weinre.server/src/weinre/server/MessageQueue.java

/*
 * 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.
 */

package weinre.server;

import java.util.LinkedList;
import java.util.List;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;

/**
 * A type of blocking queue.
 *
 * - can be shutdown; subsequent add() or getAll() calls throw ISE
 * - getAll() takes all items off the queue
 * - if there are simultaneous getAll() calls, queued items may be split between them
 * - current use case calls for one reader, so previous item not relevant
 */
public class MessageQueue<E> {

    private BlockingQueue<E> queue;
    private boolean          closed;
    private Object           closeLock;

    //---------------------------------------------------------------
    public MessageQueue() {
        super();

        queue     = new LinkedBlockingQueue<E>();
        closed    = false;
        closeLock = new Object();
    }

    //---------------------------------------------------------------
    public void shutdown() {
        synchronized(closeLock) {
            if (closed) return;

            closed = true;
            queue.clear();
        }
    }

    //---------------------------------------------------------------
    public void add(E item) {
        synchronized(closeLock) {
            if (closed) throw new IllegalStateException("the blocking queue is closed");
        }

        queue.add(item);
    }

    //---------------------------------------------------------------
    public List<E> getAll(int timeout, TimeUnit timeUnit) throws InterruptedException {
        synchronized(closeLock) {
            if (closed) throw new IllegalStateException("the blocking queue is closed");
        }

        // create our result list
        List<E> result = new LinkedList<E>();

        // wait for the first item
        E item = queue.poll(timeout, timeUnit);

        // nothing there?  return empty list
        if (null == item) return result;

        // add the first item to the list
        result.add(item);

        // get anything else on the queue
        // - not appropriate for simultaneous calls to this method
        while ((item = queue.poll()) != null) {
            result.add(item);
        }

        // return list
        return result;
    }

    //---------------------------------------------------------------
    public String toString()  {
        return getClass().getName() + "{" + queue.size() + "}";
    }
}