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import transformers
import torch
import torch.nn as nn
from torch.utils.data.sampler import RandomSampler
from torch.utils.data.distributed import DistributedSampler
from torch.utils.data.dataloader import DataLoader
from transformers.data.data_collator import DataCollator
from transformers.data.data_collator import DataCollatorWithPadding, InputDataClass
from typing import TYPE_CHECKING, Any, Callable, Dict, List, Optional, Tuple, Union
from transformers import is_torch_tpu_available
import numpy as np
class MultitaskModel(transformers.PreTrainedModel):
def __init__(self, encoder, taskmodels_dict):
"""
Setting MultitaskModel up as a PretrainedModel allows us
to take better advantage of Trainer features
"""
super().__init__(transformers.PretrainedConfig())
self.encoder = encoder
self.taskmodels_dict = nn.ModuleDict(taskmodels_dict)
@classmethod
def create(cls, model_name, model_type_dict, model_config_dict):
"""
This creates a MultitaskModel using the model class and config objects
from single-task models.
We do this by creating each single-task model, and having them share
the same encoder transformer.
"""
shared_encoder = None
taskmodels_dict = {}
do = nn.Dropout(p=0.2)
for task_name, model_type in model_type_dict.items():
model = model_type.from_pretrained(
model_name,
config=model_config_dict[task_name],
)
if shared_encoder is None:
shared_encoder = getattr(
model, cls.get_encoder_attr_name(model))
else:
setattr(model, cls.get_encoder_attr_name(
model), shared_encoder)
taskmodels_dict[task_name] = model
return cls(encoder=shared_encoder, taskmodels_dict=taskmodels_dict)
@classmethod
def get_encoder_attr_name(cls, model):
"""
The encoder transformer is named differently in each model "architecture".
This method lets us get the name of the encoder attribute
"""
model_class_name = model.__class__.__name__
if model_class_name.startswith("Bert"):
return "bert"
elif model_class_name.startswith("Roberta"):
return "roberta"
elif model_class_name.startswith("Albert"):
return "albert"
else:
raise KeyError(f"Add support for new model {model_class_name}")
def forward(self, task_name, **kwargs):
return self.taskmodels_dict[task_name](**kwargs)
def get_model(self, task_name):
return self.taskmodels_dict[task_name]
class NLPDataCollator(DataCollatorWithPadding): # DataCollatorWithPadding
"""
Extending the existing DataCollator to work with NLP dataset batches
"""
def collate_batch(self, features: List[Union[InputDataClass, Dict]]) -> Dict[str, torch.Tensor]:
first = features[0]
batch = None
if isinstance(first, dict):
# NLP data sets current works presents features as lists of dictionary
# (one per example), so we will adapt the collate_batch logic for that
if "labels" in first and first["labels"] is not None:
if first["labels"].dtype == torch.int64:
labels = torch.tensor([f["labels"]
for f in features], dtype=torch.long)
else:
labels = torch.tensor([f["labels"]
for f in features], dtype=torch.float)
batch = {"labels": labels}
for k, v in first.items():
if k != "labels" and v is not None and not isinstance(v, str):
batch[k] = torch.stack([f[k] for f in features])
return batch
else:
# otherwise, revert to using the default collate_batch
return DataCollatorWithPadding().collate_batch(features)
class StrIgnoreDevice(str):
"""
This is a hack. The Trainer is going call .to(device) on every input
value, but we need to pass in an additional `task_name` string.
This prevents it from throwing an error
"""
def to(self, device):
return self
class DataLoaderWithTaskname:
"""
Wrapper around a DataLoader to also yield a task name
"""
def __init__(self, task_name, data_loader):
self.task_name = task_name
self.data_loader = data_loader
self.batch_size = data_loader.batch_size
self.dataset = data_loader.dataset
def __len__(self):
return len(self.data_loader)
def __iter__(self):
for batch in self.data_loader:
batch["task_name"] = StrIgnoreDevice(self.task_name)
yield batch
class MultitaskDataloader:
"""
Data loader that combines and samples from multiple single-task
data loaders.
"""
def __init__(self, dataloader_dict):
self.dataloader_dict = dataloader_dict
self.num_batches_dict = {
task_name: len(dataloader)
for task_name, dataloader in self.dataloader_dict.items()
}
self.task_name_list = list(self.dataloader_dict)
self.dataset = [None] * sum(
len(dataloader.dataset)
for dataloader in self.dataloader_dict.values()
)
def __len__(self):
return sum(self.num_batches_dict.values())
def __iter__(self):
"""
For each batch, sample a task, and yield a batch from the respective
task Dataloader.
We use size-proportional sampling, but you could easily modify this
to sample from some-other distribution.
"""
task_choice_list = []
for i, task_name in enumerate(self.task_name_list):
task_choice_list += [i] * self.num_batches_dict[task_name]
task_choice_list = np.array(task_choice_list)
np.random.shuffle(task_choice_list)
dataloader_iter_dict = {
task_name: iter(dataloader)
for task_name, dataloader in self.dataloader_dict.items()
}
for task_choice in task_choice_list:
task_name = self.task_name_list[task_choice]
yield next(dataloader_iter_dict[task_name])
class MultitaskTrainer(transformers.Trainer):
def get_single_train_dataloader(self, task_name, train_dataset):
"""
Create a single-task data loader that also yields task names
"""
if self.train_dataset is None:
raise ValueError("Trainer: training requires a train_dataset.")
if False and is_torch_tpu_available():
train_sampler = get_tpu_sampler(train_dataset)
else:
train_sampler = (
RandomSampler(train_dataset)
if self.args.local_rank == -1
else DistributedSampler(train_dataset)
)
data_loader = DataLoaderWithTaskname(
task_name=task_name,
data_loader=DataLoader(
train_dataset,
batch_size=self.args.train_batch_size,
sampler=train_sampler,
collate_fn=self.data_collator.collate_batch,
),
)
return data_loader
def get_train_dataloader(self):
"""
Returns a MultitaskDataloader, which is not actually a Dataloader
but an iterable that returns a generator that samples from each
task Dataloader
"""
return MultitaskDataloader({
task_name: self.get_single_train_dataloader(
task_name, task_dataset)
for task_name, task_dataset in self.train_dataset.items()
})
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