Interrupt of the python console doesn't work on windows

[jonvanausdeln]

System details:

Windows 11

Positron and OS details:

All builds

Interpreter details:

Python 3.12.2 (but version doesn't matter)

Describe the issue:

In the python console, interrupting a long running process doesn't work. This could be an issue for users using packages like Vetiver

Steps to reproduce the issue:

1. Start a python cosole
2. In the console run

   >>> import time
   >>> time.sleep(60)

3. Click the interrupt button (red box)

This doesn't stop the process, instead I get

Expected or desired behavior:

Process to be interrupted

Were there any error messages in the UI, Output panel, or Developer Tools console?

[Python] [PositronIPKernelApp] ERROR | Interrupt message not supported on Windows

[jmcphers]

Without digging into the code too much, I would speculate that this is caused by us relying on sending the interrupt_request Jupyter message on all platforms to interrupt Python. Not all kernels support this message on all platforms; at least according to spec, the kernel should declare (in its kernelspec) an interrupt_mode indicating whether interrupts can use this message or whether they need to send an OS-level signal.

https://jupyter-client.readthedocs.io/en/latest/kernels.html#kernel-specs

We don't read kernelspecs in Positron since we don't require that the kernel be pre-registered with Jupyter in any way, so we probably just need some built-in knowledge, along with the ability to deliver an OS signal to interrupt if needed.

[juliasilge]

We think we may solve this with the new Jupyter kernel supervisor.

[jmcphers]

I have a candidate fix for this in the new kernel supervisor; it now sends SIGINT to kernels that don't support an interrupt message.

[jmcphers]

Update: The candidate fix doesn't work, because (and I totally should have known this already) SIGINT isn't supported on Windows.

https://learn.microsoft.com/en-us/cpp/c-runtime-library/reference/signal?view=msvc-170

Instead we need to do some very Windows-specific stuff with an interrupt handle. Here's how Jupyter Client does it:

https://github.com/jupyter/jupyter_client/blob/5.2.3/jupyter_client/win_interrupt.py

[jmcphers]

Some more research..

Interrupting time.sleep(...) also does not work in VS Code's notebooks.

The interrupt handler used by the Jupyter extension is here; it uses the same technique and environment variable (JPY_INTERRUPT_EVENT) as the Jupyter client. https://github.com/microsoft/vscode-jupyter/blob/fb42c2069afd743d23a71c2fd340295909dfb58a/pythonFiles/vscode_datascience_helpers/kernel_interrupt_daemon.py

So:

• it seems like ipykernel's interrupt polling does not happen during a time.sleep(...) event, and no solution will allow us to make that particular statement interruptible
• we still need to implement interrupts for Windows and the only reasonable way to do it is to implement this Windows kernel event
• this implementation will need to live in the supervisor

[jmcphers]

I have a branch in the supervisor repo with an implementation of interrupts that uses Windows events, but haven't been able to get it to work (no errors, but the signal raised on the supervisor is not received in the spawned kernel for reasons that aren't clear yet).

[kvbhelios]

Is there an update on this bug?

I think not being able to interrupt Python code is a big dealbreaker - is there a temporary solution for interrupting code which is not a time.sleep()-call?

[jmcphers]

Not at present, sorry! IPyKernel doesn't expose a way to interrupt computations other than the Windows event, and there is no reasonable way to generate those yourself. We agree that this is important, and it's targeted to be fixed before Positron's first release.