# Runtime Error with Concurrent User Sessions - Models must be owned by only a single document

**URL:** <https://discourse.holoviz.org/t/runtime-error-with-concurrent-user-sessions-models-must-be-owned-by-only-a-single-document/8558>\
**Category:** Panel\
**Tags:** param, bokeh, holoviews\
**Created:** [February 5, 2025, 3:59pm UTC](https://discourse.holoviz.org/t/runtime-error-with-concurrent-user-sessions-models-must-be-owned-by-only-a-single-document/8558 "2025-02-05T15:59:12Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![RishikaSatheesh](https://discourse.holoviz.org/user_avatar/discourse.holoviz.org/rishikasatheesh/32/7117_2.png) [@RishikaSatheesh](https://discourse.holoviz.org/u/RishikaSatheesh)\
**Post date:** [February 5, 2025, 3:59pm UTC](https://discourse.holoviz.org/t/runtime-error-with-concurrent-user-sessions-models-must-be-owned-by-only-a-single-document/8558/1 "2025-02-05T15:59:12Z")

</div>

Hi, I’m deploying an application that uses Param and Panel to create an interactive visualization tool. However, I’m encountering the following error when multiple users open sessions concurrently and click the Submit button on a tab:

RuntimeError: Models must be owned by only a single document, ImportedStyleSheet(id=‘p1503’, …) is already in a doc

I’ve already tried the --num-procs approach, which helps to some extent, but I’m looking for a more robust solution. Specifically, I’d like to know:  
• Is there a better approach to ensure user sessions remain isolated?  
• Can this issue be addressed through code modifications rather than using --num-procs approach?

Here’s the link to a minimal reproducible example of the error:

> **[GitHub - RishikaSatheesh/panel-code: Viz application using Param and Panel](https://github.com/RishikaSatheesh/panel-code/tree/main)**
>
> main

The code in sample.py makes use of class Common in common.py and class Rectangle in rectangle.py to create the dashboard.

I have used the panel serve command to launch the application from the commandline.  
Any insights or suggestions would be greatly appreciated. Thanks in advance!

---

<div class="post-metadata">

**Author:** ![ahuang11](https://discourse.holoviz.org/user_avatar/discourse.holoviz.org/ahuang11/32/4947_2.png) [@ahuang11](https://discourse.holoviz.org/u/ahuang11)\
**Post date:** [February 7, 2025, 6:24am UTC](https://discourse.holoviz.org/t/runtime-error-with-concurrent-user-sessions-models-must-be-owned-by-only-a-single-document/8558/2 "2025-02-07T06:24:02Z")

</div>

Do you use `pn.serve` or `obj.servable()`

---

<div class="post-metadata">

**Author:** ![RishikaSatheesh](https://discourse.holoviz.org/user_avatar/discourse.holoviz.org/rishikasatheesh/32/7117_2.png) [@RishikaSatheesh](https://discourse.holoviz.org/u/RishikaSatheesh)\
**Post date:** [February 7, 2025, 7:20am UTC](https://discourse.holoviz.org/t/runtime-error-with-concurrent-user-sessions-models-must-be-owned-by-only-a-single-document/8558/3 "2025-02-07T07:20:34Z")

</div>

I’ve used obj.servable()

---

<div class="post-metadata">

**Author:** ![ahuang11](https://discourse.holoviz.org/user_avatar/discourse.holoviz.org/ahuang11/32/4947_2.png) [@ahuang11](https://discourse.holoviz.org/u/ahuang11)\
**Post date:** [February 8, 2025, 12:25am UTC](https://discourse.holoviz.org/t/runtime-error-with-concurrent-user-sessions-models-must-be-owned-by-only-a-single-document/8558/4 "2025-02-08T00:25:07Z")

</div>

> dynamically generating input widgets accordingly.

My guess is you need a `clone` somewhere, for whatever you’re returning dynamically, e.g. button.clone()

---

<div class="post-metadata">

**Author:** ![RishikaSatheesh](https://discourse.holoviz.org/user_avatar/discourse.holoviz.org/rishikasatheesh/32/7117_2.png) [@RishikaSatheesh](https://discourse.holoviz.org/u/RishikaSatheesh)\
**Post date:** [February 11, 2025, 8:40am UTC](https://discourse.holoviz.org/t/runtime-error-with-concurrent-user-sessions-models-must-be-owned-by-only-a-single-document/8558/5 "2025-02-11T08:40:50Z")

</div>

I tried that, unfortunately, that does not work.

---

<div class="post-metadata">

**Author:** ![Marc](https://discourse.holoviz.org/user_avatar/discourse.holoviz.org/marc/32/24_2.png) [@Marc](https://discourse.holoviz.org/u/Marc)\
**Post date:** [February 11, 2025, 9:00am UTC](https://discourse.holoviz.org/t/runtime-error-with-concurrent-user-sessions-models-must-be-owned-by-only-a-single-document/8558/6 "2025-02-11T09:00:05Z")

</div>

The problem is that you declare (and share) `button = Button()` on your `rectangle` class.

Try changing the `reactangle.py` file to

```python
import param
import panel as pn
import pandas as pd
from common import Common
import logging

class rectangle(param.Parameterized):
    length1 = param.Number(default=1, step=1, bounds=(1, 100))
    width1 = param.Number(default=1, step=1, bounds=(1, 100))
    length2 = param.Number(default=1, step=1, bounds=(1, 100))
    width2 = param.Number(default=1, step=1, bounds=(1, 100))
    submit = param.Event()
    common = param.ClassSelector(class_=Common)
    df = pd.DataFrame()

    def get_data(self):
        lengths = []
        widths = []
        perimeters = []
        areas = []

        for i in range(1, self.common.number_of_shapes + 1):
            lengths.append(getattr(self, f'length{i}'))
            widths.append(getattr(self, f'width{i}'))
            perimeters.append(2 * (lengths[i - 1] + widths[i - 1]))
            areas.append(lengths[i - 1] * widths[i - 1])

        self.df = pd.DataFrame({
            'Length': lengths,
            'Width': widths,
            'Perimeter': perimeters,
            'Area': areas
        })

    @param.depends('common.select_button')
    def get_first_dashboard(self):
        dimensions = pn.GridBox(ncols=self.common.number_of_shapes)
        for i in range(self.common.number_of_shapes):
            dimensions.append(
                pn.WidgetBox(
                    pn.Param(
                        self,
                        parameters=[f'length{i + 1}'],
                        widgets={
                            f'length{i + 1}': {
                                'widget_type': pn.widgets.IntInput,
                                'name': 'Length:',
                                'width': 115
                            }
                        },
                        show_name=False,
                        default_layout=pn.Column
                    ),
                    pn.Param(
                        self,
                        parameters=[f'width{i + 1}'],
                        widgets={
                            f'width{i + 1}': {
                                'widget_type': pn.widgets.FloatInput,
                                'name': 'Width:',
                                'width': 115
                            }
                        },
                        show_name=False,
                        default_layout=pn.Column
                    ),
                    margin=(4, 2, 4, 2)
                )
            )

        return dimensions

    def get_submit_button(self):
        return pn.widgets.Button.from_param(self.param.submit)

    @pn.depends('common.select_button', 'submit')
    def get_second_dashboard(self):
        self.get_data()
        logging.info("Done")
        return pn.Card(pn.widgets.Tabulator(self.df))

```

That works for me.

---

<div class="post-metadata">

**Author:** ![RishikaSatheesh](https://discourse.holoviz.org/user_avatar/discourse.holoviz.org/rishikasatheesh/32/7117_2.png) [@RishikaSatheesh](https://discourse.holoviz.org/u/RishikaSatheesh)\
**Post date:** [February 12, 2025, 1:25pm UTC](https://discourse.holoviz.org/t/runtime-error-with-concurrent-user-sessions-models-must-be-owned-by-only-a-single-document/8558/7 "2025-02-12T13:25:44Z")

</div>

Thanks a lot, Marc. This seems to solve my issue. 😃