[Memory ordering] Fix data races in event manager startup/shutdown
This is part of a large-scale refactoring of our use of atomic memory operations (or, rather, fixing the lack therefore) in the runtime system. See !2642 (merged) for details.
This is part of a large-scale refactoring of our use of atomic memory operations (or, rather, fixing the lack therefore) in the runtime system. See !2642 (merged) for details.