/* * 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 com.google.common.annotations.Beta; import static java.lang.Double.doubleToRawLongBits; import static java.lang.Double.longBitsToDouble; 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. * *
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:
* It is possible to write a more scalable updater, at the cost of
* giving up strict atomicity. See for example
*
* and
* .
*
* @author Doug Lea
* @author Martin Buchholz
* @since 11.0
*/
@Beta
public class AtomicDouble extends Number implements java.io.Serializable {
private static final long serialVersionUID = 0L;
private transient volatile long value;
private static final AtomicLongFieldUpdater May
* fail spuriously
* and does not provide ordering guarantees, so is only rarely an
* appropriate alternative to {@code compareAndSet}.
*
* @param expect the expected value
* @param update the new value
* @return {@code true} if successful
*/
public final boolean weakCompareAndSet(double expect, double update) {
return updater.weakCompareAndSet(this,
doubleToRawLongBits(expect),
doubleToRawLongBits(update));
}
/**
* Atomically adds the given value to the current value.
*
* @param delta the value to add
* @return the previous value
*/
public final double getAndAdd(double delta) {
while (true) {
long current = value;
double currentVal = longBitsToDouble(current);
double nextVal = currentVal + delta;
long next = doubleToRawLongBits(nextVal);
if (updater.compareAndSet(this, current, next)) {
return currentVal;
}
}
}
/**
* Atomically adds the given value to the current value.
*
* @param delta the value to add
* @return the updated value
*/
public final double addAndGet(double delta) {
while (true) {
long current = value;
double currentVal = longBitsToDouble(current);
double nextVal = currentVal + delta;
long next = doubleToRawLongBits(nextVal);
if (updater.compareAndSet(this, current, next)) {
return nextVal;
}
}
}
/**
* Returns the String representation of the current value.
* @return the String representation of the current value
*/
public String toString() {
return Double.toString(get());
}
/**
* Returns the value of this {@code AtomicDouble} as an {@code int}
* after a narrowing primitive conversion.
*/
public int intValue() {
return (int) get();
}
/**
* Returns the value of this {@code AtomicDouble} as a {@code long}
* after a narrowing primitive conversion.
*/
public long longValue() {
return (long) get();
}
/**
* Returns the value of this {@code AtomicDouble} as a {@code float}
* after a narrowing primitive conversion.
*/
public float floatValue() {
return (float) get();
}
/**
* Returns the value of this {@code AtomicDouble} as a {@code double}.
*/
public double doubleValue() {
return get();
}
/**
* Saves the state to a stream (that is, serializes it).
*
* @serialData The current value is emitted (a {@code double}).
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
s.defaultWriteObject();
s.writeDouble(get());
}
/**
* Reconstitutes the instance from a stream (that is, deserializes it).
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
set(s.readDouble());
}
}
{@code
* static boolean bitEquals(double x, double y) {
* long xBits = Double.doubleToRawLongBits(x);
* long yBits = Double.doubleToRawLongBits(y);
* return xBits == yBits;
* }}
*
*