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6959259: Minor improvements to static Random field caching

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Cache fields in locals; small javadoc clarifications

Reviewed-by: emcmanus, dholmes, forax, dl
This commit is contained in:
Martin Buchholz 2010-06-10 15:55:26 -07:00
parent e267adc80a
commit d6dea71e06
3 changed files with 28 additions and 22 deletions
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21
jdk/src/share/classes/java/lang/Math.java
View File

@ -681,9 +681,9 @@ public final class Math {
private static Random randomNumberGenerator;
private static synchronized void initRNG() {
if (randomNumberGenerator == null)
randomNumberGenerator = new Random();
private static synchronized Random initRNG() {
Random rnd = randomNumberGenerator;
return (rnd == null) ? (randomNumberGenerator = new Random()) : rnd;
}
/**
@ -694,9 +694,11 @@ public final class Math {
*
* <p>When this method is first called, it creates a single new
* pseudorandom-number generator, exactly as if by the expression
* <blockquote>{@code new java.util.Random}</blockquote> This
* new pseudorandom-number generator is used thereafter for all
* calls to this method and is used nowhere else.
*
* <blockquote>{@code new java.util.Random()}</blockquote>
*
* This new pseudorandom-number generator is used thereafter for
* all calls to this method and is used nowhere else.
*
* <p>This method is properly synchronized to allow correct use by
* more than one thread. However, if many threads need to generate
@ -705,11 +707,12 @@ public final class Math {
*
* @return a pseudorandom {@code double} greater than or equal
* to {@code 0.0} and less than {@code 1.0}.
* @see java.util.Random#nextDouble()
* @see Random#nextDouble()
*/
public static double random() {
if (randomNumberGenerator == null) initRNG();
return randomNumberGenerator.nextDouble();
Random rnd = randomNumberGenerator;
if (rnd == null) rnd = initRNG();
return rnd.nextDouble();
}
/**

21
jdk/src/share/classes/java/lang/StrictMath.java
View File

@ -667,9 +667,9 @@ public final class StrictMath {
private static Random randomNumberGenerator;
private static synchronized void initRNG() {
if (randomNumberGenerator == null)
randomNumberGenerator = new Random();
private static synchronized Random initRNG() {
Random rnd = randomNumberGenerator;
return (rnd == null) ? (randomNumberGenerator = new Random()) : rnd;
}
/**
@ -680,9 +680,11 @@ public final class StrictMath {
*
* <p>When this method is first called, it creates a single new
* pseudorandom-number generator, exactly as if by the expression
* <blockquote>{@code new java.util.Random}</blockquote> This
* new pseudorandom-number generator is used thereafter for all
* calls to this method and is used nowhere else.
*
* <blockquote>{@code new java.util.Random()}</blockquote>
*
* This new pseudorandom-number generator is used thereafter for
* all calls to this method and is used nowhere else.
*
* <p>This method is properly synchronized to allow correct use by
* more than one thread. However, if many threads need to generate
@ -691,11 +693,12 @@ public final class StrictMath {
*
* @return a pseudorandom {@code double} greater than or equal
* to {@code 0.0} and less than {@code 1.0}.
* @see java.util.Random#nextDouble()
* @see Random#nextDouble()
*/
public static double random() {
if (randomNumberGenerator == null) initRNG();
return randomNumberGenerator.nextDouble();
Random rnd = randomNumberGenerator;
if (rnd == null) rnd = initRNG();
return rnd.nextDouble();
}
/**

8
jdk/src/share/classes/java/util/Collections.java
View File

@ -463,10 +463,10 @@ public class Collections {
* its list-iterator does not support the <tt>set</tt> operation.
*/
public static void shuffle(List<?> list) {
if (r == null) {
r = new Random();
}
shuffle(list, r);
Random rnd = r;
if (rnd == null)
r = rnd = new Random();
shuffle(list, rnd);
}
private static Random r;