broker-core/src/main/java/org/apache/qpid/server/queue/QueueRunner.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 org.apache.qpid.server.queue;

import java.security.AccessControlContext;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.qpid.server.util.ConnectionScopedRuntimeException;

/**
 * QueueRunners are Runnables used to process a queue when requiring
 * asynchronous message delivery to consumers, which is necessary
 * when straight-through delivery of a message to a consumer isn't
 * possible during the enqueue operation.
 */
public class QueueRunner implements Runnable
{
    private static final Logger _logger = LoggerFactory.getLogger(QueueRunner.class);

    private final AbstractQueue _queue;

    private static int IDLE = 0;
    private static int SCHEDULED = 1;
    private static int RUNNING = 2;

    private final AtomicInteger _scheduled = new AtomicInteger(IDLE);

    private final AtomicBoolean _stateChange = new AtomicBoolean();

    private final AtomicLong _lastRunAgain = new AtomicLong();
    private final AtomicLong _lastRunTime = new AtomicLong();
    private final AccessControlContext _context;
    private final String _taskName;

    public QueueRunner(AbstractQueue queue, AccessControlContext context)
    {
        _queue = queue;
        _context = context;
        _taskName = "Queue Runner[" + _queue.getName() + "]";
    }

    @Override
    public void run()
    {
        if(_scheduled.compareAndSet(SCHEDULED,RUNNING))
        {
            long runAgain = Long.MIN_VALUE;
            _stateChange.set(false);
            try
            {
                runAgain = _queue.processQueue(QueueRunner.this);
            }
            catch (ConnectionScopedRuntimeException e)
            {
                final String errorMessage = "Problem during asynchronous delivery by " + toString();
                if(_logger.isDebugEnabled())
                {
                    _logger.debug(errorMessage, e);
                }
                else
                {
                    _logger.info(errorMessage + ' ' + e.getMessage());
                }
            }
            finally
            {
                _scheduled.compareAndSet(RUNNING, IDLE);
                final long stateChangeCount = _queue.getStateChangeCount();
                _lastRunAgain.set(runAgain);
                _lastRunTime.set(System.nanoTime());
                if(runAgain == 0L || runAgain != stateChangeCount || _stateChange.compareAndSet(true,false))
                {
                    if(_scheduled.compareAndSet(IDLE, SCHEDULED))
                    {
                        _queue.execute(_taskName, QueueRunner.this, _context);
                    }
                }
            }
        }
    }

    @Override
    public String toString()
    {
        return "QueueRunner-" + _queue.getLogSubject().toLogString();
    }

    public void execute()
    {
        _stateChange.set(true);
        if(_scheduled.compareAndSet(IDLE, SCHEDULED))
        {
            _queue.execute(_taskName, this, _context);
        }
    }

    public boolean isIdle()
    {
        return _scheduled.get() == IDLE;
    }

}