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假设我有一个 GUI 应用程序，它有一个在应用程序的生命周期内运行的后台线程。当我关闭应用程序时，我想干净地关闭任何这些后台线程。实际上，我经常运行一些线程来执行数据收集和处理活动，而无需挂起 GUI。

下面的例子演示了这个问题；也就是说，如果您取消后台工作人员，它会尝试在主线程上调用工作人员完成方法。如果不调用Application::DoEvents()代码只会无限期地挂起，但我之前遇到过调用问题DoEvents，我的直觉告诉我这是不好的做法。

所以问题是；当我的应用程序退出时，干净地关闭后台工作线程的正确方法是什么？

using namespace System;
using namespace System::ComponentModel;
using namespace System::Collections;
using namespace System::Windows::Forms;
using namespace System::Data;
using namespace System::Drawing;

/// <summary>
/// Summary for Form1
///
/// WARNING: If you change the name of this class, you will need to change the
///          'Resource File Name' property for the managed resource compiler tool
///          associated with all .resx files this class depends on.  Otherwise,
///          the designers will not be able to interact properly with localized
///          resources associated with this form.
/// </summary>
public ref class Form1 : public System::Windows::Forms::Form
{
private: System::ComponentModel::BackgroundWorker^  backgroundWorker1;

public:
    Form1(void)
    {
        InitializeComponent();

        // 
        // backgroundWorker1
        // 
        this->backgroundWorker1 = (gcnew System::ComponentModel::BackgroundWorker());
        this->backgroundWorker1->DoWork += gcnew System::ComponentModel::DoWorkEventHandler(this, &Form1::backgroundWorker1_DoWork);
        this->backgroundWorker1->RunWorkerCompleted += gcnew System::ComponentModel::RunWorkerCompletedEventHandler(this, &Form1::backgroundWorker1_RunWorkerCompleted);
        this->backgroundWorker1->ProgressChanged += gcnew System::ComponentModel::ProgressChangedEventHandler(this, &Form1::backgroundWorker1_ProgressChanged);
        this->backgroundWorker1->WorkerReportsProgress = true;
        this->backgroundWorker1->WorkerSupportsCancellation = true;

        //
        //TODO: Add the constructor code here
        //
        backgroundWorker1->RunWorkerAsync();
    }

protected:
    /// <summary>
    /// Clean up any resources being used.
    /// </summary>
    ~Form1()
    {
        if( backgroundWorker1 != nullptr )
        {
            backgroundWorker1->CancelAsync();
        }

        while( backgroundWorker1->IsBusy == true )
        {
            System::Diagnostics::Debug::WriteLine("Waiting for background worker to exit..");
            System::Threading::Thread::Sleep(1000);
            // Application::DoEvents(); <-- Don't want to do this but what are the alternatives?
        }

        System::Diagnostics::Debug::WriteLine("Form1 destructor complete!");
    }

private: System::Void backgroundWorker1_DoWork(System::Object^  sender, System::ComponentModel::DoWorkEventArgs^  e) {
             while( backgroundWorker1->CancellationPending == false )
             {
                 System::Diagnostics::Debug::WriteLine("Working..");
                 System::Threading::Thread::Sleep(1000);
             }
         }

private: System::Void backgroundWorker1_ProgressChanged(System::Object^  sender, System::ComponentModel::ProgressChangedEventArgs^  e) {
         }

private: System::Void backgroundWorker1_RunWorkerCompleted(System::Object^  sender, System::ComponentModel::RunWorkerCompletedEventArgs^  e)
         {
            System::Diagnostics::Debug::WriteLine("Exiting..");
            System::Threading::Thread::Sleep(1000);

         }

private:
    /// <summary>
    /// Required designer variable.
    /// </summary>
    System::ComponentModel::Container ^components;

#pragma region Windows Form Designer generated code
    /// <summary>
    /// Required method for Designer support - do not modify
    /// the contents of this method with the code editor.
    /// </summary>
    void InitializeComponent(void)
    {
        this->SuspendLayout();
        // 
        // Form1
        // 
        this->AutoScaleDimensions = System::Drawing::SizeF(6, 13);
        this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
        this->ClientSize = System::Drawing::Size(443, 343);
        this->Name = L"Form1";
        this->Text = L"Form1";
        this->ResumeLayout(false);

    }
#pragma endregion

};
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1 回答 1

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当 BackgroundWorker 触发 RunWorkerCompleted 事件时，它会在主 GUI 线程上执行此操作，这是运行析构函数的线程。当您调用 DoEvents 时，它使框架有机会运行等待在该线程上运行的其他任务，包括 RunWorkerCompleted 事件。

我添加Thread::CurrentThread->ManagedThreadId到您的调试消息中（并且未注释Application::DoEvents()），这就是我得到的：

Starting background worker from thread 1
Working on thread 3..
Working on thread 3..
Waiting on thread 1 for background worker to exit..
Exiting on thread 1..
Form1 destructor complete!

所以，如果你不想使用 Application::DoEvents()，我会使用不同的机制来告诉 UI 线程 worker 已经退出。ManualResetEvent 在这里可以很好地解决问题。

private:
    ManualResetEvent^ mre;

public:
    Form1(void)
    {
        InitializeComponent();

        this->backgroundWorker1 = (gcnew System::ComponentModel::BackgroundWorker());
        this->backgroundWorker1->DoWork += gcnew System::ComponentModel::DoWorkEventHandler(this, &Form1::backgroundWorker1_DoWork);
        // Don't use this->backgroundWorker1->RunWorkerCompleted
        this->backgroundWorker1->ProgressChanged += gcnew System::ComponentModel::ProgressChangedEventHandler(this, &Form1::backgroundWorker1_ProgressChanged);
        this->backgroundWorker1->WorkerReportsProgress = true;
        this->backgroundWorker1->WorkerSupportsCancellation = true;

        this->mre = gcnew ManualResetEvent(false);

        System::Diagnostics::Debug::WriteLine("Starting background worker from thread {0}", Thread::CurrentThread->ManagedThreadId);
        backgroundWorker1->RunWorkerAsync();
    }

protected:
    ~Form1()
    {
        if( backgroundWorker1 != nullptr )
        {
            backgroundWorker1->CancelAsync();
        }

        System::Diagnostics::Debug::WriteLine("Waiting on thread {0} for background worker to exit..", Thread::CurrentThread->ManagedThreadId);
        this->mre->WaitOne();

        System::Diagnostics::Debug::WriteLine("Form1 destructor complete!");
    }

private:
    System::Void backgroundWorker1_DoWork(System::Object^  sender, System::ComponentModel::DoWorkEventArgs^  e)
        {
            try
            {
                while( backgroundWorker1->CancellationPending == false )
                {
                    System::Diagnostics::Debug::WriteLine("Working on thread {0}..", Thread::CurrentThread->ManagedThreadId);
                    System::Threading::Thread::Sleep(1000);
                }
            }
            finally
            {
                this->mre->Set();
            }
        }

现在，说了这么多，您可能要考虑在这里使用常规线程，而不是 BackgroundWorker。通过在 UI 线程上触发“完成”和“进度”事件，我认为它更适合直接在 UI 线程上执行的任务太长，但结果将在几秒钟后在 UI 中可见。（在 UI 线程上触发事件可以很容易地使用操作结果更新 UI 控件。）对于您在此处显示的内容，在表单打开的整个过程中都在运行的东西，您并没有得到很大从 BackgroundWorker 中受益，因此您可以创建一个线程并自己做。

于 2012-07-10T21:37:23.423 回答