Server occaionaly logs error when a websocket disconnects

[0x26res]

Bug Report

Steps to Reproduce:

This is very similar to #2132 which was fixed but came back recently.
There's been a lot of changes since then.

1. run the python-tornado-streaming example
2. refresh the webpage very quickly (like press CTRL+R very fast)

I found it is easier to reproduce if you reduce the size of the data set, from 2500 to 25 and reduce the def data_source() update size as well.

Expected Result:

it should work fine

Actual Result:

I can see this in the std err:

2025-04-03 15:40:31,865 - asyncio - ERROR - Task exception was never retrieved
future: <Task finished name='Task-68583' coro=<WebSocketProtocol13.write_message.<locals>.wrapper() done, defined at /opt/pysetup/.venv/lib/python3.12/site-packages/tornado/websocket.py:1086> exception=WebSocketClosedError()>
Traceback (most recent call last):
  File "/opt/pysetup/.venv/lib/python3.12/site-packages/tornado/websocket.py", line 1088, in wrapper
    await fut
tornado.iostream.StreamClosedError: Stream is closed

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/opt/pysetup/.venv/lib/python3.12/site-packages/tornado/websocket.py", line 1090, in wrapper
    raise WebSocketClosedError()
tornado.websocket.WebSocketClosedError
2025-04-03 15:40:31,870 - tornado.application - ERROR - Exception in callback functools.partial(<built-in method poll of perspective.PySyncSession object at 0x7f98eb977510>)
Traceback (most recent call last):
  File "/opt/pysetup/.venv/lib/python3.12/site-packages/tornado/ioloop.py", line 750, in _run_callback
    ret = callback()
          ^^^^^^^^^^
ValueError: Session RwLock { value: None } already deleted

Though the server keeps working fine.

Environment:

For Python

• Python 3.12.9
• perspective-python==3.4.3