Source code

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.annotations.J2ktIncompatible;
021import com.google.common.primitives.ImmutableLongArray;
022import com.google.errorprone.annotations.CanIgnoreReturnValue;
023import java.io.IOException;
024import java.io.ObjectInputStream;
025import java.io.ObjectOutputStream;
026import java.io.Serializable;
027import java.util.concurrent.atomic.AtomicLongArray;
028
029/**
030 * A {@code double} array in which elements may be updated atomically. See the {@link
031 * java.util.concurrent.atomic} package specification for description of the properties of atomic
032 * variables.
033 *
034 * <p><a id="bitEquals"></a>This class compares primitive {@code double} values in methods such as
035 * {@link #compareAndSet} by comparing their bitwise representation using {@link
036 * Double#doubleToRawLongBits}, which differs from both the primitive double {@code ==} operator and
037 * from {@link Double#equals}, as if implemented by:
038 *
039 * <pre>{@code
040 * static boolean bitEquals(double x, double y) {
041 *   long xBits = Double.doubleToRawLongBits(x);
042 *   long yBits = Double.doubleToRawLongBits(y);
043 *   return xBits == yBits;
044 * }
045 * }</pre>
046 *
047 * @author Doug Lea
048 * @author Martin Buchholz
049 * @since 11.0
050 */
051@GwtIncompatible
052@J2ktIncompatible
053public class AtomicDoubleArray implements Serializable {
054  private static final long serialVersionUID = 0L;
055
056  // Making this non-final is the lesser evil according to Effective
057  // Java 2nd Edition Item 76: Write readObject methods defensively.
058  private transient AtomicLongArray longs;
059
060  /**
061   * Creates a new {@code AtomicDoubleArray} of the given length, with all elements initially zero.
062   *
063   * @param length the length of the array
064   */
065  public AtomicDoubleArray(int length) {
066    this.longs = new AtomicLongArray(length);
067  }
068
069  /**
070   * Creates a new {@code AtomicDoubleArray} with the same length as, and all elements copied from,
071   * the given array.
072   *
073   * @param array the array to copy elements from
074   * @throws NullPointerException if array is null
075   */
076  public AtomicDoubleArray(double[] array) {
077    int len = array.length;
078    long[] longArray = new long[len];
079    for (int i = 0; i < len; i++) {
080      longArray[i] = doubleToRawLongBits(array[i]);
081    }
082    this.longs = new AtomicLongArray(longArray);
083  }
084
085  /**
086   * Returns the length of the array.
087   *
088   * @return the length of the array
089   */
090  public final int length() {
091    return longs.length();
092  }
093
094  /**
095   * Gets the current value at position {@code i}.
096   *
097   * @param i the index
098   * @return the current value
099   */
100  public final double get(int i) {
101    return longBitsToDouble(longs.get(i));
102  }
103
104  /**
105   * Atomically sets the element at position {@code i} to the given value.
106   *
107   * @param i the index
108   * @param newValue the new value
109   */
110  public final void set(int i, double newValue) {
111    long next = doubleToRawLongBits(newValue);
112    longs.set(i, next);
113  }
114
115  /**
116   * Eventually sets the element at position {@code i} to the given value.
117   *
118   * @param i the index
119   * @param newValue the new value
120   */
121  public final void lazySet(int i, double newValue) {
122    long next = doubleToRawLongBits(newValue);
123    longs.lazySet(i, next);
124  }
125
126  /**
127   * Atomically sets the element at position {@code i} to the given value and returns the old value.
128   *
129   * @param i the index
130   * @param newValue the new value
131   * @return the previous value
132   */
133  public final double getAndSet(int i, double newValue) {
134    long next = doubleToRawLongBits(newValue);
135    return longBitsToDouble(longs.getAndSet(i, next));
136  }
137
138  /**
139   * Atomically sets the element at position {@code i} to the given updated value if the current
140   * value is <a href="#bitEquals">bitwise equal</a> to the expected value.
141   *
142   * @param i the index
143   * @param expect the expected value
144   * @param update the new value
145   * @return true if successful. False return indicates that the actual value was not equal to the
146   *     expected value.
147   */
148  public final boolean compareAndSet(int i, double expect, double update) {
149    return longs.compareAndSet(i, doubleToRawLongBits(expect), doubleToRawLongBits(update));
150  }
151
152  /**
153   * Atomically sets the element at position {@code i} to the given updated value if the current
154   * value is <a href="#bitEquals">bitwise equal</a> to the expected value.
155   *
156   * <p>May <a
157   * href="http://download.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/package-summary.html#Spurious">
158   * fail spuriously</a> and does not provide ordering guarantees, so is only rarely an appropriate
159   * alternative to {@code compareAndSet}.
160   *
161   * @param i the index
162   * @param expect the expected value
163   * @param update the new value
164   * @return true if successful
165   */
166  public final boolean weakCompareAndSet(int i, double expect, double update) {
167    return longs.weakCompareAndSet(i, doubleToRawLongBits(expect), doubleToRawLongBits(update));
168  }
169
170  /**
171   * Atomically adds the given value to the element at index {@code i}.
172   *
173   * @param i the index
174   * @param delta the value to add
175   * @return the previous value
176   */
177  @CanIgnoreReturnValue
178  public final double getAndAdd(int i, double delta) {
179    while (true) {
180      long current = longs.get(i);
181      double currentVal = longBitsToDouble(current);
182      double nextVal = currentVal + delta;
183      long next = doubleToRawLongBits(nextVal);
184      if (longs.compareAndSet(i, current, next)) {
185        return currentVal;
186      }
187    }
188  }
189
190  /**
191   * Atomically adds the given value to the element at index {@code i}.
192   *
193   * @param i the index
194   * @param delta the value to add
195   * @return the updated value
196   * @since 31.1
197   */
198  @CanIgnoreReturnValue
199  public double addAndGet(int i, double delta) {
200    while (true) {
201      long current = longs.get(i);
202      double currentVal = longBitsToDouble(current);
203      double nextVal = currentVal + delta;
204      long next = doubleToRawLongBits(nextVal);
205      if (longs.compareAndSet(i, current, next)) {
206        return nextVal;
207      }
208    }
209  }
210
211  /**
212   * Returns the String representation of the current values of array.
213   *
214   * @return the String representation of the current values of array
215   */
216  @Override
217  public String toString() {
218    int iMax = length() - 1;
219    if (iMax == -1) {
220      return "[]";
221    }
222
223    // Double.toString(Math.PI).length() == 17
224    StringBuilder b = new StringBuilder((17 + 2) * (iMax + 1));
225    b.append('[');
226    for (int i = 0; ; i++) {
227      b.append(longBitsToDouble(longs.get(i)));
228      if (i == iMax) {
229        return b.append(']').toString();
230      }
231      b.append(',').append(' ');
232    }
233  }
234
235  /**
236   * Saves the state to a stream (that is, serializes it).
237   *
238   * @serialData The length of the array is emitted (int), followed by all of its elements (each a
239   *     {@code double}) in the proper order.
240   */
241  private void writeObject(ObjectOutputStream s) throws 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  /** Reconstitutes the instance from a stream (that is, deserializes it). */
255  private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException {
256    s.defaultReadObject();
257
258    int length = s.readInt();
259    ImmutableLongArray.Builder builder = ImmutableLongArray.builder();
260    for (int i = 0; i < length; i++) {
261      builder.add(doubleToRawLongBits(s.readDouble()));
262    }
263    this.longs = new AtomicLongArray(builder.build().toArray());
264  }
265}