The classic paper "The Incremental Garbage Collection of Processes" ( http://citeseer.ist.psu.edu/baker77incremental.html) describes "futures" and how particularly garbage collecting them when their pending result is no longer referenced. I've been playing with an implementation of futures in Concurrent Haskell (http://haskell.org/haskellwiki/Reactive), using MVars, and I'm stumped about how to GC non-winning threads in a race between futures ("parallel or"). I'm having winner kill loser, which seems to work fine, though is potentially dangerous w.r.t locked resources. Still, the elegance of a GC-based solution appeals to me. Has anyone explored process GC ideas for Concurrent Haskell (or STM)? Futures are implemented using Concurrent Haskell's MVars. I first tried using STM and TVars, simply using orElse to implement mappend for futures. However, I didn't see how to avoid nesting "atomically", which yielded a run-time error. If anyone has ideas about using STM & TVars for futures, I'd love to hear. Thanks, - Conal