On Aug 21 2013, at 17:01 , David M. Lloyd wrote: > On 8/21/13 5:37 PM, Brian Burkhalter wrote: >> With respect to this issue >> >> http://bugs.sun.com/view_bug.do?bug_id=6470700 >> >> the code of concern from java.lang.Math is >> >> 701 private static Random randomNumberGenerator; >> 702 >> 703 private static synchronized Random initRNG() { >> 704 Random rnd = randomNumberGenerator; >> 705 return (rnd == null) ? (randomNumberGenerator = new Random()) : >> rnd; >> 706 } >> >> 731 public static double random() { >> 732 Random rnd = randomNumberGenerator; >> 733 if (rnd == null) rnd = initRNG(); >> 734 return rnd.nextDouble(); >> 735 } >> >> where the class variable "randomNumberGenerator" is not used anywhere else >> in the class. The complaint is that this is an instance of the broken >> double-checked locking pattern. While at first glance this might appear to >> be the case, it does not seem so to me. It looks more like an attempt to >> avoid calling a synchronized method if "randomNumberGenerator" has already >> been initialized. >> >> A more typical pattern would be >> >> private static Random randomNumberGenerator; >> >> private static synchronized Random getRNG() { >> if (randomNumberGenerator == null) { >> randomNumberGenerator = new Random(); >> } >> return randomNumberGenerator; >> } >> >> public static double random() { >> return getRNG().nextDouble(); >> } >> >> Comments, please. > > I don't think you'd want to introduce the overhead of synchronization here. > It may be better in this case to use this kind of lazy init pattern: > > static final class Holder { > static final Random RNG = new Random(); > } > > public static double random() { > return Holder.RNG.nextDouble(); > } > > -- > - DML
David's suggestion seems very reasonable. Mike
