_pending_writes should be non-None when we have a document lock

[xavArtley]

import panel as pn
import tkinter as tk
from threading import Thread
from panel.io import get_server
from functools import partial

slider = pn.widgets.FloatSlider()

import asyncio


def get_server_in_thread(**kwargs):
    asyncio.set_event_loop(asyncio.new_event_loop())
    get_server(**kwargs)

class Display():

    def __init__(self):
        Thread(target=partial(get_server_in_thread,panel=slider,start=True,show=True,port=5010)).start()
        self.root = tk.Tk()
        self.slider = tk.Scale(self.root, from_=0., to=1., resolution=0.1,
                               orient=tk.HORIZONTAL, command=self.on_slider_change)
        self.slider.pack()
        self.root.mainloop()


    def on_slider_change(self, event):
        slider.value = float(event)

display = Display()

[xavArtley]

May be a windows related issue

[philippjfr]

Thanks, I'll try to set this up on my windows machine.

[xavArtley]

This is call stacks, left when there is error, right when the update succeed

It seems like the callback is called from the wrong thread (main)

[philippjfr]

That's odd, I'd expect this to schedule an event on the IO loop which should then be run on the thread:

    def on_slider_change(self, event):
        slider.value = float(event)

What I think is happening is that for whatever reason pn.state.curdoc is defined, which causes it to skip the scheduling. Could you insert some print statements panel.io.state.curdoc and see what is setting the curdoc?

[philippjfr]

When I try this locally (where it is working) pn.state.curdoc is always defined when the JS slider is dragged and is None when the Tk slider is dragged, which is what I'd expect.

[xavArtley]

[xavArtley]

Mine is always state00002

[philippjfr]

Not looking for the value of state itself, it's state.curdoc I'm interested in. It should be none whenever the tk slider is dragged.

[xavArtley]

none when tk slider and document when bokeh one

[philippjfr]

That's bizarre, I don't know how the error can occur if it is None. Here is the relevant code, if it is None it should go into the else branch but it seems to be going into the first branch:

if comm or doc is state.curdoc:
    self._update_model(events, msg, root, model, doc, comm)
    if comm and 'embedded' not in root.tags:
        push(doc, comm)
else:
    cb = partial(self._update_model, events, msg, root, model, doc, comm)
    doc.add_next_tick_callback(cb)

[philippjfr]

What I can try to do is record the thread id, and if we're on the wrong thread it would force it to go down the else branch.

[xavArtley]

Indeed if I force using the else part there is no problem