AtomicDouble.java
/*
* 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 static java.lang.Double.doubleToRawLongBits;
import static java.lang.Double.longBitsToDouble;
import com.google.common.annotations.GwtIncompatible;
import com.google.errorprone.annotations.CanIgnoreReturnValue;
import com.google.j2objc.annotations.ReflectionSupport;
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.
*
* <p><a id="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>
*
* <p>It is possible to write a more scalable updater, at the cost of giving up strict atomicity.
* See for example <a
* href="http://gee.cs.oswego.edu/dl/jsr166/dist/docs/java.base/java/util/concurrent/atomic/DoubleAdder.html">
* DoubleAdder</a>.
*
* @author Doug Lea
* @author Martin Buchholz
* @since 11.0
*/
@GwtIncompatible
@ReflectionSupport(value = ReflectionSupport.Level.FULL)
@ElementTypesAreNonnullByDefault
public class AtomicDouble extends Number implements java.io.Serializable {
private static final long serialVersionUID = 0L;
private transient volatile long value;
private static final AtomicLongFieldUpdater<AtomicDouble> updater =
AtomicLongFieldUpdater.newUpdater(AtomicDouble.class, "value");
/**
* Creates a new {@code AtomicDouble} with the given initial value.
*
* @param initialValue the initial value
*/
public AtomicDouble(double initialValue) {
value = doubleToRawLongBits(initialValue);
}
/** Creates a new {@code AtomicDouble} with initial value {@code 0.0}. */
public AtomicDouble() {
// assert doubleToRawLongBits(0.0) == 0L;
}
/**
* Gets the current value.
*
* @return the current value
*/
public final double get() {
return longBitsToDouble(value);
}
/**
* Sets to the given value.
*
* @param newValue the new value
*/
public final void set(double newValue) {
long next = doubleToRawLongBits(newValue);
value = next;
}
/**
* Eventually sets to the given value.
*
* @param newValue the new value
*/
public final void lazySet(double newValue) {
long next = doubleToRawLongBits(newValue);
updater.lazySet(this, next);
}
/**
* Atomically sets to the given value and returns the old value.
*
* @param newValue the new value
* @return the previous value
*/
public final double getAndSet(double newValue) {
long next = doubleToRawLongBits(newValue);
return longBitsToDouble(updater.getAndSet(this, next));
}
/**
* Atomically sets the value to the given updated value if the current value is <a
* href="#bitEquals">bitwise equal</a> to the expected value.
*
* @param expect the expected value
* @param update the new value
* @return {@code true} if successful. False return indicates that the actual value was not
* bitwise equal to the expected value.
*/
public final boolean compareAndSet(double expect, double update) {
return updater.compareAndSet(this, doubleToRawLongBits(expect), doubleToRawLongBits(update));
}
/**
* Atomically sets the value 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 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
*/
@CanIgnoreReturnValue
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
*/
@CanIgnoreReturnValue
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
*/
@Override
public String toString() {
return Double.toString(get());
}
/**
* Returns the value of this {@code AtomicDouble} as an {@code int} after a narrowing primitive
* conversion.
*/
@Override
public int intValue() {
return (int) get();
}
/**
* Returns the value of this {@code AtomicDouble} as a {@code long} after a narrowing primitive
* conversion.
*/
@Override
public long longValue() {
return (long) get();
}
/**
* Returns the value of this {@code AtomicDouble} as a {@code float} after a narrowing primitive
* conversion.
*/
@Override
public float floatValue() {
return (float) get();
}
/** Returns the value of this {@code AtomicDouble} as a {@code double}. */
@Override
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());
}
}