Java example source code file (AtomicDouble.java)

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Java - Java tags/keywords

atomicdouble, atomiclongfieldupdater, canignorereturnvalue, classnotfoundexception, gwtincompatible, number, string

The AtomicDouble.java Java example source code

/*
 * Written by Doug Lea and Martin Buchholz with assistance from
 * members of JCP JSR-166 Expert Group and released to the public
 * domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

/*
 * Source:
 * http://gee.cs.oswego.edu/cgi-bin/viewcvs.cgi/jsr166/src/jsr166e/extra/AtomicDouble.java?revision=1.13
 * (Modified to adapt to guava coding conventions and
 * to use AtomicLongFieldUpdater instead of sun.misc.Unsafe)
 */

package com.google.common.util.concurrent;

import static java.lang.Double.doubleToRawLongBits;
import static java.lang.Double.longBitsToDouble;

import com.google.common.annotations.GwtIncompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;

import java.util.concurrent.atomic.AtomicLongFieldUpdater;

/**
 * A {@code double} value that may be updated atomically.  See the
 * {@link java.util.concurrent.atomic} package specification for
 * description of the properties of atomic variables.  An {@code
 * AtomicDouble} is used in applications such as atomic accumulation,
 * and cannot be used as a replacement for a {@link Double}.  However,
 * this class does extend {@code Number} to allow uniform access by
 * tools and utilities that deal with numerically-based classes.
 *
 * <p>This class compares primitive {@code double}
 * values in methods such as {@link #compareAndSet} by comparing their
 * bitwise representation using {@link Double#doubleToRawLongBits},
 * which differs from both the primitive double {@code ==} operator
 * and from {@link Double#equals}, as if implemented by:
 *  <pre> {@code
 * static boolean bitEquals(double x, double y) {
 *   long xBits = Double.doubleToRawLongBits(x);
 *   long yBits = Double.doubleToRawLongBits(y);
 *   return xBits == yBits;
 * }}</pre>
 *
 * <p>It is possible to write a more scalable updater, at the cost of
 * giving up strict atomicity.  See for example
 * <a href="http://gee.cs.oswego.edu/dl/jsr166/dist/jsr166edocs/jsr166e/DoubleAdder.html">
 * DoubleAdder</a>
 * and
 * <a href="http://gee.cs.oswego.edu/dl/jsr166/dist/jsr166edocs/jsr166e/DoubleMaxUpdater.html">
 * DoubleMaxUpdater</a>.
 *
 * @author Doug Lea
 * @author Martin Buchholz
 * @since 11.0
 */
@GwtIncompatible
public class AtomicDouble extends Number implements java.io.Serializable {
  private static final long serialVersionUID = 0L;

  private transient volatile long value;

  private static final AtomicLongFieldUpdater<AtomicDouble> updater =
      AtomicLongFieldUpdater.newUpdater(AtomicDouble.class, "value");

  /**
   * Creates a new {@code AtomicDouble} with the given initial value.
   *
   * @param initialValue the initial value
   */
  public AtomicDouble(double initialValue) {
    value = doubleToRawLongBits(initialValue);
  }

  /**
   * Creates a new {@code AtomicDouble} with initial value {@code 0.0}.
   */
  public AtomicDouble() {
    // assert doubleToRawLongBits(0.0) == 0L;
  }

  /**
   * Gets the current value.
   *
   * @return the current value
   */
  public final double get() {
    return longBitsToDouble(value);
  }

  /**
   * Sets to the given value.
   *
   * @param newValue the new value
   */
  public final void set(double newValue) {
    long next = doubleToRawLongBits(newValue);
    value = next;
  }

  /**
   * Eventually sets to the given value.
   *
   * @param newValue the new value
   */
  public final void lazySet(double newValue) {
    set(newValue);
    // TODO(user): replace with code below when jdk5 support is dropped.
    // long next = doubleToRawLongBits(newValue);
    // updater.lazySet(this, next);
  }

  /**
   * Atomically sets to the given value and returns the old value.
   *
   * @param newValue the new value
   * @return the previous value
   */
  public final double getAndSet(double newValue) {
    long next = doubleToRawLongBits(newValue);
    return longBitsToDouble(updater.getAndSet(this, next));
  }

  /**
   * Atomically sets the value to the given updated value
   * if the current value is <a href="#bitEquals">bitwise equal
   * to the expected value.
   *
   * @param expect the expected value
   * @param update the new value
   * @return {@code true} if successful. False return indicates that
   * the actual value was not bitwise equal to the expected value.
   */
  public final boolean compareAndSet(double expect, double update) {
    return updater.compareAndSet(this,
                                 doubleToRawLongBits(expect),
                                 doubleToRawLongBits(update));
  }

  /**
   * Atomically sets the value to the given updated value
   * if the current value is <a href="#bitEquals">bitwise equal
   * to the expected value.
   *
   * <p>May 

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