Breaking change for chained callbacks in dash>=2.9.0

[celia-lm]

Describe the bug

"Click" button is the Input for two callbacks. When we click it, both should be triggered:

• the first one takes a long time (e.g. 3 seconds), and when it ends, it should update the "stop" button, which triggers the second callback too.
• the second callback returns quickly, it should return a "Progress" notification with the first trigger (when the "click" button triggers it) and a "Complete" notification when the "Stop" button triggers it - after the first callbacks finishes running.
• So these are chained callbacks apart from the "Click" button being an Input for both.
• Bug: we only see the "Progress" notification and after 3 seconds, when the first callbacks finishes running. The second callback is never triggered by the "Stop" button update as a result of the chained callback (we can see this by checking the triggered ids).

Screen.Recording.2024-02-21.at.17.28.05.mov

The developer who reported this experienced after upgrading from dash==2.6.2 to dash==2.15.0.

Hypothesis: this might be due to the 2.9.0 changes to accommodate duplicate outputs.

Code to reproduce the issue:

from dash import Output, Input, html, dcc, ctx, callback
from dash_iconify import DashIconify
import dash_mantine_components as dmc
import time
import dash
import random

app = dash.Dash(__name__)
app.layout =dmc.NotificationsProvider( html.Div([
    html.Button("click", id="btn-start"),
    html.Button("stop", id="btn-stop"), #style={'display': 'none'}),
    html.Div(id="notify-container"),
    ]
))

@callback(
    Output("btn-stop", "n_clicks"),
    Input("btn-start", "n_clicks"),
)
def make_api_call(nc1):
    # print("CALLBACK 1")
    changed_id = [p['prop_id'] for p in ctx.triggered][0]
    if "btn-start" in changed_id:
        # making api call
        print("api call")
        time.sleep(3)
        return 1 
    else :
        return dash.no_update   

@callback(
    Output("notify-container", "children"),
    Input("btn-start", "n_clicks"),
    Input("btn-stop", "n_clicks"),
    prevent_initial_call=True,
)
def notify(nc1, nc2):
    # print("CALLBACK 2")
    button_id = [p['prop_id'] for p in dash.callback_context.triggered][0]
    if "start" in button_id:
        return dmc.Notification(
            id="my-notification",
            title="Process initiated",
            message="The process has started.",
            loading=True,
            color="orange",
            action="show",
            autoClose=False,
            disallowClose=True,
        )
    elif "stop" in button_id:
        return dmc.Notification(
            id="my-notification",
            title="Data loaded",
            message="The process has started.",
            color="green",
            #action="show",
            action="update",
            icon=DashIconify(icon="akar-icons:circle-check"),
        )
    else : 
        return dash.no_update

if __name__ == '__main__':
    app.run(debug=True)

Expected behavior

"Click" button should trigger both callbacks at the same time, which would result in "Progress" notification showing immediately and lasting 3 seconds, and then "Complete" notification replacing it:

Screen.Recording.2024-02-21.at.17.22.04.mov

This behaviour can be reproduced with dash>=2.9.x if we use duplicate outputs, but for users this would mean rewriting several callbacks, as this would be a breaking change otherwise:

from dash import Output, Input, html, callback_context as ctx, callback
import dash_mantine_components as dmc
from dash_iconify import DashIconify
import time
import dash
import random

app = dash.Dash(__name__)
app.layout =dmc.NotificationsProvider( html.Div([
    html.Button("click", id="btn-start"),
    html.Button("stop", id="btn-stop"), #style={'display': 'none'}),
    html.Div(id="notify-container"),
    ]
))

@callback(
    Output("btn-stop", "n_clicks"),
    Input("btn-start", "n_clicks"),
    prevent_initial_call=True
)
def make_api_call(nc1):
    print("CALLBACK 1")
    changed_id = ctx.triggered_id
    if "btn-start" in changed_id:
        # making api call
        print("api call")
        time.sleep(3)
        return 1 
    else :
        return dash.no_update   

@callback(
    Output("notify-container", "children", allow_duplicate=True),
    Input("btn-start", "n_clicks"),
    prevent_initial_call=True,
)
def notify(nc1):
    print("CALLBACK 2")
    button_id = ctx.triggered_id
    if "start" in button_id:
        return dmc.Notification(
            id="my-notification",
            title="Process initiated",
            message="The process has started.",
            loading=True,
            color="orange",
            action="show",
            autoClose=False,
            disallowClose=True,
        )
    else : 
        return dash.no_update

@callback(
    Output("notify-container", "children"),
    Input("btn-stop", "n_clicks"),
    prevent_initial_call=True,
)
def notify(nc1):
    print("CALLBACK 3")
    button_id = ctx.triggered_id
    if "stop" in button_id:
        return dmc.Notification(
            id="my-notification",
            title="Data loaded",
            message="The process has started.",
            color="green",
            #action="show",
            action="update",
            icon=DashIconify(icon="akar-icons:circle-check"),
        )
    else : 
        return dash.no_update

if __name__ == '__main__':
    app.run(debug=True)

Describe your context

• replace the result of pip list | grep dash below

dash==2.15.0 # 2.6.2
dash-ag-grid==1.2.1
dash-bootstrap-components==1.0.3
dash-colorscales==0.0.4
dash-core-components==2.0.0
dash-cron==0.0.1
dash-dangerously-set-inner-html==0.0.2
dash-daq==0.5.0
dash-design-kit==1.6.7
dash-draggable==0.1.2
dash-embedded==2.0.0
dash-enterprise-auth==0.0.5
dash-html-components==2.0.0
dash-iconify==0.1.2
dash-mantine-components==0.12.1
dash-notes==0.0.3
dash-snapshots==1.4.6
dash-split-pane==1.0.0
dash-table==5.0.0

[Lew-Goldstein]

Hi @nicolearksey1, reaching out on this bug report as a DE customer is expecting a quick turnaround, i.e. 2 days. I know this is unrealistic, but wanted to make sure this is on your radar. Might we be able to accelerate this fix to some reasonable time frame and provide them an SLA for a patch release.

cc: @mjainGH

[celia-lm]

@michaelbabyn found that this change could be the cause: #1519 (this was merged in 2.7.1:

dash/CHANGELOG.md

Line 267 in 6b31a8f

- [#2344](https://github.com/plotly/dash/pull/2344) Fix [#1519](https://github.com/plotly/dash/issues/1519), a case where dependent callbacks can be called too many times and with inconsistent inputs

)

[michaelbabyn]

I modified Celia's example slightly so that it reproduces the desired behaviour in 2.7.0 but it breaks in 2.7.1

from dash import Output, Input, html, dcc, ctx, callback
from dash_iconify import DashIconify
import dash_mantine_components as dmc
import time
import dash
import random

app = dash.Dash(__name__)
app.layout = dmc.NotificationsProvider(
    html.Div(
        [
            html.Button("click", id="btn-start"),
            html.Button("stop", id="btn-stop"),  # style={'display': 'none'}),
            html.Div(id="notify-container"),
            html.Div(id="intermediate-value", style={"display": "none"}),
        ]
    )
)

# start button updates intermediate value
@callback(
    Output("intermediate-value", "children"),
    Input("btn-start", "n_clicks"),
    prevent_initial_call=True,
)
def start_process(n_clicks):
    print("CALLBACK 0")
    return n_clicks


@callback(
    Output("btn-stop", "n_clicks"),
    Input("intermediate-value", "children"),
)
def make_api_call(nc1):
    # print("CALLBACK 1")
    # print(f"nc1: {nc1}")
    changed_id = [p["prop_id"] for p in ctx.triggered][0]
    if "intermediate" in changed_id:
        # making api call
        print("api call")
        time.sleep(3)
        return nc1
    # else :
    #     return dash.no_update


@callback(
    Output("notify-container", "children"),
    Input("btn-start", "n_clicks"),
    Input("btn-stop", "n_clicks"),
    # prevent_initial_call=True,
)
def notify(nc1, nc2):
    # print("CALLBACK 2")
    button_id = [p["prop_id"] for p in dash.callback_context.triggered][0]
    if "start" in button_id:
        return dmc.Notification(
            id="my-notification",
            title="Process initiated",
            message="The process has started.",
            loading=True,
            color="orange",
            action="show",
            autoClose=False,
            disallowClose=True,
        )
    elif "stop" in button_id:
        return dmc.Notification(
            id="my-notification",
            title="Data loaded",
            message="The process has started.",
            color="green",
            # action="show",
            action="update",
            icon=DashIconify(icon="akar-icons:circle-check"),
        )
    else:
        return dash.no_update


if __name__ == "__main__":
    app.run(debug=True, port=8021)

[Lew-Goldstein]

See Slack thread for additional details.

[AnnMarieW]

@celia-lm Is this issue closed by using the callback running arg available in Dash 2.16?
https://dash.plotly.com/advanced-callbacks#updating-component-properties-when-a-callback-is-running