Multiple errors in threaded apps with Panel 1.10.0

Theom · October 29, 2026, 4:42pm

When migrating a threaded app to Panel 1.10.0 with pn.ui components, I’m seeing errors I was not seeing before when loading components and updating DynamicMaps.

First, I have issues where a plot does not respond to a widget update after being loaded, and I see the following:

2026-10-29 16:18:44,132 error handling message
 message: Message 'PATCH-DOC' content: {'events': [{'kind': 'ModelChanged', 'model': {'id': 'p1607096'}, 'attr': 'value_throttled', 'new': 10}]}
 error: UnknownReferenceError("can't resolve reference 'p1607096'")
Traceback (most recent call last):
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/server/protocol_handler.py", line 94, in handle
    work = await handler(message, connection)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/server/session.py", line 153, in _needs_document_lock_wrapper
    raise error
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/server/session.py", line 138, in _needs_document_lock_wrapper
    result = await result
             ^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/server/session.py", line 380, in _handle_patch
    await _run_in_executor(message.apply_to_document, self.document, self)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/util/asyncio.py", line 104, in _run_in_executor
    return await _wait_for_task(worker)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/util/asyncio.py", line 78, in _wait_for_task
    result = await asyncio.shield(task)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/asyncio/threads.py", line 25, in to_thread
    return await loop.run_in_executor(None, func_call)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.12/concurrent/futures/thread.py", line 58, in run
    result = self.fn(*self.args, **self.kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/protocol/messages/patch_doc.py", line 102, in apply_to_document
    invoke_with_curdoc(doc, lambda: doc.apply_json_patch(self.payload, setter=setter))
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/callbacks.py", line 468, in invoke_with_curdoc
    return f()
           ^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/protocol/messages/patch_doc.py", line 102, in <lambda>
    invoke_with_curdoc(doc, lambda: doc.apply_json_patch(self.payload, setter=setter))
                                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/panel/io/document.py", line 325, in _apply_json_patch
    return apply_json_patch(doc, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/document.py", line 463, in apply_json_patch
    patch: PatchJson = deserializer.deserialize(patch_json)
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/serialization.py", line 523, in deserialize
    return self.decode(obj.content, obj.buffers)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/serialization.py", line 538, in decode
    return self._decode(obj)
           ^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/serialization.py", line 579, in _decode
    return {key: self._decode(val) for key, val in obj.items()}
                 ^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/serialization.py", line 581, in _decode
    return [self._decode(entry) for entry in obj]
            ^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/serialization.py", line 579, in _decode
    return {key: self._decode(val) for key, val in obj.items()}
                 ^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/serialization.py", line 577, in _decode
    return self._decode_ref(cast(Ref, obj))
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/serialization.py", line 591, in _decode_ref
    self.error(UnknownReferenceError(id))
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/serialization.py", line 744, in error
    raise error
bokeh.core.serialization.UnknownReferenceError: can't resolve reference 'p1607096'

I also encounter quite a lot of the following error, when updating a DynamicMap plot:

2026-10-29 16:09:27,567 ERROR:
Traceback (most recent call last):
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/util.py", line 960, in wrapper
    return f(self, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/element.py", line 2711, in update_frame
    self._update_ranges(style_element, ranges)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/element.py", line 1606, in _update_ranges
    self._update_main_ranges(element, x_range, y_range, ranges)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/element.py", line 1827, in _update_main_ranges
    self._update_range(
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/element.py", line 1902, in _update_range
    axis_range.update(**{k: new})
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/has_props.py", line 538, in update
    setattr(self, k, v)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/has_props.py", line 392, in __setattr__
    return super().__setattr__(name, value)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/property/descriptors.py", line 361, in __set__
    self._set(obj, old, value, setter=setter)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/property/descriptors.py", line 645, in _set
    self._trigger(obj, old, value, hint=hint, setter=setter)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/property/descriptors.py", line 723, in _trigger
    cast(_HasTrigger, obj).trigger(self.name, old, value, hint, setter)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/model/model.py", line 593, in trigger
    super().trigger(descriptor.name, old, new, hint=hint, setter=setter)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/util/callback_manager.py", line 181, in trigger
    self.document.callbacks.notify_change(cast(Model, self), attr, old, new, hint, setter, invoke)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/callbacks.py", line 266, in notify_change
    self.trigger_on_change(event)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/callbacks.py", line 438, in trigger_on_change
    invoke_with_curdoc(doc, invoke_callbacks)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/callbacks.py", line 468, in invoke_with_curdoc
    return f()
           ^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/callbacks.py", line 437, in invoke_callbacks
    cb(event)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/callbacks.py", line 293, in <lambda>
    self._change_callbacks[receiver] = lambda event: event.dispatch(receiver)
                                                     ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/events.py", line 397, in dispatch
    super().dispatch(receiver)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/events.py", line 252, in dispatch
    receiver._document_patched(self)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/server/session.py", line 313, in _document_patched
    raise RuntimeError("_pending_writes should be non-None when we have a document lock, and we should have the lock when the document changes")
RuntimeError: _pending_writes should be non-None when we have a document lock, and we should have the lock when the document changes

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.12/concurrent/futures/thread.py", line 58, in run
    result = self.fn(*self.args, **self.kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/panel/reactive.py", line 567, in _change_event
    self._process_events(events)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/panel/widgets/slider.py", line 112, in _process_events
    super()._process_events(events)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/panel/reactive.py", line 510, in _process_events
    raise e
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/panel/reactive.py", line 491, in _process_events
    self.param.update(**self_params)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/param/parameterized.py", line 3164, in update
    restore = {**(self_._update(arg, **kwargs))}
                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/param/parameterized.py", line 3205, in _update
    self_._batch_call_watchers()
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/param/parameterized.py", line 3455, in _batch_call_watchers
    self_._execute_watcher(watcher, events)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/param/parameterized.py", line 3417, in _execute_watcher
    watcher.fn(*args, **kwargs)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/panel/pane/holoviews.py", line 409, in _widget_callback
    self._update_plot(plot, pane)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/panel/pane/holoviews.py", line 394, in _update_plot
    plot.update(key)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/holoviews/plotting/plot.py", line 1087, in update
    item = self.__getitem__(key)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/holoviews/plotting/plot.py", line 506, in __getitem__
    self.update_frame(frame)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/holoviews/plotting/bokeh/util.py", line 962, in wrapper
    self.state.hold_render = hold
    ^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/models/plots.py", line 131, in __setattr__
    super().__setattr__(name, value)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/has_props.py", line 392, in __setattr__
    return super().__setattr__(name, value)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/property/descriptors.py", line 361, in __set__
    self._set(obj, old, value, setter=setter)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/property/descriptors.py", line 645, in _set
    self._trigger(obj, old, value, hint=hint, setter=setter)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/core/property/descriptors.py", line 723, in _trigger
    cast(_HasTrigger, obj).trigger(self.name, old, value, hint, setter)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/model/model.py", line 593, in trigger
    super().trigger(descriptor.name, old, new, hint=hint, setter=setter)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/util/callback_manager.py", line 181, in trigger
    self.document.callbacks.notify_change(cast(Model, self), attr, old, new, hint, setter, invoke)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/callbacks.py", line 266, in notify_change
    self.trigger_on_change(event)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/callbacks.py", line 438, in trigger_on_change
    invoke_with_curdoc(doc, invoke_callbacks)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/callbacks.py", line 468, in invoke_with_curdoc
    return f()
           ^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/callbacks.py", line 437, in invoke_callbacks
    cb(event)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/callbacks.py", line 293, in <lambda>
    self._change_callbacks[receiver] = lambda event: event.dispatch(receiver)
                                                     ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/events.py", line 397, in dispatch
    super().dispatch(receiver)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/document/events.py", line 252, in dispatch
    receiver._document_patched(self)
  File "/home/user/workspace/.venv/lib/python3.12/site-packages/bokeh/server/session.py", line 313, in _document_patched
    raise RuntimeError("_pending_writes should be non-None when we have a document lock, and we should have the lock when the document changes")
RuntimeError: _pending_writes should be non-None when we have a document lock, and we should have the lock when the document changes

These do not seem to occur in a non-threaded app.

I’m still working out a way to build minimal reproducible examples so that I can create issues on GitHub. In the meantime, are there specific patterns to avoid or things to look out for when dynamically updating content in a threaded app?

I’m on bokeh 3.10.1

ahuang11 · October 29, 2026, 10:48pm

Thanks for reporting. How are you creating those DynamicMaps?

Theom · October 30, 2026, 10:44am

Thank you @ahuang11 for your reply.

Things happen in the main area of a pn.ui.Page. The app is config-driven, with a fairly generic code to build the DynamicMap:

dmap = hv.DynamicMap(
                functools.partial(
                    self._make_dmap_plot,
                    df=df,
                    kdims=kdims,
                    vdims=vdims,
                    plot_cfg=plot_cfg,
                    label=label,
                ),
                kdims=interactive_dims,
            )
            dmap = dmap.redim.values(
                **{dim.name: df[dim.name].unique().tolist() for dim in interactive_dims}
            )

self._make_dmap_plot itself is a static method:

    @staticmethod
    def _make_dmap_plot(
        *selected_values, df=None, kdims=None, vdims=None, plot_cfg=None, label=None
    ):
        dframe = df.loc[
            (
                df[[dim.id for dim in plot_cfg.interactive_dims]]
                == list(selected_values)
            ).all(axis=1)
        ]
        return ELEMENT_TYPE[plot_cfg.type](
            dframe, kdims=kdims, vdims=vdims, group=plot_cfg.id, label=label
        ).opts(framewise=True)

where ELEMENT_TYPE is a global dictionary holding hv element types.

The DynamicMap is then wrapped in a hv.Overlay (even if it’s alone), which is then collated (overlay = overlay.collate()) and then with pn.panel this way:

            obj = pn.panel(
                overlay,
                widgets=widgets,
                widget_layout=pn.Row,
                widget_location="top",
            )

where widgets is a kdim -> widget_class mapping (pn.ui.Select or pn.ui.DiscreteSlider in this case).

The collection of plots are then passed to pn.viewable.Viewer object that updates its content to include the dmap(s).

ahuang11 · October 30, 2026, 7:13pm

Two things that stand out to me:

functools.partial
collate

Does the issue still appear with these two excluded

Theom · November 2, 2026, 10:56am

Thanks @ahuang11, I finally tracked it down to simply using the Page template. Filing another issue on github!