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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * 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.
 *
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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,  Peter Jones/**
 * 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 /** value of the referent's "identity" hash code */
    private int hashValue;

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

    
Create a new WeakRef to the given object.
/**
     * 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.
/**
     * 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).
/**
     * 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).
/**
     * 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.
/**
     * 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.
/**
     * 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;
        }
    }
}