Java example source code file (RefQueueWorker.java)

This example source code file (RefQueueWorker.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java tags/keywords

deprecated, illegalargumentexception, interruptedexception, override, referencequeue, refqueuehandler, refqueueworker, runnable, string, thread

The RefQueueWorker.java example source code

/*
 * ====================================================================
 *
 *  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;

/**
 * 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.
 *
 * @deprecated do not use
 */
@Deprecated
public class RefQueueWorker implements Runnable {

    /** 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 ignore) {
            }
        }
    }


    /**
     * 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