/*
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
* or visit www.oracle.com if you need additional information or have any
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*/
/*
* This file is available under and governed by the GNU General Public
* License version 2 only, as published by the Free Software Foundation.
* However, the following notice accompanied the original version of this
* file:
*
* 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.*;
/** {@collect.stats}
* {@description.open}
* 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.
* {@description.close}
* @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 + (long) i * scale;
}
/** {@collect.stats}
* {@description.open}
* Creates a new AtomicReferenceArray of given length.
* {@description.close}
* @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);
}
/** {@collect.stats}
* {@description.open}
* Creates a new AtomicReferenceArray with the same length as, and
* all elements copied from, the given array.
* {@description.close}
*
* @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);
}
}
/** {@collect.stats}
* {@description.open}
* Returns the length of the array.
* {@description.close}
*
* @return the length of the array
*/
public final int length() {
return array.length;
}
/** {@collect.stats}
* {@description.open}
* Gets the current value at position {@code i}.
* {@description.close}
*
* @param i the index
* @return the current value
*/
public final E get(int i) {
return (E) unsafe.getObjectVolatile(array, rawIndex(i));
}
/** {@collect.stats}
* {@description.open}
* Sets the element at position {@code i} to the given value.
* {@description.close}
*
* @param i the index
* @param newValue the new value
*/
public final void set(int i, E newValue) {
unsafe.putObjectVolatile(array, rawIndex(i), newValue);
}
/** {@collect.stats}
* {@description.open}
* Eventually sets the element at position {@code i} to the given value.
* {@description.close}
*
* @param i the index
* @param newValue the new value
* @since 1.6
*/
public final void lazySet(int i, E newValue) {
unsafe.putOrderedObject(array, rawIndex(i), newValue);
}
/** {@collect.stats}
* {@description.open}
* Atomically sets the element at position {@code i} to the given
* value and returns the old value.
* {@description.close}
*
* @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;
}
}
/** {@collect.stats}
* {@description.open}
* Atomically sets the element at position {@code i} to the given
* updated value if the current value {@code ==} the expected value.
* {@description.close}
* @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);
}
/** {@collect.stats}
* {@description.open}
* Atomically sets the element at position {@code i} to the given
* updated value if the current value {@code ==} the expected value.
*
* <p>May <a href="package-summary.html#Spurious">fail spuriously</a>
* and does not provide ordering guarantees, so is only rarely an
* appropriate alternative to {@code compareAndSet}.
* {@description.close}
*
* @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);
}
/** {@collect.stats}
* {@description.open}
* Returns the String representation of the current values of array.
* {@description.close}
* @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);
}
}