/*

 * 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.  Sun designates this

 * particular file as subject to the "Classpath" exception as provided

 * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

 * CA 95054 USA or visit www.sun.com if you need additional information or

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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;

/**

 * An {@code AtomicStampedReference} maintains an object reference

 * along with an integer "stamp", that can be updated atomically.

 *

 * <p> Implementation note. This implementation maintains stamped

 * references by creating internal objects representing "boxed"

 * [reference, integer] pairs.

 *

 * @since 1.5

 * @author Doug Lea

 * @param <V> The type of object referred to by this reference

 */

public class AtomicStampedReference<V>  {

    private static class ReferenceIntegerPair<T> {

        private final T reference;

        private final int integer;

        ReferenceIntegerPair(T r, int i) {

            reference = r; integer = i;

        }

    }

    private final AtomicReference<ReferenceIntegerPair<V>>  atomicRef;

    /**

     * Creates a new {@code AtomicStampedReference} with the given

     * initial values.

     *

     * @param initialRef the initial reference

     * @param initialStamp the initial stamp

     */

    public AtomicStampedReference(V initialRef, int initialStamp) {

        atomicRef = new AtomicReference<ReferenceIntegerPair<V>>

            (new ReferenceIntegerPair<V>(initialRef, initialStamp));

    }

    /**

     * Returns the current value of the reference.

     *

     * @return the current value of the reference

     */

    public V getReference() {

        return atomicRef.get().reference;

    }

    /**

     * Returns the current value of the stamp.

     *

     * @return the current value of the stamp

     */

    public int getStamp() {

        return atomicRef.get().integer;

    }

    /**

     * Returns the current values of both the reference and the stamp.

     * Typical usage is {@code int[1] holder; ref = v.get(holder); }.

     *

     * @param stampHolder an array of size of at least one.  On return,

     * {@code stampholder[0]} will hold the value of the stamp.

     * @return the current value of the reference

     */

    public V get(int[] stampHolder) {

        ReferenceIntegerPair<V> p = atomicRef.get();

        stampHolder[0] = p.integer;

        return p.reference;

    }

    /**

     * Atomically sets the value of both the reference and stamp

     * to the given update values if the

     * current reference is {@code ==} to the expected reference

     * and the current stamp is equal to the expected stamp.

     *

     * <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 expectedReference the expected value of the reference

     * @param newReference the new value for the reference

     * @param expectedStamp the expected value of the stamp

     * @param newStamp the new value for the stamp

     * @return true if successful

     */

    public boolean weakCompareAndSet(V      expectedReference,

                                     V      newReference,

                                     int    expectedStamp,

                                     int    newStamp) {

        ReferenceIntegerPair<V> current = atomicRef.get();

        return  expectedReference == current.reference &&

            expectedStamp == current.integer &&

            ((newReference == current.reference &&

              newStamp == current.integer) ||

             atomicRef.weakCompareAndSet(current,

                                     new ReferenceIntegerPair<V>(newReference,

                                                              newStamp)));

    }

    /**

     * Atomically sets the value of both the reference and stamp

     * to the given update values if the

     * current reference is {@code ==} to the expected reference

     * and the current stamp is equal to the expected stamp.

     *

     * @param expectedReference the expected value of the reference

     * @param newReference the new value for the reference

     * @param expectedStamp the expected value of the stamp

     * @param newStamp the new value for the stamp

     * @return true if successful

     */

    public boolean compareAndSet(V      expectedReference,

                                 V      newReference,

                                 int    expectedStamp,

                                 int    newStamp) {

        ReferenceIntegerPair<V> current = atomicRef.get();

        return  expectedReference == current.reference &&

            expectedStamp == current.integer &&

            ((newReference == current.reference &&

              newStamp == current.integer) ||

             atomicRef.compareAndSet(current,

                                     new ReferenceIntegerPair<V>(newReference,

                                                              newStamp)));

    }

    /**

     * Unconditionally sets the value of both the reference and stamp.

     *

     * @param newReference the new value for the reference

     * @param newStamp the new value for the stamp

     */

    public void set(V newReference, int newStamp) {

        ReferenceIntegerPair<V> current = atomicRef.get();

        if (newReference != current.reference || newStamp != current.integer)

            atomicRef.set(new ReferenceIntegerPair<V>(newReference, newStamp));

    }

    /**

     * Atomically sets the value of the stamp to the given update value

     * if the current reference is {@code ==} to the expected

     * reference.  Any given invocation of this operation may fail

     * (return {@code false}) spuriously, but repeated invocation

     * when the current value holds the expected value and no other

     * thread is also attempting to set the value will eventually

     * succeed.

     *

     * @param expectedReference the expected value of the reference

     * @param newStamp the new value for the stamp

     * @return true if successful

     */

    public boolean attemptStamp(V expectedReference, int newStamp) {

        ReferenceIntegerPair<V> current = atomicRef.get();

        return  expectedReference == current.reference &&

            (newStamp == current.integer ||

             atomicRef.compareAndSet(current,

                                     new ReferenceIntegerPair<V>(expectedReference,

                                                              newStamp)));

    }

}