/*
 * 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
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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/publicdomain/zero/1.0/
 */

package java.util.concurrent.atomic;

import java.util.Objects;

import org.naniteproject.annotation.NaniteNotImplemented;

/**
 * A reflection-based utility that enables atomic updates to
 * designated {@code volatile} reference fields of designated
 * classes.  This class is designed for use in atomic data structures
 * in which several reference fields of the same node are
 * independently subject to atomic updates. For example, a tree node
 * might be declared as
 *
 * <pre> {@code
 * class Node {
 *   private volatile Node left, right;
 *
 *   private static final AtomicReferenceFieldUpdater<Node, Node> leftUpdater =
 *     AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "left");
 *   private static AtomicReferenceFieldUpdater<Node, Node> rightUpdater =
 *     AtomicReferenceFieldUpdater.newUpdater(Node.class, Node.class, "right");
 *
 *   Node getLeft() { return left; }
 *   boolean compareAndSetLeft(Node expect, Node update) {
 *     return leftUpdater.compareAndSet(this, expect, update);
 *   }
 *   // ... and so on
 * }}</pre>
 *
 * <p>Note that the guarantees of the {@code compareAndSet}
 * method in this class are weaker than in other atomic classes.
 * Because this class cannot ensure that all uses of the field
 * are appropriate for purposes of atomic access, it can
 * guarantee atomicity only with respect to other invocations of
 * {@code compareAndSet} and {@code set} on the same updater.
 *
 * @since 1.5
 * @author Doug Lea
 * @param <T> The type of the object holding the updatable field
 * @param <V> The type of the field
 */
@NaniteNotImplemented("Atomic operations require reflection")
public abstract class AtomicReferenceFieldUpdater<T, V> {

    /**
     * Creates and returns an updater for objects with the given field.
     * The Class arguments are needed to check that reflective types and
     * generic types match.
     *
     * @param tclass the class of the objects holding the field.
     * @param vclass the class of the field
     * @param fieldName the name of the field to be updated.
     * @param <U> the type of instances of tclass
     * @param <W> the type of instances of vclass
     * @return the updater
     * @throws IllegalArgumentException if the field is not a volatile reference type.
     * @throws RuntimeException with a nested reflection-based
     * exception if the class does not hold field or is the wrong type,
     * or the field is inaccessible to the caller according to Java language
     * access control
     */

    public static <U, W> AtomicReferenceFieldUpdater<U,W> newUpdater(Class<U> tclass, Class<W> vclass, String fieldName) {
        //return new AtomicReferenceFieldUpdaterImpl<U,W>(tclass,
        //                                                vclass,
        //                                                fieldName,
        //                                                Reflection.getCallerClass());
        return null;
    }

    /**
     * Protected do-nothing constructor for use by subclasses.
     */
    protected AtomicReferenceFieldUpdater() {
    }

    /**
     * Atomically sets the field of the given object managed by this updater
     * to the given updated value if the current value {@code ==} the
     * expected value. This method is guaranteed to be atomic with respect to
     * other calls to {@code compareAndSet} and {@code set}, but not
     * necessarily with respect to other changes in the field.
     *
     * @param obj An object whose field to conditionally set
     * @param expect the expected value
     * @param update the new value
     * @return true if successful.
     */
    public abstract boolean compareAndSet(T obj, V expect, V update);

    /**
     * Atomically sets the field of the given object managed by this updater
     * to the given updated value if the current value {@code ==} the
     * expected value. This method is guaranteed to be atomic with respect to
     * other calls to {@code compareAndSet} and {@code set}, but not
     * necessarily with respect to other changes in the field.
     *
     * <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 obj An object whose field to conditionally set
     * @param expect the expected value
     * @param update the new value
     * @return true if successful.
     */
    public abstract boolean weakCompareAndSet(T obj, V expect, V update);

    /**
     * Sets the field of the given object managed by this updater to the
     * given updated value. This operation is guaranteed to act as a volatile
     * store with respect to subsequent invocations of {@code compareAndSet}.
     *
     * @param obj An object whose field to set
     * @param newValue the new value
     */
    public abstract void set(T obj, V newValue);

    /**
     * Eventually sets the field of the given object managed by this
     * updater to the given updated value.
     *
     * @param obj An object whose field to set
     * @param newValue the new value
     * @since 1.6
     */
    public abstract void lazySet(T obj, V newValue);

    /**
     * Gets the current value held in the field of the given object managed
     * by this updater.
     *
     * @param obj An object whose field to get
     * @return the current value
     */
    public abstract V get(T obj);

    /**
     * Atomically sets the field of the given object managed by this updater
     * to the given value and returns the old value.
     *
     * @param obj An object whose field to get and set
     * @param newValue the new value
     * @return the previous value
     */
    public V getAndSet(T obj, V newValue) {
        for (;;) {
            V current = get(obj);
            if (compareAndSet(obj, current, newValue))
                return current;
        }
    }
}
