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