Exploration of Celery Issue #1671

chain_runner.py

from celerydemo.chain_tasks import a, b, c
from celery import *

## BASE CASE
a.apply_async()
b.apply_async()
c.apply_async()

## BASE CHAIN CASE
chain(a.si())()
chain(a.si(), a.si())()

## BASE GROUP CASE
group(a.si(), b.si())()

## chain -> group nesting
chain(group(a.si(),b.si()))()
chain(group(a.si(),b.si()), group(c.si()))()

## chain -> (group -> chain), group
## EXPECTED (A, B, C, C) or (A, C, B, C)
## GOT A, C, B, C
chain(group(chain(a.si(),b.si()), c.si()), group(c.si()))()


## chain -> (group -> (chain -> group -> (task, task), task), group -> task), task
## *->*->*->*->.  .->. 
## \  \     \->. /
##  \  \->*->.  /
##   \---------/
## EXPECTED (A, B, C, C, C) or (A, C, B, C, C)
## GOT A, B, C
## BROKEN CASE SEE:https://github.com/celery/celery/issues/1671 
chain( group( chain( group( a.si(),b.si())), c.si()), group( c.si()), c.si())()

## group -> (chain, chain)
## EXPECTED A, B, A, B or A, A, B, B
## GOT A, A, B, B AND A, B, A, B 
group(chain(a.si(), b.si()), chain(a.si(), b.si()))()

## group -> (chain -> (group), chain -> (group))
## EXPECTED 
### A, A, B, B, C, C
### A, B, A, B, C, C
### B, B, A, A, C, C
### B, A, B, A, C, C
### B, A, A, B, C, C
### A, A, B, C, B, C
### A, B, A, C, B, C
### A, B, B, C, A, C
### B, A, A, C, B, C
### A, B, C, A, B, C
### A, B, C, B, A, C
### B, A, C, A, B, C
### B, A, C, B, A, C
group(chain(group(a.si(), b.si()), c.si()), chain(group(a.si(), b.si()), c.si()))()

## group -> chain -> (group, chain)
##  EXPECTED
### A, B, A, B
### B, A, A, B
group(chain(group(a.si(), b.si()), chain(a.si(), b.si())))()

## group -> (chain -> (group, chain), task)
##  EXPECTED
### C, A, B, A, B
### C, B, A, A, B
### A, C, B, A, B
### B, C, A, A, B
### A, B, C, A, B
### B, A, C, A, B
### A, B, A, C, B
### B, A, A, C, B
### A, B, A, B, C
### B, A, A, B, C
group(chain(group(a.si(), b.si()), chain(a.si(), b.si())), c.si())()

chain_tasks.py

from celeryconfig import app
from celery import chord, group, chain

# Test Basic Chain functionality

@app.task
def a():
    print 'A'

@app.task
def b():
    print 'B'

@app.task
def c():
    print 'C'