Bokeh figure axes collapse on dynamic creation

[cdeil]

With Bokeh 3.2.2 and Panel 1.3.0a3 (but also earlier versions I think since Panel 1.0) we saw a bug where Bokeh figure axes sometimes collapse in the case where the figure is created dynamically on widget interaction.

We see this in Panel apps and an example is below. But it might very well be a Bokeh bug, e.g. bokeh/bokeh#13340 sounds similar and overall this looks like a state synchronisation or race condition bug.

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Screenshot showing collapsed axes:

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To reproduce the bug, run this with panel serve and the in the browser drag a bit the two sliders to see the bug come and go.
It can probably be simplified further, e.g. bokeh/bokeh#13340 already shows a Bokeh-only bug that might be related.

import numpy as np
import pandas as pd
import bokeh
import panel as pn


def make_one_figure(n_points, width, height, start="2023-01-01", end="2023-12-31"):
    rng = np.random.default_rng()
    x = pd.date_range(start=start, end=end, periods=n_points, tz="utc")
    y = rng.random(n_points)
    df = pd.DataFrame({"x": x, "y": y})
    p = bokeh.plotting.figure(width=width, height=height, x_axis_type="datetime")
    p.step(x="x", y="y", source=df)
    return p


def make_many_figures(n_figures=3, n_points=1000, width=500, height=100):
    col = pn.Column("# Plots", sizing_mode="stretch_both")
    for _ in range(n_figures):
        fig = make_one_figure(n_points, width, height)
        col.append(fig)
    return col


def make_app():
    n_figures = pn.widgets.IntSlider(name="n_figures", start=0, end=10, value=3)
    n_points = pn.widgets.IntSlider(name="n_points", start=0, end=1000, value=100)
    main = pn.bind(make_many_figures, n_figures, n_points)

    pn.extension(template="material")
    template = pn.template.MaterialTemplate(title="Lotsa plots")
    template.sidebar[:] = [n_figures, n_points]
    template.main.append(main)

    return template


app = make_app()
app.show()

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Often the bug (figure collapse) occurs but no warning or error in the panel server terminal or web browser console.

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Sometimes a warning or error does occur though that might give you a hint at the root couse of the issue:

Warning:

[bokeh] could not set initial ranges

Error:

RuntimeError: _pending_writes should be non-None when we have a document lock, and we should have the lock when the document changes

Screenshots:

[cdeil]

In our app we no longer see this issue after we changed to class-based views.

However for the example app above with panel 1.4.0rc4 and bokeh 3.4.0 if I drag the sliders I still get errors sometimes.

So might still be a bug in Panel or Bokeh affecting such apps.

[philippjfr]

Thanks, that's pretty bizarre. Not sure how a stylesheet can end up without a URL but I can put a guard around that.