102 lines
3.7 KiB
Python
102 lines
3.7 KiB
Python
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"""Async API.
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This module contains the API for parallelism in TorchScript, notably:
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* torch.jit.fork
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* torch.jit.wait
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This is not intended to be imported directly; please use the exposed
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functionalities in `torch.jit`.
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"""
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import torch
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from torch._jit_internal import Future
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from torch.jit._builtins import _register_builtin
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from torch.utils import set_module
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set_module(Future, "torch.jit")
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def fork(func, *args, **kwargs):
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r"""
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Create an asynchronous task executing `func` and a reference to the value of the result of this execution.
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`fork` will return immediately, so the return value of `func` may not have been computed yet. To force completion
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of the task and access the return value invoke `torch.jit.wait` on the Future. `fork` invoked
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with a `func` which returns `T` is typed as `torch.jit.Future[T]`. `fork` calls can be arbitrarily
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nested, and may be invoked with positional and keyword arguments.
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Asynchronous execution will only occur when run in TorchScript. If run in pure python,
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`fork` will not execute in parallel. `fork` will also not execute in parallel when invoked
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while tracing, however the `fork` and `wait` calls will be captured in the exported IR Graph.
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.. warning::
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`fork` tasks will execute non-deterministically. We recommend only spawning
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parallel fork tasks for pure functions that do not modify their inputs,
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module attributes, or global state.
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Args:
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func (callable or torch.nn.Module): A Python function or `torch.nn.Module`
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that will be invoked. If executed in TorchScript, it will execute asynchronously,
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otherwise it will not. Traced invocations of fork will be captured in the IR.
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``*args``, ``**kwargs``: arguments to invoke `func` with.
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Returns:
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`torch.jit.Future[T]`: a reference to the execution of `func`. The value `T`
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can only be accessed by forcing completion of `func` through `torch.jit.wait`.
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Example (fork a free function):
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.. code-block:: python
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import torch
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from torch import Tensor
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def foo(a : Tensor, b : int) -> Tensor:
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return a + b
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def bar(a):
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fut : torch.jit.Future[Tensor] = torch.jit.fork(foo, a, b=2)
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return torch.jit.wait(fut)
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script_bar = torch.jit.script(bar)
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input = torch.tensor(2)
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# only the scripted version executes asynchronously
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assert script_bar(input) == bar(input)
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# trace is not run asynchronously, but fork is captured in IR
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graph = torch.jit.trace(bar, (input,)).graph
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assert "fork" in str(graph)
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Example (fork a module method):
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.. code-block:: python
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import torch
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from torch import Tensor
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class AddMod(torch.nn.Module):
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def forward(self, a: Tensor, b : int):
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return a + b
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class Mod(torch.nn.Module):
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def __init__(self):
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super(self).__init__()
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self.mod = AddMod()
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def forward(self, input):
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fut = torch.jit.fork(self.mod, a, b=2)
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return torch.jit.wait(fut)
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input = torch.tensor(2)
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mod = Mod()
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assert mod(input) == torch.jit.script(mod).forward(input)
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"""
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return torch._C.fork(func, *args, **kwargs)
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def wait(future):
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r"""
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Force completion of a `torch.jit.Future[T]` asynchronous task, returning the result of the task.
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See :func:`~fork` for docs and examples.
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Args:
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future (torch.jit.Future[T]): an asynchronous task reference, created through `torch.jit.fork`
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Returns:
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`T`: the return value of the completed task
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"""
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return torch._C.wait(future)
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_register_builtin(wait, "aten::wait")
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