python - Celery, run task once at a specified time

Question

How can I run a celery task at a given time, but only once?

I read the documentation and couldn't find any example of this.

Answer 1

You can use parameter eta when calling the task. Example:

from datetime import datetime, timedelta

@app.task()
def hello(self):
    return 'hello world'


tomorrow = datetime.utcnow() + timedelta(days=1)
hello.apply_async(eta=tomorrow)

Documentation: http://docs.celeryproject.org/en/latest/userguide/calling.html#eta-and-countdown

Alternatively, when you want to call hello multiple times and to be sure it is executed only one at the time, you can use locking - more about it in the documentation: http://docs.celeryproject.org/en/latest/tutorials/task-cookbook.html#ensuring-a-task-is-only-executed-one-at-a-time