On May 25, 11:29 am, Peter <peter.r.fos...@gmail.com> wrote: > Hi Rich, > > If you set up your object dependencies correctly then the objects you > want will stay in memory. Your history list would be a list of > WeakReference so it could be GC'd. > > This is nothing about read tracking, more about setting the correct > object dependencies so that the GC doesn't remove objects you aren't > quite finished with yet. > > I been writing up a description here. It's a simplified version of > what I've been playing > with.http://creativereality.com.au/notes/concurrency/54-mvcc-stm-gcd-ref-h... > > I kept the Transaction objects on the list, but you could consider > keeping a smaller object with just has a collection in it; associated > with the transaction. > >
I took a look at your notes. I have a few problems with it: First, and foremost, it creates interaction relationships between transactions that otherwise have no overlap. You see this in the memory blowup during overlapping transactions. This rubs against a design objective in Clojure's STM to absolutely minimize transactional overlap and interaction. Second, you do a lot of work in createNewTransaction (get a new timestamp, modify existing head, make new transaction the head). How is that made consistent? You really need a lock, and at that point have moved to a much heavier contention point than in the current Clojure STM. Third, I'm wary of such extensive use of WeakReferences. That may just be conservatism on my part. I had considered and implemented similar designs in the early stages of developing Clojure's STM, and, while they have some appeal, I think these 3 points will eventually cause pain in practice. Rich -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
