AfflictionNetworks/samskivert
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Provide access to Randoms that use a faster thread-local Random.

Browse Source 
git-svn-id: https://samskivert.googlecode.com/svn/trunk@2903 6335cc39-0255-0410-8fd6-9bcaacd3b74c
This commit is contained in:
ray.j.greenwell
2010-10-01 00:14:39 +00:00
parent e398039478
commit c917825410
1 changed files with 203 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files
src/main/java/com/samskivert/util/Randoms.java
+203
View File
@@ -46,6 +46,25 @@ public class Randoms
return new Randoms(rand);
}
/**
* Get a thread-local Randoms instance that will not contend with any other thread
* for random number generation.
*
* <p><b>Note:</b> while all Randoms instances are thread-safe, normally they use a
* java.util.Random internally that must protect against multiple threads generating
* psuedorandom numbers with it simultaneously. This method will return a Randoms
* that uses an internal Random subclass with no such safeguards, resulting in much
* less overhead. However, you should probably not store a reference to the result,
* but instead always use it immediately as in the following example:
* <pre style="code">
* Puppy pick = Randoms.threadLocal().pick(Puppy.LITTER, null);
* </pre>
*/
public static Randoms threadLocal ()
{
return _localRandoms.get();
}
/**
* Returns a pseudorandom, uniformly distributed <code>int</code> value between 0 (inclusive)
* and the specified value (exclusive).
@@ -261,4 +280,188 @@ public class Randoms
/** The random number generator. */
protected final Random _r;
/** A ThreadLocal for accessing a thread-local version of Randoms. */
protected static final ThreadLocal<Randoms> _localRandoms = new ThreadLocal<Randoms>() {
public Randoms initialValue () {
return with(new ThreadLocalRandom());
}
};
/*
* TODO: This can be updated and this inner class removed
* when the samskivert library is JDK 1.7 compatible.
*-----------------------------------------------------------------
*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/licenses/publicdomain
*
* A random number generator isolated to the current thread. Like the
* global {@link java.util.Random} generator used by the {@link
* java.lang.Math} class, a {@code ThreadLocalRandom} is initialized
* with an internally generated seed that may not otherwise be
* modified. When applicable, use of {@code ThreadLocalRandom} rather
* than shared {@code Random} objects in concurrent programs will
* typically encounter much less overhead and contention. Use of
* {@code ThreadLocalRandom} is particularly appropriate when multiple
* tasks (for example, each a {@link ForkJoinTask}) use random numbers
* in parallel in thread pools.
*
* <p>Usages of this class should typically be of the form:
* {@code ThreadLocalRandom.current().nextX(...)} (where
* {@code X} is {@code Int}, {@code Long}, etc).
* When all usages are of this form, it is never possible to
* accidently share a {@code ThreadLocalRandom} across multiple threads.
*
* <p>This class also provides additional commonly used bounded random
* generation methods.
*
* @since 1.7
* @author Doug Lea
*/
static class ThreadLocalRandom extends Random {
// same constants as Random, but must be redeclared because private
private final static long multiplier = 0x5DEECE66DL;
private final static long addend = 0xBL;
private final static long mask = (1L << 48) - 1;
/**
* The random seed. We can't use super.seed.
*/
private long rnd;
/**
* Initialization flag to permit calls to setSeed to succeed only
* while executing the Random constructor. We can't allow others
* since it would cause setting seed in one part of a program to
* unintentionally impact other usages by the thread.
*/
boolean initialized;
// Padding to help avoid memory contention among seed updates in
// different TLRs in the common case that they are located near
// each other.
private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
/**
* Constructor called only by localRandom.initialValue.
*/
ThreadLocalRandom() {
super();
initialized = true;
}
/**
* Throws {@code UnsupportedOperationException}. Setting seeds in
* this generator is not supported.
*
* @throws UnsupportedOperationException always
*/
public void setSeed(long seed) {
if (initialized)
throw new UnsupportedOperationException();
rnd = (seed ^ multiplier) & mask;
}
protected int next(int bits) {
rnd = (rnd * multiplier + addend) & mask;
return (int) (rnd >>> (48-bits));
}
// as of JDK 1.6, this method does not exist in java.util.Random
// /**
// * Returns a pseudorandom, uniformly distributed value between the
// * given least value (inclusive) and bound (exclusive).
// *
// * @param least the least value returned
// * @param bound the upper bound (exclusive)
// * @throws IllegalArgumentException if least greater than or equal
// * to bound
// * @return the next value
// */
// public int nextInt(int least, int bound) {
// if (least >= bound)
// throw new IllegalArgumentException();
// return nextInt(bound - least) + least;
// }
/**
* Returns a pseudorandom, uniformly distributed value
* between 0 (inclusive) and the specified value (exclusive).
*
* @param n the bound on the random number to be returned. Must be
* positive.
* @return the next value
* @throws IllegalArgumentException if n is not positive
*/
public long nextLong(long n) {
if (n <= 0)
throw new IllegalArgumentException("n must be positive");
// Divide n by two until small enough for nextInt. On each
// iteration (at most 31 of them but usually much less),
// randomly choose both whether to include high bit in result
// (offset) and whether to continue with the lower vs upper
// half (which makes a difference only if odd).
long offset = 0;
while (n >= Integer.MAX_VALUE) {
int bits = next(2);
long half = n >>> 1;
long nextn = ((bits & 2) == 0) ? half : n - half;
if ((bits & 1) == 0)
offset += n - nextn;
n = nextn;
}
return offset + nextInt((int) n);
}
/**
* Returns a pseudorandom, uniformly distributed value between the
* given least value (inclusive) and bound (exclusive).
*
* @param least the least value returned
* @param bound the upper bound (exclusive)
* @return the next value
* @throws IllegalArgumentException if least greater than or equal
* to bound
*/
public long nextLong(long least, long bound) {
if (least >= bound)
throw new IllegalArgumentException();
return nextLong(bound - least) + least;
}
/**
* Returns a pseudorandom, uniformly distributed {@code double} value
* between 0 (inclusive) and the specified value (exclusive).
*
* @param n the bound on the random number to be returned. Must be
* positive.
* @return the next value
* @throws IllegalArgumentException if n is not positive
*/
public double nextDouble(double n) {
if (n <= 0)
throw new IllegalArgumentException("n must be positive");
return nextDouble() * n;
}
/**
* Returns a pseudorandom, uniformly distributed value between the
* given least value (inclusive) and bound (exclusive).
*
* @param least the least value returned
* @param bound the upper bound (exclusive)
* @return the next value
* @throws IllegalArgumentException if least greater than or equal
* to bound
*/
public double nextDouble(double least, double bound) {
if (least >= bound)
throw new IllegalArgumentException();
return nextDouble() * (bound - least) + least;
}
private static final long serialVersionUID = -5851777807851030925L;
}
}