On Feb 23, 2009, at 3:44 PM, Mark Volkmann wrote:
> > On Mon, Feb 23, 2009 at 2:31 PM, Dan <redalas...@gmail.com> wrote: >>> If I understand correctly, when there is an attempt to modify a Ref >>> that has been modified in another thread since the current >>> transaction >>> began then the current transaction will retry immediately. Isn't it >>> true that it has no chance of completing until the transaction that >>> changed that Ref either commits or rolls back? If that is true, >>> wouldn't it make sense to make the retry wait until that other >>> transaction is finished? Maybe the point of retrying immediately is >>> that it can at least get through some of its work (the part before >>> it >>> tries to change the Ref in question) before it has to check on that >>> other transaction again. >> >> Until there is a commit, no one but the transaction knows that >> those refs >> are meant to hold new values. > > Ah ... I didn't know that. I did know that the new value wasn't > visible outside the uncommitted transaction, but I thought other > transactions were aware that some other transaction was changing it. > Thanks for explaining that! > >> When your transaction notices something is >> wrong and retries, the other transaction will *always* be finished. >> Which of >> course doesn't mean another transaction might not prevent it to >> finish >> again. > This stuff is not right. You really shouldn't be concerned about the details of what happens when *inside* a transaction. The guarantees of http://clojure.org/refs are met, but the exact flow can get complex - there is blocking, deadlock avoidance and conflict resolution, aging and barging etc. I frequently see these "this happens then that happens" imaginings about what happens inside transactions. Nothing other than what is documented is guaranteed, and those guarantees are about what a transaction sees, and what its effects are on commit, not the order of operations inside a transaction. If you're not doing side effects in transactions, you shouldn't care, and you shouldn't be doing side effects in transactions. 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 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 -~----------~----~----~----~------~----~------~--~---
