/*

 * 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/publicdomain/zero/1.0/

 */

package java.util.concurrent.atomic;

import java.lang.reflect.Field;

import java.lang.reflect.Modifier;

import java.security.AccessController;

import java.security.PrivilegedActionException;

import java.security.PrivilegedExceptionAction;

import java.util.Objects;

import java.util.function.IntBinaryOperator;

import java.util.function.IntUnaryOperator;

import jdk.internal.misc.Unsafe;

import jdk.internal.reflect.CallerSensitive;

import jdk.internal.reflect.Reflection;

/**

 * A reflection-based utility that enables atomic updates to

 * designated {@code volatile int} fields of designated classes.

 * This class is designed for use in atomic data structures in which

 * several fields of the same node are independently subject to atomic

 * updates.

 *

 * <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.

 *

 * <p>Object arguments for parameters of type {@code T} that are not

 * instances of the class passed to {@link #newUpdater} will result in

 * a {@link ClassCastException} being thrown.

 *

 * @since 1.5

 * @author Doug Lea

 * @param <T> The type of the object holding the updatable field

 */

public abstract class AtomicIntegerFieldUpdater<T> {

    /**

     * Creates and returns an updater for objects with the given field.

     * The Class argument is needed to check that reflective types and

     * generic types match.

     *

     * @param tclass the class of the objects holding the field

     * @param fieldName the name of the field to be updated

     * @param <U> the type of instances of tclass

     * @return the updater

     * @throws IllegalArgumentException if the field is not a

     * volatile integer 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

     */

    @CallerSensitive

    public static <U> AtomicIntegerFieldUpdater<U> newUpdater(Class<U> tclass,

                                                              String fieldName) {

        return new AtomicIntegerFieldUpdaterImpl<U>

            (tclass, fieldName, Reflection.getCallerClass());

    }

    /**

     * Protected do-nothing constructor for use by subclasses.

     */

    protected AtomicIntegerFieldUpdater() {

    }

    /**

     * 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 {@code true} if successful

     */

    public abstract boolean compareAndSet(T obj, int expect, int 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><a href="package-summary.html#weakCompareAndSet">May fail

     * spuriously and does not provide ordering guarantees</a>, 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 {@code true} if successful

     */

    public abstract boolean weakCompareAndSet(T obj, int expect, int 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, int 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, int newValue);

    /**

     * Returns 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 int 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 int getAndSet(T obj, int newValue) {

        int prev;

        do {

            prev = get(obj);

        } while (!compareAndSet(obj, prev, newValue));

        return prev;

    }

    /**

     * Atomically increments by one the current value of the field of the

     * given object managed by this updater.

     *

     * @param obj An object whose field to get and set

     * @return the previous value

     */

    public int getAndIncrement(T obj) {

        int prev, next;

        do {

            prev = get(obj);

            next = prev + 1;

        } while (!compareAndSet(obj, prev, next));

        return prev;

    }

    /**

     * Atomically decrements by one the current value of the field of the

     * given object managed by this updater.

     *

     * @param obj An object whose field to get and set

     * @return the previous value

     */

    public int getAndDecrement(T obj) {

        int prev, next;

        do {

            prev = get(obj);

            next = prev - 1;

        } while (!compareAndSet(obj, prev, next));

        return prev;

    }

    /**

     * Atomically adds the given value to the current value of the field of

     * the given object managed by this updater.

     *

     * @param obj An object whose field to get and set

     * @param delta the value to add

     * @return the previous value

     */

    public int getAndAdd(T obj, int delta) {

        int prev, next;

        do {

            prev = get(obj);

            next = prev + delta;

        } while (!compareAndSet(obj, prev, next));

        return prev;

    }

    /**

     * Atomically increments by one the current value of the field of the

     * given object managed by this updater.

     *

     * @param obj An object whose field to get and set

     * @return the updated value

     */

    public int incrementAndGet(T obj) {

        int prev, next;

        do {

            prev = get(obj);

            next = prev + 1;

        } while (!compareAndSet(obj, prev, next));

        return next;

    }

    /**

     * Atomically decrements by one the current value of the field of the

     * given object managed by this updater.

     *

     * @param obj An object whose field to get and set

     * @return the updated value

     */

    public int decrementAndGet(T obj) {

        int prev, next;

        do {

            prev = get(obj);

            next = prev - 1;

        } while (!compareAndSet(obj, prev, next));

        return next;

    }

    /**

     * Atomically adds the given value to the current value of the field of

     * the given object managed by this updater.

     *

     * @param obj An object whose field to get and set

     * @param delta the value to add

     * @return the updated value

     */

    public int addAndGet(T obj, int delta) {

        int prev, next;

        do {

            prev = get(obj);

            next = prev + delta;

        } while (!compareAndSet(obj, prev, next));

        return next;

    }

    /**

     *

     * @param obj An object whose field to get and set

     * @param updateFunction a side-effect-free function

     * @return the previous value

     * @since 1.8

     */

    public final int getAndUpdate(T obj, IntUnaryOperator updateFunction) {

        int prev, next;

        do {

            prev = get(obj);

            next = updateFunction.applyAsInt(prev);

        } while (!compareAndSet(obj, prev, next));

        return prev;

    }

    /**

     *

     * @param obj An object whose field to get and set

     * @param updateFunction a side-effect-free function

     * @return the updated value

     * @since 1.8

     */

    public final int updateAndGet(T obj, IntUnaryOperator updateFunction) {

        int prev, next;

        do {

            prev = get(obj);

            next = updateFunction.applyAsInt(prev);

        } while (!compareAndSet(obj, prev, next));

        return next;

    }

    /**

     *

     * @param obj An object whose field to get and set

     * @param x the update value

     * @param accumulatorFunction a side-effect-free function of two arguments

     * @return the previous value

     * @since 1.8

     */

    public final int getAndAccumulate(T obj, int x,

                                      IntBinaryOperator accumulatorFunction) {

        int prev, next;

        do {

            prev = get(obj);

            next = accumulatorFunction.applyAsInt(prev, x);

        } while (!compareAndSet(obj, prev, next));

        return prev;

    }

    /**

     *

     * @param obj An object whose field to get and set

     * @param x the update value

     * @param accumulatorFunction a side-effect-free function of two arguments

     * @return the updated value

     * @since 1.8

     */

    public final int accumulateAndGet(T obj, int x,

                                      IntBinaryOperator accumulatorFunction) {

        int prev, next;

        do {

            prev = get(obj);

            next = accumulatorFunction.applyAsInt(prev, x);

        } while (!compareAndSet(obj, prev, next));

        return next;

    }

    /**

     * Standard hotspot implementation using intrinsics.

     */

    private static final class AtomicIntegerFieldUpdaterImpl<T>

        extends AtomicIntegerFieldUpdater<T> {

        private static final Unsafe U = Unsafe.getUnsafe();

        private final long offset;

        /**

         * if field is protected, the subclass constructing updater, else

         * the same as tclass

         */

        private final Class<?> cclass;

        /** class holding the field */

        private final Class<T> tclass;

        AtomicIntegerFieldUpdaterImpl(final Class<T> tclass,

                                      final String fieldName,

                                      final Class<?> caller) {

            final Field field;

            final int modifiers;

            try {

                field = AccessController.doPrivileged(

                    new PrivilegedExceptionAction<Field>() {

                        public Field run() throws NoSuchFieldException {

                            return tclass.getDeclaredField(fieldName);

                        }

                    });

                modifiers = field.getModifiers();

                sun.reflect.misc.ReflectUtil.ensureMemberAccess(

                    caller, tclass, null, modifiers);

                ClassLoader cl = tclass.getClassLoader();

                ClassLoader ccl = caller.getClassLoader();

                if ((ccl != null) && (ccl != cl) &&

                    ((cl == null) || !isAncestor(cl, ccl))) {

                    sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);

                }

            } catch (PrivilegedActionException pae) {

                throw new RuntimeException(pae.getException());

            } catch (Exception ex) {

                throw new RuntimeException(ex);

            }

            if (field.getType() != int.class)

                throw new IllegalArgumentException("Must be integer type");

            if (!Modifier.isVolatile(modifiers))

                throw new IllegalArgumentException("Must be volatile type");

            // Access to protected field members is restricted to receivers only

            // of the accessing class, or one of its subclasses, and the

            // accessing class must in turn be a subclass (or package sibling)

            // of the protected member's defining class.

            // If the updater refers to a protected field of a declaring class

            // outside the current package, the receiver argument will be

            // narrowed to the type of the accessing class.

            this.cclass = (Modifier.isProtected(modifiers) &&

                           tclass.isAssignableFrom(caller) &&

                           !isSamePackage(tclass, caller))

                          ? caller : tclass;

            this.tclass = tclass;

            this.offset = U.objectFieldOffset(field);

        }

        /**

         * Returns true if the second classloader can be found in the first

         * classloader's delegation chain.

         * Equivalent to the inaccessible: first.isAncestor(second).

         */

        private static boolean isAncestor(ClassLoader first, ClassLoader second) {

            ClassLoader acl = first;

            do {

                acl = acl.getParent();

                if (second == acl) {

                    return true;

                }

            } while (acl != null);

            return false;

        }

        /**

         * Returns true if the two classes have the same class loader and

         * package qualifier

         */

        private static boolean isSamePackage(Class<?> class1, Class<?> class2) {

            return class1.getClassLoader() == class2.getClassLoader()

                   && Objects.equals(class1.getPackageName(), class2.getPackageName());

        }

        /**

         * Checks that target argument is instance of cclass.  On

         * failure, throws cause.

         */

        private final void accessCheck(T obj) {

            if (!cclass.isInstance(obj))

                throwAccessCheckException(obj);

        }

        /**

         * Throws access exception if accessCheck failed due to

         * protected access, else ClassCastException.

         */

        private final void throwAccessCheckException(T obj) {

            if (cclass == tclass)

                throw new ClassCastException();

            else

                throw new RuntimeException(

                    new IllegalAccessException(

                        "Class " +

                        cclass.getName() +

                        " can not access a protected member of class " +

                        tclass.getName() +

                        " using an instance of " +

                        obj.getClass().getName()));

        }

        public final boolean compareAndSet(T obj, int expect, int update) {

            accessCheck(obj);

            return U.compareAndSetInt(obj, offset, expect, update);

        }

        public final boolean weakCompareAndSet(T obj, int expect, int update) {

            accessCheck(obj);

            return U.compareAndSetInt(obj, offset, expect, update);

        }

        public final void set(T obj, int newValue) {

            accessCheck(obj);

            U.putIntVolatile(obj, offset, newValue);

        }