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.PhantomReference;
020    import java.lang.ref.ReferenceQueue;
021    
022    /**
023     * Phantom reference with a {@code finalizeReferent()} method which a background thread invokes
024     * after the garbage collector reclaims the referent. This is a simpler alternative to using a
025     * {@link ReferenceQueue}.
026     *
027     * <p>Unlike a normal phantom reference, this reference will be cleared automatically.
028     *
029     * @author Bob Lee
030     * @since 2.0 (imported from Google Collections Library)
031     */
032    public
033    abstract class FinalizablePhantomReference<T> extends PhantomReference<T>
034        implements FinalizableReference {
035      /**
036       * Constructs a new finalizable phantom reference.
037       *
038       * @param referent to phantom reference
039       * @param queue that should finalize the referent
040       * @deprecated FinalizableReferenceQueue is an unsound mechanism for cleaning up references,
041       *     because (1) it's single thread can be easily overloaded, and (2) it's insistance on running
042       *     a background thread is problematic in certain environments. <b>This class is scheduled for
043       *     deletion in December 2012.</b>
044       */
045      @Deprecated
046      protected FinalizablePhantomReference(T referent, FinalizableReferenceQueue queue) {
047        super(referent, queue.queue);
048        queue.cleanUp();
049      }
050    }