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;
* }}
*
* @author Doug Lea
* @author Martin Buchholz
*/
public class AtomicDoubleArray implements java.io.Serializable {
private static final long serialVersionUID = -2308431214976778248L;
private final transient long[] array;
private long checkedByteOffset(int i) {
if (i < 0 || i >= array.length)
throw new IndexOutOfBoundsException("index " + i);
return byteOffset(i);
}
private static long byteOffset(int i) {
return ((long) i << shift) + base;
}
/**
* 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) {
array = new long[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) {
// Visibility guaranteed by final field guarantees
final int len = array.length;
final long[] a = new long[len];
for (int i = 0; i < len; i++)
a[i] = doubleToRawLongBits(array[i]);
this.array = a;
}
/**
* Returns the length of the array.
*
* @return the length of the array
*/
public final int length() {
return array.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(getRaw(checkedByteOffset(i)));
}
private long getRaw(long offset) {
return unsafe.getLongVolatile(array, offset);
}
/**
* 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);
unsafe.putLongVolatile(array, checkedByteOffset(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) {
long next = doubleToRawLongBits(newValue);
unsafe.putOrderedLong(array, checkedByteOffset(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);
long offset = checkedByteOffset(i);
while (true) {
long current = getRaw(offset);
if (compareAndSetRaw(offset, current, next))
return longBitsToDouble(current);
}
}
/**
* Atomically sets the element at position {@code i} to the given
* updated value
* if the current value is bitwise equal
* 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 compareAndSetRaw(checkedByteOffset(i),
doubleToRawLongBits(expect),
doubleToRawLongBits(update));
}
private boolean compareAndSetRaw(long offset, long expect, long update) {
return unsafe.compareAndSwapLong(array, offset, expect, update);
}
/**
* Atomically sets the element at position {@code i} 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 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 compareAndSet(i, expect, 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) {
long offset = checkedByteOffset(i);
while (true) {
long current = getRaw(offset);
double currentVal = longBitsToDouble(current);
double nextVal = currentVal + delta;
long next = doubleToRawLongBits(nextVal);
if (compareAndSetRaw(offset, 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) {
long offset = checkedByteOffset(i);
while (true) {
long current = getRaw(offset);
double currentVal = longBitsToDouble(current);
double nextVal = currentVal + delta;
long next = doubleToRawLongBits(nextVal);
if (compareAndSetRaw(offset, 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 = array.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(getRaw(byteOffset(i))));
if (i == iMax)
return b.append(']').toString();
b.append(',').append(' ');
}
}
/**
* 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 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).
* @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();
// Read in array length and allocate array
int length = s.readInt();
unsafe.putObjectVolatile(this, arrayOffset, new long[length]);
// Read in all elements in the proper order.
for (int i = 0; i < length; i++)
set(i, s.readDouble());
}
// Unsafe mechanics
private static final sun.misc.Unsafe unsafe = getUnsafe();
private static final long arrayOffset;
private static final int base = unsafe.arrayBaseOffset(long[].class);
private static final int shift;
static {
try {
Class k = AtomicDoubleArray.class;
arrayOffset = unsafe.objectFieldOffset
(k.getDeclaredField("array"));
int scale = unsafe.arrayIndexScale(long[].class);
if ((scale & (scale - 1)) != 0)
throw new Error("data type scale not a power of two");
shift = 31 - Integer.numberOfLeadingZeros(scale);
} catch (Exception e) {
throw new Error(e);
}
}
/**
* 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