pytorch

030fa6cf - Split out reusable CUDAFuture from FutureNCCL (#48506)

Split out reusable CUDAFuture from FutureNCCL (#48506) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/48506 This commit is part of a stack that reworks FutureNCCL in order to extract a generic CUDA-aware Future subclass. The stack deliberately breaks up this transition into elementary changes, to make it easier to verify that the behavior is preserved (or to highlight how it gets changed). --- FutureNCCL is now a general-purpose type-agnostic multi-device class, so in this commit I extract it from ProcessGroupNCCL to make it available for wider use (notably by the RPC module). We'll call this new class CUDAFuture. We'll keep FutureNCCL as a subclass of CUDAFuture to deal with some NCCL peculiarity, namely the fact that the future becomes complete immediately upon creation. We can clean this up for good once we're done merging Future and Work. I'm not exactly sure of where to put CUDAFuture. It needs to be available to both c10d and RPC (which lives under torch/csrc). If I figured CMake out correctly (and that's a big if) I think c10d can only depend on ATen (I'll maybe add a comment with how I tracked that down). Hence we cannot put CUDAFuture in torch/csrc. On the other hand, RPC currently depends on c10d, because RPC agents use ProcessGroups internally, so it would be "ok" to put CUDAFuture in c10d. However, we want to get rid of ProcessGroups in RPC, and at that point RPC should in principle not depend on c10d. In that case, the only shared dep between the two that I see is ATen itself. While I'm a bit wary of putting it right in ATen, I think it might actually make sense. CUDAFuture is intended to be a general-purpose component that can be reused in all settings and is not particularly tied to c10d or RPC. Moreover, ATen already contains ivalue::Future, and it contains a lot of CUDA helpers, so CUDAFuture definitely belongs to the "closure" of what's already there. ghstack-source-id: 118180030 Test Plan: Unit tests? Reviewed By: wanchaol Differential Revision: D25180532 fbshipit-source-id: 697f655240dbdd3be22a568d5102ab27691f86d4