001    /*
002     * Copyright (C) 2007 The Guava Authors
003     *
004     * Licensed under the Apache License, Version 2.0 (the "License");
005     * you may not use this file except in compliance with the License.
006     * You may obtain a copy of the License at
007     *
008     * http://www.apache.org/licenses/LICENSE-2.0
009     *
010     * Unless required by applicable law or agreed to in writing, software
011     * distributed under the License is distributed on an "AS IS" BASIS,
012     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013     * See the License for the specific language governing permissions and
014     * limitations under the License.
015     */
016    
017    package com.google.common.base;
018    
019    import java.lang.ref.ReferenceQueue;
020    import java.lang.ref.WeakReference;
021    
022    /**
023     * Weak reference with a {@code finalizeReferent()} method which a background thread invokes after
024     * the garbage collector reclaims the referent. This is a simpler alternative to using a {@link
025     * ReferenceQueue}.
026     *
027     * @author Bob Lee
028     * @since 2.0 (imported from Google Collections Library)
029     */
030    public
031    abstract class FinalizableWeakReference<T> extends WeakReference<T>
032        implements FinalizableReference {
033      /**
034       * Constructs a new finalizable weak reference.
035       *
036       * @param referent to weakly reference
037       * @param queue that should finalize the referent
038       * @deprecated FinalizableReferenceQueue is an unsound mechanism for cleaning up references,
039       *     because (1) it's single thread can be easily overloaded, and (2) it's insistance on running
040       *     a background thread is problematic in certain environments. <b>This class is scheduled for
041       *     deletion in December 2012.</b>
042       */
043      @Deprecated
044      protected FinalizableWeakReference(T referent, FinalizableReferenceQueue queue) {
045        super(referent, queue.queue);
046        queue.cleanUp();
047      }
048    }