/* * 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;import java.lang.reflect.*; /** * 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. * * @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     * @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     */    public static <U> AtomicIntegerFieldUpdater<U> newUpdater(Class<U> tclass, String fieldName) {        return new AtomicIntegerFieldUpdaterImpl<U>(tclass, fieldName);    }     /**     * 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 true if successful     * @throws ClassCastException if {@code obj} is not an instance     * of the class possessing the field established in the constructor     */    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>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     * @throws ClassCastException if {@code obj} is not an instance     * of the class possessing the field established in the constructor     */    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);      /**     * 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 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) {        for (;;) {            int current = get(obj);            if (compareAndSet(obj, current, newValue))                return current;        }    }     /**     * 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) {        for (;;) {            int current = get(obj);            int next = current + 1;            if (compareAndSet(obj, current, next))                return current;        }    }     /**     * 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) {        for (;;) {            int current = get(obj);            int next = current - 1;            if (compareAndSet(obj, current, next))                return current;        }    }     /**     * 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) {        for (;;) {            int current = get(obj);            int next = current + delta;            if (compareAndSet(obj, current, next))                return current;        }    }     /**     * 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) {        for (;;) {            int current = get(obj);            int next = current + 1;            if (compareAndSet(obj, current, 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) {        for (;;) {            int current = get(obj);            int next = current - 1;            if (compareAndSet(obj, current, 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) {        for (;;) {            int current = get(obj);            int next = current + delta;            if (compareAndSet(obj, current, next))                return next;        }    }     /**     * Standard hotspot implementation using intrinsics     */    private static class AtomicIntegerFieldUpdaterImpl<T> extends AtomicIntegerFieldUpdater<T> {        private static final Unsafe unsafe = Unsafe.getUnsafe();        private final long offset;        private final Class<T> tclass;        private final Class cclass;         AtomicIntegerFieldUpdaterImpl(Class<T> tclass, String fieldName) {            Field field = null;            Class caller = null;            int modifiers = 0;            try {                field = tclass.getDeclaredField(fieldName);                caller = sun.reflect.Reflection.getCallerClass(3);                modifiers = field.getModifiers();                sun.reflect.misc.ReflectUtil.ensureMemberAccess(                    caller, tclass, null, modifiers);                sun.reflect.misc.ReflectUtil.checkPackageAccess(tclass);            } catch (Exception ex) {                throw new RuntimeException(ex);            }             Class fieldt = field.getType();            if (fieldt != int.class)                throw new IllegalArgumentException("Must be integer type");             if (!Modifier.isVolatile(modifiers))                throw new IllegalArgumentException("Must be volatile type");             this.cclass = (Modifier.isProtected(modifiers) &&                           caller != tclass) ? caller : null;            this.tclass = tclass;            offset = unsafe.objectFieldOffset(field);        }         private void fullCheck(T obj) {            if (!tclass.isInstance(obj))                throw new ClassCastException();            if (cclass != null)                ensureProtectedAccess(obj);        }         public boolean compareAndSet(T obj, int expect, int update) {            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);            return unsafe.compareAndSwapInt(obj, offset, expect, update);        }         public boolean weakCompareAndSet(T obj, int expect, int update) {            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);            return unsafe.compareAndSwapInt(obj, offset, expect, update);        }         public void set(T obj, int newValue) {            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);            unsafe.putIntVolatile(obj, offset, newValue);        }         public void lazySet(T obj, int newValue) {            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);            unsafe.putOrderedInt(obj, offset, newValue);        }         public final int get(T obj) {            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);            return unsafe.getIntVolatile(obj, offset);        }         private void ensureProtectedAccess(T obj) {            if (cclass.isInstance(obj)) {                return;            }            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()                )            );        }    }}