https://clojuredocs.org/clojure.core/ensure
Must be called in a transaction. Protects the ref from modification by other transactions. Returns the in-transaction-value of ref. Allows for more concurrency than (ref-set ref @ref) This can be read in two contradictory ways. Protecting a ref during a transaction sounds like it increases contention and slows the app down. "Allows for more concurrency" can be read as "Allows you to use a huge number of refs while still ensuring consistency." In other words, it sounds like it offers safety at the cost of speed. On Monday, March 6, 2017 at 6:06:46 AM UTC-5, bertschi wrote: > > For a lecture I have implemented the write-skew example from Mark > Volkmann's article: > > (defn write-skew [] > (let [cats (ref 1) > dogs (ref 1) > > john (future > (dosync > (when (< (+ @cats @dogs) 3) > (alter cats inc)))) > mary (future > (dosync > (when (< (+ @cats @dogs) 3) > (alter dogs inc))))] > (do @john @mary) > (dosync > (> (+ @cats @dogs) 3)))) > > (defn write-skew-demo [] > (let [count-write-skews (atom 0)] > (doseq [_ (range 25)] > (when (write-skew) > (swap! count-write-skews inc))) > @count-write-skews)) > > (write-skew-demo) > > When I try to fix this program using ensure, i.e. using (ensure dogs) in > john and (ensure cats) in mary, I find that it sometimes runs very slow. > > From the docs it says "Allows for more concurrency than (ref-set ref > @ref)". I would read that as "runs at least as fast as (ref-set ref @ref)", > but using (ref-set dogs @dogs) instead of (ensure dogs) and the same with > cats, does not exhibit these occasional runtime spikes. > > Am I misunderstanding something or is it a bug in ensure? > > > Nils > -- 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 --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
