatures.
See Also:
:ref:`guide-canvas` for the complete guide.
Arguments:
task (Union[Type[celery.app.task.Task], str]): Either a task
class/instance, or the name of a task.
args (Tuple): Positional arguments to apply.
kwargs (Dict): Keyword arguments to apply.
options (Dict): Additional options to :meth:`Task.apply_async`.
Note:
If the first argument is a :class:`dict`, the other
arguments will be ignored and the values in the dict will be used
instead::
>>> s = signature('tasks.add', args=(2, 2))
>>> signature(s)
{'task': 'tasks.add', args=(2, 2), kwargs={}, options={}}
"""
TYPES = {}
_app = _type = None
# The following fields must not be changed during freezing/merging because
# to do so would disrupt completion of parent tasks
_IMMUTABLE_OPTIONS = {"group_id"}
@classmethod
def register_type(cls, name=None):
def _inner(subclass):
cls.TYPES[name or subclass.__name__] = subclass
return subclass
return _inner
@classmethod
def from_dict(cls, d, app=None):
typ = d.get('subtask_type')
if typ:
target_cls = cls.TYPES[typ]
if target_cls is not cls:
return target_cls.from_dict(d, app=app)
return Signature(d, app=app)
def __init__(self, task=None, args=None, kwargs=None, options=None,
type=None, subtask_type=None, immutable=False,
app=None, **ex):
self._app = app
if isinstance(task, dict):
super().__init__(task) # works like dict(d)
else:
# Also supports using task class/instance instead of string name.
try:
task_name = task.name
except AttributeError:
task_name = task
else:
self._type = task
super().__init__(
task=task_name, args=tuple(args or ()),
kwargs=kwargs or {},
options=dict(options or {}, **ex),
subtask_type=subtask_type,
immutable=immutable,
)
def __call__(self, *partial_args, **partial_kwargs):
"""Call the task directly (in the current process)."""
args, kwargs, _ = self._merge(partial_args, partial_kwargs, None)
return self.type(*args, **kwargs)
def delay(self, *partial_args, **partial_kwargs):
"""Shortcut to :meth:`apply_async` using star arguments."""
return self.apply_async(partial_args, partial_kwargs)
def apply(self, args=None, kwargs=None, **options):
"""Call task locally.
Same as :meth:`apply_async` but executed the task inline instead
of sending a task message.
"""
args = args if args else ()
kwargs = kwargs if kwargs else {}
# Extra options set to None are dismissed
options = {k: v for k, v in options.items() if v is not None}
# For callbacks: extra args are prepended to the stored args.
args, kwargs, options = self._merge(args, kwargs, options)
return self.type.apply(args, kwargs, **options)
def apply_async(self, args=None, kwargs=None, route_name=None, **options):
"""Apply this task asynchronously.
Arguments:
args (Tuple): Partial args to be prepended to the existing args.
kwargs (Dict): Partial kwargs to be merged with existing kwargs.
options (Dict): Partial options to be merged
with existing options.
Returns:
~@AsyncResult: promise of future evaluation.
See also:
:meth:`~@Task.apply_async` and the :ref:`guide-calling` guide.
"""
args = args if args else ()
kwargs = kwargs if kwargs else {}
# Extra options set to None are dismissed
options = {k: v for k, v in options.items() if v is not None}
try:
_apply = self._apply_async
except IndexError: # pragma: no cover
# no tasks for chain, etc to find type
return
# For callbacks: extra args are prepended to the stored args.
if args or kwargs or options:
args, kwargs, options = self._merge(args, kwargs, options)
else:
args, kwargs, options = self.args, self.kwargs, self.options
# pylint: disable=too-many-function-args
# Borks on this, as it's a property
return _apply(args, kwargs, **options)
def _merge(self, args=None, kwargs=None, options=None, force=False):
args = args if args else ()
kwargs = kwargs if kwargs else {}
if options is not None:
# We build a new options dictionary where values in `options`
# override values in `self.options` except for keys which are
# noted as being immutable (unrelated to signature immutability)
# implying that allowing their value to change would stall tasks
new_options = dict(self.options, **{
k: v for k, v in options.items()
if k not in self._IMMUTABLE_OPTIONS or k not in self.options
})
else:
new_options = self.options
if self.immutable and not force:
return (self.args, self.kwargs, new_options)
return (tuple(args) + tuple(self.args) if args else self.args,
dict(self.kwargs, **kwargs) if kwargs else self.kwargs,
new_options)
def clone(self, args=None, kwargs=None, **opts):
"""Create a copy of this signature.
Arguments:
args (Tuple): Partial args to be prepended to the existing args.
kwargs (Dict): Partial kwargs to be merged with existing kwargs.
options (Dict): Partial options to be merged with
existing options.
"""
args = args if args else ()
kwargs = kwargs if kwargs else {}
# need to deepcopy options so origins links etc. is not modified.
if args or kwargs or opts:
args, kwargs, opts = self._merge(args, kwargs, opts)
else:
args, kwargs, opts = self.args, self.kwargs, self.options
signature = Signature.from_dict({'task': self.task,
'args': tuple(args),
'kwargs': kwargs,
'options': deepcopy(opts),
'subtask_type': self.subtask_type,
'immutable': self.immutable},
app=self._app)
signature._type = self._type
return signature
partial = clone
def freeze(self, _id=None, group_id=None, chord=None,
root_id=None, parent_id=None, group_index=None):
"""Finalize the signature by adding a concrete task id.
The task won't be called and you shouldn't call the signature
twice after freezing it as that'll result in two task messages
using the same task id.
Returns:
~@AsyncResult: promise of future evaluation.
"""
# pylint: disable=redefined-outer-name
# XXX chord is also a class in outer scope.
opts = self.options
try:
# if there is already an id for this task, return it
tid = opts['task_id']
except KeyError:
# otherwise, use the _id sent to this function, falling back on a generated UUID
tid = opts['task_id'] = _id or uuid()
if root_id:
opts['root_id'] = root_id
if parent_id:
opts['parent_id'] = parent_id
if 'reply_to' not in opts:
# fall back on unique ID for this thread in the app
opts['reply_to'] = self.app.thread_oid
if group_id and "group_id" not in opts:
opts['group_id'] = group_id
if chord:
opts['chord'] = chord
if group_index is not None:
opts['group_index'] = group_index
# pylint: disable=too-many-function-args
# Borks on this, as it's a property.
return self.AsyncResult(tid)
_freeze = freeze
def replace(self, args=None, kwargs=None, options=None):
"""Replace the args, kwargs or options set for this signature.
These are only replaced if the argument for the section is
not :const:`None`.
"""
signature = self.clone()
if args is not None:
signature.args = args
if kwargs is not None:
signature.kwargs = kwargs
if options is not None:
signature.options = options
return signature
def set(self, immutable=None, **options):
"""Set arbitrary execution options (same as ``.options.update(…)``).
Returns:
Signature: This is a chaining method call
(i.e., it will return ``self``).
"""
if immutable is not None:
self.set_immutable(immutable)
self.options.update(options)
return self
def set_immutable(self, immutable):
self.immutable = immutable
def _with_list_option(self, key):
items = self.options.setdefault(key, [])
if not isinstance(items, MutableSequence):
items = self.options[key] = [items]
return items
def append_to_list_option(self, key, value):
items = self._with_list_option(key)
if value not in items:
items.append(value)
return value
def extend_list_option(self, key, value):
items = self._with_list_option(key)
items.extend(maybe_list(value))
def link(self, callback):
"""Add callback task to be applied if this task succeeds.
Returns:
Signature: the argument passed, for chaining
or use with :func:`~functools.reduce`.
"""
return self.append_to_list_option('link', callback)
def link_error(self, errback):
"""Add callback task to be applied on error in task execution.
Returns:
Signature: the argument passed, for chaining
or use with :func:`~functools.reduce`.
"""
return self.append_to_list_option('link_error', errback)
def on_error(self, errback):
"""Version of :meth:`link_error` that supports chaining.
on_error chains the original signature, not the errback so::
>>> add.s(2, 2).on_error(errback.s()).delay()
calls the ``add`` task, not the ``errback`` task, but the
reverse is true for :meth:`link_error`.
"""
self.link_error(errback)
return self
def flatten_links(self):
"""Return a recursive list of dependencies.
"unchain" if you will, but with links intact.
"""
return list(itertools.chain.from_iterable(itertools.chain(
[[self]],
(link.flatten_links()
for link in maybe_list(self.options.get('link')) or [])
)))
def __or__(self, other):
if isinstance(other, _chain):
# task | chain -> chain
return _chain(seq_concat_seq(
(self,), other.unchain_tasks()), app=self._app)
elif isinstance(other, group):
# unroll group with one member
other = maybe_unroll_group(other)
# task | group() -> chain
return _chain(self, other, app=self.app)
elif isinstance(other, Signature):
# task | task -> chain
return _chain(self, other, app=self._app)
return NotImplemented
def __ior__(self, other):
# Python 3.9 introduces | as the merge operator for dicts.
# We override the in-place version of that operator
# so that canvases continue to work as they did before.
return self.__or__(other)
def election(self):
type = self.type
app = type.app
tid = self.options.get('task_id') or uuid()
with app.producer_or_acquire(None) as producer:
props = type.backend.on_task_call(producer, tid)
app.control.election(tid, 'task',
self.clone(task_id=tid, **props),
connection=producer.connection)
return type.AsyncResult(tid)
def reprcall(self, *args, **kwargs):
args, kwargs, _ = self._merge(args, kwargs, {}, force=True)
return reprcall(self['task'], args, kwargs)
def __deepcopy__(self, memo):
memo[id(self)] = self
return dict(self)
def __invert__(self):
return self.apply_async().get()
def __reduce__(self):
# for serialization, the task type is lazily loaded,
# and not stored in the dict itself.
return signature, (dict(self),)
def __json__(self):
return dict(self)
def __repr__(self):
return self.reprcall()
def items(self):
for k, v in super().items():
yield k.decode() if isinstance(k, bytes) else k, v
@property
def name(self):
# for duck typing compatibility with Task.name
return self.task
@cached_property
def type(self):
return self._type or self.app.tasks[self['task']]
@cached_property
def app(self):
return self._app or current_app
@cached_property
def AsyncResult(self):
try:
return self.type.AsyncResult
except KeyError: # task not registered
return self.app.AsyncResult
@cached_property
def _apply_async(self):
try:
return self.type.apply_async
except KeyError:
return _partial(self.app.send_task, self['task'])
id = getitem_property('options.task_id', 'Task UUID')
parent_id = getitem_property('options.parent_id', 'Task parent UUID.')
root_id = getitem_property('options.root_id', 'Task root UUID.')
task = getitem_property('task', 'Name of task.')
args = getitem_property('args', 'Positional arguments to task.')
kwargs = getitem_property('kwargs', 'Keyword arguments to task.')
options = getitem_property('options', 'Task execution options.')
subtask_type = getitem_property('subtask_type', 'Type of signature')
immutable = getitem_property(
'immutable', 'Flag set if no longer accepts new arguments')
def _prepare_chain_from_options(options, tasks, use_link):
# When we publish groups we reuse the same options dictionary for all of
# the tasks in the group. See:
# https://github.com/celery/celery/blob/fb37cb0b8/celery/canvas.py#L1022.
# Issue #5354 reported that the following type of canvases
# causes a Celery worker to hang:
# group(
# add.s(1, 1),
# add.s(1, 1)
# ) | tsum.s() | add.s(1) | group(add.s(1), add.s(1))
# The resolution of #5354 in PR #5681 was to only set the `chain` key
# in the options dictionary if it is not present.
# Otherwise we extend the existing list of tasks in the chain with the new
# tasks: options['chain'].extend(chain_).
# Before PR #5681 we overrode the `chain` key in each iteration
# of the loop which applies all the tasks in the group:
# options['chain'] = tasks if not use_link else None
# This caused Celery to execute chains correctly in most cases since
# in each iteration the `chain` key would reset itself to a new value
# and the side effect of mutating the key did not propagate
# to the next task in the group.
# Since we now mutated the `chain` key, a *list* which is passed
# by *reference*, the next task in the group will extend the list
# of tasks in the chain instead of setting a new one from the chain_
# variable above.
# This causes Celery to execute a chain, even though there might not be
# one to begin with. Alternatively, it causes Celery to execute more tasks
# that were previously present in the previous task in the group.
# The solution is to be careful and never mutate the options dictionary
# to begin with.
# Here is an example of a canvas which triggers this issue:
# add.s(5, 6) | group((add.s(1) | add.s(2), add.s(3))).
# The expected result is [14, 14]. However, when we extend the `chain`
# key the `add.s(3)` task erroneously has `add.s(2)` in its chain since
# it was previously applied to `add.s(1)`.
# Without being careful not to mutate the options dictionary, the result
# in this case is [16, 14].
# To avoid deep-copying the entire options dictionary every single time we
# run a chain we use a ChainMap and ensure that we never mutate
# the original `chain` key, hence we use list_a + list_b to create a new
# list.
if use_link:
return ChainMap({'chain': None}, options)
elif 'chain' not in options:
return ChainMap({'chain': tasks}, options)
elif tasks is not None:
# chain option may already be set, resulting in
# "multiple values for keyword argument 'chain'" error.
# Issue #3379.
# If a chain already exists, we need to extend it with the next
# tasks in the chain.
# Issue #5354.
# WARNING: Be careful not to mutate `options['chain']`.
return ChainMap({'chain': options['chain'] + tasks},
options)
@Signature.register_type(name='chain')
class _chain(Signature):
tasks = getitem_property('kwargs.tasks', 'Tasks in chain.')
@classmethod
def from_dict(cls, d, app=None):
tasks = d['kwargs']['tasks']
if tasks:
if isinstance(tasks, tuple): # aaaargh
tasks = d['kwargs']['tasks'] = list(tasks)
tasks = [maybe_signature(task, app=app) for task in tasks]
return _chain(tasks, app=app, **d['options'])
def __init__(self, *tasks, **options):
tasks = (regen(tasks[0]) if len(tasks) == 1 and is_list(tasks[0])
else tasks)
super().__init__('celery.chain', (), {'tasks': tasks}, **options
)
self._use_link = options.pop('use_link', None)
self.subtask_type = 'chain'
self._frozen = None
def __call__(self, *args, **kwargs):
if self.tasks:
return self.apply_async(args, kwargs)
def __or__(self, other):
if isinstance(other, group):
# unroll group with one member
other = maybe_unroll_group(other)
# chain | group() -> chain
tasks = self.unchain_tasks()
if not tasks:
# If the chain is empty, return the group
return other
return _chain(seq_concat_item(
tasks, other), app=self._app)
elif isinstance(other, _chain):
# chain | chain -> chain
return _chain(seq_concat_seq(
self.unchain_tasks(), other.unchain_tasks()), app=self._app)
elif isinstance(other, Signature):
if self.tasks and isinstance(self.tasks[-1], group):
# CHAIN [last item is group] | TASK -> chord
sig = self.clone()
sig.tasks[-1] = chord(
sig.tasks[-1], other, app=self._app)
return sig
elif self.tasks and isinstance(self.tasks[-1], chord):
# CHAIN [last item is chord] -> chain with chord body.
sig = self.clone()
sig.tasks[-1].body = sig.tasks[-1].body | other
return sig
else:
# chain | task -> chain
return _chain(seq_concat_item(
self.unchain_tasks(), other), app=self._app)
else:
return NotImplemented
def clone(self, *args, **kwargs):
to_signature = maybe_signature
signature = super().clone(*args, **kwargs)
signature.kwargs['tasks'] = [
to_signature(sig, app=self._app, clone=True)
for sig in signature.kwargs['tasks']
]
return signature
def unchain_tasks(self):
# Clone chain's tasks assigning signatures from link_error
# to each task
tasks = [t.clone() for t in self.tasks]
for sig in self.options.get('link_error', []):
for task in tasks:
task.link_error(sig)
return tasks
def apply_async(self, args=None, kwargs=None, **options):
# python is best at unpacking kwargs, so .run is here to do that.
args = args if args else ()
kwargs = kwargs if kwargs else []
app = self.app
if app.conf.task_always_eager:
with allow_join_result():
return self.apply(args, kwargs, **options)
return self.run(args, kwargs, app=app, **(
dict(self.options, **options) if options else self.options))
def run(self, args=None, kwargs=None, group_id=None, chord=None,
task_id=None, link=None, link_error=None, publisher=None,
producer=None, root_id=None, parent_id=None, app=None,
group_index=None, **options):
# pylint: disable=redefined-outer-name
# XXX chord is also a class in outer scope.
args = args if args else ()
kwargs = kwargs if kwargs else []
app = app or self.app
use_link = self._use_link
if use_link is None and app.conf.task_protocol == 1:
use_link = True
args = (tuple(args) + tuple(self.args)
if args and not self.immutable else self.args)
tasks, results_from_prepare = self.prepare_steps(
args, kwargs, self.tasks, root_id, parent_id, link_error, app,
task_id, group_id, chord, group_index=group_index,
)
if results_from_prepare:
if link:
tasks[0].extend_list_option('link', link)
first_task = tasks.pop()
options = _prepare_chain_from_options(options, tasks, use_link)
result_from_apply = first_task.apply_async(**options)
# If we only have a single task, it may be important that we pass
# the real result object rather than the one obtained via freezing.
# e.g. For `GroupResult`s, we need to pass back the result object
# which will actually have its promise fulfilled by the subtasks,
# something that will never occur for the frozen result.
if not tasks:
return result_from_apply
else:
return results_from_prepare[0]
# in order for a chain to be frozen, each of the members of the chain individually needs to be frozen
# TODO figure out why we are always cloning before freeze
def freeze(self, _id=None, group_id=None, chord=None,
root_id=None, parent_id=None, group_index=None):
# pylint: disable=redefined-outer-name
# XXX chord is also a class in outer scope.
_, results = self._frozen = self.prepare_steps(
self.args, self.kwargs, self.tasks, root_id, parent_id, None,
self.app, _id, group_id, chord, clone=False,
group_index=group_index,
)
return results[0]
def prepare_steps(self, args, kwargs, tasks,
root_id=None, parent_id=None, link_error=None, app=None,
last_task_id=None, group_id=None, chord_body=None,
clone=True, from_dict=Signature.from_dict,
group_index=None):
app = app or self.app
# use chain message field for protocol 2 and later.
# this avoids pickle blowing the stack on the recursion
# required by linking task together in a tree structure.
# (why is pickle using recursion? or better yet why cannot python
# do tail call optimization making recursion actually useful?)
use_link = self._use_link
if use_link is None and app.conf.task_protocol == 1:
use_link = True
steps = deque(tasks)
# optimization: now the pop func is a local variable
steps_pop = steps.pop
steps_extend = steps.extend
prev_task = None
prev_res = None
tasks, results = [], []
i = 0
# NOTE: We are doing this in reverse order.
# The result is a list of tasks in reverse order, that is
# passed as the ``chain`` message field.
# As it's reversed the worker can just do ``chain.pop()`` to
# get the next task in the chain.
while steps:
task = steps_pop()
# if steps is not empty, this is the first task - reverse order
# if i = 0, this is the last task - again, because we're reversed
is_first_task, is_last_task = not steps, not i
if not isinstance(task, abstract.CallableSignature):
task = from_dict(task, app=app)
if isinstance(task, group):
# when groups are nested, they are unrolled - all tasks within
# groups within groups should be called in parallel
task = maybe_unroll_group(task)
# first task gets partial args from chain
if clone:
if is_first_task:
task = task.clone(args, kwargs)
else:
task = task.clone()
elif is_first_task:
task.args = tuple(args) + tuple(task.args)
if isinstance(task, _chain):
# splice (unroll) the chain
steps_extend(task.tasks)
continue
# TODO why isn't this asserting is_last_task == False?
if isinstance(task, group) and prev_task:
# automatically upgrade group(...) | s to chord(group, s)
# for chords we freeze by pretending it's a normal
# signature instead of a group.
tasks.pop()
results.pop()
try:
task = chord(
task, body=prev_task,
task_id=prev_res.task_id, root_id=root_id, app=app,
)
except AttributeError:
# A GroupResult does not have a task_id since it consists
# of multiple tasks.
# We therefore, have to construct the chord without it.
# Issues #5467, #3585.
task = chord(
task, body=prev_task,
root_id=root_id, app=app,
)
if is_last_task:
# chain(task_id=id) means task id is set for the last task
# in the chain. If the chord is part of a chord/group
# then that chord/group must synchronize based on the
# last task in the chain, so we only set the group_id and
# chord callback for the last task.
res = task.freeze(
last_task_id,
root_id=root_id, group_id=group_id, chord=chord_body,
group_index=group_index,
)
else:
res = task.freeze(root_id=root_id)
i += 1
if prev_task:
if use_link:
# link previous task to this task.
task.link(prev_task)
if prev_res and not prev_res.parent:
prev_res.parent = res
if link_error:
for errback in maybe_list(link_error):
task.link_error(errback)
tasks.append(task)
results.append(res)
prev_task, prev_res = task, res
if isinstance(task, chord):
app.backend.ensure_chords_allowed()
# If the task is a chord, and the body is a chain
# the chain has already been prepared, and res is
# set to the last task in the callback chain.
# We need to change that so that it points to the
# group result object.
node = res
while node.parent:
node = node.parent
prev_res = node
return tasks, results
def apply(self, args=None, kwargs=None, **options):
args = args if args else ()
kwargs = kwargs if kwargs else {}
last, (fargs, fkwargs) = None, (args, kwargs)
for task in self.tasks:
res = task.clone(fargs, fkwargs).apply(
last and (last.get(),), **dict(self.options, **options))
res.parent, last, (fargs, fkwargs) = last, res, (None, None)
return last
@property
def app(self):
app = self._app
if app is None:
try:
app = self.tasks[0]._app
except LookupError:
pass
return app or current_app
def __repr__(self):
if not self.tasks:
return f'<{type(self).__name__}@{id(self):#x}: empty>'
return remove_repeating_from_task(
self.tasks[0]['task'],
' | '.join(repr(t) for t in self.tasks))
[docs]class chain(_chain):
"""Chain tasks together.
Each tasks follows one another,
by being applied as a callback of the previous task.
Note:
If called with only one argument, then that argument must
be an iterable of tasks to chain: this allows us
to use generator expressions.
Example:
This is effectively :math:`((2 + 2) + 4)`:
.. code-block:: pycon
>>> res = chain(add.s(2, 2), add.s(4))()
>>> res.get()
8
Calling a chain will return the result of the last task in the chain.
You can get to the other tasks by following the ``result.parent``'s:
.. code-block:: pycon
>>> res.parent.get()
4
Using a generator expression:
.. code-block:: pycon
>>> lazy_chain = chain(add.s(i) for i in range(10))
>>> res = lazy_chain(3)
Arguments:
*tasks (Signature): List of task signatures to chain.
If only one argument is passed and that argument is
an iterable, then that'll be used as the list of signatures
to chain instead. This means that you can use a generator
expression.
Returns:
~celery.chain: A lazy signature that can be called to apply the first
task in the chain. When that task succeeds the next task in the
chain is applied, and so on.
"""
# could be function, but must be able to reference as :class:`chain`.
def __new__(cls, *tasks, **kwargs):
# This forces `chain(X, Y, Z)` to work the same way as `X | Y | Z`
if not kwargs and tasks:
if len(tasks) != 1 or is_list(tasks[0]):
tasks = tasks[0] if len(tasks) == 1 else tasks
# if is_list(tasks) and len(tasks) == 1:
# return super(chain, cls).__new__(cls, tasks, **kwargs)
return reduce(operator.or_, tasks, chain())
return super().__new__(cls, *tasks, **kwargs)
class _basemap(Signature):
_task_name = None
_unpack_args = itemgetter('task', 'it')
@classmethod
def from_dict(cls, d, app=None):
return cls(*cls._unpack_args(d['kwargs']), app=app, **d['options'])
def __init__(self, task, it, **options):
super().__init__(self._task_name, (),
{'task': task, 'it': regen(it)}, immutable=True, **options
)
def apply_async(self, args=None, kwargs=None, **opts):
# need to evaluate generators
args = args if args else ()
kwargs = kwargs if kwargs else {}
task, it = self._unpack_args(self.kwargs)
return self.type.apply_async(
(), {'task': task, 'it': list(it)},
route_name=task_name_from(self.kwargs.get('task')), **opts
)
@Signature.register_type()
class xmap(_basemap):
"""Map operation for tasks.
Note:
Tasks executed sequentially in process, this is not a
parallel operation like :class:`group`.
"""
_task_name = 'celery.map'
def __repr__(self):
task, it = self._unpack_args(self.kwargs)
return f'[{task.task}(x) for x in {truncate(repr(it), 100)}]'
@Signature.register_type()
class xstarmap(_basemap):
"""Map operation for tasks, using star arguments."""
_task_name = 'celery.starmap'
def __repr__(self):
task, it = self._unpack_args(self.kwargs)
return f'[{task.task}(*x) for x in {truncate(repr(it), 100)}]'
@Signature.register_type()
class chunks(Signature):
"""Partition of tasks into chunks of size n."""
_unpack_args = itemgetter('task', 'it', 'n')
@classmethod
def from_dict(cls, d, app=None):
return chunks(*cls._unpack_args(d['kwargs']), app=app, **d['options'])
def __init__(self, task, it, n, **options):
super().__init__('celery.chunks', (),
{'task': task, 'it': regen(it), 'n': n},
immutable=True, **options
)
def __call__(self, **options):
return self.apply_async(**options)
def apply_async(self, args=None, kwargs=None, **opts):
args = args if args else ()
kwargs = kwargs if kwargs else {}
return self.group().apply_async(
args, kwargs,
route_name=task_name_from(self.kwargs.get('task')), **opts
)
def group(self):
# need to evaluate generators
task, it, n = self._unpack_args(self.kwargs)
return group((xstarmap(task, part, app=self._app)
for part in _chunks(iter(it), n)),
app=self._app)
@classmethod
def apply_chunks(cls, task, it, n, app=None):
return cls(task, it, n, app=app)()
def _maybe_group(tasks, app):
if isinstance(tasks, dict):
tasks = signature(tasks, app=app)
if isinstance(tasks, (group, _chain)):
tasks = tasks.tasks
elif isinstance(tasks, abstract.CallableSignature):
tasks = [tasks]
else:
if isinstance(tasks, GeneratorType):
tasks = regen(signature(t, app=app) for t in tasks)
else:
tasks = [signature(t, app=app) for t in tasks]
return tasks
[docs]@Signature.register_type()
class group(Signature):
"""Creates a group of tasks to be executed in parallel.
A group is lazy so you must call it to take action and evaluate
the group.
Note:
If only one argument is passed, and that argument is an iterable
then that'll be used as the list of tasks instead: this
allows us to use ``group`` with generator expressions.
Example:
>>> lazy_group = group([add.s(2, 2), add.s(4, 4)])
>>> promise = lazy_group() # <-- evaluate: returns lazy result.
>>> promise.get() # <-- will wait for the task to return
[4, 8]
Arguments:
*tasks (List[Signature]): A list of signatures that this group will
call. If there's only one argument, and that argument is an
iterable, then that'll define the list of signatures instead.
**options (Any): Execution options applied to all tasks
in the group.
Returns:
~celery.group: signature that when called will then call all of the
tasks in the group (and return a :class:`GroupResult` instance
that can be used to inspect the state of the group).
"""
tasks = getitem_property('kwargs.tasks', 'Tasks in group.')
@classmethod
def from_dict(cls, d, app=None):
# We need to mutate the `kwargs` element in place to avoid confusing
# `freeze()` implementations which end up here and expect to be able to
# access elements from that dictionary later and refer to objects
# canonicalized here
orig_tasks = d["kwargs"]["tasks"]
d["kwargs"]["tasks"] = rebuilt_tasks = type(orig_tasks)(
maybe_signature(task, app=app) for task in orig_tasks
)
return group(rebuilt_tasks, app=app, **d['options'])
def __init__(self, *tasks, **options):
if len(tasks) == 1:
tasks = tasks[0]
if isinstance(tasks, group):
tasks = tasks.tasks
if isinstance(tasks, abstract.CallableSignature):
tasks = [tasks.clone()]
if not isinstance(tasks, _regen):
tasks = regen(tasks)
super().__init__('celery.group', (), {'tasks': tasks}, **options
)
self.subtask_type = 'group'
def __call__(self, *partial_args, **options):
return self.apply_async(partial_args, **options)
def __or__(self, other):
# group() | task -> chord
return chord(self, body=other, app=self._app)
def skew(self, start=1.0, stop=None, step=1.0):
it = fxrange(start, stop, step, repeatlast=True)
for task in self.tasks:
task.set(countdown=next(it))
return self
def apply_async(self, args=None, kwargs=None, add_to_parent=True,
producer=None, link=None, link_error=None, **options):
args = args if args else ()
if link is not None:
raise TypeError('Cannot add link to group: use a chord')
if link_error is not None:
raise TypeError(
'Cannot add link to group: do that on individual tasks')
app = self.app
if app.conf.task_always_eager:
return self.apply(args, kwargs, **options)
if not self.tasks:
return self.freeze()
options, group_id, root_id = self._freeze_gid(options)
tasks = self._prepared(self.tasks, [], group_id, root_id, app)
p = barrier()
results = list(self._apply_tasks(tasks, producer, app, p,
args=args, kwargs=kwargs, **options))
result = self.app.GroupResult(group_id, results, ready_barrier=p)
p.finalize()
# - Special case of group(A.s() | group(B.s(), C.s()))
# That is, group with single item that's a chain but the
# last task in that chain is a group.
#
# We cannot actually support arbitrary GroupResults in chains,
# but this special case we can.
if len(result) == 1 and isinstance(result[0], GroupResult):
result = result[0]
parent_task = app.current_worker_task
if add_to_parent and parent_task:
parent_task.add_trail(result)
return result
def apply(self, args=None, kwargs=None, **options):
args = args if args else ()
kwargs = kwargs if kwargs else {}
app = self.app
if not self.tasks:
return self.freeze() # empty group returns GroupResult
options, group_id, root_id = self._freeze_gid(options)
tasks = self._prepared(self.tasks, [], group_id, root_id, app)
return app.GroupResult(group_id, [
sig.apply(args=args, kwargs=kwargs, **options) for sig, _, _ in tasks
])
def set_immutable(self, immutable):
for task in self.tasks:
task.set_immutable(immutable)
def link(self, sig):
# Simply link to first task. Doing this is slightly misleading because
# the callback may be executed before all children in the group are
# completed and also if any children other than the first one fail.
#
# The callback signature is cloned and made immutable since it the
# first task isn't actually capable of passing the return values of its
# siblings to the callback task.
sig = sig.clone().set(immutable=True)
return self.tasks[0].link(sig)
def link_error(self, sig):
# Any child task might error so we need to ensure that they are all
# capable of calling the linked error signature. This opens the
# possibility that the task is called more than once but that's better
# than it not being called at all.
#
# We return a concretised tuple of the signatures actually applied to
# each child task signature, of which there might be none!
return tuple(child_task.link_error(sig) for child_task in self.tasks)
def _prepared(self, tasks, partial_args, group_id, root_id, app,
CallableSignature=abstract.CallableSignature,
from_dict=Signature.from_dict,
isinstance=isinstance, tuple=tuple):
for task in tasks:
if isinstance(task, CallableSignature):
# local sigs are always of type Signature, and we
# clone them to make sure we don't modify the originals.
task = task.clone()
else:
# serialized sigs must be converted to Signature.
task = from_dict(task, app=app)
if isinstance(task, group):
# needs yield_from :(
unroll = task._prepared(
task.tasks, partial_args, group_id, root_id, app,
)
yield from unroll
else:
if partial_args and not task.immutable:
task.args = tuple(partial_args) + tuple(task.args)
yield task, task.freeze(group_id=group_id, root_id=root_id), group_id
def _apply_tasks(self, tasks, producer=None, app=None, p=None,
add_to_parent=None, chord=None,
args=None, kwargs=None, **options):
# pylint: disable=redefined-outer-name
# XXX chord is also a class in outer scope.
app = app or self.app
with app.producer_or_acquire(producer) as producer:
# Iterate through tasks two at a time. If tasks is a generator,
# we are able to tell when we are at the end by checking if
# next_task is None. This enables us to set the chord size
# without burning through the entire generator. See #3021.
chord_size = 0
for task_index, (current_task, next_task) in enumerate(
lookahead(tasks)
):
# We expect that each task must be part of the same group which
# seems sensible enough. If that's somehow not the case we'll
# end up messing up chord counts and there are all sorts of
# awful race conditions to think about. We'll hope it's not!
sig, res, group_id = current_task
chord_obj = chord if chord is not None else sig.options.get("chord")
# We need to check the chord size of each contributing task so
# that when we get to the final one, we can correctly set the
# size in the backend and the chord can be sensible completed.
chord_size += _chord._descend(sig)
if chord_obj is not None and next_task is None:
# Per above, sanity check that we only saw one group
app.backend.set_chord_size(group_id, chord_size)
sig.apply_async(producer=producer, add_to_parent=False,
chord=chord_obj, args=args, kwargs=kwargs,
**options)
# adding callback to result, such that it will gradually
# fulfill the barrier.
#
# Using barrier.add would use result.then, but we need
# to add the weak argument here to only create a weak
# reference to the object.
if p and not p.cancelled and not p.ready:
p.size += 1
res.then(p, weak=True)
yield res # <-- r.parent, etc set in the frozen result.
def _freeze_gid(self, options):
# remove task_id and use that as the group_id,
# if we don't remove it then every task will have the same id...
options = dict(self.options, **options)
options['group_id'] = group_id = (
options.pop('task_id', uuid()))
return options, group_id, options.get('root_id')
def _freeze_group_tasks(self, _id=None, group_id=None, chord=None,
root_id=None, parent_id=None, group_index=None):
# pylint: disable=redefined-outer-name
# XXX chord is also a class in outer scope.
opts = self.options
try:
gid = opts['task_id']
except KeyError:
gid = opts['task_id'] = group_id or uuid()
if group_id:
opts['group_id'] = group_id
if chord:
opts['chord'] = chord
if group_index is not None:
opts['group_index'] = group_index
root_id = opts.setdefault('root_id', root_id)
parent_id = opts.setdefault('parent_id', parent_id)
if isinstance(self.tasks, _regen):
# We are draining from a generator here.
# tasks1, tasks2 are each a clone of self.tasks
tasks1, tasks2 = itertools.tee(self._unroll_tasks(self.tasks))
# freeze each task in tasks1, results now holds AsyncResult for each task
results = regen(self._freeze_tasks(tasks1, group_id, chord, root_id, parent_id))
# TODO figure out why this makes sense -
# we freeze all tasks in the clone tasks1, and then zip the results
# with the IDs of tasks in the second clone, tasks2. and then, we build
# a generator that takes only the task IDs from tasks2.
self.tasks = regen(x[0] for x in zip(tasks2, results))
else:
new_tasks = []
# Need to unroll subgroups early so that chord gets the
# right result instance for chord_unlock etc.
results = list(self._freeze_unroll(
new_tasks, group_id, chord, root_id, parent_id,
))
if isinstance(self.tasks, MutableSequence):
self.tasks[:] = new_tasks
else:
self.tasks = new_tasks
return gid, results
def freeze(self, _id=None, group_id=None, chord=None,
root_id=None, parent_id=None, group_index=None):
return self.app.GroupResult(*self._freeze_group_tasks(
_id=_id, group_id=group_id,
chord=chord, root_id=root_id, parent_id=parent_id, group_index=group_index
))
_freeze = freeze
def _freeze_tasks(self, tasks, group_id, chord, root_id, parent_id):
yield from (task.freeze(group_id=group_id,
chord=chord,
root_id=root_id,
parent_id=parent_id,
group_index=group_index)
for group_index, task in enumerate(tasks))
def _unroll_tasks(self, tasks):
# should be refactored to: (maybe_signature(task, app=self._app, clone=True) for task in tasks)
yield from (maybe_signature(task, app=self._app).clone() for task in tasks)
def _freeze_unroll(self, new_tasks, group_id, chord, root_id, parent_id):
# pylint: disable=redefined-outer-name
# XXX chord is also a class in outer scope.
stack = deque(self.tasks)
group_index = 0
while stack:
task = maybe_signature(stack.popleft(), app=self._app).clone()
# if this is a group, flatten it by adding all of the group's tasks to the stack
if isinstance(task, group):
stack.extendleft(task.tasks)
else:
new_tasks.append(task)
yield task.freeze(group_id=group_id,
chord=chord, root_id=root_id,
parent_id=parent_id,
group_index=group_index)
group_index += 1
def __repr__(self):
if self.tasks:
return remove_repeating_from_task(
self.tasks[0]['task'],
f'group({self.tasks!r})')
return 'group(<empty>)'
def __len__(self):
return len(self.tasks)
@property
def app(self):
app = self._app
if app is None:
try:
app = self.tasks[0].app
except LookupError:
pass
return app if app is not None else current_app
@Signature.register_type(name="chord")
class _chord(Signature):
r"""Barrier synchronization primitive.
A chord consists of a header and a body.
The header is a group of tasks that must complete before the callback is
called. A chord is essentially a callback for a group of tasks.
The body is applied with the return values of all the header
tasks as a list.
Example:
The chord:
.. code-block:: pycon
>>> res = chord([add.s(2, 2), add.s(4, 4)])(sum_task.s())
is effectively :math:`\Sigma ((2 + 2) + (4 + 4))`:
.. code-block:: pycon
>>> res.get()
12
"""
@classmethod
def from_dict(cls, d, app=None):
options = d.copy()
args, options['kwargs'] = cls._unpack_args(**options['kwargs'])
return cls(*args, app=app, **options)
@staticmethod
def _unpack_args(header=None, body=None, **kwargs):
# Python signatures are better at extracting keys from dicts
# than manually popping things off.
return (header, body), kwargs
def __init__(self, header, body=None, task='celery.chord',
args=None, kwargs=None, app=None, **options):
args = args if args else ()
kwargs = kwargs if kwargs else {'kwargs': {}}
super().__init__(task, args,
{**kwargs, 'header': _maybe_group(header, app),
'body': maybe_signature(body, app=app)}, app=app, **options
)
self.subtask_type = 'chord'
def __call__(self, body=None, **options):
return self.apply_async((), {'body': body} if body else {}, **options)
def __or__(self, other):
if (not isinstance(other, (group, _chain)) and
isinstance(other, Signature)):
# chord | task -> attach to body
sig = self.clone()
sig.body = sig.body | other
return sig
else:
return super().__or__(other)
def freeze(self, _id=None, group_id=None, chord=None,
root_id=None, parent_id=None, group_index=None):
# pylint: disable=redefined-outer-name
# XXX chord is also a class in outer scope.
if not isinstance(self.tasks, group):
self.tasks = group(self.tasks, app=self.app)
# first freeze all tasks in the header
header_result = self.tasks.freeze(
parent_id=parent_id, root_id=root_id, chord=self.body)
# secondly freeze all tasks in the body: those that should be called after the header
body_result = self.body.freeze(
_id, root_id=root_id, chord=chord, group_id=group_id,
group_index=group_index)
# we need to link the body result back to the group result,
# but the body may actually be a chain,
# so find the first result without a parent
node = body_result
seen = set()
while node:
if node.id in seen:
raise RuntimeError('Recursive result parents')
seen.add(node.id)
if node.parent is None:
node.parent = header_result
break
node = node.parent
self.id = self.tasks.id
return body_result
def apply_async(self, args=None, kwargs=None, task_id=None,
producer=None, publisher=None, connection=None,
router=None, result_cls=None, **options):
args = args if args else ()
kwargs = kwargs if kwargs else {}
args = (tuple(args) + tuple(self.args)
if args and not self.immutable else self.args)
body = kwargs.pop('body', None) or self.kwargs['body']
kwargs = dict(self.kwargs['kwargs'], **kwargs)
body = body.clone(**options)
app = self._get_app(body)
tasks = (self.tasks.clone() if isinstance(self.tasks, group)
else group(self.tasks, app=app))
if app.conf.task_always_eager:
with allow_join_result():
return self.apply(args, kwargs,
body=body, task_id=task_id, **options)
merged_options = dict(self.options, **options) if options else self.options
option_task_id = merged_options.pop("task_id", None)
if task_id is None:
task_id = option_task_id
# chord([A, B, ...], C)
return self.run(tasks, body, args, task_id=task_id, **merged_options)
def apply(self, args=None, kwargs=None,
propagate=True, body=None, **options):
args = args if args else ()
kwargs = kwargs if kwargs else {}
body = self.body if body is None else body
tasks = (self.tasks.clone() if isinstance(self.tasks, group)
else group(self.tasks, app=self.app))
return body.apply(
args=(tasks.apply(args, kwargs).get(propagate=propagate),),
)
@classmethod
def _descend(cls, sig_obj):
# Sometimes serialized signatures might make their way here
if not isinstance(sig_obj, Signature) and isinstance(sig_obj, dict):
sig_obj = Signature.from_dict(sig_obj)
if isinstance(sig_obj, group):
# Each task in a group counts toward this chord
subtasks = getattr(sig_obj.tasks, "tasks", sig_obj.tasks)
return sum(cls._descend(task) for task in subtasks)
elif isinstance(sig_obj, _chain):
# The last non-empty element in a chain counts toward this chord
for child_sig in sig_obj.tasks[-1::-1]:
child_size = cls._descend(child_sig)
if child_size > 0:
return child_size
else:
# We have to just hope this chain is part of some encapsulating
# signature which is valid and can fire the chord body
return 0
elif isinstance(sig_obj, chord):
# The child chord's body counts toward this chord
return cls._descend(sig_obj.body)
elif isinstance(sig_obj, Signature):
# Each simple signature counts as 1 completion for this chord
return 1
# Any other types are assumed to be iterables of simple signatures
return len(sig_obj)
def __length_hint__(self):
tasks = getattr(self.tasks, "tasks", self.tasks)
return sum(self._descend(task) for task in tasks)
def run(self, header, body, partial_args, app=None, interval=None,
countdown=1, max_retries=None, eager=False,
task_id=None, **options):
app = app or self._get_app(body)
group_id = header.options.get('task_id') or uuid()
root_id = body.options.get('root_id')
options = dict(self.options, **options) if options else self.options
if options:
options.pop('task_id', None)
body.options.update(options)
bodyres = body.freeze(task_id, root_id=root_id)
# Chains should not be passed to the header tasks. See #3771
options.pop('chain', None)
# Neither should chords, for deeply nested chords to work
options.pop('chord', None)
options.pop('task_id', None)
header_result_args = header._freeze_group_tasks(group_id=group_id, chord=body, root_id=root_id)
if header.tasks:
app.backend.apply_chord(
header_result_args,
body,
interval=interval,
countdown=countdown,
max_retries=max_retries,
)
header_result = header(*partial_args, task_id=group_id, **options)
# The execution of a chord body is normally triggered by its header's
# tasks completing. If the header is empty this will never happen, so
# we execute the body manually here.
else:
body.delay([])
header_result = self.app.GroupResult(*header_result_args)
bodyres.parent = header_result
return bodyres
def clone(self, *args, **kwargs):
signature = super().clone(*args, **kwargs)
# need to make copy of body
try:
signature.kwargs['body'] = maybe_signature(
signature.kwargs['body'], clone=True)
except (AttributeError, KeyError):
pass
return signature
def link(self, callback):
self.body.link(callback)
return callback
def link_error(self, errback):
self.body.link_error(errback)
return errback
def set_immutable(self, immutable):
# changes mutability of header only, not callback.
for task in self.tasks:
task.set_immutable(immutable)
def __repr__(self):
if self.body:
if isinstance(self.body, _chain):
return remove_repeating_from_task(
self.body.tasks[0]['task'],
'%({} | {!r})'.format(
self.body.tasks[0].reprcall(self.tasks),
chain(self.body.tasks[1:], app=self._app),
),
)
return '%' + remove_repeating_from_task(
self.body['task'], self.body.reprcall(self.tasks))
return f'<chord without body: {self.tasks!r}>'
@cached_property
def app(self):
return self._get_app(self.body)
def _get_app(self, body=None):
app = self._app
if app is None:
try:
tasks = self.tasks.tasks # is a group
except AttributeError:
tasks = self.tasks
if tasks:
app = tasks[0]._app
if app is None and body is not None:
app = body._app
return app if app is not None else current_app
tasks = getitem_property('kwargs.header', 'Tasks in chord header.')
body = getitem_property('kwargs.body', 'Body task of chord.')
# Add a back-compat alias for the previous `chord` class name which conflicts
# with keyword arguments elsewhere in this file
chord = _chord
[docs]def signature(varies, *args, **kwargs):
"""Create new signature.
- if the first argument is a signature already then it's cloned.
- if the first argument is a dict, then a Signature version is returned.
Returns:
Signature: The resulting signature.
"""
app = kwargs.get('app')
if isinstance(varies, dict):
if isinstance(varies, abstract.CallableSignature):
return varies.clone()
return Signature.from_dict(varies, app=app)
return Signature(varies, *args, **kwargs)
subtask = signature # XXX compat
def maybe_signature(d, app=None, clone=False):
"""Ensure obj is a signature, or None.
Arguments:
d (Optional[Union[abstract.CallableSignature, Mapping]]):
Signature or dict-serialized signature.
app (celery.Celery):
App to bind signature to.
clone (bool):
If d' is already a signature, the signature
will be cloned when this flag is enabled.
Returns:
Optional[abstract.CallableSignature]
"""
if d is not None:
if isinstance(d, abstract.CallableSignature):
if clone:
d = d.clone()
elif isinstance(d, dict):
d = signature(d)
if app is not None:
d._app = app
return d
maybe_subtask = maybe_signature # XXX compat
