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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