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/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group and released to the public domain, as explained at
* http://creativecommons.org/licenses/publicdomain
*/
package java.util.concurrent.atomic;
import sun.misc.Unsafe;
import java.util.*;
/**
* An <tt>int</tt> array in which elements may be updated atomically.
* See the {@link java.util.concurrent.atomic} package
* specification for description of the properties of atomic
* variables.
* @since 1.5
* @author Doug Lea
*/
public class AtomicIntegerArray implements java.io.Serializable {
private static final long serialVersionUID = 2862133569453604235L;
// setup to use Unsafe.compareAndSwapInt for updates
private static final Unsafe unsafe = Unsafe.getUnsafe();
private static final int base = unsafe.arrayBaseOffset(int[].class);
private static final int scale = unsafe.arrayIndexScale(int[].class);
private final int[] array;
private long rawIndex(int i) {
if (i < 0 || i >= array.length)
throw new IndexOutOfBoundsException("index " + i);
return base + i * scale;
}
/**
* Creates a new AtomicIntegerArray of given length.
*
* @param length the length of the array
*/
public AtomicIntegerArray(int length) {
array = new int[length];
// must perform at least one volatile write to conform to JMM
if (length > 0)
unsafe.putIntVolatile(array, rawIndex(0), 0);
}
/**
* Creates a new AtomicIntegerArray 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 AtomicIntegerArray(int[] array) {
if (array == null)
throw new NullPointerException();
int length = array.length;
this.array = new int[length];
if (length > 0) {
int last = length-1;
for (int i = 0; i < last; ++i)
this.array[i] = array[i];
// Do the last write as volatile
unsafe.putIntVolatile(this.array, rawIndex(last), array[last]);
}
}
/**
* 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 <tt>i</tt>.
*
* @param i the index
* @return the current value
*/
public final int get(int i) {
return unsafe.getIntVolatile(array, rawIndex(i));
}
/**
* Sets the element at position <tt>i</tt> to the given value.
*
* @param i the index
* @param newValue the new value
*/
public final void set(int i, int newValue) {
unsafe.putIntVolatile(array, rawIndex(i), newValue);
}
/**
* Eventually sets the element at position <tt>i</tt> to the given value.
*
* @param i the index
* @param newValue the new value
* @since 1.6
*/
public final void lazySet(int i, int newValue) {
unsafe.putOrderedInt(array, rawIndex(i), newValue);
}
/**
* Atomically sets the element at position <tt>i</tt> to the given
* value and returns the old value.
*
* @param i the index
* @param newValue the new value
* @return the previous value
*/
public final int getAndSet(int i, int newValue) {
while (true) {
int current = get(i);
if (compareAndSet(i, current, newValue))
return current;
}
}
/**
* Atomically sets the element at position <tt>i</tt> to the given
* updated value if the current value <tt>==</tt> 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, int expect, int update) {
return unsafe.compareAndSwapInt(array, rawIndex(i),
expect, update);
}
/**
* Atomically sets the element at position <tt>i</tt> to the given
* updated value if the current value <tt>==</tt> the expected value.
* May fail spuriously and does not provide ordering guarantees,
* so is only rarely an appropriate alternative to <tt>compareAndSet</tt>.
*
* @param i the index
* @param expect the expected value
* @param update the new value
* @return true if successful.
*/
public final boolean weakCompareAndSet(int i, int expect, int update) {
return compareAndSet(i, expect, update);
}
/**
* Atomically increments by one the element at index <tt>i</tt>.
*
* @param i the index
* @return the previous value
*/
public final int getAndIncrement(int i) {
while (true) {
int current = get(i);
int next = current + 1;
if (compareAndSet(i, current, next))
return current;
}
}
/**
* Atomically decrements by one the element at index <tt>i</tt>.
*
* @param i the index
* @return the previous value
*/
public final int getAndDecrement(int i) {
while (true) {
int current = get(i);
int next = current - 1;
if (compareAndSet(i, current, next))
return current;
}
}
/**
* Atomically adds the given value to the element at index <tt>i</tt>.
*
* @param i the index
* @param delta the value to add
* @return the previous value
*/
public final int getAndAdd(int i, int delta) {
while (true) {
int current = get(i);
int next = current + delta;
if (compareAndSet(i, current, next))
return current;
}
}
/**
* Atomically increments by one the element at index <tt>i</tt>.
*
* @param i the index
* @return the updated value
*/
public final int incrementAndGet(int i) {
while (true) {
int current = get(i);
int next = current + 1;
if (compareAndSet(i, current, next))
return next;
}
}
/**
* Atomically decrements by one the element at index <tt>i</tt>.
*
* @param i the index
* @return the updated value
*/
public final int decrementAndGet(int i) {
while (true) {
int current = get(i);
int next = current - 1;
if (compareAndSet(i, current, next))
return next;
}
}
/**
* Atomically adds the given value to the element at index <tt>i</tt>.
*
* @param i the index
* @param delta the value to add
* @return the updated value
*/
public final int addAndGet(int i, int delta) {
while (true) {
int current = get(i);
int next = current + delta;
if (compareAndSet(i, current, next))
return next;
}
}
/**
* Returns the String representation of the current values of array.
* @return the String representation of the current values of array.
*/
public String toString() {
if (array.length > 0) // force volatile read
get(0);
return Arrays.toString(array);
}
}
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