concurrent/atomic/AtomicLongFieldUpdater.java

/*
 * 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 dalvik.system.VMStack; // android-added
import sun.misc.Unsafe;
import java.lang.reflect.Field;
import java.lang.reflect.Modifier;

/**
 * A reflection-based utility that enables atomic updates to
 * designated {@code volatile long} 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 AtomicLongFieldUpdater<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 long 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> AtomicLongFieldUpdater<U> newUpdater(Class<U> tclass, String fieldName) {
        if (AtomicLong.VM_SUPPORTS_LONG_CAS)
            return new CASUpdater<U>(tclass, fieldName);
        else
            return new LockedUpdater<U>(tclass, fieldName);
    }

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

    /**
     * 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, long expect, long 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 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, long expect, long 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, long 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, long 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 long 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 long getAndSet(T obj, long newValue) {
        for (;;) {
            long 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 long getAndIncrement(T obj) {
        for (;;) {
            long current = get(obj);
            long 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 long getAndDecrement(T obj) {
        for (;;) {
            long current = get(obj);
            long 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 long getAndAdd(T obj, long delta) {
        for (;;) {
            long current = get(obj);
            long 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 long incrementAndGet(T obj) {
        for (;;) {
            long current = get(obj);
            long 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 long decrementAndGet(T obj) {
        for (;;) {
            long current = get(obj);
            long 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 long addAndGet(T obj, long delta) {
        for (;;) {
            long current = get(obj);
            long next = current + delta;
            if (compareAndSet(obj, current, next))
                return next;
        }
    }

    private static class CASUpdater<T> extends AtomicLongFieldUpdater<T> {
        private static final Unsafe unsafe = Unsafe.getUnsafe();
        private final long offset;
        private final Class<T> tclass;
        private final Class<?> cclass;

        CASUpdater(Class<T> tclass, String fieldName) {
            final Field field;
            final Class<?> caller;
            final int modifiers;
            try {
                field = tclass.getDeclaredField(fieldName); // android-changed
                caller = VMStack.getStackClass2(); // android-changed
                modifiers = field.getModifiers();
                // BEGIN android-removed
                // 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);
                // }
                // END android-removed
            // BEGIN android-removed
            // } catch (PrivilegedActionException pae) {
            //    throw new RuntimeException(pae.getException());
            // END android-removed
            } catch (Exception ex) {
                throw new RuntimeException(ex);
            }

            Class<?> fieldt = field.getType();
            if (fieldt != long.class)
                throw new IllegalArgumentException("Must be long 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, long expect, long update) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            return unsafe.compareAndSwapLong(obj, offset, expect, update);
        }

        public boolean weakCompareAndSet(T obj, long expect, long update) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            return unsafe.compareAndSwapLong(obj, offset, expect, update);
        }

        public void set(T obj, long newValue) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            unsafe.putLongVolatile(obj, offset, newValue);
        }

        public void lazySet(T obj, long newValue) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            unsafe.putOrderedLong(obj, offset, newValue);
        }

        public long get(T obj) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            return unsafe.getLongVolatile(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()
                )
            );
        }
    }


    private static class LockedUpdater<T> extends AtomicLongFieldUpdater<T> {
        private static final Unsafe unsafe = Unsafe.getUnsafe();
        private final long offset;
        private final Class<T> tclass;
        private final Class<?> cclass;

        LockedUpdater(Class<T> tclass, String fieldName) {
            Field field = null;
            Class<?> caller = null;
            int modifiers = 0;
            try {
                field = tclass.getDeclaredField(fieldName); // android-changed
                caller = VMStack.getStackClass2(); // android-changed
                modifiers = field.getModifiers();
                // BEGIN android-removed
                // 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);
                // }
                // END android-removed
            // BEGIN android-removed
            // } catch (PrivilegedActionException pae) {
            //     throw new RuntimeException(pae.getException());
            // END android-removed
            } catch (Exception ex) {
                throw new RuntimeException(ex);
            }

            Class<?> fieldt = field.getType();
            if (fieldt != long.class)
                throw new IllegalArgumentException("Must be long 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, long expect, long update) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            synchronized (this) {
                long v = unsafe.getLong(obj, offset);
                if (v != expect)
                    return false;
                unsafe.putLong(obj, offset, update);
                return true;
            }
        }

        public boolean weakCompareAndSet(T obj, long expect, long update) {
            return compareAndSet(obj, expect, update);
        }

        public void set(T obj, long newValue) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            synchronized (this) {
                unsafe.putLong(obj, offset, newValue);
            }
        }

        public void lazySet(T obj, long newValue) {
            set(obj, newValue);
        }

        public long get(T obj) {
            if (obj == null || obj.getClass() != tclass || cclass != null) fullCheck(obj);
            synchronized (this) {
                return unsafe.getLong(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()
                )
            );
        }
    }

    // BEGIN android-removed
    // /**
    //  * 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;
    // }
    // END android-removed
}