[BUG] Long Callbacks: Raising Error Causes Infinite Loop (Including PreventUpdate)

[Robbie-Palmer]

Environment

python               3.9.7
dash                 2.0.0

Describe the bug

If an error is raised within a long callback, an infinite loop of re-raising this error is triggered, as a new process tries again and again
This is triggered by the _long_callback_interval_1.n_intervals property

Expected behavior

The error would be handled like with normal callbacks, and the long callback wouldn't be called by new processes

Minimum Reproducible Example

import time

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

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

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

app.layout = html.Div(
    [
        html.Div([html.P(id="paragraph_id", children=["Button not clicked"])]),
        html.Button(id="button_id", children="Run Job!"),
    ]
)


@app.long_callback(
    output=Output("paragraph_id", "children"),
    inputs=Input("button_id", "n_clicks"),
    running=[
        (Output("button_id", "disabled"), True, False),
    ],
)
def callback(n_clicks):
    if n_clicks == 2:
        raise dash.exceptions.PreventUpdate(dash.callback_context.triggered[0]['prop_id'])
    time.sleep(2.0)
    return [f"Clicked {n_clicks} times"]


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

In the above example, can safely click the button once, then on the second click raising PreventUpdate causes the infinite loop
With logged messages of:

Process Process-3:
Traceback (most recent call last):
  File "./python3.9/site-packages/multiprocess/process.py", line 315, in _bootstrap
    self.run()
  File "./python3.9/site-packages/multiprocess/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "./python3.9/site-packages/dash/long_callback/managers/diskcache_manager.py", line 143, in job_fn
    user_callback_output = fn(*maybe_progress, *user_callback_args)
  File "./reprex_long_callback_infinite_loop_on_error.py", line 31, in callback
    raise dash.exceptions.PreventUpdate(dash.callback_context.triggered[0]['prop_id'])
dash.exceptions.PreventUpdate: button_id.n_clicks
Process Process-4:
Traceback (most recent call last):
  File "./python3.9/site-packages/multiprocess/process.py", line 315, in _bootstrap
    self.run()
  File "./python3.9/site-packages/multiprocess/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "./python3.9/site-packages/dash/long_callback/managers/diskcache_manager.py", line 143, in job_fn
    user_callback_output = fn(*maybe_progress, *user_callback_args)
  File "./reprex_long_callback_infinite_loop_on_error.py", line 31, in callback
    raise dash.exceptions.PreventUpdate(dash.callback_context.triggered[0]['prop_id'])
dash.exceptions.PreventUpdate: _long_callback_interval_1.n_intervals
Process Process-5:
Traceback (most recent call last):
  File "./python3.9/site-packages/multiprocess/process.py", line 315, in _bootstrap
    self.run()
  File "./python3.9/site-packages/multiprocess/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "./python3.9/site-packages/dash/long_callback/managers/diskcache_manager.py", line 143, in job_fn
    user_callback_output = fn(*maybe_progress, *user_callback_args)
  File "./reprex_long_callback_infinite_loop_on_error.py", line 31, in callback
    raise dash.exceptions.PreventUpdate(dash.callback_context.triggered[0]['prop_id'])
dash.exceptions.PreventUpdate: _long_callback_interval_1.n_intervals
Process Process-6:
Traceback (most recent call last):
  File "./python3.9/site-packages/multiprocess/process.py", line 315, in _bootstrap
    self.run()
  File "./python3.9/site-packages/multiprocess/process.py", line 108, in run
    self._target(*self._args, **self._kwargs)
  File "./python3.9/site-packages/dash/long_callback/managers/diskcache_manager.py", line 143, in job_fn
    user_callback_output = fn(*maybe_progress, *user_callback_args)
  File "./reprex_long_callback_infinite_loop_on_error.py", line 31, in callback
    raise dash.exceptions.PreventUpdate(dash.callback_context.triggered[0]['prop_id'])
dash.exceptions.PreventUpdate: _long_callback_interval_1.n_intervals
Process Process-7:
...

[SteveYgq]

我遇见了同样的问题,无法正常使用,请求解决方案,我使用案例文档案例也出现了同样的问题

代码如下:
import time
import dash
from dash import html
from dash.long_callback import CeleryLongCallbackManager
from dash.dependencies import Input, Output
from celery import Celery

celery_app = Celery(
name, broker="redis://localhost:6379/0", backend="redis://localhost:6379/1"
)
long_callback_manager = CeleryLongCallbackManager(celery_app)

app = dash.Dash(name, long_callback_manager=long_callback_manager)

app.layout = html.Div(
[
html.Div([html.P(id="paragraph_id", children=["Button not clicked"])]),
html.Button(id="button_id", children="Run Job!"),
html.Button(id="cancel_button_id", children="Cancel Running Job!"),
]
)

@app.long_callback(
output=Output("paragraph_id", "children"),
inputs=Input("button_id", "n_clicks"),
running=[
(Output("button_id", "disabled"), True, False),
(Output("cancel_button_id", "disabled"), False, True),
],
cancel=[Input("cancel_button_id", "n_clicks")],
)
def callback(n_clicks):
time.sleep(2.0)
return [f"Clicked {n_clicks} times"]

if name == "main":
app.run_server(debug=True)

效果是这样的

[isCopyman]

I have a similar problem, I click the button which will fire a long_callback, when the long_callback is finished, it will be fired again. A infinite loop

[kiwifoxtrot]

I have a similar problem, I click the button which will fire a long_callback, when the long_callback is finished, it will be fired again. A infinite loop

If the callback takes longer than 1000ms to download to the browser, it will continuously loop. In the dash.py file, there is a hardcoded setting for interval_time. Try setting it to 10000ms instead, that fixed my issue.