pytorch

a2b4177c - Add barrier() at the end of init_process_group and new_group. (#45181)

Add barrier() at the end of init_process_group and new_group. (#45181) Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/45181 `init_process_group` and `new_group` update a bunch of global variables after initializing the actual process group. As a result, there is a race that after initializing the process group on say rank 0, if we immediately check the default process group on rank 1 (say via RPC), we might actually get an error since rank 1 hasn't yet updated its _default_pg variable. To resolve this issue, I've added barrier() at the end of both of these calls. This ensures that once these calls return we are guaranteed about correct initialization on all ranks. Since these calls are usually done mostly during initialization, it should be fine to add the overhead of a barrier() here. #Closes: https://github.com/pytorch/pytorch/issues/40434, https://github.com/pytorch/pytorch/issues/40378 ghstack-source-id: 112923112 Test Plan: Reproduced the failures in https://github.com/pytorch/pytorch/issues/40434 and https://github.com/pytorch/pytorch/issues/40378 and verified that this PR fixes the issue. Reviewed By: mrshenli Differential Revision: D23858025 fbshipit-source-id: c4d5e46c2157981caf3ba1525dec5310dcbc1830