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
014package com.google.common.util.concurrent;
015
016import static java.lang.Double.doubleToRawLongBits;
017import static java.lang.Double.longBitsToDouble;
018
019import com.google.common.annotations.Beta;
020import com.google.common.primitives.ImmutableLongArray;
021
022import java.util.concurrent.atomic.AtomicLongArray;
023
024/**
025 * A {@code double} array in which elements may be updated atomically.
026 * See the {@link java.util.concurrent.atomic} package specification
027 * for description of the properties of atomic variables.
028 *
029 * <p><a name="bitEquals">This class compares primitive {@code double}
030 * values in methods such as {@link #compareAndSet} by comparing their
031 * bitwise representation using {@link Double#doubleToRawLongBits},
032 * which differs from both the primitive double {@code ==} operator
033 * and from {@link Double#equals}, as if implemented by:
034 *  <pre> {@code
035 * static boolean bitEquals(double x, double y) {
036 *   long xBits = Double.doubleToRawLongBits(x);
037 *   long yBits = Double.doubleToRawLongBits(y);
038 *   return xBits == yBits;
039 * }}</pre>
040 *
041 * @author Doug Lea
042 * @author Martin Buchholz
043 * @since 11.0
044 */
045@Beta
046public class AtomicDoubleArray implements java.io.Serializable {
047  private static final long serialVersionUID = 0L;
048
049  // Making this non-final is the lesser evil according to Effective
050  // Java 2nd Edition Item 76: Write readObject methods defensively.
051  private transient AtomicLongArray longs;
052
053  /**
054   * Creates a new {@code AtomicDoubleArray} of the given length,
055   * with all elements initially zero.
056   *
057   * @param length the length of the array
058   */
059  public AtomicDoubleArray(int length) {
060    this.longs = new AtomicLongArray(length);
061  }
062
063  /**
064   * Creates a new {@code AtomicDoubleArray} with the same length
065   * as, and all elements copied from, the given array.
066   *
067   * @param array the array to copy elements from
068   * @throws NullPointerException if array is null
069   */
070  public AtomicDoubleArray(double[] array) {
071    final int len = array.length;
072    long[] longArray = new long[len];
073    for (int i = 0; i < len; i++) {
074      longArray[i] = doubleToRawLongBits(array[i]);
075    }
076    this.longs = new AtomicLongArray(longArray);
077  }
078
079  /**
080   * Returns the length of the array.
081   *
082   * @return the length of the array
083   */
084  public final int length() {
085    return longs.length();
086  }
087
088  /**
089   * Gets the current value at position {@code i}.
090   *
091   * @param i the index
092   * @return the current value
093   */
094  public final double get(int i) {
095    return longBitsToDouble(longs.get(i));
096  }
097
098  /**
099   * Sets the element at position {@code i} to the given value.
100   *
101   * @param i the index
102   * @param newValue the new value
103   */
104  public final void set(int i, double newValue) {
105    long next = doubleToRawLongBits(newValue);
106    longs.set(i, next);
107  }
108
109  /**
110   * Eventually sets the element at position {@code i} to the given value.
111   *
112   * @param i the index
113   * @param newValue the new value
114   */
115  public final void lazySet(int i, double newValue) {
116    set(i, newValue);
117    // TODO(user): replace with code below when jdk5 support is dropped.
118    // long next = doubleToRawLongBits(newValue);
119    // longs.lazySet(i, next);
120  }
121
122  /**
123   * Atomically sets the element at position {@code i} to the given value
124   * and returns the old value.
125   *
126   * @param i the index
127   * @param newValue the new value
128   * @return the previous value
129   */
130  public final double getAndSet(int i, double newValue) {
131    long next = doubleToRawLongBits(newValue);
132    return longBitsToDouble(longs.getAndSet(i, next));
133  }
134
135  /**
136   * Atomically sets the element at position {@code i} to the given
137   * updated value
138   * if the current value is <a href="#bitEquals">bitwise equal</a>
139   * to the expected value.
140   *
141   * @param i the index
142   * @param expect the expected value
143   * @param update the new value
144   * @return true if successful. False return indicates that
145   * the actual value was not equal to the expected value.
146   */
147  public final boolean compareAndSet(int i, double expect, double update) {
148    return longs.compareAndSet(i,
149                               doubleToRawLongBits(expect),
150                               doubleToRawLongBits(update));
151  }
152
153  /**
154   * Atomically sets the element at position {@code i} to the given
155   * updated value
156   * if the current value is <a href="#bitEquals">bitwise equal</a>
157   * to the expected value.
158   *
159   * <p>May <a
160   * href="http://download.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/package-summary.html#Spurious">
161   * fail spuriously</a>
162   * and does not provide ordering guarantees, so is only rarely an
163   * appropriate alternative to {@code compareAndSet}.
164   *
165   * @param i the index
166   * @param expect the expected value
167   * @param update the new value
168   * @return true if successful
169   */
170  public final boolean weakCompareAndSet(int i, double expect, double update) {
171    return longs.weakCompareAndSet(i,
172                                   doubleToRawLongBits(expect),
173                                   doubleToRawLongBits(update));
174  }
175
176  /**
177   * Atomically adds the given value to the element at index {@code i}.
178   *
179   * @param i the index
180   * @param delta the value to add
181   * @return the previous value
182   */
183  public final double getAndAdd(int i, double delta) {
184    while (true) {
185      long current = longs.get(i);
186      double currentVal = longBitsToDouble(current);
187      double nextVal = currentVal + delta;
188      long next = doubleToRawLongBits(nextVal);
189      if (longs.compareAndSet(i, current, next)) {
190        return currentVal;
191      }
192    }
193  }
194
195  /**
196   * Atomically adds the given value to the element at index {@code i}.
197   *
198   * @param i the index
199   * @param delta the value to add
200   * @return the updated value
201   */
202  public double addAndGet(int i, double delta) {
203    while (true) {
204      long current = longs.get(i);
205      double currentVal = longBitsToDouble(current);
206      double nextVal = currentVal + delta;
207      long next = doubleToRawLongBits(nextVal);
208      if (longs.compareAndSet(i, current, next)) {
209        return nextVal;
210      }
211    }
212  }
213
214  /**
215   * Returns the String representation of the current values of array.
216   * @return the String representation of the current values of array
217   */
218  public String toString() {
219    int iMax = length() - 1;
220    if (iMax == -1) {
221      return "[]";
222    }
223
224    // Double.toString(Math.PI).length() == 17
225    StringBuilder b = new StringBuilder((17 + 2) * (iMax + 1));
226    b.append('[');
227    for (int i = 0;; i++) {
228      b.append(longBitsToDouble(longs.get(i)));
229      if (i == iMax) {
230        return b.append(']').toString();
231      }
232      b.append(',').append(' ');
233    }
234  }
235
236  /**
237   * Saves the state to a stream (that is, serializes it).
238   *
239   * @serialData The length of the array is emitted (int), followed by all
240   *             of its elements (each a {@code double}) in the proper order.
241   */
242  private void writeObject(java.io.ObjectOutputStream s)
243      throws java.io.IOException {
244    s.defaultWriteObject();
245
246    // Write out array length
247    int length = length();
248    s.writeInt(length);
249
250    // Write out all elements in the proper order.
251    for (int i = 0; i < length; i++) {
252      s.writeDouble(get(i));
253    }
254  }
255
256  /**
257   * Reconstitutes the instance from a stream (that is, deserializes it).
258   */
259  private void readObject(java.io.ObjectInputStream s)
260      throws java.io.IOException, ClassNotFoundException {
261    s.defaultReadObject();
262
263    int length = s.readInt();
264      ImmutableLongArray.Builder builder = ImmutableLongArray.builder();
265
266      for (int i = 0; i < length; i++) {
267          builder.add(doubleToRawLongBits(s.readDouble()));
268      }
269      this.longs = new AtomicLongArray(builder.build().toArray());
270  }
271}