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/*
* 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 jersey.repackaged.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 jersey.repackaged.jsr166e.DoubleAdder
* @see jersey.repackaged.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() {
public sun.misc.Unsafe run() throws Exception {
Class k = sun.misc.Unsafe.class;
for (java.lang.reflect.Field f : k.getDeclaredFields()) {
f.setAccessible(true);
Object x = f.get(null);
if (k.isInstance(x))
return k.cast(x);
}
throw new NoSuchFieldError("the Unsafe");
}});
} catch (java.security.PrivilegedActionException e) {
throw new RuntimeException("Could not initialize intrinsics",
e.getCause());
}
}
}