[gloo] dont hold locks in calls to buffer in ProcessGroupGloo:RecvWork::wait() and (#33926)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/33926
The UnboundBuffer calls here are already protected by a mutex. We only
need to hold the lock while writing the shared structures completed_ and
exception_.
ghstack-source-id: 99315427
Test Plan:
CI
CI
Differential Revision: D20154546
fbshipit-source-id: d1b74508c917b21acdcd0f6a914eb0455437ca0e
