Django Celery tasks queue

Question

I have an application made it with django using redis and celery for some asynchronous tasks. I am using the celery tasks to execute some stored procedures. This SP take from 5 mins to 30 mins to execute completely(depending in amount of records). Everything works great. But I need the be able to execute the tasks several times. but right now when I run task and another user run the task too, the two tasks are executed at the same time. I need the task enter in queue and only executed when the first task finish. My settings.py:

BROKER_URL = 'redis://localhost:6379/0'
CELERY_IMPORTS = ("pc.tasks", )
CELERY_ACCEPT_CONTENT = ['json']
CELERY_TASK_SERIALIZER = 'json'
CELERY_RESULT_SERIALIZER = 'json'
CELERY_RESULT_BACKEND='djcelery.backends.cache:CacheBackend'

tasks.py

from __future__ import absolute_import
from celery.decorators import task
from celery import task, shared_task
from .models import Servicio, Proveedor, Lectura_FTP, Actualizar_Descarga
from .models import Lista_Archivos, Lista_Final, Buscar_Conci

@task
def carga_ftp():
    tabla = Proc_Carga()
    sp = tabla.carga()
    return None

@task
def conci(idprov,pfecha):
    conci = Buscar_Conci()
    spconc = conci.buscarcon(idprov,pfecha)

I call the tasks in my view in this way:

conci.delay(prov,DateV);

How can I create or setup a queue list of taks and everry tasks is executed only when the previous taks is finished

Thanks in advance

Answer 1

您可以限制工作人员的任务，由于您的原因，我认为您一次只需要一名工作人员，因此在致电djcelery时只需启动一名工作人员即可。

python manage.py celery worker -B --concurrency=1

Answer 2

You can use lock, for example (from one of my projects):

def send_queued_emails(*args, **kwargs):
  from mailer.models import Message
  my_lock = redis.Redis().lock("send_mail")

  try:
    have_lock = my_lock.acquire(blocking=False)
    if have_lock:
        logging.info("send_mail lock ACQUIRED")
        from celery import group

        if Message.objects.non_deferred().all().count() > 0:
            t = EmailSenderTask()
            g = (group(t.s(message=msg) for msg in Message.objects.non_deferred().all()[:200]) | release_redis_lock.s(lock_name="send_mail"))
            g()
        else:
            logging.info("send_mail lock RELEASED")
            my_lock.release()
    else:
        logging.info("send_mail lock NOT ACQUIRED")

  except redis.ResponseError as e:
        logging.error("Redis throw exception : {}".format(e))
  except:
    my_lock.release()
    logging.error("send_mail lock RELEASED because of exception")