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import torch
from ._functions import Scatter, Gather
def scatter(inputs, target_gpus, dim=0):
r"""
Slices tensors into approximately equal chunks and
distributes them across given GPUs. Duplicates
references to objects that are not tensors.
"""
def scatter_map(obj):
if isinstance(obj, torch.Tensor):
return Scatter.apply(target_gpus, None, dim, obj)
if isinstance(obj, tuple) and len(obj) > 0:
return list(zip(*map(scatter_map, obj)))
if isinstance(obj, list) and len(obj) > 0:
return list(map(list, zip(*map(scatter_map, obj))))
if isinstance(obj, dict) and len(obj) > 0:
return list(map(type(obj), zip(*map(scatter_map, obj.items()))))
return [obj for targets in target_gpus]
# After scatter_map is called, a scatter_map cell will exist. This cell
# has a reference to the actual function scatter_map, which has references
# to a closure that has a reference to the scatter_map cell (because the
# fn is recursive). To avoid this reference cycle, we set the function to
# None, clearing the cell
try:
res = scatter_map(inputs)
finally:
scatter_map = None
return res
def scatter_kwargs(inputs, kwargs, target_gpus, dim=0):
r"""Scatter with support for kwargs dictionary"""
inputs = scatter(inputs, target_gpus, dim) if inputs else []
kwargs = scatter(kwargs, target_gpus, dim) if kwargs else []
if len(inputs) < len(kwargs):
inputs.extend([() for _ in range(len(kwargs) - len(inputs))])
elif len(kwargs) < len(inputs):
kwargs.extend([{} for _ in range(len(inputs) - len(kwargs))])
inputs = tuple(inputs)
kwargs = tuple(kwargs)
return inputs, kwargs
def gather(outputs, target_device, dim=0):
r"""
Gathers tensors from different GPUs on a specified device
(-1 means the CPU).
"""
def gather_map(outputs):
out = outputs[0]
if isinstance(out, torch.Tensor):
return Gather.apply(target_device, dim, *outputs)
if out is None:
return None
if isinstance(out, dict):
if not all((len(out) == len(d) for d in outputs)):
raise ValueError('All dicts must have the same number of keys')
return type(out)(((k, gather_map([d[k] for d in outputs]))
for k in out))
return type(out)(map(gather_map, zip(*outputs)))
# Recursive function calls like this create reference cycles.
# Setting the function to None clears the refcycle.
try:
res = gather_map(outputs)
finally:
gather_map = None
return res
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