Expose torch.futures.Future (#39008)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39008
This commit adds a `torch.futures.Future` type and exposes its ctor,
`wait`, `then`, and `set_result` APIs. This type is currently a
wrapper of `c10::ivalue::Future` and mainly used by RPC for now. Later,
we could revamp c10d APIs to return this `Future` type as well. More
utils will be added into `torch.futures` package in followup PRs.
Test Plan: Imported from OSS
Differential Revision: D21723022
Pulled By: mrshenli
fbshipit-source-id: 92e56160544e9bf00d11db3e8347a1b9707882c9
