Hey Boost, After struggling with breaking shared_ptr cycles in my app, I wrote a little concurrent garbage collector which uses boost::lockfree::queue. Its actually fairly general purpose, and I've released the code here: https://gist.github.com/wtholliday/5793270 Inspired by my question on stack overflow: http://stackoverflow.com/questions/17116189/concurrent-garbage-collection-fo... I'm also working on releasing my unit test... its just quite dependent on other code. For the interface: the basic idea is you have a RootPtr<T> used to manage the collector's root set (please forgive my propensity for CamelCase). You have to explicitly manage references between collectable objects (via AddEdge and RemoveEdge functions), but I think that could be made safe using another smart pointer type which knows the collectable object which owns it. At this point I'm not too concerned about performance, as my object graphs aren't that big. I bet a GC guru could implement this without using a queue of events. Anyway, this is the kind of thing I'd love to see in boost someday, so it would be great to read your opinions of it :-) cheers - Taylor W. Taylor Holliday, Owner/Founder Subatomic Software, San Francisco