Reuse MQMessage object

Question

I have this test code that listens for messages forever. If it gets one it prints it out. What I want to do is avoid having to construct a MQMessage object prior to each get(). How do i reuse a MQMessage for multiple calls to get()?

using System;
using IBM.WMQ;

namespace WMQ {
    class Program {
        static void Main(string[] args) {
            string QueueManagerName = "A1PATA00";
            string channelName = "ECACHE";
            string connectionName = "A1PATA00.WORLDSPAN.COM(1414)";
            var queueManager = new MQQueueManager(QueueManagerName, channelName, connectionName);
            MQQueue get = queueManager.AccessQueue("SPLASH.ECAC.2", MQC.MQOO_INPUT_AS_Q_DEF | MQC.MQGMO_FAIL_IF_QUIESCING);
            var gmo = new MQGetMessageOptions();
            gmo.Options = MQC.MQGMO_FAIL_IF_QUIESCING | MQC.MQGMO_WAIT;
            gmo.WaitInterval = 10000000;// wait time
            // var queueMessage = new MQMessage();  <--- i want to do this new once!
            while (true) {
                var queueMessage = new MQMessage(); // <-- only works if I do this every time i do a get
                get.Get(queueMessage, gmo);
                var strReturn = queueMessage.ReadString(queueMessage.MessageLength);
                Console.WriteLine(strReturn);
            }
        }
    }
}

Answer 1

1. When I see questions like this, I shake my head. You do not understand object oriented concepts in the .NET VM (framework) and garbage collection.
2. Also, why don't you write pure C# code?
3. Finally, in a world where security is very important, your code does not support either SSL/TLS and/or UserID & Password authentication.

(1) Please notice where I am defining the MQMessage object (very important).

There is basically no difference in memory usage or speed between the following 2 code snippets:

(A)

MQMessage msg = null;
while (true)
{
   msg = new MQMessage();
   get.Get(msg, gmo);
   Console.WriteLine(msg.ReadString(msg.MessageLength));
}

(B)

MQMessage msg = new MQMessage();
while (true)
{
   get.Get(msg, gmo);
   Console.WriteLine(msg.ReadString(msg.MessageLength));
   msg.ClearMessage();
   msg.MessageId = MQC.MQMI_NONE;
   msg.CorrelationId = MQC.MQCI_NONE;
}

I prefer (A) because it is cleaner and easier to read.

(2) When you use 'var', you are forcing the .NET framework to guess at what you are doing. Do pure object oriented programming. i.e.

MQMessage msg = new MQMessage();

(3) Explicitly setting the channel name and connection name in the MQQueueManager does not allow setting of MQ security information. Also, do NOT use the MQEnvironment class as it is NOT thread safe. It is far better to put all the information in a Hashtable and pass the Hashtable to the MQQueueManager class. Here is a MQ .NET managed-mode example using a Hashtable for MQ connection information:

using System;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using IBM.WMQ;

namespace MQTest02
{
   class MQTest02
   {
      private Hashtable inParms = null;
      private Hashtable qMgrProp = null;
      private System.String qManager;
      private System.String outputQName;

      /*
      * The constructor
      */
      public MQTest02()
         : base()
      {
      }

      /// <summary> Make sure the required parameters are present.</summary>
      /// <returns> true/false
      /// </returns>
      private bool allParamsPresent()
      {
         bool b = inParms.ContainsKey("-h") && inParms.ContainsKey("-p") &&
                  inParms.ContainsKey("-c") && inParms.ContainsKey("-m") &&
                  inParms.ContainsKey("-q");
         if (b)
         {
            try
            {
               System.Int32.Parse((System.String)inParms["-p"]);
            }
            catch (System.FormatException e)
            {
               b = false;
            }
         }

         return b;
      }

      /// <summary> Extract the command-line parameters and initialize the MQ variables.</summary>
      /// <param name="args">
      /// </param>
      /// <throws>  IllegalArgumentException </throws>
      private void init(System.String[] args)
      {
         inParms = Hashtable.Synchronized(new Hashtable());
         if (args.Length > 0 && (args.Length % 2) == 0)
         {
            for (int i = 0; i < args.Length; i += 2)
            {
               inParms[args[i]] = args[i + 1];
            }
         }
         else
         {
            throw new System.ArgumentException();
         }

         if (allParamsPresent())
         {
            qManager = ((System.String)inParms["-m"]);
            outputQName = ((System.String)inParms["-q"]);

            qMgrProp = new Hashtable();
            qMgrProp.Add(MQC.TRANSPORT_PROPERTY, MQC.TRANSPORT_MQSERIES_MANAGED);

            qMgrProp.Add(MQC.HOST_NAME_PROPERTY, ((System.String)inParms["-h"]));
            qMgrProp.Add(MQC.CHANNEL_PROPERTY, ((System.String)inParms["-c"]));

            try
            {
               qMgrProp.Add(MQC.PORT_PROPERTY, System.Int32.Parse((System.String)inParms["-p"]));
            }
            catch (System.FormatException e)
            {
               qMgrProp.Add(MQC.PORT_PROPERTY, 1414);
            }

            if (inParms.ContainsKey("-u"))
               qMgrProp.Add(MQC.USER_ID_PROPERTY, ((System.String)inParms["-u"]));

            if (inParms.ContainsKey("-x"))
               qMgrProp.Add(MQC.PASSWORD_PROPERTY, ((System.String)inParms["-x"]));

            if (inParms.ContainsKey("-s"))
               qMgrProp.Add(MQC.SECURITY_EXIT_PROPERTY, ((System.String)inParms["-s"]));

            System.Console.Out.WriteLine("MQTest02:");
            Console.WriteLine("  QMgrName ='{0}'", qManager);
            Console.WriteLine("  Output QName ='{0}'", outputQName);

            System.Console.Out.WriteLine("QMgr Property values:");
            foreach (DictionaryEntry de in qMgrProp)
            {
               Console.WriteLine("  {0} = '{1}'", de.Key, de.Value);
            }
         }
         else
         {
            throw new System.ArgumentException();
         }
      }

      /// <summary> Connect, open queue, read a message, close queue and disconnect.
      ///
      /// </summary>
      /// <throws>  MQException </throws>
      private void testReceive()
      {
         MQQueueManager qMgr = null;
         MQQueue queue = null;
         int openOptions = MQC.MQOO_INPUT_AS_Q_DEF + MQC.MQOO_FAIL_IF_QUIESCING;
         MQGetMessageOptions gmo = new MQGetMessageOptions();
         MQMessage receiveMsg = null;

         try
         {
            qMgr = new MQQueueManager(qManager, qMgrProp);
            System.Console.Out.WriteLine("MQTest02 successfully connected to " + qManager);

            queue = qMgr.AccessQueue(outputQName, openOptions, null, null, null); // no alternate user id
            System.Console.Out.WriteLine("MQTest02 successfully opened " + outputQName);

            receiveMsg = new MQMessage();

            queue.Get(receiveMsg, gmo);
            System.Console.Out.WriteLine("Message Data>>>" + receiveMsg.ReadString(receiveMsg.MessageLength));
         }
         catch (MQException mqex)
         {
            System.Console.Out.WriteLine("MQTest02 cc=" + mqex.CompletionCode + " : rc=" + mqex.ReasonCode);
         }
         catch (System.IO.IOException ioex)
         {
            System.Console.Out.WriteLine("MQTest02 ioex=" + ioex);
         }
         finally
         {
            try
            {
               queue.Close();
               System.Console.Out.WriteLine("MQTest02 closed: " + outputQName);
            }
            catch (MQException mqex)
            {
               System.Console.Out.WriteLine("MQTest02 cc=" + mqex.CompletionCode + " : rc=" + mqex.ReasonCode);
            }
            try
            {
               qMgr.Disconnect();
               System.Console.Out.WriteLine("MQTest02 disconnected from " + qManager);
            }
            catch (MQException mqex)
            {
               System.Console.Out.WriteLine("MQTest02 cc=" + mqex.CompletionCode + " : rc=" + mqex.ReasonCode);
            }
         }
      }

      /// <summary> main line</summary>
      /// <param name="args">
      /// </param>
      //        [STAThread]
      public static void Main(System.String[] args)
      {
         MQTest02 mqt = new MQTest02();

         try
         {
            mqt.init(args);
            mqt.testReceive();
         }
         catch (System.ArgumentException e)
         {
            System.Console.Out.WriteLine("Usage: MQTest02 -h host -p port -c channel -m QueueManagerName -q QueueName [-u userID] [-x passwd] [-s securityExit]");
            System.Environment.Exit(1);
         }
         catch (MQException e)
         {
            System.Console.Out.WriteLine(e);
            System.Environment.Exit(1);
         }

         System.Environment.Exit(0);
      }
   }
}

To run MQTest02 using your information, it would be:

MQTest02.exe -h A1PATA00.WORLDSPAN.COM -p 1414 -m A1PATA00 -c ECACHE -q SPLASH.ECAC.2

Answer 2

In the IBM MQ Knowledge center page "ClearMessage method" it documents the following:

This method clears the data buffer portion of the MQMessage object. Any Message Data in the data buffer is lost, because MessageLength, DataLength, and DataOffset are all set to zero.

---

The Message Descriptor (MQMD) portion is unaffected; an application might need to modify some of the MQMD fields before reusing the MQMessage object. To set the MQMD fields back use New to replace the object with a new instance.

In the IBM MQ Knowledge center page "MQMessage .NET class" it documents the following:

public byte[] MessageId {get; set;}

For an MQQueue.Get call, this field specifies the message identifier of the message to be retrieved. Normally, the queue manager returns the first message with a message identifier and correlation identifier that match the message descriptor fields. Allow any message identifier to match using the special value MQC.MQMI_NONE.

public byte[] CorrelationId {get; set;}

For an MQQueue.Get call, the correlation identifier of the message to be retrieved. The queue manager returns the first message with a message identifier and a correlation identifier that match the message descriptor fields. The default value, MQC.MQCI_NONE, helps any correlation identifier to match.

Try this:

            var queueMessage = new MQMessage();  <--- i want to do this new once!
            while (true) {
                //var queueMessage = new MQMessage(); // <-- only works if I do this every time i do a get
                queueMessage.ClearMessage();
                queueMessage.MessageId = MQC.MQMI_NONE;
                queueMessage.CorrelationId = MQC.MQCI_NONE; 
                get.Get(queueMessage, gmo);