result.get hangs if result backend not set

[anuraguniyal]

Original problem:
I have two different django projects say projA and projB, each have its own celery daemon running on separate queues but same vhost, projA have a task taskA and projB have a task taskB, I try to run taskB from inside taskA e.g.

@task(routing_key='taskA')
def taskA(event_id):
    # do some work , then call taskB and wait for result
    result = send_task('taskB',routing_key='taskB')
    res = result.get(timeout=20)

I can see in logs of projB that taskB finished within a second, but taskA keeps on waiting for result and times out after 20 seconds

For backend I have rabbitmq.

Solution:
Setting the result back-end fixes the problem

CELERY_RESULT_BACKEND = "amqp"
CELERY_AMQP_TASK_RESULT_EXPIRES = 1000 

IMO if result back-end is not set result.get should throw error or at-least log a warning

[ask]

Are you not using 2.3? This is the expected behaviour there:

>>> add.delay(2, 2).get()
Traceback (most recent call last):
    File "<stdin>", line 1, in <module>
    File "/opt/devel/celery/celery/result.py", line 83, in get
        interval=interval)
    File "/opt/devel/celery/celery/backends/base.py", line 369, in _is_disabled
      raise NotImplementedError("No result backend configured.  "
NotImplementedError: No result backend configured.  Please see the documentation for more information.

[ask]

Btw, you should not wait for tasks inside a task, see the Task user guide for information.

[anuraguniyal]

yes I have read that, but sometime asynchronous callbacks makes simple tasks really complex

I am using 2.2.6