BackgroundWorker thread is not stopping winforms c#

Question

I am using BackgroundWorker thread to call a small routine which is receiving messages from MSMQ as soon as the message comes to MSMQ queue(messages comes to msmq in every 5 seconds) it comes to my application which is using BackgroundWorker thread. Below is my Win Form class. I am new to threading so please appology if I am doing something wrong

Problem: My application is MDI application, when I am executing my application first time it works perfectly fine and receives the MSMQ message as soon as it comes to the queue, which is every 5 seconds but when ever I close this form which is a child form it closes fine, but right after opening this same form I am receiving messages from MSMQ with 10 seconds of dalay, so it means I am messing up something in the background worker thread, I tried to cancel this background worker thread but I am failed and unable to properly cancle or terminate the thread. Please help and share your experience. below is my form code.

public partial class FrmBooking : BookingManager.Core.BaseForm.BaseForm
{
    internal const string queName = @"messageServer\private$\Response";
    private Int32 counter = 0;
    BackgroundWorker backgroundWorker1 = new BackgroundWorker();


    public FrmBooking()
    {
        InitializeComponent();
        backgroundWorker1.WorkerReportsProgress = true;
        backgroundWorker1.WorkerSupportsCancellation = true;
        backgroundWorker1.RunWorkerCompleted+=new RunWorkerCompletedEventHandler(backgroundWorker1_RunWorkerCompleted);
        backgroundWorker1.ProgressChanged+=new ProgressChangedEventHandler(backgroundWorker1_ProgressChanged);
        backgroundWorker1.DoWork+=new DoWorkEventHandler(backgroundWorker1_DoWork);

    }           

    private void backgroundWorker1_DoWork(object sender, DoWorkEventArgs e)
    {
        BackgroundWorker bgWorker = sender as BackgroundWorker;

        if (bgWorker.CancellationPending)
        {
            e.Cancel = true;
            return;
        }


            try
            {

                MessageQueue messageQueue = null;
                if (MessageQueue.Exists(queName))
                {
                    messageQueue = new MessageQueue(queName);
                }
                else
                {
                    MessageQueue.Create(queName);
                }

                messageQueue.Formatter = new XmlMessageFormatter(new Type[] { typeof(String) });

                System.Messaging.Message msg = messageQueue.Receive();



                bgWorker.ReportProgress(100, msg);

            }
            catch (Exception ex) { }


    }
    private void backgroundWorker1_RunWorkerCompleted(object sender, RunWorkerCompletedEventArgs e)
    {
        if (!e.Cancelled)
        {
            backgroundWorker1.RunWorkerAsync();
        }


    }
    private void backgroundWorker1_ProgressChanged(object sender, ProgressChangedEventArgs e)
    {

        System.Messaging.Message msg = e.UserState as System.Messaging.Message;

        listBoxControl1.Items.Add(msg.Body.ToString());
        counter++;
        labelControl1.Text = String.Format("Total messages received {0}", counter.ToString());
    }

    private void FrmBooking_Load(object sender, EventArgs e)
    {
        backgroundWorker1.RunWorkerAsync();

    }
}

Answer 1

You have two options here:

1) In the Form's Closing event, call backgroundWorker1.CancelAsync().

2) A better approach would be to remove your background worker altogether and use the the MessageQueue's native asynchronous processing mechanism for this. You can start the queue request using the BeginReceive method after adding a ReceivedCompleted event handler, then in the completed event handler, process the message and restart the request.

The issue is that if you issue a Receive request, it will block the background worker thread until a message is received in the queue, and CancelAsync will only request that the background worker be stopped, it won't cancel the Receive request.

For example (updated):

public partial class FrmBooking : BookingManager.Core.BaseForm.BaseForm
{
    public FrmBooking()
    {
        InitializeComponent();

        this.FormClosing += new FormClosingEventHandler(FrmBooking_FormClosing);
    }

    internal const string queName = @"messageServer\private$\Response";
    private Int32 counter = 0;
    private MessageQueue messageQueue = null;

    private bool formIsClosed = false;

    private void FrmBooking_Load(object sender, EventArgs e)
    {
        StartQueue();
    }

    void FrmBooking_FormClosing(object sender, FormClosingEventArgs e)
    {
        // Set the flag to indicate the form is closed
        formIsClosed = true;

        // If the messagequeue exists, close it
        if (messageQueue != null)
        {
            messageQueue.Close();
        }
    }

    private void StartQueue()
    {
        if (MessageQueue.Exists(queName))
        {
            messageQueue = new MessageQueue(queName);
        }
        else
        {
            MessageQueue.Create(queName);
        }

        messageQueue.Formatter = new XmlMessageFormatter(new Type[] { typeof(String) });

        // Add an event handler for the ReceiveCompleted event.
        messageQueue.ReceiveCompleted += new ReceiveCompletedEventHandler(MessageReceived);

        messageQueue.BeginReceive(TimeSpan.FromSeconds(15));
    }

    // Provides an event handler for the ReceiveCompleted event.
    private void MessageReceived(Object source, ReceiveCompletedEventArgs asyncResult)
    {
        if (!this.formIsClosed)
        {
            // End the asynchronous receive operation.
            System.Messaging.Message msg = messageQueue.EndReceive(asyncResult.AsyncResult);

            // Display the message information on the screen.
            listBoxControl1.Items.Add(msg.Body.ToString());
            counter++;
            labelControl1.Text = String.Format("Total messages received {0}", counter.ToString());

            // Start receiving the next message
            messageQueue.BeginReceive(TimeSpan.FromSeconds(15));
        }
    }

}

Answer 2

When you close the form, do you terminate the worker? If not, if there is a reference to the form or to the worker somewhere (event handlers?) then it will not get GCd and stays around. Upon opening the second instance you may have two background workers running....