Make listenLoopInternal non-virtual (#37265)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/37265
In PGA, `listenLoopInternal` should not be virtual - PGA doesn't have any child classes that override this. Re-arranged some comments for `listenLoop` as well.
ghstack-source-id: 102880792
Test Plan: Sandcastle/CI
Differential Revision: D21238761
fbshipit-source-id: 5ec5058bc462182cf970faca9a734c11c7be2a32
