Functions run very slow when they are called under use_thread

[hkayabilisim]

Problem A function runs very slow when it is run under solara.use_thread.

How much slow: On my Mac, it is about 20 times. On Hugging Face (which uses Linux), 26 times slower.

How to reproduce: I deployed the code to https://huggingface.co/spaces/hkayabilisim/test_solara_use_thread for you to repeat the case. For demonstration, I used the prime checking code here: https://github.com/widgetti/solara/blob/master/solara/website/pages/api/use_thread.py To test the code, use large primes such as 160423, 203789, 364289, 991961, 1203793, 1667321, 3704053.

Screenshot

[hkayabilisim]

Update: I found a workaround: Setting intrusive_cancel=False seems to solve the issue: solara.use_thread(..., intrusive_cancel=False.

cancel_guard context around the function call seems the source of the slowness problem. @maartenbreddels do you have a recommendation for that? Is it an expected behavior?

[maartenbreddels]

Yes, when we tested this, it was tested with calls to pandas or vaex, which didn't have much overhead. We recently found out when we created use_task and task that indeed the overhead was larger than expected, and we therefore didn't enable it yet for task and use_task.

I think the docs should say instead: WARNING: When intrusive_cancel=True, a tracer is installed into the thread, which will throw a special exception to cancel the thread. This gives a significant runtime overhead for running Python code (up to 20x)

What do you think?

[hkayabilisim]

Thank you for the explanation! Yes, I think adding this information to use_thread doc will be helpful and enough. So, I'm not planning to investigate this issue any further because the workaround works just fine and I don't need "cancelling" option in near future.
Thank you again!