BackgroundWorker 线程没有停止 winforms c#

Question

我正在使用BackgroundWorker 线程调用一个小例程，该例程在消息到达 MSMQ 队列后立即从 MSMQ 接收消息（消息每 5 秒到达 msmq）它来到我使用 @987654322 的应用程序@ 线。下面是我的 Win Form 课程。我是线程新手，所以如果我做错了什么请道歉

问题：我的应用程序是 MDI 应用程序，当我第一次执行我的应用程序时，它工作得非常好，并且一旦它进入队列就会收到 MSMQ 消息，每 5 秒一次，但是当我关闭这个表单时是一个子窗体，它关闭得很好，但是在打开同一个窗体后，我正在接收来自 MSMQ 的消息，时间为 10 秒，所以这意味着我在后台工作线程中搞砸了一些东西，我试图取消这个后台工作线程但是我失败了，无法正确取消或终止线程。请帮助并分享您的经验。下面是我的表单代码。

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

你有两个选择：

1) 在Form的Closing事件中，调用backgroundWorker1.CancelAsync()。

2) 更好的方法是完全删除您的后台工作人员并为此使用 MessageQueue 的本机异步处理机制。您可以在添加 ReceivedCompleted 事件处理程序后使用BeginReceive 方法启动队列请求，然后在完成的事件处理程序中处理消息并重新启动请求。

问题是如果你发出一个 Receive 请求，它会阻塞后台工作线程，直到队列中收到一条消息，而 CancelAsync 只会请求停止后台工作线程，它不会取消 Receive 请求.

例如（更新）：

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

当您关闭表单时，您会终止工作人员吗？如果没有，如果在某处有对表单或工作人员的引用（事件处理程序？），那么它将不会获得 GCd 并保留。打开第二个实例后，您可能有两个后台工作人员正在运行....