| /* |
| * 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 |
| * questions. |
| */ |
| |
| /* |
| * 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/publicdomain/zero/1.0/ |
| */ |
| |
| package java.util.concurrent.atomic; |
| import sun.misc.Unsafe; |
| |
| /** |
| * An object reference that 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 <V> The type of object referred to by this reference |
| */ |
| public class AtomicReference<V> implements java.io.Serializable { |
| private static final long serialVersionUID = -1848883965231344442L; |
| |
| private static final Unsafe unsafe = Unsafe.getUnsafe(); |
| private static final long valueOffset; |
| |
| static { |
| try { |
| valueOffset = unsafe.objectFieldOffset |
| (AtomicReference.class.getDeclaredField("value")); |
| } catch (Exception ex) { throw new Error(ex); } |
| } |
| |
| private volatile V value; |
| |
| /** |
| * Creates a new AtomicReference with the given initial value. |
| * |
| * @param initialValue the initial value |
| */ |
| public AtomicReference(V initialValue) { |
| value = initialValue; |
| } |
| |
| /** |
| * Creates a new AtomicReference with null initial value. |
| */ |
| public AtomicReference() { |
| } |
| |
| /** |
| * Gets the current value. |
| * |
| * @return the current value |
| */ |
| public final V get() { |
| return value; |
| } |
| |
| /** |
| * Sets to the given value. |
| * |
| * @param newValue the new value |
| */ |
| public final void set(V newValue) { |
| value = newValue; |
| } |
| |
| /** |
| * Eventually sets to the given value. |
| * |
| * @param newValue the new value |
| * @since 1.6 |
| */ |
| public final void lazySet(V newValue) { |
| unsafe.putOrderedObject(this, valueOffset, newValue); |
| } |
| |
| /** |
| * Atomically sets the value to the given updated value |
| * if the current value {@code ==} the expected value. |
| * @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(V expect, V update) { |
| return unsafe.compareAndSwapObject(this, valueOffset, expect, update); |
| } |
| |
| /** |
| * Atomically sets the value 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}. |
| * |
| * @param expect the expected value |
| * @param update the new value |
| * @return true if successful. |
| */ |
| public final boolean weakCompareAndSet(V expect, V update) { |
| return unsafe.compareAndSwapObject(this, valueOffset, expect, update); |
| } |
| |
| /** |
| * Atomically sets to the given value and returns the old value. |
| * |
| * @param newValue the new value |
| * @return the previous value |
| */ |
| public final V getAndSet(V newValue) { |
| while (true) { |
| V x = get(); |
| if (compareAndSet(x, newValue)) |
| return x; |
| } |
| } |
| |
| /** |
| * Returns the String representation of the current value. |
| * @return the String representation of the current value. |
| */ |
| public String toString() { |
| return String.valueOf(get()); |
| } |
| |
| } |