If there is a callback that is triggered every 1 second with the Interval component, but the callback function has an execution time of say 5 seconds, will dash app choke and get stuck? I want to understand what could be happening in the background in this case. layout = html.Div(children = [ html…

working sample code import time import dash import dash_core_components as dcc import dash_html_components as html from dash.dependencies import Input, Output app = dash.Dash(__name__) app.layout = html.Div( [ html.P(id="update_p"), dcc.Interval(id="refresh", interval=1 * 100…

@byronz thanks so much for the input!

Hi, I am using your code to see how dash.Interval really works. I can see that the calls from Interval component are queued up like you showed in the gif, but the layout is not updated with n_intervals number. However, if I reduce the sleep time to 0.5 seconds in which case the interval time (1s) is…

I’m having the same issue, where I’m triggering a callback once per second, but they seem to be piling up in the browser and eventually crashing the app. Two questions: how can I effectively delay the start of the interval callback until the page that finished its initial load of the layout (most …

I guess the simplest approach would be to create an is-running flag serverside (in a file, a memory cache, anything). You then set it to true before starting the task and false afterwards. And before starting the task, you check if it’s already running; if it is, raise a PreventUpdate exception.

That general approach sounds reasonable, but wouldn’t I want that state flag to exist on the client side, not the server side? The pile-up seems to be happening on the client. If so, does dash have some easy built-in mechanism for writing/reading a session variable that would enable this?

If your callback is clientside, the flag should reside clientside. If your callback is serverside (i.e. normal callbacks written in python), the flag should be serverside (unless you make a callback chain with a client-side flag; that’s also an option). There have been some changes to the callback l…

Hi @Emil , I have a similar situation where I have a 4 second interval triggering a callback that generally takes 2 seconds but sometimes because of network latency the requests get piled up. I understand the simplest approach is to “create an is-running flag serverside”. I’ve been trying to think/im…

I think it would be much simpler with a server side flag. Alternatively you could check out this thread, [image] Preventing Wasteful Parallel Callbacks When Running Multiple Processes and Caching Dash Python Looks like the issue is the default start method on MacOS change…

Agree, it would be simpler, but how can that be done? Currently, I have a 4 second interval that is an input to trigger the callback, but if intervals pile up then they will also trigger the callback even if the prior interval call back is still running. I can add an is_running_flag in the callback …

1 sec refresh Interval for a 5 sec task

Dash Python

Emil March 17, 2021, 6:15pm 10

I think it would be much simpler with a server side flag. Alternatively you could check out this thread,

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1 sec refresh Interval for a 5 sec task

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