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.GwtIncompatible;
020import com.google.common.primitives.ImmutableLongArray;
021import com.google.errorprone.annotations.CanIgnoreReturnValue;
022import java.util.concurrent.atomic.AtomicLongArray;
023
024/**
025 * A {@code double} array in which elements may be updated atomically. See the {@link
026 * java.util.concurrent.atomic} package specification for description of the properties of atomic
027 * variables.
028 *
029 * <p><a id="bitEquals"></a>This class compares primitive {@code double} values in methods such as
030 * {@link #compareAndSet} by comparing their bitwise representation using {@link
031 * Double#doubleToRawLongBits}, which differs from both the primitive double {@code ==} operator and
032 * from {@link Double#equals}, as if implemented by:
033 *
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 * }
040 * }</pre>
041 *
042 * @author Doug Lea
043 * @author Martin Buchholz
044 * @since 11.0
045 */
046@GwtIncompatible
047public class AtomicDoubleArray implements java.io.Serializable {
048  private static final long serialVersionUID = 0L;
049
050  // Making this non-final is the lesser evil according to Effective
051  // Java 2nd Edition Item 76: Write readObject methods defensively.
052  private transient AtomicLongArray longs;
053
054  /**
055   * Creates a new {@code AtomicDoubleArray} of the given length, 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 as, and all elements copied from,
065   * 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    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 and returns the old value.
122   *
123   * @param i the index
124   * @param newValue the new value
125   * @return the previous value
126   */
127  public final double getAndSet(int i, double newValue) {
128    long next = doubleToRawLongBits(newValue);
129    return longBitsToDouble(longs.getAndSet(i, next));
130  }
131
132  /**
133   * Atomically sets the element at position {@code i} to the given updated value if the current
134   * value is <a href="#bitEquals">bitwise equal</a> to the expected value.
135   *
136   * @param i the index
137   * @param expect the expected value
138   * @param update the new value
139   * @return true if successful. False return indicates that the actual value was not equal to the
140   *     expected value.
141   */
142  public final boolean compareAndSet(int i, double expect, double update) {
143    return longs.compareAndSet(i, doubleToRawLongBits(expect), doubleToRawLongBits(update));
144  }
145
146  /**
147   * Atomically sets the element at position {@code i} to the given updated value if the current
148   * value is <a href="#bitEquals">bitwise equal</a> to the expected value.
149   *
150   * <p>May <a
151   * href="http://download.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/package-summary.html#Spurious">
152   * fail spuriously</a> and does not provide ordering guarantees, so is only rarely an appropriate
153   * alternative to {@code compareAndSet}.
154   *
155   * @param i the index
156   * @param expect the expected value
157   * @param update the new value
158   * @return true if successful
159   */
160  public final boolean weakCompareAndSet(int i, double expect, double update) {
161    return longs.weakCompareAndSet(i, doubleToRawLongBits(expect), doubleToRawLongBits(update));
162  }
163
164  /**
165   * Atomically adds the given value to the element at index {@code i}.
166   *
167   * @param i the index
168   * @param delta the value to add
169   * @return the previous value
170   */
171  @CanIgnoreReturnValue
172  public final double getAndAdd(int i, double delta) {
173    while (true) {
174      long current = longs.get(i);
175      double currentVal = longBitsToDouble(current);
176      double nextVal = currentVal + delta;
177      long next = doubleToRawLongBits(nextVal);
178      if (longs.compareAndSet(i, current, next)) {
179        return currentVal;
180      }
181    }
182  }
183
184  /**
185   * Atomically adds the given value to the element at index {@code i}.
186   *
187   * @param i the index
188   * @param delta the value to add
189   * @return the updated value
190   */
191  @CanIgnoreReturnValue
192  public double addAndGet(int i, double delta) {
193    while (true) {
194      long current = longs.get(i);
195      double currentVal = longBitsToDouble(current);
196      double nextVal = currentVal + delta;
197      long next = doubleToRawLongBits(nextVal);
198      if (longs.compareAndSet(i, current, next)) {
199        return nextVal;
200      }
201    }
202  }
203
204  /**
205   * Returns the String representation of the current values of array.
206   *
207   * @return the String representation of the current values of array
208   */
209  @Override
210  public String toString() {
211    int iMax = length() - 1;
212    if (iMax == -1) {
213      return "[]";
214    }
215
216    // Double.toString(Math.PI).length() == 17
217    StringBuilder b = new StringBuilder((17 + 2) * (iMax + 1));
218    b.append('[');
219    for (int i = 0; ; i++) {
220      b.append(longBitsToDouble(longs.get(i)));
221      if (i == iMax) {
222        return b.append(']').toString();
223      }
224      b.append(',').append(' ');
225    }
226  }
227
228  /**
229   * Saves the state to a stream (that is, serializes it).
230   *
231   * @serialData The length of the array is emitted (int), followed by all of its elements (each a
232   *     {@code double}) in the proper order.
233   */
234  private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
235    s.defaultWriteObject();
236
237    // Write out array length
238    int length = length();
239    s.writeInt(length);
240
241    // Write out all elements in the proper order.
242    for (int i = 0; i < length; i++) {
243      s.writeDouble(get(i));
244    }
245  }
246
247  /** Reconstitutes the instance from a stream (that is, deserializes it). */
248  private void readObject(java.io.ObjectInputStream s)
249      throws java.io.IOException, ClassNotFoundException {
250    s.defaultReadObject();
251
252    int length = s.readInt();
253    ImmutableLongArray.Builder builder = ImmutableLongArray.builder();
254    for (int i = 0; i < length; i++) {
255      builder.add(doubleToRawLongBits(s.readDouble()));
256    }
257    this.longs = new AtomicLongArray(builder.build().toArray());
258  }
259}