Chains

Sometimes you want to run tasks sequentially. For that you can use the async_chain() function:

# async a chain of tasks
from django_q.tasks import async_chain, result_group

# the chain must be in the format
# [(func,(args),{kwargs}),(func,(args),{kwargs}),..]
group_id = async_chain([('math.copysign', (1, -1)),
                          ('math.floor', (1,))])

# get group result
result_group(group_id, count=2)

A slightly more convenient way is to use a Chain instance:

# Chain async
from django_q.tasks import Chain

# create a chain that uses the cache backend
chain = Chain(cached=True)

# add some tasks
chain.append('math.copysign', 1, -1)
chain.append('math.floor', 1)

# run it
chain.run()

print(chain.result())

[-1.0, 1]

Reference

async_chain(chain, group=None, cached=Conf.CACHED, sync=Conf.SYNC, broker=None)

Async a chain of tasks. See also the Chain class.

Parameters

  • chain (list) – a list of tasks in the format [(func,(args),{kwargs}), (func,(args),{kwargs})]

  • group (str) – an optional group name.

  • cached (bool) – run this against the cache backend

  • sync (bool) – execute this inline instead of asynchronous

class Chain(chain=None, group=None, cached=Conf.CACHED, sync=Conf.SYNC)

A sequential chain of tasks. Acts as a convenient wrapper for async_chain() You can pass the task chain at construction or you can append individual tasks before running them.

param list chain

a list of task in the format [(func,(args),{kwargs}), (func,(args),{kwargs})]

param str group

an optional group name.

param bool cached

run this against the cache backend

param bool sync

execute this inline instead of asynchronous

append(func, *args, **kwargs)

Append a task to the chain. Takes the same arguments as async_task()

return

the current number of tasks in the chain

rtype

int

run()

Start queueing the chain to the worker cluster.

return

the chains group id

result(wait=0)

return the full list of results from the chain when it finishes. Blocks until timeout or result.

param int wait

how many milliseconds to wait for a result

return

an unsorted list of results

fetch(failures=True, wait=0)

get the task result objects from the chain when it finishes. Blocks until timeout or result.

param failures

include failed tasks

param int wait

how many milliseconds to wait for a result

return

an unsorted list of task objects

current()

get the index of the currently executing chain element

return int

current chain index

length()

get the length of the chain

return int

length of the chain