Use parallel=True by default can be problematic in multiprocessing applications about resampy HOT 8 CLOSED

Thanks for raising this - can you provide a bit more context about how you're using the library? (I.e., are you calling it directly, or through some other package?) Would it be easy to just add parallel=False to your call site?

I don't think a warning is necessarily appropriate, but we can certainly consider reverting the default back to parallel=False. The thinking here was that multiprocessing applications like yours are probably not the default / most common setting, but we do want to make it easy to limit multi-core usage for exactly this kind of application.

It does sound like for your application, it would actually make a lot of sense to limit numba core usage globally (and not just for resampy) - that way it would apply to all numba-parallel usage and not just our package. This can be done through a global environment variable as noted in #106 .

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Thanks for the quick reply!
So yes, if there's a way to auto-detect being in a subprocess, and disable it accordingly, that would also be great.

Looking at #106, I think what they are seeing is this exact same problem. I'm also using librosa, and librosa hasn't updated their call to resampy.resample to specify parallel. So I don't have the control of turning it off. Took me some time to finally get to the bottom of this...

I'll test numba.set_num_threads(1) to see if it works as well.

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So yes, if there's a way to auto-detect being in a subprocess, and disable it accordingly, that would also be great.

That seems pretty unlikely to me. I wouldn't trust such an auto-detection to be reliable, since there are many ways in which an upstream caller might be executing in parallel. I'd rather just have a good default setting and be upfront about documentation.

Looking at #106, I think what they are seeing is this exact same problem.

That seems likely, but their example seems very complicated and not something I could easily reproduce locally.

I'll test numba.set_num_threads(1) to see if it works as well.

Please report back if it works!

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Ah it doesn't work unfortunately. That line effectively sets numba threads to 1, but I still got this error: Terminating: fork() called from a process already using GNU OpenMP, this is unsafe.
I'm guessing it's because numba will still try to spawn the processes even though num_threads is set to one? I don't know, this is really outside of my domain haha.

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That's a bummer, but good to know! To the previous question: are you able to call resampy directly with parallel=False? That will force it to use the single-threaded implementation, and should also fix it for you. The catch here is that if you're using resampy through an intermediate library (eg librosa) the API isn't directly exposed yet.

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Yeah you're right. I'll explore that option as well when I get time. For now the old version works well.

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We had the same problem with librosa. It was finally traced to a problem with the dependency package resampy. I'm here to leave a comment. The easiest way to reproduce this is to use the multiprocessing library and run it in parallel.

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Have same issue with huggingface huggingface/datasets#4820

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