[4/n] [torch/elastic] Fix the finalizer of PeriodicTimer (#56532)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/56532
This PR fixes a subtle issue with the finalizer implementation of `_PeriodicTimer`.
We avoid using a regular finalizer (a.k.a. `__del__`) for stopping the timer as joining a daemon thread during the interpreter shutdown can cause deadlocks. The `weakref.finalize` is a superior alternative that provides a consistent behavior regardless of the GC implementation.
ghstack-source-id: 126978904
Test Plan: Run the existing unit tests as there is no behavioral change.
Reviewed By: H-Huang
Differential Revision: D27889289
fbshipit-source-id: a248cf6fd1abc4da8bef90e160fa9669a4961fa5
