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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 1.14 by jsr166, Thu Jun 3 01:03:13 2010 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
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>.
12	>	* A random number generator isolated to the current thread.  Like the
13	>	* global {@link java.util.Random} generator used by the {@link
14	>	* java.lang.Math} class, a {@code ThreadLocalRandom} is initialized
15	>	* with an internally generated seed that may not otherwise be
16	>	* modified. When applicable, use of {@code ThreadLocalRandom} rather
17	>	* than shared {@code Random} objects in concurrent programs will
18	>	* typically encounter much less overhead and contention.  Use of
19	>	* {@code ThreadLocalRandom} is particularly appropriate when multiple
20	>	* tasks (for example, each a {@link ForkJoinTask}) use random numbers
21	>	* 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 a {@code ThreadLocalRandom} 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.
47	>	* Initialization flag to permit calls to setSeed to succeed only
48	>	* while executing the Random constructor.  We can't allow others
49	>	* since it would cause setting seed in one part of a program to
50	>	* 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	>	*/
73	>	ThreadLocalRandom() {
74	>	super();
75	>	initialized = true;
76		}
77
78		/**
79	<	* Returns the current Thread's ThreadLocalRandom
80	<	* @return the current Thread's ThreadLocalRandom
79	>	* Returns the current thread's {@code ThreadLocalRandom}.
80	>	*
81	>	* @return the current thread's {@code ThreadLocalRandom}
82		*/
83		public static ThreadLocalRandom current() {
84		return localRandom.get();
85		}
86
87		/**
88	<	* Throws UnsupportedOperationException. Setting seeds in this
89	<	* generator is unsupported.
90	<	* @throw UnsupportedOperationException always
88	>	* Throws {@code UnsupportedOperationException}.  Setting seeds in
89	>	* this generator is not supported.
90	>	*
91	>	* @throws UnsupportedOperationException always
92		*/
93	<	public void setSeed(long seed) {
93	>	public void setSeed(long seed) {
94		if (initialized)
95		throw new UnsupportedOperationException();
74	–	initialized = true;
96		rnd = (seed ^ multiplier) & mask;
97		}
98
99		protected int next(int bits) {
100	<	return (int)((rnd = (rnd * multiplier + addend) & mask) >>> (48-bits));
100	>	rnd = (rnd * multiplier + addend) & mask;
101	>	return (int) (rnd >>> (48-bits));
102		}
103
104		/**
105		* Returns a pseudorandom, uniformly distributed value between the
106		* given least value (inclusive) and bound (exclusive).
107	+	*
108		* @param least the least value returned
109		* @param bound the upper bound (exclusive)
110		* @throws IllegalArgumentException if least greater than or equal
#	Line 96 | Line 119 | public class ThreadLocalRandom extends R
119
120		/**
121		* Returns a pseudorandom, uniformly distributed value
122	<	* between 0 (inclusive) and the specified value (exclusive)
122	>	* between 0 (inclusive) and the specified value (exclusive).
123	>	*
124		* @param n the bound on the random number to be returned.  Must be
125		*        positive.
126		* @return the next value
#	Line 105 | Line 129 | public class ThreadLocalRandom extends R
129		public long nextLong(long n) {
130		if (n <= 0)
131		throw new IllegalArgumentException("n must be positive");
132	+	// Divide n by two until small enough for nextInt. On each
133	+	// iteration (at most 31 of them but usually much less),
134	+	// randomly choose both whether to include high bit in result
135	+	// (offset) and whether to continue with the lower vs upper
136	+	// half (which makes a difference only if odd).
137		long offset = 0;
138	<	while (n >= Integer.MAX_VALUE) { // randomly pick half range
139	<	int bits = next(2); // 2nd bit for odd vs even split
138	>	while (n >= Integer.MAX_VALUE) {
139	>	int bits = next(2);
140		long half = n >>> 1;
141	<	long nextn = ((bits & 2) == 0)? half : n - half;
141	>	long nextn = ((bits & 2) == 0) ? half : n - half;
142		if ((bits & 1) == 0)
143		offset += n - nextn;
144		n = nextn;
145		}
146	<	return offset + nextInt((int)n);
146	>	return offset + nextInt((int) n);
147		}
148
149		/**
150		* Returns a pseudorandom, uniformly distributed value between the
151		* given least value (inclusive) and bound (exclusive).
152	+	*
153		* @param least the least value returned
154		* @param bound the upper bound (exclusive)
155		* @return the next value
#	Line 134 | Line 164 | public class ThreadLocalRandom extends R
164
165		/**
166		* Returns a pseudorandom, uniformly distributed {@code double} value
167	<	* between 0 (inclusive) and the specified value (exclusive)
167	>	* between 0 (inclusive) and the specified value (exclusive).
168	>	*
169		* @param n the bound on the random number to be returned.  Must be
170		*        positive.
171		* @return the next value
#	Line 149 | Line 180 | public class ThreadLocalRandom extends R
180		/**
181		* Returns a pseudorandom, uniformly distributed value between the
182		* given least value (inclusive) and bound (exclusive).
183	+	*
184		* @param least the least value returned
185		* @param bound the upper bound (exclusive)
186		* @return the next value
#	Line 161 | Line 193 | public class ThreadLocalRandom extends R
193		return nextDouble() * (bound - least) + least;
194		}
195
196	<	}
196	>	private static final long serialVersionUID = -5851777807851030925L;
197	>	}

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