pytorch

5c8535d5 - Make C++ RpcAgent::currentRPCAgent_ the source of truth of current RPC Agent (#32633)

Make C++ RpcAgent::currentRPCAgent_ the source of truth of current RPC Agent (#32633) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/32633 There were 2 sources of current RPC agent. - One is in Python world, `torch.distributedrpc.api._agent`. - The other is in C++ world, `RpcAgent::defaultRpcAgent_` Setting Python `_agent` to `None`, does not necessarily reset the C++ `defaultRpcAgent_` to `nullptr`. i.e. ``` torch.distributedrpc.api._agent = None ``` does not translate to ``` RpcAgent::defaultRpcAgent_ = nullptr ``` This PR is to remove this ambiguity, and use the C++ pointer as source of truth. The solution is to leverage a pybind11 behavior that it implicitly casts C++ `shared_ptr<RpcAgent>(nullptr)` to Python `None`. ghstack-source-id: 97293315 Test Plan: ``` buck test mode/dev-nosan //caffe2/test/distributed/rpc:rpc_fork -- test_duplicate_name buck build mode/dev-nosan //caffe2/test/distributed/rpc:rpc_fork buck-out/gen/caffe2/test/distributed/rpc/rpc_fork\#binary.par -r test_process_group_debug_info ``` ``` buck test mode/dev-nosan //caffe2/torch/fb/distributed/pytorch/tests:test_remote_module buck test mode/dev-nosan //caffe2/torch/fb/distributed/modules/tests:test_sharded_embedding buck test mode/dev-nosan //caffe2/torch/fb/distributed/modules/tests:test_sharded_pairwise_attention_pooling buck test mode/dev-nosan //caffe2/torch/fb/distributed/pytorch/tests:test_rpc ``` Differential Revision: D5733066 fbshipit-source-id: b3e6032ee975f19ca556497edbbf40b517b25be8