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.
- 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