How do I run parallel tasks with Celery?

Question

I am using Celery to run some tasks that take a long time to complete. There is an initial task that needs to complete before two sub-tasks can run. The tasks that I created are file system operations and don't return a result.

I would like the subtasks to run at the same time, but when I use a group for these tasks they run sequentially and not in parallel.

I have tried:

g = group([secondary_task(), secondary_tasks2()])
chain(initial_task(),g)

I've also tried running the group directly in the first task, but that doesn't seem to work either.

Is what I'm trying to accomplish doable with Celery?

    First Task
/                \
Second Task      Third Task

Not:

First Task
     |
Second Task
     | 
Third Task

Answer 1

The chain is definitely the right approach.

I would expect this to work: chain(initial_task.s(), g)()

Do you have more than one celery worker running to be able to run more than one task at the same time?