/* * 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 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
*/
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 */ 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 */ 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()); } } }