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root/jsr166/jsr166/src/jsr166y/ThreadLocalRandom.java

Comparing jsr166/src/jsr166y/ThreadLocalRandom.java (file contents):
Revision 1.1 by dl, Mon Jan 12 17:16:18 2009 UTC vs.
Revision 1.10 by jsr166, Sat Jul 25 00:34:00 2009 UTC

#	Line 5 | Line 5
5		*/
6
7		package jsr166y;
8	<	import java.util.*;
8	>
9	>	import java.util.Random;
10
11		/**
12	<	* A Random number generator with the same properties as {@link
12	>	* A random number generator with the same properties as class {@link
13		* Random} but isolated to the current Thread.  Like the global
14	<	* generator used by {@link java.lang.Math}, a ThreadLocalRandom is
15	<	* initialized with an internally generated seed that may not
16	<	* otherwise be modified. When applicable, use of ThreadLocalRandom
17	<	* rather than shared Random objects in concurrent programs will
18	<	* typically encounter less overhead and contention. The most common
19	<	* usage form is: <code>ThreadLocalRandom.current().nextX()</code>.
14	>	* generator used by the {@link java.lang.Math} class, a
15	>	* ThreadLocalRandom is initialized with an internally generated seed
16	>	* that may not otherwise be modified. When applicable, use of
17	>	* ThreadLocalRandom rather than shared Random objects in concurrent
18	>	* programs will typically encounter much less overhead and
19	>	* contention.  ThreadLocalRandoms are particularly appropriate when
20	>	* multiple tasks (for example, each a {@link ForkJoinTask}), use
21	>	* random numbers in parallel in thread pools.
22	>	*
23	>	* <p>Usages of this class should typically be of the form:
24	>	* {@code ThreadLocalRandom.current().nextX(...)} (where
25	>	* {@code X} is {@code Int}, {@code Long}, etc).
26	>	* When all usages are of this form, it is never possible to
27	>	* accidently share ThreadLocalRandoms across multiple threads.
28		*
29		* <p>This class also provides additional commonly used bounded random
30		* generation methods.
31	+	*
32	+	* @since 1.7
33	+	* @author Doug Lea
34		*/
35		public class ThreadLocalRandom extends Random {
36		// same constants as Random, but must be redeclared because private
#	Line 27 | Line 39 | public class ThreadLocalRandom extends R
39		private final static long mask = (1L << 48) - 1;
40
41		/**
42	<	* The random seed. We can't use super.seed
42	>	* The random seed. We can't use super.seed.
43		*/
44	<	private long rnd;
44	>	private long rnd;
45
46		/**
47		* Initialization flag to permit the first and only allowed call
48		* to setSeed (inside Random constructor) to succeed.  We can't
49		* allow others since it would cause setting seed in one part of a
50	<	* program to inintentionally impact other usages by the thread.
50	>	* program to unintentionally impact other usages by the thread.
51		*/
52		boolean initialized;
53
#	Line 44 | Line 56 | public class ThreadLocalRandom extends R
56		// each other.
57		private long pad0, pad1, pad2, pad3, pad4, pad5, pad6, pad7;
58
59	+	/**
60	+	* The actual ThreadLocal
61	+	*/
62		private static final ThreadLocal<ThreadLocalRandom> localRandom =
63		new ThreadLocal<ThreadLocalRandom>() {
64		protected ThreadLocalRandom initialValue() {
#	Line 51 | Line 66 | public class ThreadLocalRandom extends R
66		}
67		};
68
69	<	ThreadLocalRandom() { // construct only in localRandom.initialValue
70	<	super(); // super constructor calls setSeed
69	>
70	>	/**
71	>	* Constructor called only by localRandom.initialValue.
72	>	* We rely on the fact that the superclass no-arg constructor
73	>	* invokes setSeed exactly once to initialize.
74	>	*/
75	>	ThreadLocalRandom() {
76	>	super();
77		}
78
79		/**
80	<	* Returns the current Thread's ThreadLocalRandom
80	>	* Returns the current Thread's ThreadLocalRandom.
81	>	*
82		* @return the current Thread's ThreadLocalRandom
83		*/
84		public static ThreadLocalRandom current() {
#	Line 66 | Line 88 | public class ThreadLocalRandom extends R
88		/**
89		* Throws UnsupportedOperationException. Setting seeds in this
90		* generator is unsupported.
91	<	* @throw UnsupportedOperationException always
91	>	*
92	>	* @throws UnsupportedOperationException always
93		*/
94	<	public void setSeed(long seed) {
94	>	public void setSeed(long seed) {
95		if (initialized)
96		throw new UnsupportedOperationException();
97		initialized = true;
#	Line 76 | Line 99 | public class ThreadLocalRandom extends R
99		}
100
101		protected int next(int bits) {
102	<	return (int)((rnd = (rnd * multiplier + addend) & mask) >>> (48-bits));
102	>	rnd = (rnd * multiplier + addend) & mask;
103	>	return (int) (rnd >>> (48-bits));
104		}
105
106		/**
107		* Returns a pseudorandom, uniformly distributed value between the
108		* given least value (inclusive) and bound (exclusive).
109	+	*
110		* @param least the least value returned
111		* @param bound the upper bound (exclusive)
112		* @throws IllegalArgumentException if least greater than or equal
#	Line 96 | Line 121 | public class ThreadLocalRandom extends R
121
122		/**
123		* Returns a pseudorandom, uniformly distributed value
124	<	* between 0 (inclusive) and the specified value (exclusive)
124	>	* between 0 (inclusive) and the specified value (exclusive).
125	>	*
126		* @param n the bound on the random number to be returned.  Must be
127		*        positive.
128		* @return the next value
#	Line 105 | Line 131 | public class ThreadLocalRandom extends R
131		public long nextLong(long n) {
132		if (n <= 0)
133		throw new IllegalArgumentException("n must be positive");
134	+	// Divide n by two until small enough for nextInt. On each
135	+	// iteration (at most 31 of them but usually much less),
136	+	// randomly choose both whether to include high bit in result
137	+	// (offset) and whether to continue with the lower vs upper
138	+	// half (which makes a difference only if odd).
139		long offset = 0;
140	<	while (n >= Integer.MAX_VALUE) { // randomly pick half range
141	<	int bits = next(2); // 2nd bit for odd vs even split
140	>	while (n >= Integer.MAX_VALUE) {
141	>	int bits = next(2);
142		long half = n >>> 1;
143	<	long nextn = ((bits & 2) == 0)? half : n - half;
143	>	long nextn = ((bits & 2) == 0) ? half : n - half;
144		if ((bits & 1) == 0)
145		offset += n - nextn;
146		n = nextn;
147		}
148	<	return offset + nextInt((int)n);
148	>	return offset + nextInt((int) n);
149		}
150
151		/**
152		* Returns a pseudorandom, uniformly distributed value between the
153		* given least value (inclusive) and bound (exclusive).
154	+	*
155		* @param least the least value returned
156		* @param bound the upper bound (exclusive)
157		* @return the next value
#	Line 134 | Line 166 | public class ThreadLocalRandom extends R
166
167		/**
168		* Returns a pseudorandom, uniformly distributed {@code double} value
169	<	* between 0 (inclusive) and the specified value (exclusive)
169	>	* between 0 (inclusive) and the specified value (exclusive).
170	>	*
171		* @param n the bound on the random number to be returned.  Must be
172		*        positive.
173		* @return the next value
#	Line 149 | Line 182 | public class ThreadLocalRandom extends R
182		/**
183		* Returns a pseudorandom, uniformly distributed value between the
184		* given least value (inclusive) and bound (exclusive).
185	+	*
186		* @param least the least value returned
187		* @param bound the upper bound (exclusive)
188		* @return the next value
#	Line 161 | Line 195 | public class ThreadLocalRandom extends R
195		return nextDouble() * (bound - least) + least;
196		}
197
198	<	}
198	>	private static final long serialVersionUID = -5851777807851030925L;
199	>	}

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