/*
* 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.
*
* <p><a name="bitEquals">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
*/
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 <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 {@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 {@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());
}
}
}