Since this is just pure java, shouldn't it be the same on all 1.5
JVMs? Would it be different on other JVM implementations? Just to
verify, I checked on my Mac OS X 10.5 and in the Sun JDK 1.5 on
Windows XP, and it does appear to be the same.
On Dec 2, 9:17 am, Stuart Halloway <[EMAIL PROTECTED]> wrote:
> Cool, that's much better. Can we establish that all (or all important)
> Java 5+ VMs use AtomicLong in next?
>
> > Ah, I didn't see the call to next. The java docs do say that is the
> > implementation for that method, but they are lying:
>
> > protected int next(int bits) {
> > long oldseed, nextseed;
> > AtomicLong seed = this.seed;
> > do {
> > oldseed = seed.get();
> > nextseed = (oldseed * multiplier + addend) & mask;
> > } while (!seed.compareAndSet(oldseed, nextseed));
> > return (int)(nextseed >>> (48 - bits));
> > }
>
> > On Dec 2, 8:05 am, Stuart Halloway <[EMAIL PROTECTED]> wrote:
> >> nextDouble calls next, which according to Java 5 docs is:
>
> >> synchronized protected int next(int bits) {
> >> seed = (seed * 0x5DEECE66DL + 0xBL) & ((1L << 48) - 1);
> >> return (int)(seed >>> (48 - bits));
> >> }
>
> >> This is exactly the kind of thing I think we shouldn't have to worry
> >> about in Clojure.
>
> >> Stuart
>
> >>> Looks like the only synchronization is for lazy initialization of
> >>> the
> >>> instance of Random used by the static method:
>
> >>> public final class Math {
>
> >>> private static Random randomNumberGenerator;
>
> >>> private static synchronized void initRNG() {
> >>> if (randomNumberGenerator == null)
> >>> randomNumberGenerator = new Random();
> >>> }
>
> >>> public static double random() {
> >>> if (randomNumberGenerator == null) initRNG();
> >>> return randomNumberGenerator.nextDouble();
> >>> }
>
> >>> }
>
> >>> public class Random implements java.io.Serializable {
> >>> public Random() { this(++seedUniquifier + System.nanoTime()); }
> >>> private static volatile long seedUniquifier = 8682522807148012L;
>
> >>> public double nextDouble() {
> >>> long l = ((long)(next(26)) << 27) + next(27);
> >>> return l / (double)(1L << 53);
> >>> }
> >>> }
>
> >>> On Dec 2, 12:04 am, Stuart Halloway <[EMAIL PROTECTED]>
> >>> wrote:
> >>>> Clojure's rand delegates to Java's Math.random(), which I am pretty
> >>>> sure has a synchronized block in it.
>
> >>>> One problem with living on top of Java is calling into methods that
> >>>> have no (conceptual) need to be synchronized. This could hurt
> >>>> performance in an app carefully written in Clojure to avoid mutable
> >>>> state and locking. Since unsynchronized PRNGs exist, I would
> >>>> suggest
> >>>> we modify rand to use one. (I am willing to take the lead on
> >>>> writing
> >>>> one in Clojure if needed.)
>
> >>>> Thoughts?
>
> >>>> Stuart
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