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	/*
	* 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 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.BinaryOperator;
	import java.util.function.UnaryOperator;
	import sun.reflect.CallerSensitive;
	import sun.reflect.Reflection;

	/**
	* 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
	*/
	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 ClassCastException if the field is of the wrong type
	* @throws IllegalArgumentException if the field is not volatile
	* @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,W> AtomicReferenceFieldUpdater<U,W> newUpdater(Class<U> tclass,
	Class<W> vclass,
	String fieldName) {
	return new AtomicReferenceFieldUpdaterImpl<U,W>
	(tclass, vclass, fieldName, Reflection.getCallerClass());
	}

	/**
	* 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 {@code 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><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, 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) {
	V prev;
	do {
	prev = get(obj);
	} while (!compareAndSet(obj, prev, newValue));
	return prev;
	}

	/**
	* 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 V getAndUpdate(T obj, UnaryOperator<V> updateFunction) {
	V prev, next;
	do {
	prev = get(obj);
	next = updateFunction.apply(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 V updateAndGet(T obj, UnaryOperator<V> updateFunction) {
	V prev, next;
	do {
	prev = get(obj);
	next = updateFunction.apply(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 V getAndAccumulate(T obj, V x,
	BinaryOperator<V> accumulatorFunction) {
	V prev, next;
	do {
	prev = get(obj);
	next = accumulatorFunction.apply(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 V accumulateAndGet(T obj, V x,
	BinaryOperator<V> accumulatorFunction) {
	V prev, next;
	do {
	prev = get(obj);
	next = accumulatorFunction.apply(prev, x);
	} while (!compareAndSet(obj, prev, next));
	return next;
	}

	private static final class AtomicReferenceFieldUpdaterImpl<T,V>
	extends AtomicReferenceFieldUpdater<T,V> {
	private static final sun.misc.Unsafe U = sun.misc.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;
	/** field value type */
	private final Class<V> vclass;

	/*
	* Internal type checks within all update methods contain
	* internal inlined optimizations checking for the common
	* cases where the class is final (in which case a simple
	* getClass comparison suffices) or is of type Object (in
	* which case no check is needed because all objects are
	* instances of Object). The Object case is handled simply by
	* setting vclass to null in constructor. The targetCheck and
	* updateCheck methods are invoked when these faster
	* screenings fail.
	*/

	AtomicReferenceFieldUpdaterImpl(final Class<T> tclass,
	final Class<V> vclass,
	final String fieldName,
	final Class<?> caller) {
	final Field field;
	final Class<?> fieldClass;
	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);
	}
	fieldClass = field.getType();
	} catch (PrivilegedActionException pae) {
	throw new RuntimeException(pae.getException());
	} catch (Exception ex) {
	throw new RuntimeException(ex);
	}

	if (vclass != fieldClass)
	throw new ClassCastException();
	if (vclass.isPrimitive())
	throw new IllegalArgumentException("Must be reference 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.vclass = vclass;
	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(getPackageName(class1), getPackageName(class2));
	}

	private static String getPackageName(Class<?> cls) {
	String cn = cls.getName();
	int dot = cn.lastIndexOf('.');
	return (dot != -1) ? cn.substring(0, dot) : "";
	}

	/**
	* 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()));
	}

	private final void valueCheck(V v) {
	if (v != null && !(vclass.isInstance(v)))
	throwCCE();
	}

	static void throwCCE() {
	throw new ClassCastException();
	}

	public final boolean compareAndSet(T obj, V expect, V update) {
	accessCheck(obj);
	valueCheck(update);
	return U.compareAndSwapObject(obj, offset, expect, update);
	}

	public final boolean weakCompareAndSet(T obj, V expect, V update) {
	// same implementation as strong form for now
	accessCheck(obj);
	valueCheck(update);
	return U.compareAndSwapObject(obj, offset, expect, update);
	}

	public final void set(T obj, V newValue) {
	accessCheck(obj);
	valueCheck(newValue);
	U.putObjectVolatile(obj, offset, newValue);
	}

	public final void lazySet(T obj, V newValue) {
	accessCheck(obj);
	valueCheck(newValue);
	U.putOrderedObject(obj, offset, newValue);
	}

	@SuppressWarnings("unchecked")
	public final V get(T obj) {
	accessCheck(obj);
	return (V)U.getObjectVolatile(obj, offset);
	}

	@SuppressWarnings("unchecked")
	public final V getAndSet(T obj, V newValue) {
	accessCheck(obj);
	valueCheck(newValue);
	return (V)U.getAndSetObject(obj, offset, newValue);
	}
	}
	}

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