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

Please have a look here, had the same issue in Django. http://stackoverflow.com/a/27303834/573034 — Paolo, Dec 09 '14 at 13:55
This is absolutely crazy. I am debugging some problems for two weeks and only few minutes ago I realised it was scheduler running twice! And Google directed me immediately here. — Pygmalion, Oct 18 '19 at 06:29

score 85 · Answer 1 · edited May 23 '17 at 12:17

85

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.

edited May 23 '17 at 12:17

Community

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answered Mar 19 '13 at 04:38

Kenny Winker

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Excellent, just the answer I needed inbound from Google. OP should accept. – DeaconDesperado Mar 21 '13 at 14:16
This answer worked for me too and is the right answer factually. Could you please accept this? – stuxnetting Feb 12 '14 at 15:40
is there no way to catch the restart signal/event. Its very bad to lose this feature only for using a scheduling lib. – Tim Schwalbe Mar 10 '20 at 15:16
https://stackoverflow.com/a/25519547/8608146 is better, no need to compromise on reloading. – Phani Rithvij Dec 14 '20 at 06:47

score 54 · Answer 2 · answered Aug 27 '14 at 05:29

54

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 Aug 27 '14 at 05:29

char101

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Yes, this helps. I tried out a lot of options, including flocked file without succeeding. – Dat TT Feb 25 '18 at 04:30
This does not work for me, because `app.debug` returns `False` even when Flask is in debug mode, i.e. `app.run(host='0.'0.0.0', port=80, debug=True)` – Pygmalion Oct 19 '19 at 06:46
It seems that the problem is that `app.run` should be the last command, and before you run `app.run` you cannot know the state of Flask. – Pygmalion Oct 19 '19 at 06:57
How would this work in django? – Llewellyn Hattingh Sep 08 '20 at 14:48
1

@Pygmalion have a config variable `MY_DEBUG=True` somewhere and use it in both places i.e. `app.run(debug=MY_DEBUG)` and `if not MY_DEBUG or ...` Also there's this [comment](https://stackoverflow.com/questions/9449101/how-to-stop-flask-from-initialising-twice-in-debug-mode#comment109713142_9476701) – Phani Rithvij Dec 14 '20 at 06:46
2

You can set `DEBUG = True` as a Config object. In this case the `app` object knows the status before `app.run()` Worked for me like a charm. – Michael Mar 21 '21 at 19:38
Can totally agree with @MichaelLossagk . So far no complications for me at all – roronoa Mar 27 '21 at 08:37
make sure that you run the flask app in debug mode. You can temporarily enable this by running this command `export FLASK_DEBUG=1`. This is applicable for your current terminal only. – roronoa Mar 29 '21 at 07:33

tuomastik · Answer 3 · 2018-09-05T05:41:52.330

19

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.

edited Sep 05 '18 at 05:41

answered Jul 21 '16 at 10:11

tuomastik

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You can use this solution along with https://networklore.com/start-task-with-flask/ to have the before_first_requested triggered with starting the server – makkasi Sep 18 '19 at 11:36
1

This is the best answer – laimison May 05 '22 at 16:25
Unfortunately the decorator before_first_request has been deprecated :( – Alex Apr 26 '23 at 17:05

score -2 · Answer 4 · edited Feb 15 '13 at 02:27

-2

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

edited Feb 15 '13 at 02:27

Sean Vieira

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answered Feb 14 '13 at 13:37

Beka Tomashvili

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score -3 · Accepted Answer · answered Feb 14 '13 at 13:16

-3

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 Feb 14 '13 at 13:16

Beka Tomashvili

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Maybe this solves your problem but your question is completely unrelated to this answer – Sepehr GH Jan 19 '22 at 07:21

apscheduler in Flask executes twice

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