/* * 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/ */ package jsr166e.extra; import static java.lang.Double.doubleToRawLongBits; import static java.lang.Double.longBitsToDouble; /** * 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: *
{@code * static boolean bitEquals(double x, double y) { * long xBits = Double.doubleToRawLongBits(x); * long yBits = Double.doubleToRawLongBits(y); * return xBits == yBits; * }}* * @see jsr166e.DoubleAdder * @see jsr166e.DoubleMaxUpdater * * @author Doug Lea * @author Martin Buchholz */ public class AtomicDouble extends Number implements java.io.Serializable { private static final long serialVersionUID = -8405198993435143622L; private transient volatile long 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); unsafe.putOrderedLong(this, valueOffset, 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); while (true) { long current = value; if (unsafe.compareAndSwapLong(this, valueOffset, current, next)) return longBitsToDouble(current); } } /** * Atomically sets the value to the given updated value * if the current value is bitwise equal * 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 unsafe.compareAndSwapLong(this, valueOffset, doubleToRawLongBits(expect), doubleToRawLongBits(update)); } /** * Atomically sets the value 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 expect the expected value
* @param update the new value
* @return {@code true} if successful
*/
public final boolean weakCompareAndSet(double expect, double update) {
return compareAndSet(expect, 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 (unsafe.compareAndSwapLong(this, valueOffset, 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 (unsafe.compareAndSwapLong(this, valueOffset, 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).
*
* @param s the stream
* @throws java.io.IOException if an I/O error occurs
* @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).
* @param s the stream
* @throws ClassNotFoundException if the class of a serialized object
* could not be found
* @throws java.io.IOException if an I/O error occurs
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
s.defaultReadObject();
set(s.readDouble());
}
// Unsafe mechanics
private static final sun.misc.Unsafe unsafe = getUnsafe();
private static final long valueOffset;
static {
try {
valueOffset = unsafe.objectFieldOffset
(AtomicDouble.class.getDeclaredField("value"));
} catch (Exception ex) { throw new Error(ex); }
}
/**
* Returns a sun.misc.Unsafe. Suitable for use in a 3rd party package.
* Replace with a simple call to Unsafe.getUnsafe when integrating
* into a jdk.
*
* @return a sun.misc.Unsafe
*/
private static sun.misc.Unsafe getUnsafe() {
try {
return sun.misc.Unsafe.getUnsafe();
} catch (SecurityException tryReflectionInstead) {}
try {
return java.security.AccessController.doPrivileged
(new java.security.PrivilegedExceptionAction