Celery - Only one instance per task/process?

Question

In the celery docs, section Instantiation (http://celery.readthedocs.org/en/latest/userguide/tasks.html#custom-task-classes) the following is stated:

A task is not instantiated for every request, but is registered in the task registry as a global instance.

This means that the init constructor will only be called once per process, and that the task class is semantically closer to an Actor.

Nevertheless, when I run the following example I see that the init method is called at least 3 times. What is wrong in the setup? The CELERYD_CONCURRENCY = 1 should make sure that there is only one process per worker, right?

$ celery -A proj beat

celery beat v3.1.17 (Cipater) is starting.
init Task1
40878160
x=1.0
init Task1
40878352
x=1.0
init Task1
40879312
x=1.0
__    -    ... __   -        _
Configuration ->
    . broker -> amqp://guest:**@localhost:5672//
    . loader -> celery.loaders.app.AppLoader
    . scheduler -> celery.beat.PersistentScheduler
    . db -> celerybeat-schedule
    . logfile -> [stderr]@%INFO
    . maxinterval -> now (0s)
[2015-02-05 23:05:21,875: INFO/MainProcess] beat: Starting...
[2015-02-05 23:05:21,971: INFO/MainProcess] Scheduler: Sending due task    task1-every-5-seconds (proj.tasks.t1)
[2015-02-05 23:05:26,972: INFO/MainProcess] Scheduler: Sending due task task1-every-5-seconds (proj.tasks.t1)

celery.py:

from __future__ import absolute_import
from datetime import timedelta
from celery import Celery

app = Celery('proj',
             broker='amqp://guest@localhost//',
             backend='amqp://',
             include=['proj.tasks'])
app.conf.update(
    CELERY_REDIRECT_STDOUTS=True,
    CELERY_TASK_RESULT_EXPIRES=60,
    CELERYD_CONCURRENCY = 1,
    CELERYBEAT_SCHEDULE = {
        'task1-every-5-seconds': {
            'task': 'proj.tasks.t1',
            'schedule': timedelta(seconds=5)
            },
        },
    CELERY_TIMEZONE = 'GMT',
)

if __name__ == '__main__':
    app.start()

tasks.py:

from __future__ import absolute_import
from proj.celery import app
from celery import Task
import time

class Foo():
    def __init__(self, x):
        self.x = x

class Task1(Task):
    abstract = True
    def __init__(self):
        print "init Task1"
        print id(self)
        self.f = Foo(1.0)
        print "x=1.0"

@app.task(base=Task1)
def t1():
    t1.f.x +=1
    print t1.f.x

Answer 1

So, as per your comment, you need to maintain one connection per thread.

Why not to use a thread storage then? It should be a safe solution in your case.

from threading import local

thread_storage = local()

def get_or_create_conntection(*args, **kwargs):
    if not hasattr(thread_storage, 'connection'):
        thread_storage.connection = Connection(*args, **kwargs)
    return thread_storage.connection

@app.task()
def do_stuff():
    connection = get_or_create_connection('some', connection='args')
    connection.ping()