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# Copied from https://github.com/NVIDIA/DeepLearningExamples/blob/master/PyTorch/LanguageModeling/Transformer-XL/pytorch/utils/distributed.py
# Copyright (c) 2019-2020, NVIDIA CORPORATION. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import os
from contextlib import contextmanager
import torch
def init_distributed(cuda):
"""
Initializes distributed backend.
:param cuda: (bool) if True initializes nccl backend, if False initializes
gloo backend
"""
world_size = int(os.environ.get('WORLD_SIZE', 1))
distributed = (world_size > 1)
if distributed:
backend = 'nccl' if cuda else 'gloo'
torch.distributed.init_process_group(backend=backend,
init_method='env://')
assert torch.distributed.is_initialized()
return distributed
def barrier():
"""
Call torch.distributed.barrier() if distritubed is in use
"""
if torch.distributed.is_available() and torch.distributed.is_initialized():
torch.distributed.barrier()
def get_rank():
"""
Gets distributed rank or returns zero if distributed is not initialized.
"""
if torch.distributed.is_available() and torch.distributed.is_initialized():
rank = torch.distributed.get_rank()
else:
rank = 0
return rank
def get_world_size():
"""
Gets total number of distributed workers or returns one if distributed is
not initialized.
"""
if torch.distributed.is_available() and torch.distributed.is_initialized():
world_size = torch.distributed.get_world_size()
else:
world_size = 1
return world_size
def all_reduce_item(value, op='sum'):
"""
All-reduces single scalar value if distributed is in use
"""
if torch.distributed.is_available() and torch.distributed.is_initialized():
if op == 'sum' or op == 'mean':
dop = torch.distributed.ReduceOp.SUM
elif op == 'min':
dop = torch.distributed.ReduceOp.MIN
elif op == 'max':
dop = torch.distributed.ReduceOp.MAX
elif op == 'product':
dop = torch.distributed.ReduceOp.PRODUCT
else:
raise RuntimeError('Unsupported reduce op')
backend = torch.distributed.get_backend()
if backend == torch.distributed.Backend.NCCL:
device = torch.device('cuda')
elif backend == torch.distributed.Backend.GLOO:
device = torch.device('cpu')
else:
raise RuntimeError('Unsupported distributed backend')
tensor = torch.tensor(value, device=device)
torch.distributed.all_reduce(tensor, dop)
if op == 'mean':
tensor /= get_world_size()
ret = tensor.item()
else:
ret = value
return ret
@contextmanager
def sync_workers():
"""
Yields distributed rank and synchronizes all workers on exit.
"""
rank = get_rank()
yield rank
barrier()
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