This document describes the current stable version of Celery (5.4). For development docs, go here.

Source code for

"""In-memory representation of cluster state.

This module implements a data-structure used to keep
track of the state of a cluster of workers and the tasks
it is working on (by consuming events).

For every event consumed the state is updated,
so the state represents the state of the cluster
at the time of the last event.

Snapshots (:mod:``) can be used to
take "pictures" of this state at regular intervals
to for example, store that in a database.
import bisect
import sys
import threading
from collections import defaultdict
from import Callable
from datetime import datetime
from decimal import Decimal
from itertools import islice
from operator import itemgetter
from time import time
from typing import Mapping, Optional  # noqa
from weakref import WeakSet, ref

from kombu.clocks import timetuple
from kombu.utils.objects import cached_property

from celery import states
from celery.utils.functional import LRUCache, memoize, pass1
from celery.utils.log import get_logger

__all__ = ('Worker', 'Task', 'State', 'heartbeat_expires')

# pylint: disable=redefined-outer-name
# We cache globals and attribute lookups, so disable this warning.
# pylint: disable=too-many-function-args
# For some reason pylint thinks ._event is a method, when it's a property.

#: Set if running PyPy
PYPY = hasattr(sys, 'pypy_version_info')

#: The window (in percentage) is added to the workers heartbeat
#: frequency.  If the time between updates exceeds this window,
#: then the worker is considered to be offline.

#: Max drift between event timestamp and time of event received
#: before we alert that clocks may be unsynchronized.

    "Substantial drift from %s may mean clocks are out of sync.  Current drift is "
    "%s seconds.  [orig: %s recv: %s]"

logger = get_logger(__name__)
warn = logger.warning

R_STATE = '<State: events={0.event_count} tasks={0.task_count}>'
R_WORKER = '<Worker: {0.hostname} ({0.status_string} clock:{0.clock})'
R_TASK = '<Task: {}({0.uuid}) {0.state} clock:{0.clock}>'

#: Mapping of task event names to task state.
    'sent': states.PENDING,
    'received': states.RECEIVED,
    'started': states.STARTED,
    'failed': states.FAILURE,
    'retried': states.RETRY,
    'succeeded': states.SUCCESS,
    'revoked': states.REVOKED,
    'rejected': states.REJECTED,

class CallableDefaultdict(defaultdict):
    """:class:`~collections.defaultdict` with configurable __call__.

    We use this for backwards compatibility in State.tasks_by_type
    etc, which used to be a method but is now an index instead.

    So you can do::

        >>> add_tasks = state.tasks_by_type['proj.tasks.add']

    while still supporting the method call::

        >>> add_tasks = list(state.tasks_by_type(
        ...     'proj.tasks.add', reverse=True))

    def __init__(self, fun, *args, **kwargs): = fun
        super().__init__(*args, **kwargs)

    def __call__(self, *args, **kwargs):
        return*args, **kwargs)


@memoize(maxsize=1000, keyfun=lambda a, _: a[0])
def _warn_drift(hostname, drift, local_received, timestamp):
    # we use memoize here so the warning is only logged once per hostname
    warn(DRIFT_WARNING, hostname, drift,

[docs] def heartbeat_expires(timestamp, freq=60, expire_window=HEARTBEAT_EXPIRE_WINDOW, Decimal=Decimal, float=float, isinstance=isinstance): """Return time when heartbeat expires.""" # some json implementations returns decimal.Decimal objects, # which aren't compatible with float. freq = float(freq) if isinstance(freq, Decimal) else freq if isinstance(timestamp, Decimal): timestamp = float(timestamp) return timestamp + (freq * (expire_window / 1e2))
def _depickle_task(cls, fields): return cls(**fields) def with_unique_field(attr): def _decorate_cls(cls): def __eq__(this, other): if isinstance(other, this.__class__): return getattr(this, attr) == getattr(other, attr) return NotImplemented cls.__eq__ = __eq__ def __hash__(this): return hash(getattr(this, attr)) cls.__hash__ = __hash__ return cls return _decorate_cls
[docs] @with_unique_field('hostname') class Worker: """Worker State.""" heartbeat_max = 4 expire_window = HEARTBEAT_EXPIRE_WINDOW _fields = ('hostname', 'pid', 'freq', 'heartbeats', 'clock', 'active', 'processed', 'loadavg', 'sw_ident', 'sw_ver', 'sw_sys') if not PYPY: # pragma: no cover __slots__ = _fields + ('event', '__dict__', '__weakref__') def __init__(self, hostname=None, pid=None, freq=60, heartbeats=None, clock=0, active=None, processed=None, loadavg=None, sw_ident=None, sw_ver=None, sw_sys=None): self.hostname = hostname = pid self.freq = freq self.heartbeats = [] if heartbeats is None else heartbeats self.clock = clock or 0 = active self.processed = processed self.loadavg = loadavg self.sw_ident = sw_ident self.sw_ver = sw_ver self.sw_sys = sw_sys self.event = self._create_event_handler() def __reduce__(self): return self.__class__, (self.hostname,, self.freq, self.heartbeats, self.clock,, self.processed, self.loadavg, self.sw_ident, self.sw_ver, self.sw_sys) def _create_event_handler(self): _set = object.__setattr__ hbmax = self.heartbeat_max heartbeats = self.heartbeats hb_pop = self.heartbeats.pop hb_append = self.heartbeats.append def event(type_, timestamp=None, local_received=None, fields=None, max_drift=HEARTBEAT_DRIFT_MAX, abs=abs, int=int, insort=bisect.insort, len=len): fields = fields or {} for k, v in fields.items(): _set(self, k, v) if type_ == 'offline': heartbeats[:] = [] else: if not local_received or not timestamp: return drift = abs(int(local_received) - int(timestamp)) if drift > max_drift: _warn_drift(self.hostname, drift, local_received, timestamp) if local_received: # pragma: no cover hearts = len(heartbeats) if hearts > hbmax - 1: hb_pop(0) if hearts and local_received > heartbeats[-1]: hb_append(local_received) else: insort(heartbeats, local_received) return event
[docs] def update(self, f, **kw): d = dict(f, **kw) if kw else f for k, v in d.items(): setattr(self, k, v)
def __repr__(self): return R_WORKER.format(self) @property def status_string(self): return 'ONLINE' if self.alive else 'OFFLINE' @property def heartbeat_expires(self): return heartbeat_expires(self.heartbeats[-1], self.freq, self.expire_window) @property def alive(self, nowfun=time): return bool(self.heartbeats and nowfun() < self.heartbeat_expires) @property def id(self): return '{0.hostname}.{}'.format(self)
[docs] @with_unique_field('uuid') class Task: """Task State.""" name = received = sent = started = succeeded = failed = retried = \ revoked = rejected = args = kwargs = eta = expires = retries = \ worker = result = exception = timestamp = runtime = traceback = \ exchange = routing_key = root_id = parent_id = client = None state = states.PENDING clock = 0 _fields = ( 'uuid', 'name', 'state', 'received', 'sent', 'started', 'rejected', 'succeeded', 'failed', 'retried', 'revoked', 'args', 'kwargs', 'eta', 'expires', 'retries', 'worker', 'result', 'exception', 'timestamp', 'runtime', 'traceback', 'exchange', 'routing_key', 'clock', 'client', 'root', 'root_id', 'parent', 'parent_id', 'children', ) if not PYPY: # pragma: no cover __slots__ = ('__dict__', '__weakref__') #: How to merge out of order events. #: Disorder is detected by logical ordering (e.g., :event:`task-received` #: must've happened before a :event:`task-failed` event). #: #: A merge rule consists of a state and a list of fields to keep from #: that state. ``(RECEIVED, ('name', 'args')``, means the name and args #: fields are always taken from the RECEIVED state, and any values for #: these fields received before or after is simply ignored. merge_rules = { states.RECEIVED: ( 'name', 'args', 'kwargs', 'parent_id', 'root_id', 'retries', 'eta', 'expires', ), } #: meth:`info` displays these fields by default. _info_fields = ( 'args', 'kwargs', 'retries', 'result', 'eta', 'runtime', 'expires', 'exception', 'exchange', 'routing_key', 'root_id', 'parent_id', ) def __init__(self, uuid=None, cluster_state=None, children=None, **kwargs): self.uuid = uuid self.cluster_state = cluster_state if self.cluster_state is not None: self.children = WeakSet( self.cluster_state.tasks.get(task_id) for task_id in children or () if task_id in self.cluster_state.tasks ) else: self.children = WeakSet() self._serializer_handlers = { 'children': self._serializable_children, 'root': self._serializable_root, 'parent': self._serializable_parent, } if kwargs: self.__dict__.update(kwargs)
[docs] def event(self, type_, timestamp=None, local_received=None, fields=None, precedence=states.precedence, setattr=setattr, task_event_to_state=TASK_EVENT_TO_STATE.get, RETRY=states.RETRY): fields = fields or {} # using .get is faster than catching KeyError in this case. state = task_event_to_state(type_) if state is not None: # sets, for example, self.succeeded to the timestamp. setattr(self, type_, timestamp) else: state = type_.upper() # custom state # note that precedence here is reversed # see implementation in celery.states.state.__lt__ if state != RETRY and self.state != RETRY and \ precedence(state) > precedence(self.state): # this state logically happens-before the current state, so merge. keep = self.merge_rules.get(state) if keep is not None: fields = { k: v for k, v in fields.items() if k in keep } else: fields.update(state=state, timestamp=timestamp) # update current state with info from this event. self.__dict__.update(fields)
[docs] def info(self, fields=None, extra=None): """Information about this task suitable for on-screen display.""" extra = [] if not extra else extra fields = self._info_fields if fields is None else fields def _keys(): for key in list(fields) + list(extra): value = getattr(self, key, None) if value is not None: yield key, value return dict(_keys())
def __repr__(self): return R_TASK.format(self)
[docs] def as_dict(self): get = object.__getattribute__ handler = self._serializer_handlers.get return { k: handler(k, pass1)(get(self, k)) for k in self._fields }
def _serializable_children(self, value): return [ for task in self.children] def _serializable_root(self, value): return self.root_id def _serializable_parent(self, value): return self.parent_id def __reduce__(self): return _depickle_task, (self.__class__, self.as_dict()) @property def id(self): return self.uuid @property def origin(self): return self.client if self.worker is None else @property def ready(self): return self.state in states.READY_STATES @cached_property def parent(self): # issue try: return self.parent_id and[self.parent_id] except KeyError: return None @cached_property def root(self): # issue try: return self.root_id and[self.root_id] except KeyError: return None
[docs] class State: """Records clusters state.""" Worker = Worker Task = Task event_count = 0 task_count = 0 heap_multiplier = 4 def __init__(self, callback=None, workers=None, tasks=None, taskheap=None, max_workers_in_memory=5000, max_tasks_in_memory=10000, on_node_join=None, on_node_leave=None, tasks_by_type=None, tasks_by_worker=None): self.event_callback = callback self.workers = (LRUCache(max_workers_in_memory) if workers is None else workers) self.tasks = (LRUCache(max_tasks_in_memory) if tasks is None else tasks) self._taskheap = [] if taskheap is None else taskheap self.max_workers_in_memory = max_workers_in_memory self.max_tasks_in_memory = max_tasks_in_memory self.on_node_join = on_node_join self.on_node_leave = on_node_leave self._mutex = threading.Lock() self.handlers = {} self._seen_types = set() self._tasks_to_resolve = {} self.rebuild_taskheap() self.tasks_by_type = CallableDefaultdict( self._tasks_by_type, WeakSet) # type: Mapping[str, WeakSet[Task]] self.tasks_by_type.update( _deserialize_Task_WeakSet_Mapping(tasks_by_type, self.tasks)) self.tasks_by_worker = CallableDefaultdict( self._tasks_by_worker, WeakSet) # type: Mapping[str, WeakSet[Task]] self.tasks_by_worker.update( _deserialize_Task_WeakSet_Mapping(tasks_by_worker, self.tasks)) @cached_property def _event(self): return self._create_dispatcher()
[docs] def freeze_while(self, fun, *args, **kwargs): clear_after = kwargs.pop('clear_after', False) with self._mutex: try: return fun(*args, **kwargs) finally: if clear_after: self._clear()
[docs] def clear_tasks(self, ready=True): with self._mutex: return self._clear_tasks(ready)
def _clear_tasks(self, ready: bool = True): if ready: in_progress = { uuid: task for uuid, task in self.itertasks() if task.state not in states.READY_STATES } self.tasks.clear() self.tasks.update(in_progress) else: self.tasks.clear() self._taskheap[:] = [] def _clear(self, ready=True): self.workers.clear() self._clear_tasks(ready) self.event_count = 0 self.task_count = 0
[docs] def clear(self, ready: bool = True): with self._mutex: return self._clear(ready)
[docs] def get_or_create_worker(self, hostname, **kwargs): """Get or create worker by hostname. Returns: Tuple: of ``(worker, was_created)`` pairs. """ try: worker = self.workers[hostname] if kwargs: worker.update(kwargs) return worker, False except KeyError: worker = self.workers[hostname] = self.Worker( hostname, **kwargs) return worker, True
[docs] def get_or_create_task(self, uuid): """Get or create task by uuid.""" try: return self.tasks[uuid], False except KeyError: task = self.tasks[uuid] = self.Task(uuid, cluster_state=self) return task, True
[docs] def event(self, event): with self._mutex: return self._event(event)
[docs] def task_event(self, type_, fields): """Deprecated, use :meth:`event`.""" return self._event(dict(fields, type='-'.join(['task', type_])))[0]
[docs] def worker_event(self, type_, fields): """Deprecated, use :meth:`event`.""" return self._event(dict(fields, type='-'.join(['worker', type_])))[0]
def _create_dispatcher(self): # pylint: disable=too-many-statements # This code is highly optimized, but not for reusability. get_handler = self.handlers.__getitem__ event_callback = self.event_callback wfields = itemgetter('hostname', 'timestamp', 'local_received') tfields = itemgetter('uuid', 'hostname', 'timestamp', 'local_received', 'clock') taskheap = self._taskheap th_append = taskheap.append th_pop = taskheap.pop # Removing events from task heap is an O(n) operation, # so easier to just account for the common number of events # for each task (PENDING->RECEIVED->STARTED->final) #: an O(n) operation max_events_in_heap = self.max_tasks_in_memory * self.heap_multiplier add_type = self._seen_types.add on_node_join, on_node_leave = self.on_node_join, self.on_node_leave tasks, Task = self.tasks, self.Task workers, Worker = self.workers, self.Worker # avoid updating LRU entry at getitem get_worker, get_task =, get_task_by_type_set = self.tasks_by_type.__getitem__ get_task_by_worker_set = self.tasks_by_worker.__getitem__ def _event(event, timetuple=timetuple, KeyError=KeyError, insort=bisect.insort, created=True): self.event_count += 1 if event_callback: event_callback(self, event) group, _, subject = event['type'].partition('-') try: handler = get_handler(group) except KeyError: pass else: return handler(subject, event), subject if group == 'worker': try: hostname, timestamp, local_received = wfields(event) except KeyError: pass else: is_offline = subject == 'offline' try: worker, created = get_worker(hostname), False except KeyError: if is_offline: worker, created = Worker(hostname), False else: worker = workers[hostname] = Worker(hostname) worker.event(subject, timestamp, local_received, event) if on_node_join and (created or subject == 'online'): on_node_join(worker) if on_node_leave and is_offline: on_node_leave(worker) workers.pop(hostname, None) return (worker, created), subject elif group == 'task': (uuid, hostname, timestamp, local_received, clock) = tfields(event) # task-sent event is sent by client, not worker is_client_event = subject == 'sent' try: task, task_created = get_task(uuid), False except KeyError: task = tasks[uuid] = Task(uuid, cluster_state=self) task_created = True if is_client_event: task.client = hostname else: try: worker = get_worker(hostname) except KeyError: worker = workers[hostname] = Worker(hostname) task.worker = worker if worker is not None and local_received: worker.event(None, local_received, timestamp) origin = hostname if is_client_event else # remove oldest event if exceeding the limit. heaps = len(taskheap) if heaps + 1 > max_events_in_heap: th_pop(0) # most events will be dated later than the previous. timetup = timetuple(clock, timestamp, origin, ref(task)) if heaps and timetup > taskheap[-1]: th_append(timetup) else: insort(taskheap, timetup) if subject == 'received': self.task_count += 1 task.event(subject, timestamp, local_received, event) task_name = if task_name is not None: add_type(task_name) if task_created: # add to tasks_by_type index get_task_by_type_set(task_name).add(task) get_task_by_worker_set(hostname).add(task) if task.parent_id: try: parent_task = self.tasks[task.parent_id] except KeyError: self._add_pending_task_child(task) else: parent_task.children.add(task) try: _children = self._tasks_to_resolve.pop(uuid) except KeyError: pass else: task.children.update(_children) return (task, task_created), subject return _event def _add_pending_task_child(self, task): try: ch = self._tasks_to_resolve[task.parent_id] except KeyError: ch = self._tasks_to_resolve[task.parent_id] = WeakSet() ch.add(task)
[docs] def rebuild_taskheap(self, timetuple=timetuple): heap = self._taskheap[:] = [ timetuple(t.clock, t.timestamp, t.origin, ref(t)) for t in self.tasks.values() ] heap.sort()
[docs] def itertasks(self, limit: Optional[int] = None): for index, row in enumerate(self.tasks.items()): yield row if limit and index + 1 >= limit: break
[docs] def tasks_by_time(self, limit=None, reverse: bool = True): """Generator yielding tasks ordered by time. Yields: Tuples of ``(uuid, Task)``. """ _heap = self._taskheap if reverse: _heap = reversed(_heap) seen = set() for evtup in islice(_heap, 0, limit): task = evtup[3]() if task is not None: uuid = task.uuid if uuid not in seen: yield uuid, task seen.add(uuid)
tasks_by_timestamp = tasks_by_time def _tasks_by_type(self, name, limit=None, reverse=True): """Get all tasks by type. This is slower than accessing :attr:`tasks_by_type`, but will be ordered by time. Returns: Generator: giving ``(uuid, Task)`` pairs. """ return islice( ((uuid, task) for uuid, task in self.tasks_by_time(reverse=reverse) if == name), 0, limit, ) def _tasks_by_worker(self, hostname, limit=None, reverse=True): """Get all tasks by worker. Slower than accessing :attr:`tasks_by_worker`, but ordered by time. """ return islice( ((uuid, task) for uuid, task in self.tasks_by_time(reverse=reverse) if task.worker.hostname == hostname), 0, limit, )
[docs] def task_types(self): """Return a list of all seen task types.""" return sorted(self._seen_types)
[docs] def alive_workers(self): """Return a list of (seemingly) alive workers.""" return (w for w in self.workers.values() if w.alive)
def __repr__(self): return R_STATE.format(self) def __reduce__(self): return self.__class__, ( self.event_callback, self.workers, self.tasks, None, self.max_workers_in_memory, self.max_tasks_in_memory, self.on_node_join, self.on_node_leave, _serialize_Task_WeakSet_Mapping(self.tasks_by_type), _serialize_Task_WeakSet_Mapping(self.tasks_by_worker), )
def _serialize_Task_WeakSet_Mapping(mapping): return {name: [ for t in tasks] for name, tasks in mapping.items()} def _deserialize_Task_WeakSet_Mapping(mapping, tasks): mapping = mapping or {} return {name: WeakSet(tasks[i] for i in ids if i in tasks) for name, ids in mapping.items()}