Hi Thomas, Normally I'd agree with you, but in my case it actually works quite well since I don't need to expire or worry about sizing. This is for caching objects on IntelliJ parse tree elements, and the element with its cached values is thrown away every time the document is parsed, so these are pretty transient caches. In this particular case the calculation isn't too heavyweight either so recalculating it in the unlikely event of contention isn't a big deal. In fact, this discussion and the related thinking has made me realise that my original solution was actually sufficient for my somewhat strange use case, which is nice :-). For more typical server side caching, I agree that Guava would be a great solution.
Cheers, Colin On 1 September 2014 20:54, Thomas Heller <th.hel...@gmail.com> wrote: > As much as I like Clojure and atoms, I do not think they are a good fit > for caching. Not only is it impossible to address the concurrency issues > related to multiple threads loading the same object, but you also have to > do expiration and size management yourself. Immutability doesn't help much > for caching either. There is core.cache that does some bits but I probably > would recommend using something like CacheBuilder from the guava libs: > > See > https://code.google.com/p/guava-libraries/ > > http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/cache/CacheBuilder.html > > Its Java but the Clojure<->Java interop is so good that it doesn't matter > much. > > On Saturday, August 30, 2014 7:27:05 AM UTC+2, Colin Fleming wrote: >> >> Hi all, >> >> I want to use a map to cache values based on a key. I'm planning to use >> an atom for this. My basic operation is "give me the value for this key" - >> if the value exists in the map then that value should be returned, >> otherwise a new value should be calculated, inserted in the map and then >> returned. My plan is to implement something like the following: >> >> >> (defn ensure [cache key] (if (contains? cache key) cache (assoc cache >> key (calc-value key))))(let [value (get (swap! cache ensure key) key)] ... >> do my thing with value ...) >> >> >> So 'ensure' ensures that the cache contains the value for key, the swap! >> operation returns the cache with the value and then I get it out. This >> works but feels a little clumsy, is there a better way to do this? >> >> Also, looking at the Atom source code, I see that this will cause a CAS >> operation even if the value returned from swap! is identical to the >> original value. It seems like a reasonable optimisation would be to check >> if the values are identical and not update if so - is there a reason this >> might not be a good idea? >> >> Thanks, >> Colin >> > -- > 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. > -- 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.
