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/*
* $HeadURL: http://svn.apache.org/repos/asf/httpcomponents/httpclient/trunk/module-client/src/main/java/org/apache/http/impl/conn/tsccm/RefQueueWorker.java $
* $Revision: 673450 $
* $Date: 2008-07-02 10:35:05 -0700 (Wed, 02 Jul 2008) $
*
* ====================================================================
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*
*/
package org.apache.http.impl.conn.tsccm;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
/**
* A worker thread for processing queued references.
* {@link Reference Reference}s can be
* {@link ReferenceQueue queued}
* automatically by the garbage collector.
* If that feature is used, a daemon thread should be executing
* this worker. It will pick up the queued references and pass them
* on to a handler for appropriate processing.
*/
public class RefQueueWorker implements Runnable {
private final Log log = LogFactory.getLog(getClass());
/** The reference queue to monitor. */
protected final ReferenceQueue<?> refQueue;
/** The handler for the references found. */
protected final RefQueueHandler refHandler;
/**
* The thread executing this handler.
* This attribute is also used as a shutdown indicator.
*/
protected volatile Thread workerThread;
/**
* Instantiates a new worker to listen for lost connections.
*
* @param queue the queue on which to wait for references
* @param handler the handler to pass the references to
*/
public RefQueueWorker(ReferenceQueue<?> queue, RefQueueHandler handler) {
if (queue == null) {
throw new IllegalArgumentException("Queue must not be null.");
}
if (handler == null) {
throw new IllegalArgumentException("Handler must not be null.");
}
refQueue = queue;
refHandler = handler;
}
/**
* The main loop of this worker.
* If initialization succeeds, this method will only return
* after {@link #shutdown shutdown()}. Only one thread can
* execute the main loop at any time.
*/
public void run() {
if (this.workerThread == null) {
this.workerThread = Thread.currentThread();
}
while (this.workerThread == Thread.currentThread()) {
try {
// remove the next reference and process it
Reference<?> ref = refQueue.remove();
refHandler.handleReference(ref);
} catch (InterruptedException e) {
//@@@ is logging really necessary? this here is the
//@@@ only reason for having a log in this class
if (log.isDebugEnabled()) {
log.debug(this.toString() + " interrupted", e);
}
}
}
}
/**
* Shuts down this worker.
* It can be re-started afterwards by another call to {@link #run run()}.
*/
public void shutdown() {
Thread wt = this.workerThread;
if (wt != null) {
this.workerThread = null; // indicate shutdown
wt.interrupt();
}
}
/**
* Obtains a description of this worker.
*
* @return a descriptive string for this worker
*/
@Override
public String toString() {
return "RefQueueWorker::" + this.workerThread;
}
} // class RefQueueWorker
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