/*
 * 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.errorprone.annotations.CanIgnoreReturnValue;

import java.util.concurrent.atomic.AtomicLongArray;

/**
 * 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.
 *
 * 

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: *

 {@code
 * static boolean bitEquals(double x, double y) {
 *   long xBits = Double.doubleToRawLongBits(x);
 *   long yBits = Double.doubleToRawLongBits(y);
 *   return xBits == yBits;
 * }}
* * @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 {@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 {@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. * * @return the length of the array */ public final int length() { return longs.length(); } /** * 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 {@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 {@code i} to the given value. * * @param i the index * @param newValue the new value */ public final void lazySet(int i, double newValue) { set(i, newValue); // TODO(user): replace with code below when jdk5 support is dropped. // long next = doubleToRawLongBits(newValue); // longs.lazySet(i, next); } /** * 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 {@code i} to the given * updated value * if the current value is bitwise equal * 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 {@code 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 {@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 {@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 {@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. * @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 {@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). */ private void readObject(java.io.ObjectInputStream s) throws java.io.IOException, ClassNotFoundException { s.defaultReadObject(); // Read in array length and allocate array int length = s.readInt(); this.longs = new AtomicLongArray(length); // Read in all elements in the proper order. for (int i = 0; i < length; i++) { set(i, s.readDouble()); } } }