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	/*
	* Copyright (c) 1996, 2012, Oracle and/or its affiliates. All rights reserved.
	* 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.
	*/
	package sun.rmi.transport;

	import java.lang.ref.*;
	import sun.rmi.runtime.Log;

	/**
	* WeakRef objects are used by the RMI runtime to hold potentially weak
	* references to exported remote objects in the local object table.
	*
	* This class extends the functionality of java.lang.ref.WeakReference in
	* several ways. The methods pin() and unpin() can be used to set
	* whether the contained reference is strong or weak (it is weak upon
	* construction). The hashCode() and equals() methods are overridden so
	* that WeakRef objects hash and compare to each other according to the
	* object identity of their referents.
	*
	* @author Ann Wollrath
	* @author Peter Jones
	*/
	class WeakRef extends WeakReference<Object> {

	/** value of the referent's "identity" hash code */
	private int hashValue;

	/** strong reference to the referent, for when this WeakRef is "pinned" */
	private Object strongRef = null;

	/**
	* Create a new WeakRef to the given object.
	*/
	public WeakRef(Object obj) {
	super(obj);
	setHashValue(obj); // cache object's "identity" hash code
	}

	/**
	* Create a new WeakRef to the given object, registered with a queue.
	*/
	public WeakRef(Object obj, ReferenceQueue<Object> q) {
	super(obj, q);
	setHashValue(obj); // cache object's "identity" hash code
	}

	/**
	* Pin the contained reference (make this a strong reference).
	*/
	public synchronized void pin() {
	if (strongRef == null) {
	strongRef = get();

	if (DGCImpl.dgcLog.isLoggable(Log.VERBOSE)) {
	DGCImpl.dgcLog.log(Log.VERBOSE,
	"strongRef = " + strongRef);
	}
	}
	}

	/**
	* Unpin the contained reference (make this a weak reference).
	*/
	public synchronized void unpin() {
	if (strongRef != null) {
	if (DGCImpl.dgcLog.isLoggable(Log.VERBOSE)) {
	DGCImpl.dgcLog.log(Log.VERBOSE,
	"strongRef = " + strongRef);
	}

	strongRef = null;
	}
	}

	/*
	* Cache referent's "identity" hash code (so that we still have the
	* value after the referent gets cleared).
	*
	* We cannot use the value from the object's hashCode() method, since
	* if the object is of a remote class not extended from RemoteObject
	* and it is trying to implement hashCode() and equals() so that it
	* can be compared to stub objects, its own hash code could not have
	* been initialized yet (see bugid 4102938). Also, object table keys
	* based on server objects are indeed matched on object identity, so
	* this is the correct hash technique regardless.
	*/
	private void setHashValue(Object obj) {
	if (obj != null) {
	hashValue = System.identityHashCode(obj);
	} else {
	hashValue = 0;
	}
	}

	/**
	* Always return the "identity" hash code of the original referent.
	*/
	public int hashCode() {
	return hashValue;
	}

	/**
	* Return true if "obj" is this identical WeakRef object, or, if the
	* contained reference has not been cleared, if "obj" is another WeakRef
	* object with the identical non-null referent. Otherwise, return false.
	*/
	public boolean equals(Object obj) {
	if (obj instanceof WeakRef) {
	if (obj == this)
	return true;

	Object referent = get();
	return (referent != null) && (referent == ((WeakRef) obj).get());
	} else {
	return false;
	}
	}
	}

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