/*
 * Written by Doug Lea 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/AtomicDoubleArray.java?revision=1.5
 * (Modified to adapt to guava coding conventions and
 * to use AtomicLongArray 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.common.primitives.ImmutableLongArray;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import java.util.concurrent.atomic.AtomicLongArray;

A double array in which elements may be updated atomically. See the atomic package specification for description of the properties of atomic variables. 
This class compares primitive double values in methods such as compareAndSet by comparing their bitwise representation using Double.doubleToRawLongBits, which differs from both the primitive double == operator and from Double.equals, as if implemented by: 

static boolean bitEquals(double x, double y) {
  long xBits = Double.doubleToRawLongBits(x);
  long yBits = Double.doubleToRawLongBits(y);
  return xBits == yBits;
 }

Author:
Doug Lea, Martin Buchholz
Since:
11.0/**
 * A {@code double} array in which elements may be updated atomically. See the {@link
 * java.util.concurrent.atomic} package specification for description of the properties of atomic
 * variables.
 *
 * <p><a name="bitEquals"></a>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>
 *
 * @author Doug Lea
 * @author Martin Buchholz
 * @since 11.0
 */
@GwtIncompatible
public class AtomicDoubleArray implements java.io.Serializable {
  private static final long serialVersionUID = 0L;

  // Making this non-final is the lesser evil according to Effective
  // Java 2nd Edition Item 76: Write readObject methods defensively.
  private transient AtomicLongArray longs;

  
Creates a new AtomicDoubleArray of the given length, with all elements initially zero. 
Params:
length – the length of the array/**
   * Creates a new {@code AtomicDoubleArray} of the given length, with all elements initially zero.
   *
   * @param length the length of the array
   */
  public AtomicDoubleArray(int length) {
    this.longs = new AtomicLongArray(length);
  }

  
Creates a new AtomicDoubleArray with the same length as, and all elements copied from, the given array. 
Params:
array – the array to copy elements from
Throws:
NullPointerException – if array is null/**
   * Creates a new {@code AtomicDoubleArray} with the same length as, and all elements copied from,
   * the given array.
   *
   * @param array the array to copy elements from
   * @throws NullPointerException if array is null
   */
  public AtomicDoubleArray(double[] array) {
    final int len = array.length;
    long[] longArray = new long[len];
    for (int i = 0; i < len; i++) {
      longArray[i] = doubleToRawLongBits(array[i]);
    }
    this.longs = new AtomicLongArray(longArray);
  }

  
Returns the length of the array.
Returns:
the length of the array/**
   * Returns the length of the array.
   *
   * @return the length of the array
   */
  public final int length() {
    return longs.length();
  }

  
Gets the current value at position i. 
Params:
i – the index
Returns:
the current value/**
   * Gets the current value at position {@code i}.
   *
   * @param i the index
   * @return the current value
   */
  public final double get(int i) {
    return longBitsToDouble(longs.get(i));
  }

  
Sets the element at position i to the given value. 
Params:
i – the index
newValue – the new value/**
   * Sets the element at position {@code i} to the given value.
   *
   * @param i the index
   * @param newValue the new value
   */
  public final void set(int i, double newValue) {
    long next = doubleToRawLongBits(newValue);
    longs.set(i, next);
  }

  
Eventually sets the element at position i to the given value. 
Params:
i – the index
newValue – the new value/**
   * Eventually sets the element at position {@code i} to the given value.
   *
   * @param i the index
   * @param newValue the new value
   */
  public final void lazySet(int i, double newValue) {
    long next = doubleToRawLongBits(newValue);
    longs.lazySet(i, next);
  }

  
Atomically sets the element at position i to the given value and returns the old value. 
Params:
i – the index
newValue – the new value
Returns:
the previous value/**
   * Atomically sets the element at position {@code i} to the given value and returns the old value.
   *
   * @param i the index
   * @param newValue the new value
   * @return the previous value
   */
  public final double getAndSet(int i, double newValue) {
    long next = doubleToRawLongBits(newValue);
    return longBitsToDouble(longs.getAndSet(i, next));
  }

  
Atomically sets the element at position i to the given updated value if the current value is bitwise equal to the expected value.
Params:
i – the index
expect – the expected value
update – the new value
Returns:
true if successful. False return indicates that the actual value was not equal to the
    expected value./**
   * Atomically sets the element at position {@code i} to the given updated value if the current
   * value is <a href="#bitEquals">bitwise equal</a> to the expected value.
   *
   * @param i the index
   * @param expect the expected value
   * @param update the new value
   * @return true if successful. False return indicates that the actual value was not equal to the
   *     expected value.
   */
  public final boolean compareAndSet(int i, double expect, double update) {
    return longs.compareAndSet(i, doubleToRawLongBits(expect), doubleToRawLongBits(update));
  }

  
Atomically sets the element at position i to the given updated value if the current value is bitwise equal to the expected value.
May 
fail spuriously and does not provide ordering guarantees, so is only rarely an appropriate alternative to compareAndSet. 
Params:
i – the index
expect – the expected value
update – the new value
Returns:
true if successful/**
   * Atomically sets the element at position {@code i} to the given updated value if the current
   * value is <a href="#bitEquals">bitwise equal</a> to the expected value.
   *
   * <p>May <a
   * href="http://download.oracle.com/javase/7/docs/api/java/util/concurrent/atomic/package-summary.html#Spurious">
   * fail spuriously</a> and does not provide ordering guarantees, so is only rarely an appropriate
   * alternative to {@code compareAndSet}.
   *
   * @param i the index
   * @param expect the expected value
   * @param update the new value
   * @return true if successful
   */
  public final boolean weakCompareAndSet(int i, double expect, double update) {
    return longs.weakCompareAndSet(i, doubleToRawLongBits(expect), doubleToRawLongBits(update));
  }

  
Atomically adds the given value to the element at index i. 
Params:
i – the index
delta – the value to add
Returns:
the previous value/**
   * Atomically adds the given value to the element at index {@code i}.
   *
   * @param i the index
   * @param delta the value to add
   * @return the previous value
   */
  @CanIgnoreReturnValue
  public final double getAndAdd(int i, double delta) {
    while (true) {
      long current = longs.get(i);
      double currentVal = longBitsToDouble(current);
      double nextVal = currentVal + delta;
      long next = doubleToRawLongBits(nextVal);
      if (longs.compareAndSet(i, current, next)) {
        return currentVal;
      }
    }
  }

  
Atomically adds the given value to the element at index i. 
Params:
i – the index
delta – the value to add
Returns:
the updated value/**
   * Atomically adds the given value to the element at index {@code i}.
   *
   * @param i the index
   * @param delta the value to add
   * @return the updated value
   */
  @CanIgnoreReturnValue
  public double addAndGet(int i, double delta) {
    while (true) {
      long current = longs.get(i);
      double currentVal = longBitsToDouble(current);
      double nextVal = currentVal + delta;
      long next = doubleToRawLongBits(nextVal);
      if (longs.compareAndSet(i, current, next)) {
        return nextVal;
      }
    }
  }

  
Returns the String representation of the current values of array.
Returns:
the String representation of the current values of array/**
   * Returns the String representation of the current values of array.
   *
   * @return the String representation of the current values of array
   */
  public String toString() {
    int iMax = length() - 1;
    if (iMax == -1) {
      return "[]";
    }

    // Double.toString(Math.PI).length() == 17
    StringBuilder b = new StringBuilder((17 + 2) * (iMax + 1));
    b.append('[');
    for (int i = 0; ; i++) {
      b.append(longBitsToDouble(longs.get(i)));
      if (i == iMax) {
        return b.append(']').toString();
      }
      b.append(',').append(' ');
    }
  }

  
Saves the state to a stream (that is, serializes it).
@serialData
The length of the array is emitted (int), followed by all of its elements (each a double) in the proper order./**
   * Saves the state to a stream (that is, serializes it).
   *
   * @serialData The length of the array is emitted (int), followed by all of its elements (each a
   *     {@code double}) in the proper order.
   */
  private void writeObject(java.io.ObjectOutputStream s) throws java.io.IOException {
    s.defaultWriteObject();

    // Write out array length
    int length = length();
    s.writeInt(length);

    // Write out all elements in the proper order.
    for (int i = 0; i < length; i++) {
      s.writeDouble(get(i));
    }
  }

  
Reconstitutes the instance from a stream (that is, deserializes it). /** Reconstitutes the instance from a stream (that is, deserializes it). */
  private void readObject(java.io.ObjectInputStream s)
      throws java.io.IOException, ClassNotFoundException {
    s.defaultReadObject();

    int length = s.readInt();
    ImmutableLongArray.Builder builder = ImmutableLongArray.builder();
    for (int i = 0; i < length; i++) {
      builder.add(doubleToRawLongBits(s.readDouble()));
    }
    this.longs = new AtomicLongArray(builder.build().toArray());
  }
}