pytorch

d5b38984 - Let RPC return FutureIValue instead of FutureMessage (#37519)

Let RPC return FutureIValue instead of FutureMessage (#37519) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/37519 closes #37446 Currently FutureMessage is used in several places: 1. `rpc_async` returns a `FutureMessage` object and we expose it as `torch.distributed.rpc.Future`. From applications perspective, they are expecting a `py::object` instead of a `Message`, and we do the conversion in the `Future.wait()` pybind method. 2. RPC autograd profiler takes `FutureMessage` and installs callbacks to it. The profiler actually only need a `Future<T>` and does not care what `T` is. 3. `OwnerRRef` exposes a `getFuture()` API which returns a `FutureMessage`. This `FutureMessage` will be marked completed when the value referenced by the `OwnerRRef` is ready. `OwnerRRef` does not need it to be a Message type either, it actually creates an empty `Message` to mark the `Future`. The above places are using `FutureMessage`, but they don't really need a `Message`, and `Message` is a communication layer type that applications or profiler or the RRef shouldn't be aware of. Another motivation for making this change is that for async RPC UDF #36071, we are going to allow application to call `markCompleted` in Python. If we still use `FutureMessage`, then in the `markCompleted` pybind function, it needs to convert the provided `py::object` into a specific message type, which is leaking communication layer code to pybind functions. Even if this is doable, we will have two entities (RPC agent and pybind Python frontend) accessing the same request callback logic. This is too messy. This commit replaces all surface `FutureMessage` with `FutureIValue`, so that `FutureMessage` is no longer visible from Python land. Note that this does not cause BC issues, as the Python Future type name and its API stay intact. Internally, we still have `FutureMessage` in the communication layer. Test Plan: Imported from OSS Reviewed By: xush6528 Differential Revision: D21308887 Pulled By: mrshenli fbshipit-source-id: 4f574f38e83125081f142813cfdde56119522089