That's fair. It read to me, from his post, that Rune was using it for context sharing as well between threads (since that's the source of the highest level Arc

That's fair. It read to me, from his post, that Rune was using it for context sharing as well between threads (since that's the source of the highest level Arc in his code example) . If it's only for ref counts then it makes sense that a concurrent GC could avoid the issue