“The Big Instance” Refactor — Python documentation
“The Big Instance” Refactor
The app branch is a work-in-progress to remove the use of a global configuration in Celery.
Celery can now be instantiated and several instances of Celery may exist in the same process space. Also, large parts can be customized without resorting to monkey patching.
Examples
Creating a Celery instance:
>>> from celery import Celery
>>> app = Celery()
>>> app.config_from_object('celeryconfig')
>>> #app.config_from_envvar('CELERY_CONFIG_MODULE')
Creating tasks:
@app.task
def add(x, y):
return x + y
Creating custom Task subclasses:
Task = celery.create_task_cls()
class DebugTask(Task):
def on_failure(self, *args, **kwargs):
import pdb
pdb.set_trace()
@app.task(base=DebugTask)
def add(x, y):
return x + y
Starting a worker:
worker = celery.Worker(loglevel='INFO')
Getting access to the configuration:
celery.conf.task_always_eager = True
celery.conf['task_always_eager'] = True
Controlling workers:
>>> celery.control.inspect().active()
>>> celery.control.rate_limit(add.name, '100/m')
>>> celery.control.broadcast('shutdown')
>>> celery.control.discard_all()
Other interesting attributes:
# Establish broker connection.
>>> celery.broker_connection()
# AMQP Specific features.
>>> celery.amqp
>>> celery.amqp.Router
>>> celery.amqp.get_queues()
>>> celery.amqp.get_task_consumer()
# Loader
>>> celery.loader
# Default backend
>>> celery.backend
As you can probably see, this really opens up another dimension of customization abilities.
Deprecated
celery.task.ping
celery.task.PingTask
Inferior to the ping remote control command. Will be removed in Celery 2.3.
Aliases (Pending deprecation)
celery.execute
.send_task
-> {app.send_task
}.delay_task
-> no alternative
celery.log
.get_default_logger
-> {app.log.get_default_logger
}.setup_logger
-> {app.log.setup_logger
}.get_task_logger
-> {app.log.get_task_logger
}.setup_task_logger
-> {app.log.setup_task_logger
}.setup_logging_subsystem
-> {app.log.setup_logging_subsystem
}.redirect_stdouts_to_logger
-> {app.log.redirect_stdouts_to_logger
}
celery.messaging
.establish_connection
-> {app.broker_connection
}.with_connection
-> {app.with_connection
}.get_consumer_set
-> {app.amqp.get_task_consumer
}.TaskPublisher
-> {app.amqp.TaskPublisher
}.TaskConsumer
-> {app.amqp.TaskConsumer
}.ConsumerSet
-> {app.amqp.ConsumerSet
}
celery.conf.*
-> {app.conf
}NOTE: All configuration keys are now named the same as in the configuration. So the key
task_always_eager
is accessed as:>>> app.conf.task_always_eager
instead of:
>>> from celery import conf >>> conf.always_eager
.get_queues
-> {app.amqp.get_queues
}
celery.utils.info
.humanize_seconds
->celery.utils.time.humanize_seconds
.textindent
->celery.utils.textindent
.get_broker_info
-> {app.amqp.get_broker_info
}.format_broker_info
-> {app.amqp.format_broker_info
}.format_queues
-> {app.amqp.format_queues
}
Default App Usage
To be backward compatible, it must be possible to use all the classes/functions without passing an explicit app instance.
This is achieved by having all app-dependent objects use default_app
if the app instance is missing.
from celery.app import app_or_default
class SomeClass:
def __init__(self, app=None):
self.app = app_or_default(app)
The problem with this approach is that there’s a chance that the app instance is lost along the way, and everything seems to be working normally. Testing app instance leaks is hard. The environment variable CELERY_TRACE_APP
can be used, when this is enabled celery.app.app_or_default()
will raise an exception whenever it has to go back to the default app instance.
App Dependency Tree
- *; {
app
}- *;*
celery.loaders.base.BaseLoader
celery.backends.base.BaseBackend
- *;*; {
app.TaskSet
}
- *;*;*
celery.task.sets.TaskSet
(app.TaskSet
)
- *;*;*
- *;*
- *;*; [
app.TaskSetResult
]
- *;*; [
- *;*;*
celery.result.TaskSetResult
(app.TaskSetResult
)
- *;*;*
app.AsyncResult
}
- *;*
celery.result.BaseAsyncResult
/celery.result.AsyncResult
celery.bin.worker.WorkerCommand
- *;* *;*;
celery.apps.worker.Worker
- *;*;* *;*;*;
celery.worker.WorkerController
- *;*;* *;*;*;
- *;*;*;* *;*;*;*;
celery.worker.consumer.Consumer
- *;*;*;* *;*;*;*;
- *;*;*;*;*
celery.worker.request.Request
- *;*;*;*;*
celery.events.EventDispatcher
- *;*;*;*;*;
celery.worker.control.ControlDispatch
- *;*;*;*;*;*
celery.worker.control.registry.Panel
- *;*;*;*;*;*
celery.pidbox.BroadcastPublisher
celery.pidbox.BroadcastConsumer
celery.beat.EmbeddedService
celery.bin.events.EvCommand
- *;* *;*;
celery.events.snapshot.evcam
- *;*;*
celery.events.snapshot.Polaroid
- *;*;*
celery.events.EventReceiver
- *;*;
celery.events.cursesmon.evtop
- *;*;
- *;*;*
celery.events.EventReceiver
- *;*;*
celery.events.cursesmon.CursesMonitor
- *;*;
celery.events.dumper
- *;*;
- *;*;*
celery.events.EventReceiver
- *;*;*
celery.bin.amqp.AMQPAdmin
celery.bin.beat.BeatCommand
- *;* *;*;
celery.apps.beat.Beat
- *;*;* *;*;*;
celery.beat.Service
- *;*;* *;*;*;
- *;*;*;*
celery.beat.Scheduler
- *;*;*;*