1/*
2 * $HeadURL: http://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk/module-client/src/main/java/org/apache/http/impl/conn/tsccm/RefQueueWorker.java $
3 * $Revision: 673450 $
4 * $Date: 2008-07-02 10:35:05 -0700 (Wed, 02 Jul 2008) $
5 *
6 * ====================================================================
7 *
8 *  Licensed to the Apache Software Foundation (ASF) under one or more
9 *  contributor license agreements.  See the NOTICE file distributed with
10 *  this work for additional information regarding copyright ownership.
11 *  The ASF licenses this file to You under the Apache License, Version 2.0
12 *  (the "License"); you may not use this file except in compliance with
13 *  the License.  You may obtain a copy of the License at
14 *
15 *      http://www.apache.org/licenses/LICENSE-2.0
16 *
17 *  Unless required by applicable law or agreed to in writing, software
18 *  distributed under the License is distributed on an "AS IS" BASIS,
19 *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
20 *  See the License for the specific language governing permissions and
21 *  limitations under the License.
22 * ====================================================================
23 *
24 * This software consists of voluntary contributions made by many
25 * individuals on behalf of the Apache Software Foundation.  For more
26 * information on the Apache Software Foundation, please see
27 * <http://www.apache.org/>.
28 *
29 */
30
31package org.apache.http.impl.conn.tsccm;
32
33import java.lang.ref.Reference;
34import java.lang.ref.ReferenceQueue;
35
36import org.apache.commons.logging.Log;
37import org.apache.commons.logging.LogFactory;
38
39
40
41/**
42 * A worker thread for processing queued references.
43 * {@link Reference Reference}s can be
44 * {@link ReferenceQueue queued}
45 * automatically by the garbage collector.
46 * If that feature is used, a daemon thread should be executing
47 * this worker. It will pick up the queued references and pass them
48 * on to a handler for appropriate processing.
49 */
50public class RefQueueWorker implements Runnable {
51
52    private final Log log = LogFactory.getLog(getClass());
53
54    /** The reference queue to monitor. */
55    protected final ReferenceQueue<?> refQueue;
56
57    /** The handler for the references found. */
58    protected final RefQueueHandler refHandler;
59
60
61    /**
62     * The thread executing this handler.
63     * This attribute is also used as a shutdown indicator.
64     */
65    protected volatile Thread workerThread;
66
67
68    /**
69     * Instantiates a new worker to listen for lost connections.
70     *
71     * @param queue     the queue on which to wait for references
72     * @param handler   the handler to pass the references to
73     */
74    public RefQueueWorker(ReferenceQueue<?> queue, RefQueueHandler handler) {
75        if (queue == null) {
76            throw new IllegalArgumentException("Queue must not be null.");
77        }
78        if (handler == null) {
79            throw new IllegalArgumentException("Handler must not be null.");
80        }
81
82        refQueue   = queue;
83        refHandler = handler;
84    }
85
86
87    /**
88     * The main loop of this worker.
89     * If initialization succeeds, this method will only return
90     * after {@link #shutdown shutdown()}. Only one thread can
91     * execute the main loop at any time.
92     */
93    public void run() {
94
95        if (this.workerThread == null) {
96            this.workerThread = Thread.currentThread();
97        }
98
99        while (this.workerThread == Thread.currentThread()) {
100            try {
101                // remove the next reference and process it
102                Reference<?> ref = refQueue.remove();
103                refHandler.handleReference(ref);
104            } catch (InterruptedException e) {
105                //@@@ is logging really necessary? this here is the
106                //@@@ only reason for having a log in this class
107                if (log.isDebugEnabled()) {
108                    log.debug(this.toString() + " interrupted", e);
109                }
110            }
111        }
112    }
113
114
115    /**
116     * Shuts down this worker.
117     * It can be re-started afterwards by another call to {@link #run run()}.
118     */
119    public void shutdown() {
120        Thread wt = this.workerThread;
121        if (wt != null) {
122            this.workerThread = null; // indicate shutdown
123            wt.interrupt();
124        }
125    }
126
127
128    /**
129     * Obtains a description of this worker.
130     *
131     * @return  a descriptive string for this worker
132     */
133    @Override
134    public String toString() {
135        return "RefQueueWorker::" + this.workerThread;
136    }
137
138} // class RefQueueWorker
139
140