This document describes Celery 2.4. For development docs, go here.
Signals¶
Signals allows decoupled applications to receive notifications when certain actions occur elsewhere in the application.
Celery ships with many signals that you application can hook into to augment behavior of certain actions.
Basics¶
Several kinds of events trigger signals, you can connect to these signals to perform actions as they trigger.
Example connecting to the task_sent
signal:
from celery.signals import task_sent
def task_sent_handler(sender=None, task_id=None, task=None, args=None,
kwargs=None, \*\*kwds):
print("Got signal task_sent for task id %s" % (task_id, ))
task_sent.connect(task_sent_handler)
Some signals also have a sender which you can filter by. For example the
task_sent
signal uses the task name as a sender, so you can
connect your handler to be called only when tasks with name “tasks.add”
has been sent by providing the sender argument to
connect
:
task_sent.connect(task_sent_handler, sender="tasks.add")
Signals¶
Task Signals¶
task_sent¶
Dispatched when a task has been sent to the broker. Note that this is executed in the client process, the one sending the task, not in the worker.
Sender is the name of the task being sent.
Provides arguments:
- task_id
Id of the task to be executed.
- task
The task being executed.
- args
the tasks positional arguments.
- kwargs
The tasks keyword arguments.
- eta
The time to execute the task.
- taskset
Id of the taskset this task is part of (if any).
task_prerun¶
Dispatched before a task is executed.
Sender is the task class being executed.
Provides arguments:
- task_id
Id of the task to be executed.
- task
The task being executed.
- args
the tasks positional arguments.
- kwargs
The tasks keyword arguments.
task_postrun¶
Dispatched after a task has been executed.
Sender is the task class executed.
Provides arguments:
- task_id
Id of the task to be executed.
- task
The task being executed.
- args
The tasks positional arguments.
- kwargs
The tasks keyword arguments.
- retval
The return value of the task.
task_failure¶
Dispatched when a task fails.
Sender is the task class executed.
Provides arguments:
- task_id
Id of the task.
- exception
Exception instance raised.
- args
Positional arguments the task was called with.
- kwargs
Keyword arguments the task was called with.
- traceback
Stack trace object.
- einfo
The
celery.datastructures.ExceptionInfo
instance.
Worker Signals¶
worker_init¶
Dispatched before the worker is started.
worker_ready¶
Dispatched when the worker is ready to accept work.
worker_process_init¶
Dispatched by each new pool worker process when it starts.
worker_shutdown¶
Dispatched when the worker is about to shut down.
Celerybeat Signals¶
beat_init¶
Dispatched when celerybeat starts (either standalone or embedded).
Sender is the celery.beat.Service
instance.
beat_embedded_init¶
Dispatched in addition to the beat_init
signal when celerybeat is
started as an embedded process. Sender is the
celery.beat.Service
instance.
Eventlet Signals¶
eventlet_pool_started¶
Sent when the eventlet pool has been started.
Sender is the celery.concurrency.eventlet.TaskPool
instance.
eventlet_pool_preshutdown¶
Sent when the worker shutdown, just before the eventlet pool is requested to wait for remaining workers.
Sender is the celery.concurrency.eventlet.TaskPool
instance.
eventlet_pool_postshutdown¶
Sent when the pool has been joined and the worker is ready to shutdown.
Sender is the celery.concurrency.eventlet.TaskPool
instance.
eventlet_pool_apply¶
Sent whenever a task is applied to the pool.
Sender is the celery.concurrency.eventlet.TaskPool
instance.
Provides arguments:
target
The target function.
args
Positional arguments.
kwargs
Keyword arguments.
Logging Signals¶
setup_logging¶
Celery won’t configure the loggers if this signal is connected, so you can use this to completely override the logging configuration with your own.
If you would like to augment the logging configuration setup by
Celery then you can use the after_setup_logger
and
after_setup_task_logger
signals.
Provides arguments:
- loglevel
The level of the logging object.
- logfile
The name of the logfile.
- format
The log format string.
- colorize
Specify if log messages are colored or not.
after_setup_logger¶
Sent after the setup of every global logger (not task loggers). Used to augment logging configuration.
Provides arguments:
- logger
The logger object.
- loglevel
The level of the logging object.
- logfile
The name of the logfile.
- format
The log format string.
- colorize
Specify if log messages are colored or not.
after_setup_task_logger¶
Sent after the setup of every single task logger. Used to augment logging configuration.
Provides arguments:
- logger
The logger object.
- loglevel
The level of the logging object.
- logfile
The name of the logfile.
- format
The log format string.
- colorize
Specify if log messages are colored or not.