update cache_dir in readme and examples

Author: thomwolf

README.md

@@ -162,13 +162,12 @@ Here is a detailed documentation of the classes in the package and how to use th
 To load one of Google AI's pre-trained models or a PyTorch saved model (an instance of `BertForPreTraining` saved with `torch.save()`), the PyTorch model classes and the tokenizer can be instantiated as
 
 ```python
-model = BERT_CLASS.from_pretrain(PRE_TRAINED_MODEL_NAME_OR_PATH)
+model = BERT_CLASS.from_pretrain(PRE_TRAINED_MODEL_NAME_OR_PATH, cache_dir=None)
 ```
 
 where
 
 - `BERT_CLASS` is either the `BertTokenizer` class (to load the vocabulary) or one of the six PyTorch model classes (to load the pre-trained weights): `BertModel`, `BertForMaskedLM`, `BertForNextSentencePrediction`, `BertForPreTraining`, `BertForSequenceClassification` or `BertForQuestionAnswering`, and
-
 - `PRE_TRAINED_MODEL_NAME_OR_PATH` is either:
 
   - the shortcut name of a Google AI's pre-trained model selected in the list:
@@ -184,7 +183,8 @@ where
       - `bert_config.json` a configuration file for the model, and
       - `pytorch_model.bin` a PyTorch dump of a pre-trained instance `BertForPreTraining` (saved with the usual `torch.save()`)
 
-If `PRE_TRAINED_MODEL_NAME_OR_PATH` is a shortcut name, the pre-trained weights will be downloaded from AWS S3 (see the links [here](pytorch_pretrained_bert/modeling.py)) and stored in a cache folder to avoid future download (the cache folder can be found at `~/.pytorch_pretrained_bert/`).
+  If `PRE_TRAINED_MODEL_NAME_OR_PATH` is a shortcut name, the pre-trained weights will be downloaded from AWS S3 (see the links [here](pytorch_pretrained_bert/modeling.py)) and stored in a cache folder to avoid future download (the cache folder can be found at `~/.pytorch_pretrained_bert/`).
+- `cache_dir` can be an optional path to a specific directory to download and cache the pre-trained model weights. This option is useful in particular when you are using distributed training: to avoid concurrent access to the same weights you can set for example `cache_dir='./pretrained_model_{}'.format(args.local_rank)` (see the section on distributed training for more information)
 
 Example:
 ```python

examples/run_classifier.py

@@ -482,7 +482,8 @@ def main():
             len(train_examples) / args.train_batch_size / args.gradient_accumulation_steps * args.num_train_epochs)
 
     # Prepare model
-    model = BertForSequenceClassification.from_pretrained(args.bert_model, len(label_list))
+    model = BertForSequenceClassification.from_pretrained(args.bert_model, len(label_list),
+                cache_dir=PYTORCH_PRETRAINED_BERT_CACHE / 'distributed_{}'.format(args.local_rank))
     if args.fp16:
         model.half()
     model.to(device)

examples/run_squad.py

@@ -821,7 +821,8 @@ def main():
             len(train_examples) / args.train_batch_size / args.gradient_accumulation_steps * args.num_train_epochs)
 
     # Prepare model
-    model = BertForQuestionAnswering.from_pretrained(args.bert_model)
+    model = BertForQuestionAnswering.from_pretrained(args.bert_model,
+                cache_dir=PYTORCH_PRETRAINED_BERT_CACHE / 'distributed_{}'.format(args.local_rank))
     if args.fp16:
         model.half()
     model.to(device)

pytorch_pretrained_bert/__init__.py

@@ -3,3 +3,4 @@
                        BertForMaskedLM, BertForNextSentencePrediction,
                        BertForSequenceClassification, BertForQuestionAnswering)
 from .optimization import BertAdam
+from .file_utils import PYTORCH_PRETRAINED_BERT_CACHE