On Sun, Sep 6, 2009 at 16:29, icemaze<icem...@gmail.com> wrote: > > Hello! > > First of all, let me congratulate with the devs for their great work: > I've been using Clojure for just a couple of weeks and I had a lot of > fun learning it and experimenting with it. > I'm starting a concurrency-heavy project and I feel Clojure is gonna > be a great choice! > > I'm thinking about opening a ticket but I'm not really sure. Let me > explain. > Both clojure.org and the > Pragmatic Bookshelf book seem to imply that Clojure's performance is > equivalent to Java. > If you need an example just look here: > http://clojure.org/java_interop, under "Support for Java Primitives". > Clojure's performance is great (much better than many other Lisps) but > I hit a "performance wall" in one of my functions. > This was not tragic at all: I just wrote a few lines of Java and I > built a new Java class. > It might be a problem with my code, but I read all performance-related > articles I > could find and I cannot improve things much more than this. > > Basically, I want to convert a short[] to a byte[], a common need when > dealing with audio. In Clojure I wrote: > > (defn shorts-to-bytes [#^shorts src #^bytes dst words] > (loop [src-offset (int 0) > dst-offset (int 0)] > (when (< src-offset words) > (let [sample (short (aget src src-offset))] > (aset-byte dst dst-offset (byte sample)) > (aset-byte dst (inc dst-offset) (byte (bit-shift-right sample > 8)))) > (recur (inc src-offset) (unchecked-add 2 dst-offset))))) > > > Adding type coercions helped a bit but it's still too slow. In Java > I wrote this method: > > public static void shortsToBytes(short[] src, byte[] dst, int len) > { > int idx = 0; > short s; > > while (len-- > 0) { > s = src[idx]; > dst[idx*2] = (byte)s; > dst[idx*2+1] = (byte)(s>>>8); > idx++; > } > }
Questions about how best to optimize clojure code to approach java performance have come up with fair regularity in the past. You might find some good ideas if you search through the archives a bit. That said, Clojure is a dynamic language with both the flexibility and overhead that this brings. It's a clever dynamic language: you can often find a set of type hints or other incantations such that the clojure compiler will produce byte code which the hotspot server vm will be able to optimize very well. This isn't always possible though, but that's where Clojure's Java interop and a little pragmatism comes in: You've got there a nice piece of Java code that does what you need and it's fast too. If you want that speed from your Clojure code, don't waste time optimizing the Clojure, just call the java implementation. (defn shorts-to-bytes [#^shorts src, #^bytes dst, words] (SomeClass/shortsToBytes src dst words)) (I guess I'm not much of a purist.) // Ben > > Then I timed them under both Clojure 1.0 and 1.1.0-SNAPSHOT and got > similar results. > > [...] > (doseq [n (range 5)] > (time (shorts-to-bytes a b 512000)) > (time (ArrayConverter/shortsToBytes a b 512000)) > (println)) > > > "Elapsed time: 516.527512 msecs" > "Elapsed time: 32.316904 msecs" > > "Elapsed time: 472.034037 msecs" > "Elapsed time: 5.096593 msecs" > > "Elapsed time: 437.755411 msecs" > "Elapsed time: 4.10872 msecs" > > "Elapsed time: 535.864767 msecs" > "Elapsed time: 3.106442 msecs" > > "Elapsed time: 880.127444 msecs" > "Elapsed time: 3.124339 msecs" > > > So Java outperforms Clojure by two orders of magnitude. > > Is there anything wrong with my code? I've been fine-tuning this code > for a couple of days now, to no avail. > > > Thank you and keep up! > Matt. > > > --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
