/*
 * 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 sun.reflect.CallerSensitive;
import sun.reflect.Reflection;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.UncheckedIOException;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Modifier;
import java.security.AccessController;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.util.function.IntBinaryOperator;
import java.util.function.IntUnaryOperator;

/**
 * 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/>
 * <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.
 *
 * @param <T> The type of the object holding the updatable field
 * @author Doug Lea
 * @since 1.5
 */
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 AtomicIntegerFieldUpdaterImpl.newInstance
            (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
     * @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/>
     * <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
     * @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) {
        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;
    }

    /**
     * Atomically updates the field of the given object managed by this updater
     * with the results of applying the given function, returning the previous
     * value. The function should be side-effect-free, since it may be
     * re-applied when attempted updates fail due to contention among threads.
     *
     * @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;
    }

    /**
     * Atomically updates the field of the given object managed by this updater
     * with the results of applying the given function, returning the updated
     * value. The function should be side-effect-free, since it may be
     * re-applied when attempted updates fail due to contention among threads.
     *
     * @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;
    }

    /**
     * Atomically updates the field of the given object managed by this
     * updater with the results of applying the given function to the
     * current and given values, returning the previous value. The
     * function should be side-effect-free, since it may be re-applied
     * when attempted updates fail due to contention among threads.  The
     * function is applied with the current value as its first argument,
     * and the given update as the second argument.
     *
     * @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;
    }

    /**
     * Atomically updates the field of the given object managed by this
     * updater with the results of applying the given function to the
     * current and given values, returning the updated value. The
     * function should be side-effect-free, since it may be re-applied
     * when attempted updates fail due to contention among threads.  The
     * function is applied with the current value as its first argument,
     * and the given update as the second argument.
     *
     * @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 abstract class AtomicIntegerFieldUpdaterImpl<T>
        extends AtomicIntegerFieldUpdater<T> {

        static final Unsafe unsafe = Unsafe.getUnsafe();

        // class bytes of template class
        static final byte[] updaterClassBytes = getClassBytes(AtomicIntegerFieldUpdaterSpec.class);

        // a way to tunnel 'cclass' parameter to the class initializer of
        // specialized VM-anonymous updater class
        static final ThreadLocal<Class<?>> cclassTL = new ThreadLocal<>();

        // specialized VM-anonymous updater classes are 'cclass' specific, so we
        // cache them as ClassValues
        private static final ClassValue<Class<?>> cclassUpdaterCV = new ClassValue<Class<?>>() {
            @Override
            protected Class<?> computeValue(Class<?> cclass) {
                cclassTL.set(cclass);
                try {
                    Class<?> updaterClass = unsafe.defineAnonymousClass(
                        AtomicIntegerFieldUpdaterImpl.class, updaterClassBytes, new Object[0]);
                    unsafe.ensureClassInitialized(updaterClass);
                    return updaterClass;
                } finally {
                    cclassTL.remove();
                }
            }
        };

        private final Class<T> tclass;
        final long offset;

        AtomicIntegerFieldUpdaterImpl(Class<T> tclass, long offset) {
            this.tclass = tclass;
            this.offset = offset;
        }

        static <T> AtomicIntegerFieldUpdaterImpl<T> newInstance(
            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 = sun.reflect.misc.ReflectUtil.ensureMemberAccessReduceModifiers(
                    caller, tclass, null, field.getModifiers()
                );
                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);
            }

            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");

            Class<?> cclass = Modifier.isProtected(modifiers) ? caller : tclass;
            long offset = unsafe.objectFieldOffset(field);

            try {
                @SuppressWarnings("unchecked")
                AtomicIntegerFieldUpdaterImpl<T> instance = (AtomicIntegerFieldUpdaterImpl<T>) cclassUpdaterCV
                        .get(cclass)
                        .getConstructor(Class.class, long.class)
                        .newInstance(tclass, offset);
                return instance;
            } catch (InvocationTargetException e) {
                throw new RuntimeException(e.getTargetException());
            } catch (IllegalAccessException | InstantiationException | NoSuchMethodException e) {
                throw new RuntimeException(e);
            }
        }

        private static byte[] getClassBytes(Class<?> clazz) {
            String resourceName = clazz.getName().replace('.', '/') + ".class";
            ClassLoader classLoader = clazz.getClassLoader();
            try (
                InputStream in = (classLoader == null)
                                 ? ClassLoader.getSystemResourceAsStream(resourceName)
                                 : classLoader.getResourceAsStream(resourceName)
            ) {
                ByteArrayOutputStream bytecode = new ByteArrayOutputStream();
                byte[] buff = new byte[8192];
                int nread;
                while ((nread = in.read(buff)) >= 0) {
                    bytecode.write(buff, 0, nread);
                }
                return bytecode.toByteArray();
            } catch (IOException e) {
                throw new UncheckedIOException(e);
            }
        }

        /**
         * 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;
        }

        final void failCheck(T obj) {
            if (!tclass.isInstance(obj))
                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()
                    )
                );
        }

        abstract Class<?> cclass();

        public final int getAndIncrement(T obj) {
            return getAndAdd(obj, 1);
        }

        public final int getAndDecrement(T obj) {
            return getAndAdd(obj, -1);
        }

        public final int incrementAndGet(T obj) {
            return getAndAdd(obj, 1) + 1;
        }

        public final int decrementAndGet(T obj) {
            return getAndAdd(obj, -1) - 1;
        }

        public final int addAndGet(T obj, int delta) {
            return getAndAdd(obj, delta) + delta;
        }
    }

    /**
     * A template class loaded multiple times. Each time as new VM-anonymous class
     */
    private static final class AtomicIntegerFieldUpdaterSpec<T>
        extends AtomicIntegerFieldUpdaterImpl<T> {

        // at class initialization time, this thread-local holds 'cclass'
        private static final Class<?> cclass = cclassTL.get();

        public AtomicIntegerFieldUpdaterSpec(Class<T> tclass, long offset) {
            super(tclass, offset);
            // validate assertion that cclass is always a subclass of tclass
            cclass.asSubclass(tclass);
        }

        @Override
        Class<?> cclass() {
            return cclass;
        }

        public boolean compareAndSet(T obj, int expect, int update) {
            if (!cclass.isInstance(obj)) failCheck(obj);
            return unsafe.compareAndSwapInt(obj, offset, expect, update);
        }

        public boolean weakCompareAndSet(T obj, int expect, int update) {
            if (!cclass.isInstance(obj)) failCheck(obj);
            return unsafe.compareAndSwapInt(obj, offset, expect, update);
        }

        public void set(T obj, int newValue) {
            if (!cclass.isInstance(obj)) failCheck(obj);
            unsafe.putIntVolatile(obj, offset, newValue);
        }

        public void lazySet(T obj, int newValue) {
            if (!cclass.isInstance(obj)) failCheck(obj);
            unsafe.putOrderedInt(obj, offset, newValue);
        }

        public final int get(T obj) {
            if (!cclass.isInstance(obj)) failCheck(obj);
            return unsafe.getIntVolatile(obj, offset);
        }

        public int getAndSet(T obj, int newValue) {
            if (!cclass.isInstance(obj)) failCheck(obj);
            return unsafe.getAndSetInt(obj, offset, newValue);
        }

        public int getAndAdd(T obj, int delta) {
            if (!cclass.isInstance(obj)) failCheck(obj);
            return unsafe.getAndAddInt(obj, offset, delta);
        }
    }
}