How do I schedule an interval job with APScheduler?

Question

I'm trying to schedule an interval job with APScheduler (v3.0.0).

I've tried:

from apscheduler.schedulers.blocking import BlockingScheduler
sched = BlockingScheduler()

def my_interval_job():
    print 'Hello World!'
sched.add_job(my_interval_job, 'interval', seconds=5)
sched.start()

and

from apscheduler.schedulers.blocking import BlockingScheduler
sched = BlockingScheduler()

@sched.scheduled_job('interval', id='my_job_id', seconds=5)
def my_interval_job():
    print 'Hello World!'
sched.start()

Either should work according to the docs, but the job never fires...

UPDATE:
It turns out there was something else, environment-related, preventing the task from running. This morning, the task is working fine without any modifications to the code from yesterday.

UPDATE 2:
After further testing, I've found that 'interval' jobs seem to be generally flaky... The above code now works in my dev environment, but not when I deploy to a staging env (I'm using a heroku app for staging). I have other apscheduler 'cron' jobs that work just fine in the staging/production envs.

When I turn on DEBUG logging for the "apscheduler.schedulers" logger, the log indicates that the interval job is added:

Added job "my_cron_job1" to job store "default"
Added job "my_cron_job2" to job store "default"
Added job "my_interval_job" to job store "default"
Scheduler started
Adding job tentatively -- it will be properly scheduled when the scheduler starts
Adding job tentatively -- it will be properly scheduled when the scheduler starts
Looking for jobs to run
Next wakeup is due at 2015-03-24 15:05:00-07:00 (in 254.210542 seconds)

How can the next wakeup be due 254 seconds from now when the interval job is set to 5 seconds??

Seibel

Answer 1

You need to keep the thread alive. Here is a example of how I used it.

from subprocess import call

import time
import os
from pytz import utc

from apscheduler.schedulers.background import BackgroundScheduler


def job():
    print("In job")
    call(['python', 'scheduler/main.py'])


if __name__ == '__main__':
    scheduler = BackgroundScheduler()
    scheduler.configure(timezone=utc)
    scheduler.add_job(job, 'interval', seconds=10)
    scheduler.start()
    print('Press Ctrl+{0} to exit'.format('Break' if os.name == 'nt' else 'C'))

    try:
        # This is here to simulate application activity (which keeps the main thread alive).
        while True:
            time.sleep(5)
    except (KeyboardInterrupt, SystemExit):
        # Not strictly necessary if daemonic mode is enabled but should be done if possible
        scheduler.shutdown()

Bharal

Answer 2

I haven't figured out what caused the original issue, but I got around it by swapping the order in which the jobs are scheduled, so that the 'interval' job is scheduled BEFORE the 'cron' jobs.

i.e. I switched from this:

def my_cron_job1():
    print "cron job 1"

def my_cron_job2():
    print "cron job 2"

def my_interval_job():
    print "interval job"

if __name__ == '__main__':
    from apscheduler.schedulers.blocking import BlockingScheduler
    sched = BlockingScheduler(timezone='MST')

    sched.add_job(my_cron_job1, 'cron', id='my_cron_job1', minute=10)
    sched.add_job(my_cron_job2, 'cron', id='my_cron_job2', minute=20)

    sched.add_job(my_interval_job, 'interval', id='my_job_id', seconds=5)

to this:

def my_cron_job1():
    print "cron job 1"

def my_cron_job2():
    print "cron job 2"

def my_interval_job():
    print "interval job"

if __name__ == '__main__':
    from apscheduler.schedulers.blocking import BlockingScheduler
    sched = BlockingScheduler(timezone='MST')

    sched.add_job(my_interval_job, 'interval', id='my_job_id', seconds=5)

    sched.add_job(my_cron_job1, 'cron', id='my_cron_job1', minute=10)
    sched.add_job(my_cron_job2, 'cron', id='my_cron_job2', minute=20)

and now both the cron jobs and the interval jobs run without a problem in both environments.

Seibel

I'd recommend not specifying a timezone like that. I just helped solve a daylight saving time issue where the developer had specified a timezone of EST. Switching to "America/New York" instead fixed the problem. Always prefer locale based time zone names because they're never ambiguous. – Butadiene

Just curious, What is the difference between the 'cron' and 'interval' you specified in the .add_job arguments. – Ponderable

Answer 3

How can the next wakeup be due 254 seconds from now when the interval job is set to 5 seconds??

It's simple: you have many pending executions as your most of the jobs didn't completed in the interval-window of time.

You could use the following parameters in order to sort this out:

 **misfire_grace_time**:    Maximum time in seconds for the job execution to be allowed to delay before it is considered a misfire 
 **coalesce**:  Roll several pending executions of jobs into one

To read more, check the documentation here.

Assentor

Answer 4

The documentation had an error there. I've fixed it now. That first line should be:

from apscheduler.schedulers.blocking import BlockingScheduler

It would've raised an ImportError though, but you didn't mention any. Did you try any of the provided examples?

Cavalryman

I actually did have from apscheduler.schedulers.blocking import BlockingScheduler in my code. I just mis-copied the line into the stackoverflow question. I fixed my original question and added some other updates. – Seibel

Answer 5

Ok, I've looked at the updated question.

The reason you're having problems may be that you could be using the wrong timezone. Your country is currently using daylight saving time in most locations, so the correct timezone would probably be MDT (Mountain Daylight Time). But that will break again when you move back to standard time. So I advise you to use a timezone like "America/Denver". That will take care of the DST switches.

Question: Are you using CentOS? So far it's the only known operating system where automatic detection of the local timezone is impossible.

Cavalryman