Mercurial > hg > icedtea9-forest > jdk
changeset 5579:944676ef3c58
7071826: Avoid benign race condition in initialization of UUID
Summary: Avoids mostly benign but sometimes expensive race condition on initialization of UUID.numberGenerator which is used by UUID.randomUUID()
Reviewed-by: alanb, chegar
author | mduigou |
---|---|
date | Fri, 11 May 2012 11:31:46 -0700 |
parents | 3e83229a3779 |
children | 85d7677a75bf |
files | src/share/classes/java/util/UUID.java test/java/util/UUID/UUIDTest.java |
diffstat | 2 files changed, 23 insertions(+), 11 deletions(-) [+] |
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--- a/src/share/classes/java/util/UUID.java Fri May 11 10:09:18 2012 +0100 +++ b/src/share/classes/java/util/UUID.java Fri May 11 11:31:46 2012 -0700 @@ -90,9 +90,11 @@ /* * The random number generator used by this class to create random - * based UUIDs. + * based UUIDs. In a holder class to defer initialization until needed. */ - private static volatile SecureRandom numberGenerator = null; + private static class Holder { + static final SecureRandom numberGenerator = new SecureRandom(); + } // Constructors and Factories @@ -137,10 +139,7 @@ * @return A randomly generated {@code UUID} */ public static UUID randomUUID() { - SecureRandom ng = numberGenerator; - if (ng == null) { - numberGenerator = ng = new SecureRandom(); - } + SecureRandom ng = Holder.numberGenerator; byte[] randomBytes = new byte[16]; ng.nextBytes(randomBytes); @@ -255,7 +254,8 @@ * The variant number has the following meaning: * <p><ul> * <li>0 Reserved for NCS backward compatibility - * <li>2 The Leach-Salz variant (used by this class) + * <li>2 <a href="http://www.ietf.org/rfc/rfc4122.txt">IETF RFC 4122</a> + * (Leach-Salz), used by this class * <li>6 Reserved, Microsoft Corporation backward compatibility * <li>7 Reserved for future definition * </ul> @@ -265,7 +265,7 @@ public int variant() { // This field is composed of a varying number of bits. // 0 - - Reserved for NCS backward compatibility - // 1 0 - The Leach-Salz variant (used by this class) + // 1 0 - The IETF aka Leach-Salz variant (used by this class) // 1 1 0 Reserved, Microsoft backward compatibility // 1 1 1 Reserved for future definition. return (int) ((leastSigBits >>> (64 - (leastSigBits >>> 62)))
--- a/test/java/util/UUID/UUIDTest.java Fri May 11 10:09:18 2012 +0100 +++ b/test/java/util/UUID/UUIDTest.java Fri May 11 11:31:46 2012 -0700 @@ -58,6 +58,12 @@ List list = new LinkedList(); for (int i=0; i<100; i++) { UUID u1 = UUID.randomUUID(); + if (4 != u1.version()) { + throw new Exception("bad version"); + } + if (2 != u1.variant()) { + throw new Exception("bad variant"); + } if (list.contains(u1)) throw new Exception("random UUID collision very unlikely"); list.add(u1); @@ -70,10 +76,16 @@ List list = new LinkedList(); for (int i=0; i<100; i++) { byteSource.nextBytes(someBytes); - UUID test = UUID.nameUUIDFromBytes(someBytes); - if (list.contains(test)) + UUID u1 = UUID.nameUUIDFromBytes(someBytes); + if (3 != u1.version()) { + throw new Exception("bad version"); + } + if (2 != u1.variant()) { + throw new Exception("bad variant"); + } + if (list.contains(u1)) throw new Exception("byte UUID collision very unlikely"); - list.add(test); + list.add(u1); } }