- /*
- * @(#)AtomicReferenceArray.java 1.6 04/01/24
- *
- * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
- * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
- */
-
- package java.util.concurrent.atomic;
- import sun.misc.Unsafe;
- import java.util.*;
-
- /**
- * An array of object references 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
- * @param <E> The base class of elements held in this array
- */
- public class AtomicReferenceArray<E> implements java.io.Serializable {
- private static final long serialVersionUID = -6209656149925076980L;
-
- private static final Unsafe unsafe = Unsafe.getUnsafe();
- private static final int base = unsafe.arrayBaseOffset(Object[].class);
- private static final int scale = unsafe.arrayIndexScale(Object[].class);
- private final Object[] array;
-
- private long rawIndex(int i) {
- if (i < 0 || i >= array.length)
- throw new IndexOutOfBoundsException("index " + i);
- return base + i * scale;
- }
-
- /**
- * Create a new AtomicReferenceArray of given length.
- * @param length the length of the array
- */
- public AtomicReferenceArray(int length) {
- array = new Object[length];
- // must perform at least one volatile write to conform to JMM
- if (length > 0)
- unsafe.putObjectVolatile(array, rawIndex(0), null);
- }
-
- /**
- * Create a new AtomicReferenceArray 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 AtomicReferenceArray(E[] array) {
- if (array == null)
- throw new NullPointerException();
- int length = array.length;
- this.array = new Object[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
- E e = array[last];
- unsafe.putObjectVolatile(this.array, rawIndex(last), e);
- }
- }
-
- /**
- * Returns the length of the array.
- *
- * @return the length of the array
- */
- public final int length() {
- return array.length;
- }
-
- /**
- * Get the current value at position <tt>i</tt>.
- *
- * @param i the index
- * @return the current value
- */
- public final E get(int i) {
- return (E) unsafe.getObjectVolatile(array, rawIndex(i));
- }
-
- /**
- * Set 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, E newValue) {
- unsafe.putObjectVolatile(array, rawIndex(i), newValue);
- }
-
- /**
- * Set the element at position <tt>i</tt> to the given value and return the
- * old value.
- *
- * @param i the index
- * @param newValue the new value
- * @return the previous value
- */
- public final E getAndSet(int i, E newValue) {
- while (true) {
- E current = get(i);
- if (compareAndSet(i, current, newValue))
- return current;
- }
- }
-
- /**
- * Atomically set the value 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, E expect, E update) {
- return unsafe.compareAndSwapObject(array, rawIndex(i),
- expect, update);
- }
-
- /**
- * Atomically set the value to the given updated value
- * if the current value <tt>==</tt> the expected value.
- * May fail spuriously.
- * @param i the index
- * @param expect the expected value
- * @param update the new value
- * @return true if successful.
- */
- public final boolean weakCompareAndSet(int i, E expect, E update) {
- return compareAndSet(i, expect, update);
- }
-
- /**
- * 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);
- }
-
- }