Ah, maybe I should have read the thread on ensure before I posted this! =) (dosync (ensure r) (alter r f))
works. On Mon, Mar 15, 2010 at 1:10 PM, Garth Sheldon-Coulson <g...@mit.edu> wrote: > Apologies in advance if this question has a simple answer that I'm > overlooking! > > Suppose I have a ref or atom and I periodically need to call a long-running > function on it: > > (def r (ref 0)) > (defn f [_] (Thread/sleep 1000) -10) > > Suppose also that the ref is being modified from other threads at shorter > intervals than the execution time of f. I'll simulate this with: > > (future (loop [] (Thread/sleep 500) (dosync (alter r inc)) (recur))) > > In this situation, the following will never return: > > (dosync (alter r f)) > > The reason is that the value of r never stays the same long enough for f to > see and then update a consistent value. > > Is there a way to cause r to be locked during the (dosync (alter r f)) so > that all other alterations will be held until after it completes? I know > this isn't normally the desired behavior, but is it possible to obtain? > > Neither of the following works: > (locking r (dosync (alter r f))) > (dosync (locking r (alter r f))) > > I could simulate part of the behavior I want with agents and await, but > then I lose the ability to synchronize alterations. > > Thanks for any insights! > > Garth > -- 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
