问题
I have a check_orders task that's executed periodically. It makes a group of tasks so that I can time how long executing the tasks took, and perform something when they're all done (this is the purpose of res.join [1] and grouped_subs) The tasks that are grouped are pairs of chained tasks.
What I want is for when the first task doesn't meet a condition (fails) don't execute the second task in the chain. I can't figure this out for the life of me and I feel this is pretty basic functionality for a job queue manager. When I try the things I have commented out after [2] (raising exceptions, removing callbacks)... we get stuck on the join() in check_orders for some reason (it breaks the group). I've tried setting ignore_result to False as well for all these tasks but it still doesn't work.
@task(ignore_result=True)
def check_orders():
# check all the orders and send out appropriate notifications
grouped_subs = []
for thingy in things:
...
grouped_subs.append(chain(is_room_open.subtask((args_sub_1, )),
notify.subtask((args_sub_2, ), immutable=True)))
res = group(grouped_subs).apply_async()
res.join() #[1]
logger.info('Done checking orders at %s' % current_task.request.id))
@task(ignore_result=True)
def is_room_open(args_sub_1):
#something time consuming
if http_req_and_parse(args_sub_1):
# go on and do the notify task
return True
else:
# [2]
# STOP THE CHAIN SOMEHOW! Don't execute the rest of the chain, how?
# None of the following things work:
# is_room_open.update_state(state='FAILURE')
# raise celery.exceptions.Ignore()
# raise Exception('spam', 'eggs')
# current_task.request.callbacks[:] = []
@task(ignore_result=True)
def notify(args_sub_2):
# something else time consuming, only do this if the first part of the chain
# passed a test (the chained tasks before this were 'successful'
notify_user(args_sub_2)
回答1:
In my opinion this is a common use-case that doesn't get enough love in the documentation.
Assuming you want to abort a chain mid-way while still reporting SUCCESS as status of the completed tasks, and not sending any error log or whatnot (else you can just raise an exception) then a way to accomplish this is:
@app.task(bind=True) # Note that we need bind=True for self to work
def task1(self, other_args):
#do_stuff
if end_chain:
self.request.callbacks = None
return
#Other stuff to do if end_chain is False
So in your example:
@app.task(ignore_result=True, bind=True)
def is_room_open(self, args_sub_1):
#something time consuming
if http_req_and_parse(args_sub_1):
# go on and do the notify task
return True
else:
self.request.callbacks = None
Will work. Note that instead of ignore_result=True and subtask() you can use the shortcut .si() as stated by @abbasov-alexander
Edited to work with EAGER mode, as suggested by @PhilipGarnero in the comments.
回答2:
It's unbelievable as a so common case isn't treated in any official documentation. I had to cope with the same issue (but using shared_tasks with bind option, so we have visibility of self object), so I wrote a custom decorator that handles automatically the revocation:
def revoke_chain_authority(a_shared_task):
"""
@see: https://gist.github.com/bloudermilk/2173940
@param a_shared_task: a @shared_task(bind=True) celery function.
@return:
"""
@wraps(a_shared_task)
def inner(self, *args, **kwargs):
try:
return a_shared_task(self, *args, **kwargs)
except RevokeChainRequested, e:
# Drop subsequent tasks in chain (if not EAGER mode)
if self.request.callbacks:
self.request.callbacks[:] = []
return e.return_value
return inner
You can use it as follows:
@shared_task(bind=True)
@revoke_chain_authority
def apply_fetching_decision(self, latitude, longitude):
#...
if condition:
raise RevokeChainRequested(False)
See the full explanation here. Hope it helps!
回答3:
Firstly, it seems if into the function exists exception ignore_result don't help you.
Secondly, you use immutable=True It means that next function (in our case is notify) does not take additional arguments. You should use notify.subtask((args_sub_2, ), immutable=False) of course if it suitable for your decision.
Third, you can use shortcuts:
notify.si(args_sub_2) instead notify.subtask((args_sub_2, ), immutable=True)
and
is_room_open.s(args_sub_1) instead is_room_open.subtask((args_sub_1, ))
Try use it code:
@task def check_orders(): # check all the orders and send out appropriate notifications grouped_subs = [] for thingy in things: ... grouped_subs.append(chain(is_room_open.s(args_sub_1), notify.s(args_sub_2))) res = group(grouped_subs).apply_async() res.join() #[1] logger.info('Done checking orders at %s' % current_task.request.id)) @task def is_room_open(args_sub_1): #something time consuming if http_req_and_parse(args_sub_1): # go on and do the notify task return True else: # [2] # STOP THE CHAIN SOMEHOW! Don't execute the rest of the chain, how? # None of the following things work: # is_room_open.update_state(state='FAILURE') # raise celery.exceptions.Ignore() # raise Exception('spam', 'eggs') # current_task.request.callbacks[:] = [] return False @task def notify(result, args_sub_2): if result: # something else time consuming, only do this if the first part of the chain # passed a test (the chained tasks before this were 'successful' notify_user(args_sub_2) return True return False
If you want catch exceptions you must use callback as so
is_room_open.s(args_sub_1, link_error=log_error.s())
from proj.celery import celery @celery.task def log_error(task_id): result = celery.AsyncResult(task_id) result.get(propagate=False) # make sure result written. with open(os.path.join('/var/errors', task_id), 'a') as fh: fh.write('--\n\n%s %s %s' % ( task_id, result.result, result.traceback))
来源：https://stackoverflow.com/questions/17461374/celery-stop-execution-of-a-chain