[BUG] Long callback function executed without being triggered

[keurfonluu]

Describe your context
Please provide us your environment, so we can easily reproduce the issue.

dash                      2.3.0
dash-bootstrap-components 1.0.3
dash-core-components      2.0.0
dash-html-components      2.0.0
dash-table                5.0.0
dash-vtk                  0.0.9

Describe the bug

I have a rather complex app where the layout content is generated by a callback (single page app). For one specific layout content, I need a long callback because one callback function takes some time to execute. The problem is that, somehow, right after the layout is generated, the long callback is triggered automatically (even when using prevent_initial_call). No problem if I use a standard callback, though.

Please find below a sample script to reproduce this issue based on the long callback example in the documentation. I also defined a validation_layout as recommended by the documentation.

import dash
from dash import html
from dash.long_callback import DiskcacheLongCallbackManager
from dash.dependencies import Input, Output

import diskcache
cache = diskcache.Cache("./cache")
long_callback_manager = DiskcacheLongCallbackManager(cache)

app = dash.Dash(
    __name__,
    suppress_callback_exceptions=True,
    long_callback_manager=long_callback_manager,
)

layout1 = html.Div(
    [
        html.Button("Generate layout", id="button_1"),
        html.Div(id="main"),
    ],
)
layout2 = html.Div(
    [
        html.Div([html.P(id="paragraph_id", children=["Button not clicked"])]),
        html.Button(id="button_id", children="Run Job!"),
    ]
)

app.layout = layout1
app.validation_layout = html.Div([layout1, layout2])

@app.callback(
    Output("main", "children"),
    Input("button_1", "n_clicks"),
    prevent_initial_call=True,
)
def generate_layout(n_clicks):
    return layout2

@app.long_callback(
    Output("paragraph_id", "children"),
    Input("button_id", "n_clicks"),
    prevent_initial_call=True,
)
def callback(n_clicks):
    return [f"Clicked {n_clicks} times"]

if __name__ == "__main__":
    app.run_server(debug=True)

Execute the app, click on "Generate layout", wait a few seconds, "paragraph_id" children will automatically change to "Clicked None times".

Expected behavior

The long callback not to be triggered after the new layout is generated. For the example above, the children property of the component "paragraph_id" to be updated only when the button is clicked.

[celia-lm]

I'm posting this here since it provides more information about why it might be happening:
https://community.plotly.com/t/long-callback-interval-1-problems/60819/4

[TheBubblePopped]

+1

[gvwilson]

Hi - we are tidying up stale issues and PRs in Plotly's public repositories so that we can focus on things that are most important to our community. If this issue is still a concern, please add a comment letting us know what recent version of our software you've checked it with so that I can reopen it and add it to our backlog. (Please note that we will give priority to reports that include a short reproducible example.) If you'd like to submit a PR, we'd be happy to prioritize a review, and if it's a request for tech support, please post in our community forum. Thank you - @gvwilson