src/main/csharp/MessageConsumer.cs

using System;
using System.Messaging;
using System.Threading;
/*
 * 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.
 */
using Apache.NMS.Util;

namespace Apache.NMS.MSMQ
{
	/// <summary>
	/// An object capable of receiving messages from some destination
	/// </summary>
	public class MessageConsumer : IMessageConsumer
	{
		protected TimeSpan zeroTimeout = new TimeSpan(0);

		private readonly Session session;
		private readonly AcknowledgementMode acknowledgementMode;
		private MessageQueue messageQueue;
		private event MessageListener listener;
		private int listenerCount = 0;
		private Thread asyncDeliveryThread = null;
		private AutoResetEvent pause = new AutoResetEvent(false);
		private Atomic<bool> asyncDelivery = new Atomic<bool>(false);

		public MessageConsumer(Session session, AcknowledgementMode acknowledgementMode, MessageQueue messageQueue)
		{
			this.session = session;
			this.acknowledgementMode = acknowledgementMode;
			this.messageQueue = messageQueue;
			if(null != this.messageQueue)
			{
				this.messageQueue.MessageReadPropertyFilter.SetAll();
			}
		}

		public event MessageListener Listener
		{
			add
			{
				listener += value;
				listenerCount++;
				StartAsyncDelivery();
			}

			remove
			{
				if(listenerCount > 0)
				{
					listener -= value;
					listenerCount--;
				}

				if(0 == listenerCount)
				{
					StopAsyncDelivery();
				}
			}
		}

		public IMessage Receive()
		{
			IMessage nmsMessage = null;

			if(messageQueue != null)
			{
				Message message;

				try
				{
					message = messageQueue.Receive(zeroTimeout);
				}
				catch
				{
					message = null;
				}

				if(null == message)
				{
					ReceiveCompletedEventHandler receiveMsg =
							delegate(Object source, ReceiveCompletedEventArgs asyncResult) {
								message = messageQueue.EndReceive(asyncResult.AsyncResult);
								pause.Set();
							};

					messageQueue.ReceiveCompleted += receiveMsg;
					messageQueue.BeginReceive();
					pause.WaitOne();
					messageQueue.ReceiveCompleted -= receiveMsg;
				}

				nmsMessage = ToNmsMessage(message);
			}

			return nmsMessage;
		}

		public IMessage Receive(TimeSpan timeout)
		{
			IMessage nmsMessage = null;

			if(messageQueue != null)
			{
				Message message = messageQueue.Receive(timeout);
				nmsMessage = ToNmsMessage(message);
			}

			return nmsMessage;
		}

		public IMessage ReceiveNoWait()
		{
			IMessage nmsMessage = null;

			if(messageQueue != null)
			{
				Message message = messageQueue.Receive(zeroTimeout);
				nmsMessage = ToNmsMessage(message);
			}

			return nmsMessage;
		}

		public void Dispose()
		{
			Close();
		}

		public void Close()
		{
			StopAsyncDelivery();
			if(messageQueue != null)
			{
				messageQueue.Dispose();
				messageQueue = null;
			}
		}

		protected virtual void StopAsyncDelivery()
		{
			if(asyncDelivery.CompareAndSet(true, false))
			{
				if(null != asyncDeliveryThread)
				{
					Tracer.Info("Stopping async delivery thread.");
					pause.Set();
					if(!asyncDeliveryThread.Join(10000))
					{
						Tracer.Info("Aborting async delivery thread.");
						asyncDeliveryThread.Abort();
					}

					asyncDeliveryThread = null;
					Tracer.Info("Async delivery thread stopped.");
				}
			}
		}

		protected virtual void StartAsyncDelivery()
		{
			if(asyncDelivery.CompareAndSet(false, true))
			{
				asyncDeliveryThread = new Thread(new ThreadStart(DispatchLoop));
				asyncDeliveryThread.Name = "Message Consumer Dispatch: " + messageQueue.QueueName;
				asyncDeliveryThread.IsBackground = true;
				asyncDeliveryThread.Start();
			}
		}

		protected virtual void DispatchLoop()
		{
			Tracer.Info("Starting dispatcher thread consumer: " + this);
			while(asyncDelivery.Value)
			{
				try
				{
					IMessage message = Receive();
					if(asyncDelivery.Value && message != null)
					{
						try
						{
							listener(message);
						}
						catch(Exception e)
						{
							HandleAsyncException(e);
						}
					}
				}
				catch(ThreadAbortException ex)
				{
					Tracer.InfoFormat("Thread abort received in thread: {0} : {1}", this, ex.Message);
					break;
				}
				catch(Exception ex)
				{
					Tracer.ErrorFormat("Exception while receiving message in thread: {0} : {1}", this, ex.Message);
				}
			}
			Tracer.Info("Stopping dispatcher thread consumer: " + this);
		}

		protected virtual void HandleAsyncException(Exception e)
		{
			session.Connection.HandleException(e);
		}

		protected virtual IMessage ToNmsMessage(Message message)
		{
			if(message == null)
			{
				return null;
			}
			return session.MessageConverter.ToNmsMessage(message);
		}
	}
}