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001 /*
002 * Written by Doug Lea with assistance from members of JCP JSR-166
003 * Expert Group and released to the public domain, as explained at
004 * http://creativecommons.org/publicdomain/zero/1.0/
005 */
006
007 /*
008 * Source:
009 * http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/extra/AtomicDoubleArray.java?revision=1.5
010 * (Modified to adapt to guava coding conventions and
011 * to use AtomicLongArray instead of sun.misc.Unsafe)
012 */
013
014 package com.google.common.util.concurrent;
015
016 import com.google.common.annotations.Beta;
017
018 import static java.lang.Double.doubleToRawLongBits;
019 import static java.lang.Double.longBitsToDouble;
020 import java.util.concurrent.atomic.AtomicLongArray;
021
022 /**
023 * A {@code double} array in which elements may be updated atomically.
024 * See the {@link java.util.concurrent.atomic} package specification
025 * for description of the properties of atomic variables.
026 *
027 * <p><a name="bitEquals">This class compares primitive {@code double}
028 * values in methods such as {@link #compareAndSet} by comparing their
029 * bitwise representation using {@link Double#doubleToRawLongBits},
030 * which differs from both the primitive double {@code ==} operator
031 * and from {@link Double#equals}, as if implemented by:
032 * <pre> {@code
033 * static boolean bitEquals(double x, double y) {
034 * long xBits = Double.doubleToRawLongBits(x);
035 * long yBits = Double.doubleToRawLongBits(y);
036 * return xBits == yBits;
037 * }}</pre>
038 *
039 * @author Doug Lea
040 * @author Martin Buchholz
041 * @since 11.0
042 */
043 @Beta
044 public class AtomicDoubleArray implements java.io.Serializable {
045 private static final long serialVersionUID = 0L;
046
047 // Making this non-final is the lesser evil according to Effective
048 // Java 2nd Edition Item 76: Write readObject methods defensively.
049 private transient AtomicLongArray longs;
050
051 /**
052 * Creates a new {@code AtomicDoubleArray} of the given length,
053 * with all elements initially zero.
054 *
055 * @param length the length of the array
056 */
057 public AtomicDoubleArray(int length) {
058 this.longs = new AtomicLongArray(length);
059 }
060
061 /**
062 * Creates a new {@code AtomicDoubleArray} with the same length
063 * as, and all elements copied from, the given array.
064 *
065 * @param array the array to copy elements from
066 * @throws NullPointerException if array is null
067 */
068 public AtomicDoubleArray(double[] array) {
069 final int len = array.length;
070 long[] longArray = new long[len];
071 for (int i = 0; i < len; i++) {
072 longArray[i] = doubleToRawLongBits(array[i]);
073 }
074 this.longs = new AtomicLongArray(longArray);
075 }
076
077 /**
078 * Returns the length of the array.
079 *
080 * @return the length of the array
081 */
082 public final int length() {
083 return longs.length();
084 }
085
086 /**
087 * Gets the current value at position {@code i}.
088 *
089 * @param i the index
090 * @return the current value
091 */
092 public final double get(int i) {
093 return longBitsToDouble(longs.get(i));
094 }
095
096 /**
097 * Sets the element at position {@code i} to the given value.
098 *
099 * @param i the index
100 * @param newValue the new value
101 */
102 public final void set(int i, double newValue) {
103 long next = doubleToRawLongBits(newValue);
104 longs.set(i, next);
105 }
106
107 /**
108 * Eventually sets the element at position {@code i} to the given value.
109 *
110 * @param i the index
111 * @param newValue the new value
112 */
113 public final void lazySet(int i, double newValue) {
114 set(i, newValue);
115 // TODO(user): replace with code below when jdk5 support is dropped.
116 // long next = doubleToRawLongBits(newValue);
117 // longs.lazySet(i, next);
118 }
119
120 /**
121 * Atomically sets the element at position {@code i} to the given value
122 * and returns the old value.
123 *
124 * @param i the index
125 * @param newValue the new value
126 * @return the previous value
127 */
128 public final double getAndSet(int i, double newValue) {
129 long next = doubleToRawLongBits(newValue);
130 return longBitsToDouble(longs.getAndSet(i, next));
131 }
132
133 /**
134 * Atomically sets the element at position {@code i} to the given
135 * updated value
136 * if the current value is <a href="#bitEquals">bitwise equal</a>
137 * to the expected value.
138 *
139 * @param i the index
140 * @param expect the expected value
141 * @param update the new value
142 * @return true if successful. False return indicates that
143 * the actual value was not equal to the expected value.
144 */
145 public final boolean compareAndSet(int i, double expect, double update) {
146 return longs.compareAndSet(i,
147 doubleToRawLongBits(expect),
148 doubleToRawLongBits(update));
149 }
150
151 /**
152 * Atomically sets the element at position {@code i} to the given
153 * updated value
154 * if the current value is <a href="#bitEquals">bitwise equal</a>
155 * to the expected value.
156 *
157 * <p>May <a
158 * href="http://download.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/package-summary.html#Spurious">
159 * fail spuriously</a>
160 * and does not provide ordering guarantees, so is only rarely an
161 * appropriate alternative to {@code compareAndSet}.
162 *
163 * @param i the index
164 * @param expect the expected value
165 * @param update the new value
166 * @return true if successful
167 */
168 public final boolean weakCompareAndSet(int i, double expect, double update) {
169 return longs.weakCompareAndSet(i,
170 doubleToRawLongBits(expect),
171 doubleToRawLongBits(update));
172 }
173
174 /**
175 * Atomically adds the given value to the element at index {@code i}.
176 *
177 * @param i the index
178 * @param delta the value to add
179 * @return the previous value
180 */
181 public final double getAndAdd(int i, double delta) {
182 while (true) {
183 long current = longs.get(i);
184 double currentVal = longBitsToDouble(current);
185 double nextVal = currentVal + delta;
186 long next = doubleToRawLongBits(nextVal);
187 if (longs.compareAndSet(i, current, next)) {
188 return currentVal;
189 }
190 }
191 }
192
193 /**
194 * Atomically adds the given value to the element at index {@code i}.
195 *
196 * @param i the index
197 * @param delta the value to add
198 * @return the updated value
199 */
200 public double addAndGet(int i, double delta) {
201 while (true) {
202 long current = longs.get(i);
203 double currentVal = longBitsToDouble(current);
204 double nextVal = currentVal + delta;
205 long next = doubleToRawLongBits(nextVal);
206 if (longs.compareAndSet(i, current, next)) {
207 return nextVal;
208 }
209 }
210 }
211
212 /**
213 * Returns the String representation of the current values of array.
214 * @return the String representation of the current values of array
215 */
216 public String toString() {
217 int iMax = length() - 1;
218 if (iMax == -1) {
219 return "[]";
220 }
221
222 // Double.toString(Math.PI).length() == 17
223 StringBuilder b = new StringBuilder((17 + 2) * (iMax + 1));
224 b.append('[');
225 for (int i = 0;; i++) {
226 b.append(longBitsToDouble(longs.get(i)));
227 if (i == iMax) {
228 return b.append(']').toString();
229 }
230 b.append(',').append(' ');
231 }
232 }
233
234 /**
235 * Saves the state to a stream (that is, serializes it).
236 *
237 * @serialData The length of the array is emitted (int), followed by all
238 * of its elements (each a {@code double}) in the proper order.
239 */
240 private void writeObject(java.io.ObjectOutputStream s)
241 throws java.io.IOException {
242 s.defaultWriteObject();
243
244 // Write out array length
245 int length = length();
246 s.writeInt(length);
247
248 // Write out all elements in the proper order.
249 for (int i = 0; i < length; i++) {
250 s.writeDouble(get(i));
251 }
252 }
253
254 /**
255 * Reconstitutes the instance from a stream (that is, deserializes it).
256 */
257 private void readObject(java.io.ObjectInputStream s)
258 throws java.io.IOException, ClassNotFoundException {
259 s.defaultReadObject();
260
261 // Read in array length and allocate array
262 int length = s.readInt();
263 this.longs = new AtomicLongArray(length);
264
265 // Read in all elements in the proper order.
266 for (int i = 0; i < length; i++) {
267 set(i, s.readDouble());
268 }
269 }
270 }
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