ValueError: cannot find context for 'fork' when processor_with_lm.batch_decode(_logits)

[elsheikh21]

System Info

## Environment info
- `transformers` version: 4.17.0
- Platform: Windows-10-10.0.22000-SP0
- Python version: 3.8.13
- PyTorch version (GPU?): 1.9.1 (True)
- Tensorflow version (GPU?): not installed (NA)
- Flax version (CPU?/GPU?/TPU?): not installed (NA)
- Jax version: not installed
- JaxLib version: not installed
- Using GPU in script?: No
- Using distributed or parallel set-up in script?: No

Who can help?

@patrickvonplaten

Information

• The official example scripts
• My own modified scripts

Tasks

• An officially supported task in the examples folder (such as GLUE/SQuAD, ...)
• My own task or dataset (give details below)

Reproduction

To reproduce

• The model I am using (Wav2Vec2.0 Large XLS-R 53 English):

• Steps to reproduce the behavior:

1. I am fine-tuning Wav2Vec with LM Head using WikiText to produce 5-grams LM. I downloaded the fine-tuned model dir locally and was able to perform inference on my audio .wav file(s)
2. Please find here, model files, test audio file, and requirements.txt if needed to reproduce the problem

Code snippet

import torch
from transformers import Wav2Vec2ForCTC, Wav2Vec2ProcessorWithLM
from datasets import load_dataset
import soundfile as sf
  

model_name = "jonatasgrosman/wav2vec2-large-xlsr-53-english"
model = Wav2Vec2ForCTC.from_pretrained(model_name)
processor_path = path_join(getcwd(), "stt_assets", "stt_model")
processor = Wav2Vec2ProcessorWithLM.from_pretrained(processor_path)
  
dataset = load_dataset("timit_asr", split="test").shuffle().shuffle().select(range(100))
char_translations = str.maketrans({"-": " ", ",": "", ".": "", "?": ""})


def prepare_example(example):
    example["speech"], _ = sf.read(example["file"])
    example["text"] = example["text"].translate(char_translations)
    example["text"] = " ".join(example["text"].split())  # clean up whitespace
    example["text"] = example["text"].lower()
    return example
  

dataset = dataset.map(prepare_example, remove_columns=["file"])
  
pprint(dataset)
features = processor(speech, sampling_rate=16_000, return_tensors="pt", padding=True)

with torch.no_grad():
    logits = model(**features).logits

# logits shape is torch.Size([100, 304, 33])
transcription = processor.batch_decode(logits)
# EXCEPTION IS RAISED in `processor.batch_decode()` ValueError: cannot find context for 'fork'
print(transcription)

Expected behavior

What I am expecting is that I get a list of transcriptions from `processor.batch_decode()` 

but I get this `ValueError: cannot find context for 'fork'` Exception. I am using Windows 11, 

I have tried to research it and I guess it is something related to multiprocessing but I could 
not really figure out how to solve it yet

[patrickvonplaten]

Related woven-planet/l5kit#129

[patrickvonplaten]

Hey @elsheikh21,

Let's try to narrow the bug further down :-)

Does the following work for you:

from multiprocessing import get_context
pool = get_context("fork").Pool(num_processes)
pool.close()

?

[elsheikh21]

Hello @patrickvonplaten

I have tried to run

from multiprocessing import get_context
num_processes = 8
pool = get_context("fork").Pool(num_processes)
pool.close()

and got the following traceback

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\AhmedElSheikh\AppData\Local\Programs\Python\Python38\lib\multiprocessing\context.py", line 239, in get_context
    return super().get_context(method)
  File "C:\Users\AhmedElSheikh\AppData\Local\Programs\Python\Python38\lib\multiprocessing\context.py", line 193, in get_context
    raise ValueError('cannot find context for %r' % method) from None
ValueError: cannot find context for 'fork'

System Information
Windows 11
Python 3.8.10

[elsheikh21]

Related woven-planet/l5kit#129

I have read this thread, yet the error itself occurs when I call processor.batch_decode and I am working on the project not just to be used on my local device only

[patrickvonplaten]

Hello @patrickvonplaten

I have tried to run

from multiprocessing import get_context
num_processes = 8
pool = get_context("fork").Pool(num_processes)
pool.close()

and got the following traceback

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\AhmedElSheikh\AppData\Local\Programs\Python\Python38\lib\multiprocessing\context.py", line 239, in get_context
    return super().get_context(method)
  File "C:\Users\AhmedElSheikh\AppData\Local\Programs\Python\Python38\lib\multiprocessing\context.py", line 193, in get_context
    raise ValueError('cannot find context for %r' % method) from None
ValueError: cannot find context for 'fork'

System Information Windows 11 Python 3.8.10

This seems to be the error then.

Could you try to replace "fork" with "spawn"?

[patrickvonplaten]

If "spawn" works then it might make most sense to just update "fork" to "spawn"

[elsheikh21]

I have tried to run with "spawn" and it works fine, but in that case I will need to change the file transformers.models.wav2vec2_with_lm.processing_wav2vec2_with_lm.py and I guess that wont work when I run the same code on another machine, is there a way to force "spawn" when "fork" does not work?

[patrickvonplaten]

Think we can just replace "fork" with "spawn" - do you want to open a PR to fix it? :-)

[elsheikh21]

Think we can just replace "fork" with "spawn" - do you want to open a PR to fix it? :-)

Yes, I would happily do that, I guess it would be something along those lines? please feel free to modify my approach. Otherwise I will start reading about collaborating and how to open PR

try:
    pool = get_context("fork").Pool(num_processes)
except ValueError as exc:
    if "cannot find context for 'fork'" in exc:
         pool = get_context("spawn").Pool(num_processes)
         logging.info("Switching to \"spawn\" as \"fork\" context is not found")

[patrickvonplaten]

I think we can actually just change "fork" to "spawn" (no need for a try, ... expect IMO). According to https://stackoverflow.com/questions/64095876/multiprocessing-fork-vs-spawn and some other docs, "spawn" is safe and given that the child process is LM-boosted decoding (which is always slow), doing the switch should be fine

[elsheikh21]

I think we can actually just change "fork" to "spawn" (no need for a try, ... expect IMO). According to https://stackoverflow.com/questions/64095876/multiprocessing-fork-vs-spawn and some other docs, "spawn" is safe and given that the child process is LM-boosted decoding (which is always slow), doing the switch should be fine

Okay let us do it your way then, I have also created a custom dataset loader (from flac/wav audio files) and model finetuner, evaluator if those can be helpful for the community I would love to share them as well

For now I will open a PR for spawn and fork

[ADD-eNavarro]

Exactly same problem here, also trying to run this under Windows 10 and getting the same error, when in processing_wav2vec2_with_lm.py, line 316, gets "fork" from context.
But since I see it's already being fixed, I'll just thank and wait 👍

[elsheikh21]

Exactly same problem here, also trying to run this under Windows 10 and getting the same error, when in processing_wav2vec2_with_lm.py, line 316, gets "fork" from context. But since I see it's already being fixed, I'll just thank and wait 👍

as a quick fix you can replace "fork" with "spawn" in the line pool = get_context("fork").Pool(num_processes), file transformers.models.wav2vec2_with_lm.processing_wav2vec2_with_lm.py

[patrickvonplaten]

@ADD-eNavarro @elsheikh21 sorry I don't work with Windows usually and am a bit buried with other issues. Regarding the PR please lemme know if anything isn't clear, happy trying to be more precise - in short I think we should try to apply the exact same solution that was applied in pyctcdecode

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