Imported Upstream version 1.0.3upstream/1.0.3

1 files changed, 197 insertions, 0 deletions

diff --git a/src/main/java/jsr166y/ThreadLocalRandom.java b/src/main/java/jsr166y/ThreadLocalRandom.java
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+++ b/src/main/java/jsr166y/ThreadLocalRandom.java
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+/*
+ * 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/publicdomain/zero/1.0/
+ */
+
+package jsr166y;
+
+import java.util.Random;
+
+/**
+ * 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
+ */
+public class ThreadLocalRandom extends Random {
+    // same constants as Random, but must be redeclared because private
+    private static final long multiplier = 0x5DEECE66DL;
+    private static final long addend = 0xBL;
+    private static final 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;
+
+    /**
+     * The actual ThreadLocal
+     */
+    private static final ThreadLocal<ThreadLocalRandom> localRandom =
+        new ThreadLocal<ThreadLocalRandom>() {
+            protected ThreadLocalRandom initialValue() {
+                return new ThreadLocalRandom();
+            }
+    };
+
+
+    /**
+     * Constructor called only by localRandom.initialValue.
+     */
+    ThreadLocalRandom() {
+        super();
+        initialized = true;
+    }
+
+    /**
+     * Returns the current thread's {@code ThreadLocalRandom}.
+     *
+     * @return the current thread's {@code ThreadLocalRandom}
+     */
+    public static ThreadLocalRandom current() {
+        return localRandom.get();
+    }
+
+    /**
+     * 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));
+    }
+
+    /**
+     * 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 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;
+}