src/jsr166y/ThreadLocalRandom.java

/*
 * 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
 */

package jsr166y;
import java.util.*;

/**
 * A Random number generator with the same properties as {@link
 * Random} but isolated to the current Thread.  Like the global
 * generator used by {@link java.lang.Math}, a ThreadLocalRandom is
 * initialized with an internally generated seed that may not
 * otherwise be modified. When applicable, use of ThreadLocalRandom
 * rather than shared Random objects in concurrent programs will
 * typically encounter less overhead and contention. The most common
 * usage form is: <code>ThreadLocalRandom.current().nextX()</code>.
 *
 * <p>This class also provides additional commonly used bounded random
 * generation methods.
 */
public 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 the first and only allowed call
     * to setSeed (inside Random constructor) to succeed.  We can't
     * allow others since it would cause setting seed in one part of a
     * program to inintentionally 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;

    private static final ThreadLocal<ThreadLocalRandom> localRandom =
        new ThreadLocal<ThreadLocalRandom>() {
            protected ThreadLocalRandom initialValue() {
                return new ThreadLocalRandom();
            }
    };

    ThreadLocalRandom() { // construct only in localRandom.initialValue
        super(); // super constructor calls setSeed
    }

    /**
     * Returns the current Thread's ThreadLocalRandom
     * @return the current Thread's ThreadLocalRandom
     */
    public static ThreadLocalRandom current() {
        return localRandom.get();
    }

    /**
     * Throws UnsupportedOperationException. Setting seeds in this
     * generator is unsupported.
     * @throw UnsupportedOperationException always
     */
    public void setSeed(long seed) { 
        if (initialized)
            throw new UnsupportedOperationException();
        initialized = true;
        rnd = (seed ^ multiplier) & mask;
    }

    protected int next(int bits) {
        return (int)((rnd = (rnd * multiplier + addend) & mask) >>> (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)
     * @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");
        long offset = 0;
        while (n >= Integer.MAX_VALUE) { // randomly pick half range
            int bits = next(2); // 2nd bit for odd vs even split
            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;
    }

}
Revision:	1.1
Committed:	Mon Jan 12 17:16:18 2009 UTC (15 years, 4 months ago) by dl
Branch:	MAIN
Log Message:	Split out ThreadLocalRandom; internal refactoring pass
#	Content
1	/*
2	* Written by Doug Lea with assistance from members of JCP JSR-166
3	* Expert Group and released to the public domain, as explained at
4	* http://creativecommons.org/licenses/publicdomain
5	*/
6
7	package jsr166y;
8	import java.util.*;
9
10	/**
11	* A Random number generator with the same properties as {@link
12	* Random} but isolated to the current Thread. Like the global
13	* generator used by {@link java.lang.Math}, a ThreadLocalRandom is
14	* initialized with an internally generated seed that may not
15	* otherwise be modified. When applicable, use of ThreadLocalRandom
16	* rather than shared Random objects in concurrent programs will
17	* typically encounter less overhead and contention. The most common
18	* usage form is: <code>ThreadLocalRandom.current().nextX()</code>.
19	*
20	* <p>This class also provides additional commonly used bounded random
21	* generation methods.
22	*/
23	public class ThreadLocalRandom extends Random {
24	// same constants as Random, but must be redeclared because private
25	private final static long multiplier = 0x5DEECE66DL;
26	private final static long addend = 0xBL;
27	private final static long mask = (1L << 48) - 1;
28
29	/**
30	* The random seed. We can't use super.seed
31	*/
32	private long rnd;
33
34	/**
35	* Initialization flag to permit the first and only allowed call
36	* to setSeed (inside Random constructor) to succeed. We can't
37	* allow others since it would cause setting seed in one part of a
38	* program to inintentionally impact other usages by the thread.
39	*/
40	boolean initialized;
41
42	// Padding to help avoid memory contention among seed updates in
43	// different TLRs in the common case that they are located near
44	// each other.
45	private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
46
47	private static final ThreadLocal<ThreadLocalRandom> localRandom =
48	new ThreadLocal<ThreadLocalRandom>() {
49	protected ThreadLocalRandom initialValue() {
50	return new ThreadLocalRandom();
51	}
52	};
53
54	ThreadLocalRandom() { // construct only in localRandom.initialValue
55	super(); // super constructor calls setSeed
56	}
57
58	/**
59	* Returns the current Thread's ThreadLocalRandom
60	* @return the current Thread's ThreadLocalRandom
61	*/
62	public static ThreadLocalRandom current() {
63	return localRandom.get();
64	}
65
66	/**
67	* Throws UnsupportedOperationException. Setting seeds in this
68	* generator is unsupported.
69	* @throw UnsupportedOperationException always
70	*/
71	public void setSeed(long seed) {
72	if (initialized)
73	throw new UnsupportedOperationException();
74	initialized = true;
75	rnd = (seed ^ multiplier) & mask;
76	}
77
78	protected int next(int bits) {
79	return (int)((rnd = (rnd * multiplier + addend) & mask) >>> (48-bits));
80	}
81
82	/**
83	* Returns a pseudorandom, uniformly distributed value between the
84	* given least value (inclusive) and bound (exclusive).
85	* @param least the least value returned
86	* @param bound the upper bound (exclusive)
87	* @throws IllegalArgumentException if least greater than or equal
88	* to bound
89	* @return the next value
90	*/
91	public int nextInt(int least, int bound) {
92	if (least >= bound)
93	throw new IllegalArgumentException();
94	return nextInt(bound - least) + least;
95	}
96
97	/**
98	* Returns a pseudorandom, uniformly distributed value
99	* between 0 (inclusive) and the specified value (exclusive)
100	* @param n the bound on the random number to be returned. Must be
101	* positive.
102	* @return the next value
103	* @throws IllegalArgumentException if n is not positive
104	*/
105	public long nextLong(long n) {
106	if (n <= 0)
107	throw new IllegalArgumentException("n must be positive");
108	long offset = 0;
109	while (n >= Integer.MAX_VALUE) { // randomly pick half range
110	int bits = next(2); // 2nd bit for odd vs even split
111	long half = n >>> 1;
112	long nextn = ((bits & 2) == 0)? half : n - half;
113	if ((bits & 1) == 0)
114	offset += n - nextn;
115	n = nextn;
116	}
117	return offset + nextInt((int)n);
118	}
119
120	/**
121	* Returns a pseudorandom, uniformly distributed value between the
122	* given least value (inclusive) and bound (exclusive).
123	* @param least the least value returned
124	* @param bound the upper bound (exclusive)
125	* @return the next value
126	* @throws IllegalArgumentException if least greater than or equal
127	* to bound
128	*/
129	public long nextLong(long least, long bound) {
130	if (least >= bound)
131	throw new IllegalArgumentException();
132	return nextLong(bound - least) + least;
133	}
134
135	/**
136	* Returns a pseudorandom, uniformly distributed {@code double} value
137	* between 0 (inclusive) and the specified value (exclusive)
138	* @param n the bound on the random number to be returned. Must be
139	* positive.
140	* @return the next value
141	* @throws IllegalArgumentException if n is not positive
142	*/
143	public double nextDouble(double n) {
144	if (n <= 0)
145	throw new IllegalArgumentException("n must be positive");
146	return nextDouble() * n;
147	}
148
149	/**
150	* Returns a pseudorandom, uniformly distributed value between the
151	* given least value (inclusive) and bound (exclusive).
152	* @param least the least value returned
153	* @param bound the upper bound (exclusive)
154	* @return the next value
155	* @throws IllegalArgumentException if least greater than or equal
156	* to bound
157	*/
158	public double nextDouble(double least, double bound) {
159	if (least >= bound)
160	throw new IllegalArgumentException();
161	return nextDouble() * (bound - least) + least;
162	}
163
164	}