Tasks

Async

Use async() from your code to quickly offload tasks to the Cluster:

from django_q import async, result

# create the task
async('math.copysign', 2, -2)

# or with import and storing the id
import math.copysign

task_id = async(copysign, 2, -2)

# get the result
task_result = result(task_id)

# result returns None if the task has not been executed yet
# so in most cases you will want to use a hook:

async('math.modf', 2.5, hook='hooks.print_result')

# hooks.py
def print_result(task):
    print(task.result)

async() can take the following optional keyword arguments:

hook

The function to call after the task has been executed. This function gets passed the complete Task object as its argument.

group

A group label. Check Groups for group functions.

save

Overrides the result backend’s save setting for this task.

timeout

Overrides the cluster’s timeout setting for this task.

sync

Simulates a task execution synchronously. Useful for testing.

redis

A redis connection. In case you want to control your own connections.

q_options

None of the option keywords get passed on to the task function. As an alternative you can also put them in a single keyword dict named q_options. This enables you to use these keywords for your function call:

# Async options in a dict

opts = {'hook': 'hooks.print_result',
        'group': 'math',
        'timeout': 30}

async('math.modf', 2.5, q_options=opts)

Please not that this will override any other option keywords.

Groups

You can group together results by passing async() the optional group keyword:

# result group example
from django_q import async, result_group

for i in range(4):
    async('math.modf', i, group='modf')

# after the tasks have finished you can get the group results
result = result_group('modf')
print(result)
[(0.0, 0.0), (0.0, 1.0), (0.0, 2.0), (0.0, 3.0)]

Take care to not limit your results database too much and call delete_group() before each run, unless you want your results to keep adding up. Instead of result_group() you can also use fetch_group() to return a queryset of Task objects.:

# fetch group example
from django_q import fetch_group, count_group, result_group

# count the number of failures
failure_count = count_group('modf', failures=True)

# only use the successes
results = fetch_group('modf')
if failure_count:
    results = results.exclude(success=False)
results =  [task.result for task in successes]

# this is the same as
results = fetch_group('modf', failures=False)
results =  [task.result for task in successes]

# and the same as
results = result_group('modf') # filters failures by default

Getting results by using result_group() is of course much faster than using fetch_group(), but it doesn’t offer the benefits of Django’s queryset functions.

Note

Although fetch_group() returns a queryset, due to the nature of the PickleField , calling Queryset.values on it will return a list of encoded results. Use list comprehension or an iterator instead.

Synchronous testing

async() can be instructed to execute a task immediately by setting the optional keyword sync=True. The task will then be injected straight into a worker and the result saved by a monitor instance:

from django_q import async, fetch

# create a synchronous task
task_id = async('my.buggy.code', sync=True)

# the task will then be available immediately
task = fetch(task_id)

# and can be examined
if not task.success:
    print('An error occurred: {}'.format(task.result))
An error occurred: ImportError("No module named 'my'",)

Note that async() will block until the task is executed and saved. This feature bypasses the Redis server and is intended for debugging and development.

Connection pooling

Django Q tries to pass redis connections around its parts as much as possible to save you from running out of connections. When you are making individual calls to async() a lot though, it can help to set up a redis connection to reuse for async():

# redis connection economy example
from django_q import async
from django_q.conf import redis_client

for i in range(50):
    async('math.modf', 2.5, redis=redis_client)

Tip

If you are using django-redis , you can configure Django Q to use its connection pool.

Reference

async(func, *args, hook=None, group=None, timeout=None, save=None, sync=False, redis=None, q_options=None, **kwargs)
Puts a task in the cluster queue
Parameters:
  • func (object) – The task function to execute
  • args (tuple) – The arguments for the task function
  • hook (object) – Optional function to call after execution
  • group (str) – An optional group identifier
  • timeout (int) – Overrides global cluster timeout.
  • save (bool) – Overrides global save setting for this task.
  • sync (bool) – If set to True, async will simulate a task execution
  • redis – Optional redis connection
  • q_options (dict) – Options dict, overrides option keywords
  • kwargs (dict) – Keyword arguments for the task function
Returns:

The uuid of the task

Return type:

str

result(task_id)

Gets the result of a previously executed task

Parameters:task_id (str) – the uuid or name of the task
Returns:The result of the executed task
fetch(task_id)

Returns a previously executed task

Parameters:name (str) – the uuid or name of the task
Returns:The task if any
Return type:Task

Changed in version 0.2.0.

Renamed from get_task

result_group(group_id, failures=False)

Returns the results of a task group

Parameters:
  • group_id (str) – the group identifier
  • failures (bool) – set this to True to include failed results
Returns:

a list of results

Return type:

list

fetch_group(group_id, failures=True)

Returns a list of tasks in a group

Parameters:
  • group_id (str) – the group identifier
  • failures (bool) – set this to False to exclude failed tasks
Returns:

a list of Tasks

Return type:

list

count_group(group_id, failures=False)

Counts the number of task results in a group.

Parameters:
  • group_id (str) – the group identifier
  • failures (bool) – counts the number of failures if True
Returns:

the number of tasks or failures in a group

Return type:

int

delete_group(group_id, tasks=False)

Deletes a group label from the database.

Parameters:
  • group_id (str) – the group identifier
  • tasks (bool) – also deletes the associated tasks if True
Returns:

the numbers of tasks affected

Return type:

int

class Task

Database model describing an executed task

id

An uuid.uuid4() identifier

name

The name of the task as a humanized version of the id

Note

This is for convenience and can be used as a parameter for most functions that take a task_id. Keep in mind that it is not guaranteed to be unique if you store very large amounts of tasks in the database.

func

The function or reference that was executed

hook

The function to call after execution.

args

Positional arguments for the function.

kwargs

Keyword arguments for the function.

result

The result object. Contains the error if any occur.

started

The moment the task was created by an async command

stopped

The moment a worker finished this task

success

Was the task executed without problems?

time_taken()

Calculates the difference in seconds between started and stopped.

Note

Time taken represents the time a task spends in the cluster, this includes any time it may have waited in the queue.

classmethod get_result(task_id)

Gets a result directly by task uuid or name.

classmethod get_result_group(group_id, failures=False)

Returns a list of results from a task group. Set failures to True to include failed results.

classmethod get_task(task_id)

Fetches a single task object by uuid or name.

classmethod get_task_group(group_id, failures=True)

Gets a queryset of tasks with this group id. Set failures to False to exclude failed tasks.

classmethod get_group_count(group_id, failures=False)

Returns a count of the number of tasks results in a group. Returns the number of failures when failures=True

classmethod delete_group(group_id, objects=False)

Deletes a group label only, by default. If objects=True it will also delete the tasks in this group from the database.

class Success

A proxy model of Task with the queryset filtered on Task.success is True.

class Failure

A proxy model of Task with the queryset filtered on Task.success is False.