Fix #19417
Previously markLiveObject was not thread-safe, which ended up breaking during parallel GC. Unfortunately, this race generally only manifests in larger programs on with larger core counts, so it's not clear what a test should look like.
Previously markLiveObject was not thread-safe, which ended up breaking during parallel GC. Unfortunately, this race generally only manifests in larger programs on with larger core counts, so it's not clear what a test should look like.