[jit] In RPC Server, handle TorchScript continuations asynchronously (#34109)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34109
This change adds glue to GraphExecutor to give the RPC server
access to the future-based Interpreter::runAsync() api.
Previously, if a server encounted a TorchScript continuation-based block
with fork/wait, it would simply block in the server thread until the handler
completed, since it uses the synchronous Interpreter::run() api.
With the ivalue::Future returned by the Interpreter, we can run the
TorchScript code asynchronously from c++ simply by connecting its
callback to the server callback.
We add test cases to cover the new logic, both rpc_async and remote.
ghstack-source-id: 101245438
Test Plan: buck test mode/dev-nosan caffe2/test/distributed/rpc/...
Differential Revision: D20194321
fbshipit-source-id: 16785ec5d9ed0b16cb1ffab0a9771a77de30fcb0
