Modify Bokeh Models#

This guide addresses how to safely modify Bokeh models to avoid running into issues with the Bokeh Document lock.

The Bokeh server that Panel builds on is designed to be thread safe which requires a set of locks to avoid multiple threads modifying the Bokeh models simultaneously. Panel being a high-level wrapper around Bokeh handles this locking for you. However, when you update Bokeh components directly you may need to schedule a callback to get around Bokeh’s document lock to avoid errors like this:

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

In the example below we will launch an application on a thread using pn.serve and make the Bokeh plot (in practice you may provide handles to this object on a class). To schedule a callback which updates the y_range by using the pn.state.execute method. This pattern will ensure that the update to the Bokeh model is executed on the correct thread:

import time
import panel as pn

from bokeh.plotting import figure

def app():
    p = figure()
    p.line([1, 2, 3], [1, 2, 3])
    return p

pn.serve(app, threaded=True)

pn.state.execute(lambda: p.y_range.update(start=0, end=4))