This document describes the current stable version of Celery (5.2). For development docs, go here.
Source code for celery.contrib.abortable
"""Abortable Tasks. Abortable tasks overview ========================= For long-running :class:`Task`'s, it can be desirable to support aborting during execution. Of course, these tasks should be built to support abortion specifically. The :class:`AbortableTask` serves as a base class for all :class:`Task` objects that should support abortion by producers. * Producers may invoke the :meth:`abort` method on :class:`AbortableAsyncResult` instances, to request abortion. * Consumers (workers) should periodically check (and honor!) the :meth:`is_aborted` method at controlled points in their task's :meth:`run` method. The more often, the better. The necessary intermediate communication is dealt with by the :class:`AbortableTask` implementation. Usage example ------------- In the consumer: .. code-block:: python from __future__ import absolute_import from celery.contrib.abortable import AbortableTask from celery.utils.log import get_task_logger from proj.celery import app logger = get_logger(__name__) @app.task(bind=True, base=AbortableTask) def long_running_task(self): results =  for i in range(100): # check after every 5 iterations... # (or alternatively, check when some timer is due) if not i % 5: if self.is_aborted(): # respect aborted state, and terminate gracefully. logger.warning('Task aborted') return value = do_something_expensive(i) results.append(y) logger.info('Task complete') return results In the producer: .. code-block:: python from __future__ import absolute_import import time from proj.tasks import MyLongRunningTask def myview(request): # result is of type AbortableAsyncResult result = long_running_task.delay() # abort the task after 10 seconds time.sleep(10) result.abort() After the `result.abort()` call, the task execution isn't aborted immediately. In fact, it's not guaranteed to abort at all. Keep checking `result.state` status, or call `result.get(timeout=)` to have it block until the task is finished. .. note:: In order to abort tasks, there needs to be communication between the producer and the consumer. This is currently implemented through the database backend. Therefore, this class will only work with the database backends. """ from celery import Task from celery.result import AsyncResult __all__ = ('AbortableAsyncResult', 'AbortableTask') """ Task States ----------- .. state:: ABORTED ABORTED ~~~~~~~ Task is aborted (typically by the producer) and should be aborted as soon as possible. """ ABORTED = 'ABORTED'[docs]class AbortableAsyncResult(AsyncResult): """Represents an abortable result. Specifically, this gives the `AsyncResult` a :meth:`abort()` method, that sets the state of the underlying Task to `'ABORTED'`. """[docs] def is_aborted(self): """Return :const:`True` if the task is (being) aborted.""" return self.state == ABORTED[docs] def abort(self): """Set the state of the task to :const:`ABORTED`. Abortable tasks monitor their state at regular intervals and terminate execution if so. Warning: Be aware that invoking this method does not guarantee when the task will be aborted (or even if the task will be aborted at all). """ # TODO: store_result requires all four arguments to be set, # but only state should be updated here return self.backend.store_result(self.id, result=None, state=ABORTED, traceback=None)[docs]class AbortableTask(Task): """Task that can be aborted. This serves as a base class for all :class:`Task`'s that support aborting during execution. All subclasses of :class:`AbortableTask` must call the :meth:`is_aborted` method periodically and act accordingly when the call evaluates to :const:`True`. """ abstract = True[docs] def AsyncResult(self, task_id): """Return the accompanying AbortableAsyncResult instance.""" return AbortableAsyncResult(task_id, backend=self.backend)[docs] def is_aborted(self, **kwargs): """Return true if task is aborted. Checks against the backend whether this :class:`AbortableAsyncResult` is :const:`ABORTED`. Always return :const:`False` in case the `task_id` parameter refers to a regular (non-abortable) :class:`Task`. Be aware that invoking this method will cause a hit in the backend (for example a database query), so find a good balance between calling it regularly (for responsiveness), but not too often (for performance). """ task_id = kwargs.get('task_id', self.request.id) result = self.AsyncResult(task_id) if not isinstance(result, AbortableAsyncResult): return False return result.is_aborted()