apscheduler in Flask executes twice

Question

I have problem when i am using apscheduler in my flask application.

In my view.py file i am writing like this

import time
from apscheduler.scheduler import Scheduler

def test_scheduler():
     print "TEST"
     print time.time()


sched = Scheduler()
sched.add_interval_job(test_scheduler, seconds=5)
sched.start()

And then this method test_scheduler() executes twice in every five second

TEST
1360844314.01
TEST
1360844314.2

Asked By: Beka Tomashvili

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Source

Answer 1

I’ve made it, I added in add_interval_job parameter to start after a certain time point

sched.add_interval_job(test_scheduler, seconds=5, start_date='2013-02-13 00:00')

Answered By: Beka Tomashvili

Answer 2

the best solution is to use add_cron_job('*') instead of add_interval_job('*')

Answered By: Beka Tomashvili

Answer 3

In debug mode, Flask’s reloader will load the flask app twice (How to stop Flask from initialising twice in Debug Mode?). I’m not sure why this is, but it causes apscheduler’s jobs to be scheduled twice. A quick print "loaded scheduler" right before sched.start() confirms this.

There are a couple ways around this, as mentioned in the linked answer. The one I found that worked best is just to disable the reloader like so:

app.run(use_reloader=False)

It means I have to reload my app manually as I develop it, but it’s a small price to pay to get apscheduler working.

Answered By: Kenny Winker

Answer 4

When using the reloader, there are the master and child processes. Your scheduler thread runs in both. You need to prevent the scheduler from running in the master process

if not app.debug or os.environ.get('WERKZEUG_RUN_MAIN') == 'true':
  sched = Scheduler()
  sched.add_interval_job(test_scheduler, seconds=5)
  sched.start()

Answered By: char101

Answer 5

You can start the scheduler in Flask’s before_first_request() decorator, which “registers a function to be run before the first request to this instance of the application“.

import time
import atexit

from apscheduler.schedulers.background import BackgroundScheduler


def print_date_time():
    print(time.strftime("%A, %d. %B %Y %I:%M:%S %p"))


@app.before_first_request
def init_scheduler():
    scheduler = BackgroundScheduler()
    scheduler.add_job(func=print_date_time, trigger="interval", seconds=3)
    scheduler.start()
    # Shut down the scheduler when exiting the app
    atexit.register(lambda: scheduler.shutdown())

Note that before_first_request() will always be called again with the first request after server reload.

Answered By: tuomastik

apscheduler in Flask executes twice

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