pytorch

339d3bf3 - [2/n] [torch/elastic] Introduce `C10dRendezvousBackend`. (#55636)

[2/n] [torch/elastic] Introduce `C10dRendezvousBackend`. (#55636) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/55636 This diff introduces: - The `C10dRendezvousBackend` type to support C10d stores as rendezvous backends. - A fix to the `TCPStore.compare_set()` function to support non-existent keys. - A placeholder `c10d-experimental` registry to instantiate C10d-baked rendezvous backends via `get_rendezvous_handler()`. ghstack-source-id: 126312162 Test Plan: Run the existing and newly-introduced unit/integration tests. Reviewed By: tierex Differential Revision: D27654492 fbshipit-source-id: 09f498138b35186de4b0e174adb33fb5b5aa4b52