Nice blog post! I also wrote a concurrent reference counted cycle collector in Rust (https://github.com/chc4/samsara, https://redvice.org/2023/samsara-garbage-collector/) though never published it to crates.io. It's neat to see the different choices that people made implementing similar goals, and dumpster works pretty differently from how I did it. I hit the same problems wrt concurrent mutation of the graph when trying to count in-degree of nodes, or adding references during a collection - I didn't even think of doing generational references and just have a RwLock...