Flask-SocketIO connection gets interrupted when code execution takes too long

Question

Hi my conversion finished stops arriving on the client side once the code execution takes too long.

This works:

@socketio.on('nifti_conversion')
def handle_message(message):
    elehelper.send_status({'code': 201, 'message':'conversion started!'})
    sleep(5)
    elehelper.send_status({'code': 202, 'message':'conversion finished!'})

while the following fails:

@socketio.on('nifti_conversion')
def handle_message(message):
    elehelper.send_status({'code': 201, 'message':'conversion started!'})
    sleep(120)
    elehelper.send_status({'code': 202, 'message':'conversion finished!'})

also note that this works:

@socketio.on('nifti_conversion')
def handle_message(message):
    elehelper.send_status({'code': 201, 'message':'conversion started!'})
    socketio.sleep(120)
    elehelper.send_status({'code': 202, 'message':'conversion finished!'})

First I expected some kind of timeout but the disconnect happened after varying times..so far I observed 90, 94, 100, 104 seconds.

On the client side the console looks like following.

Working 5 seconds case:

Failing 120 seconds case:

score 3 · Accepted Answer · answered Mar 06 '18 at 23:25

There is ping_timeout parameter for SocketIO that has default value 60 seconds. You can play with it to adjust wait time.

However for executing any long operations, it is recommended not to block current thread since it is blocking next requests.

Consider any of next approaches for your implementation:

Async execution using threads or separate processes https://docs.python.org/3/library/concurrent.futures.html
Celery based background tasks http://flask.pocoo.org/docs/0.12/patterns/celery
Asyncio's coroutine http://flask-aiohttp.readthedocs.io/en/latest/coroutine.html

Thank you this is extremely helpful. On what parameters should I base my choice for one of the three suggested approaches? My application has only one client and is served on localhost so it would be acceptable if the thread is blocked as there are no further requests, but still it would be good to learn about these async approaches. — florian, Mar 07 '18 at 07:15

Flask-SocketIO connection gets interrupted when code execution takes too long

1 Answers1