filelock hangs for example script "run_language_modeling.py"
## Environment info

- `transformers` version: 3.4.0
- Platform: Linux-3.10.0-957.27.2.el7.x86_64-x86_64-with-centos-7.8.2003-Core
- Python version: 3.6.9
- PyTorch version (GPU?): 1.7.0 (True)
- Tensorflow version (GPU?): not installed (NA)
- Using GPU in script?: yes
- Using distributed or parallel set-up in script?: no

### Who can help
@julien-c (most frequent commiter on `git log examples/language-modeling/run_language_modeling.py`)

## Information

Model I am using (Bert, XLNet ...): CamemBERT

The problem arises when using:
* [x] the official example scripts: (give details below)
* [ ] my own modified scripts: (give details below)

The tasks I am working on is:
* [x] an official GLUE/SQUaD task: (give the name) lm
* [ ] my own task or dataset: (give details below)

## To reproduce

Context: my training dir is ~200 files of ~30MB, as per documentation instructions to keep train files small for the tokenizer (however since I'm finetuning from CamemBERT I wouldn't expect a tokenizer "train" to be run?)
I'm unable to figure out why this freezes, looking for pointers
getting the same behaviour with a single 30MB training file

```
python run_language_modeling.py \
       --output_dir=output \
       --model_name_or_path=camembert-base \
       --do_train \
       --train_data_files='/home/theo_nabla_com/data/mydata-corpus/chunk*' \
       --do_eval \
       --eval_data_file=/home/theo_nabla_com/data/mydata-corpus/valid \
       --mlm \
       --whole_word_mask
10/29/2020 08:09:13 - WARNING - __main__ -   Process rank: -1, device: cuda:0, n_gpu: 1, distributed training: False, 16-bits training: False
10/29/2020 08:09:13 - INFO - __main__ -   Training/evaluation parameters TrainingArguments(output_dir='output', overwrite_output_dir=False, do_train=True, do_eval=True, do_predict=False, evaluate_during_training=False, evaluation_strategy=<EvaluationStrategy.NO: 'no'>, prediction_loss_only=False, per_device_train_batch_size=8, per_device_eval_batch_size=8, per_gpu_train_batch_size=None, per_gpu_eval_batch_size=None, gradient_accumulation_steps=1, eval_accumulation_steps=None, learning_rate=5e-05, weight_decay=0.0, adam_beta1=0.9, adam_beta2=0.999, adam_epsilon=1e-08, max_grad_norm=1.0, num_train_epochs=3.0, max_steps=-1, warmup_steps=0, logging_dir='runs/Oct29_08-09-13_google3-theo', logging_first_step=False, logging_steps=500, save_steps=500, save_total_limit=None, no_cuda=False, seed=42, fp16=False, fp16_opt_level='O1', local_rank=-1, tpu_num_cores=None, tpu_metrics_debug=False, debug=False, dataloader_drop_last=False, eval_steps=500, dataloader_num_workers=0, past_index=-1, run_name='output', disable_tqdm=False, remove_unused_columns=True, label_names=None, load_best_model_at_end=False, metric_for_best_model=None, greater_is_better=None)
10/29/2020 08:09:13 - DEBUG - urllib3.connectionpool -   Starting new HTTPS connection (1): s3.amazonaws.com:443
10/29/2020 08:09:14 - DEBUG - urllib3.connectionpool -   https://s3.amazonaws.com:443 "HEAD /models.huggingface.co/bert/camembert-base-config.json HTTP/1.1" 200 0
10/29/2020 08:09:14 - DEBUG - urllib3.connectionpool -   Starting new HTTPS connection (1): s3.amazonaws.com:443
10/29/2020 08:09:14 - DEBUG - urllib3.connectionpool -   https://s3.amazonaws.com:443 "HEAD /models.huggingface.co/bert/camembert-base-config.json HTTP/1.1" 200 0
10/29/2020 08:09:14 - DEBUG - urllib3.connectionpool -   Starting new HTTPS connection (1): s3.amazonaws.com:443
10/29/2020 08:09:14 - DEBUG - urllib3.connectionpool -   https://s3.amazonaws.com:443 "HEAD /models.huggingface.co/bert/camembert-base-sentencepiece.bpe.model HTTP/1.1" 200 0
/home/theo_nabla_com/code/transformers/src/transformers/modeling_auto.py:822: FutureWarning: The class `AutoModelWithLMHead` is deprecated and will be removed in a future version. Please use `AutoModelForCausalLM` for causal language models, `AutoModelForMaskedLM` for masked language models and `AutoModelForSeq2SeqLM` for encoder-decoder models.
  FutureWarning,
10/29/2020 08:09:14 - DEBUG - urllib3.connectionpool -   Starting new HTTPS connection (1): cdn.huggingface.co:443
10/29/2020 08:09:14 - DEBUG - urllib3.connectionpool -   https://cdn.huggingface.co:443 "HEAD /camembert-base-pytorch_model.bin HTTP/1.1" 200 0
Some weights of CamembertForMaskedLM were not initialized from the model checkpoint at camembert-base and are newly initialized: ['lm_head.decoder.bias']
You should probably TRAIN this model on a down-stream task to be able to use it for predictions and inference.
/home/theo_nabla_com/code/transformers/src/transformers/tokenization_utils_base.py:1421: FutureWarning: The `max_len` attribute has been deprecated and will be removed in a future version, use `model_max_length` instead.
  FutureWarning,
10/29/2020 08:09:19 - DEBUG - filelock -   Attempting to acquire lock 140320072690936 on /home/theo_nabla_com/data/mydata-corpus/cached_lm_CamembertTokenizer_510_chunkaj.lock
10/29/2020 08:09:19 - INFO - filelock -   Lock 140320072690936 acquired on /home/theo_nabla_com/data/mydata-corpus/cached_lm_CamembertTokenizer_510_chunkaj.lock
```

(posted this on the discuss but it didn't get attention, [here](https://discuss.huggingface.co/t/hang-in-language-modelling-script/1792))
Pinging @sgugger<|||||>How long did you let the script hang for? It's probably tokenizing your dataset, which might take a while. Did you try with smaller files to see if it still hanged?<|||||>Hi @LysandreJik, I did try with a single 30MB file as reported, still hanging. It's hanging for hours. 
Lately I've thought that it was because of a download, as per your source code where filelock is used, but I've used the model in a notebook before so it should be cached?

EDIT: I'm very sorry, it is actually running now on the small file, I'm baffled - could've sworn it was stuck this week-end.
Culprit could the tokenizer then indeed, but I'm unclear why the filelock would be the breaking point.
I had modified the script file to force the logging level to be debug, and it does get stuck for multiple hours on one of the files when using the globbing pattern with `--train_data_files`<|||||>The issue with the `run_language_modeling.py` script is that it does not leverage the fast tokenizers, so it can take a while to tokenize every file.

This script has been deprecated for a couple of days now, and we have introduced several different scripts in the [`examples/language-modeling` directory](https://github.com/huggingface/transformers/tree/master/examples/language-modeling).

These updated scripts now leverage the fast tokenizers by default, which should make it way faster to tokenize your files *and* you won't need to split your files into multiple small files anymore.

Let me know if you get to use that script, and if it fits your needs.<|||||>Yup I've actually tried right after my last comment to actually debug it and saw you had pushed a new script. Using it right now, seems to go smoothly for now (tokenizing the 7GB file, entering a third progress bar, first two lasted 40min each, i'm assuming it's the tokenizer).
Thanks, closing this!<|||||>Glad it works!