Try to set! *warn-on-reflection* to true and you'll find out that there's a lot of reflection going on when using direct java interop.
Try benchmarking (.length ^String sss) and you'll see the difference Geo writes: > I am writing an expensive algorithms in Clojure and while trying to > optimize the code I discovered something that puzzled me. Clojure count and > get functions are much faster on strings than direct interop with .length > and .charAt. On my machine I get the following: > > (def sss (apply str (repeat 10000000 \a))) > > I execute each of the following tests a few times: > > (time (dotimes [_ 1000] (count sss))) > "Elapsed time: 0.56 msecs" > "Elapsed time: 0.539 msecs" > "Elapsed time: 0.551 msecs" > "Elapsed time: 0.453 msecs" > "Elapsed time: 0.612 msecs" > > (time (dotimes [_ 1000] (.length sss))) > "Elapsed time: 170.819 msecs" > "Elapsed time: 114.892 msecs" > "Elapsed time: 10.111 msecs" > "Elapsed time: 32.106 msecs" > "Elapsed time: 10.803 msecs" > > Even after something under the hood warms up (feel free to enlighten me :). > .length is still significantly slower. > > (time (dotimes [_ 1000] (get sss (rand-int 1000)))) > "Elapsed time: 4.651 msecs" > "Elapsed time: 3.699 msecs" > "Elapsed time: 3.672 msecs" > "Elapsed time: 4.561 msecs" > "Elapsed time: 3.742 msecs" > > (time (dotimes [_ 1000] (.charAt sss (rand-int 1000)))) > "Elapsed time: 13.211 msecs" > "Elapsed time: 14.874 msecs" > "Elapsed time: 32.044 msecs" > "Elapsed time: 13.849 msecs" > "Elapsed time: 39.493 msecs" > > .charAt is also significantly slower than get. > > By replacing .length with count and .charAt with get I was able to reduce > the running time of my algo by orders of magnitude. > > These results are surprising and puzzling. You'd think direct interop with > Java would be the faster. Can anyone venture a guess or explain what's > going on here? > > -- -- -- 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/groups/opt_out.
