Reconnecting to IBM MQ Queue on connection failure

Question

Following code snippet has my connection and subscription logic for an IBM MQ Queue. When ever there is a connection failure, I am using IConnection.ExceptionListener delegate to establish a new connection to by queue and resubscribing for the messages. But the problem is, I can see multiple queue handles. How can I make sure I close the previous connection handle and establish a new connection where ever there is a connection break due to network issues or MQ server restarts?

private CancellationToken _cancellationToken;
private IConnection _connection;
private IConnectionFactory _connectionfactory;
private IMessageConsumer _consumer;
private IDestination _destination;
private MessageFormat _msgFormat;
private IMessageProducer _producer;
private ISession _session;

private void CreateWebsphereQueueConnection () {
    SetConnectionFactory ();

    //Connection
    _connection = _connectionfactory.CreateConnection (null, null);
    _connection.ExceptionListener = new ExceptionListener (OnConnectionException);

    //Session
    _session = _connection.CreateSession (false, AcknowledgeMode.AutoAcknowledge);

    //Destination
    _destination = _session.CreateQueue ("queue://My.Queue.Name");
    _destination.SetIntProperty (XMSC.DELIVERY_MODE, 2);
    _destination.SetIntProperty (XMSC.WMQ_TARGET_CLIENT, 0);

    //Consumer
    _consumer = _session.CreateConsumer (_destination);
}

private IConnectionFactory SetConnectionFactory () {
    XMSFactoryFactory factoryFactory = XMSFactoryFactory.GetInstance (XMSC.CT_WMQ);
    IConnectionFactory cf = factoryFactory.CreateConnectionFactory ();

    // Set the properties
    cf.SetStringProperty (XMSC.WMQ_CHANNEL, ConnectionSettings.Channel);
    cf.SetIntProperty (XMSC.WMQ_CONNECTION_MODE, XMSC.WMQ_CM_CLIENT);
    cf.SetIntProperty (XMSC.WMQ_FAIL_IF_QUIESCE, XMSC.WMQ_FIQ_YES);
    cf.SetStringProperty (XMSC.WMQ_QUEUE_MANAGER, ConnectionSettings.QueueManager);
    cf.SetStringProperty (XMSC.WMQ_CONNECTION_NAME_LIST, ConnectionSettings.ConnectionList);
    cf.SetIntProperty (XMSC.WMQ_CLIENT_RECONNECT_TIMEOUT, ConnectionSettings.ReconnectTimeout);
    cf.SetIntProperty (XMSC.WMQ_CLIENT_RECONNECT_OPTIONS, ConnectionSettings.ReconnectOptions);

    cf.SetStringProperty (XMSC.WMQ_PROVIDER_VERSION, XMSC.WMQ_PROVIDER_VERSION_DEFAULT);
    cf.SetBooleanProperty (XMSC.WMQ_SYNCPOINT_ALL_GETS, true);
    return cf;
}

public override void Subscribe<T> (Action<T> onMessageReceived) {
    try {

        _connection.ExceptionListener = delegate (Exception connectionException) {
            //Using any of these two statements is termination my code. Debugger doesn't move to CreateWebsphereQueueConnection() line of code at all
            //_conection.Stop()
            //_conection.Close()
            CreateWebsphereQueueConnection ();
            Subscribe (onMessageReceived);
        };

        MessageListener messageListener = new MessageListener ((msg) => {
            onMessageReceived (message);
        });
        _consumer.MessageListener = messageListener;

        // Start the connection
        _connection.Start ();
    } catch (Exception ex) {
        //Log exception details
    }
}

Answer 1

IBM.XMS.dll will take care of MQ fail over or restarts done with -r switch. But, if there was a restart wit out asking the connected clients to reconnect, XMS library will not attempt to reconnect and the costumers will have to handle this situation manually as pointed out by @Shashi and @JoshMc.

I had to handle this situation and changing my Connection ExceptionListener as follows helped me:

private CancellationToken _cancellationToken;
private IConnection _connection;
private IConnectionFactory _connectionfactory;
private IMessageConsumer _consumer;
private IDestination _destination;
private MessageFormat _msgFormat;
private IMessageProducer _producer;
private ISession _session;
private bool _reConnectOnConnectionBreak = false;
private bool _connected = false;
private void CreateWebsphereQueueConnection () {
    SetConnectionFactory ();

    while (!_connected || _reConnectOnConnectionBreak) {
        try {
            //Connection
            _connection = _connectionfactory.CreateConnection (null, null);
            _connection.ExceptionListener = new ExceptionListener (OnConnectionException);

            //Session
            _session = _connection.CreateSession (false, AcknowledgeMode.AutoAcknowledge);

            //Destination
            _destination = _session.CreateQueue ("queue://My.Queue.Name");
            _destination.SetIntProperty (XMSC.DELIVERY_MODE, 2);
            _destination.SetIntProperty (XMSC.WMQ_TARGET_CLIENT, 0);

            //Consumer
            _consumer = _session.CreateConsumer (_destination);
            _connected = true;
        } catch (Exception ex) {
            _connected = false;
        }

    }
}

private IConnectionFactory SetConnectionFactory () {
    XMSFactoryFactory factoryFactory = XMSFactoryFactory.GetInstance (XMSC.CT_WMQ);
    IConnectionFactory cf = factoryFactory.CreateConnectionFactory ();

    // Set the properties
    cf.SetStringProperty (XMSC.WMQ_CHANNEL, ConnectionSettings.Channel);
    cf.SetIntProperty (XMSC.WMQ_CONNECTION_MODE, XMSC.WMQ_CM_CLIENT);
    cf.SetIntProperty (XMSC.WMQ_FAIL_IF_QUIESCE, XMSC.WMQ_FIQ_YES);
    cf.SetStringProperty (XMSC.WMQ_QUEUE_MANAGER, ConnectionSettings.QueueManager);
    cf.SetStringProperty (XMSC.WMQ_CONNECTION_NAME_LIST, ConnectionSettings.ConnectionList);
    cf.SetIntProperty (XMSC.WMQ_CLIENT_RECONNECT_TIMEOUT, ConnectionSettings.ReconnectTimeout);
    cf.SetIntProperty (XMSC.WMQ_CLIENT_RECONNECT_OPTIONS, ConnectionSettings.ReconnectOptions);

    cf.SetStringProperty (XMSC.WMQ_PROVIDER_VERSION, XMSC.WMQ_PROVIDER_VERSION_DEFAULT);
    cf.SetBooleanProperty (XMSC.WMQ_SYNCPOINT_ALL_GETS, true);
    return cf;
}

public override void Subscribe<T> (Action<T> onMessageReceived) {
    try {

        _connection.ExceptionListener = delegate (Exception connectionException) {
            XMSException xmsError = (XMSException) connectionException;
            int reasonCode = ((IBM.WMQ.MQException) (xmsError).LinkedException).ReasonCode;
            if (reasonCode == MQC.MQRC_Q_MGR_QUIESCING || reasonCode == MQC.MQRC_CONNECTION_BROKEN) {
                _reConnectOnConnectionBreak = true;
                _connection.Close ();

                CreateWebsphereQueueConnection ();
                Subscribe (onMessageReceived);
                _reConnectOnConnectionBreak = false;
            }
        }

        MessageListener messageListener = new MessageListener ((msg) => {
            onMessageReceived (message);
        });
        _consumer.MessageListener = messageListener;

        // Start the connection
        _connection.Start ();
    } catch (Exception ex) {
        //Log exception details
    }
}

There is no better way to check the state of the connection IConnection in IBM MQ version 8. So, I had to use thereason codes. In IBM MQ version 9, we can use the rest API exposed by the server to check the connection state.