当一个线程完成时，启动一个新的线程:为什么我不在一个新的线程中

Question

这基本上就是代码:

private void TaskGestioneCartelle()
{
    Task.Factory.StartNew(() => GeneraListaCartelle())
        .ContinueWith(t => GeneraListaCartelleCompletata()
        , CancellationToken.None
        , TaskContinuationOptions.None
        , TaskScheduler.FromCurrentSynchronizationContext());
}
private void GeneraListaCartelle()
{
    // ... code
}
private void GeneraListaCartelleCompletata()
{
    Task.Factory.StartNew(() => CopiaCartelle())
        .ContinueWith(t => CopiaCartelleCompletato()
        , CancellationToken.None
        , TaskContinuationOptions.None
        , TaskScheduler.FromCurrentSynchronizationContext());
}
private void CopiaCartelle()
{
    // long operation...
}

事实上，当CopiaCartelle启动时，我不进入新线程，因为它需要很多时间，UI完全冻结(而在GeneraListaCartelle()上，这也需要很长时间，这不会发生)。也因为我可以在UI中编写控件而不使用InvokeRequired和MethodInvoker。

我漏了一些点吗?

Answer 1

尝试更改Task.Factory.StartNew(() => CopiaCartelle())

Task.Factory.StartNew(() => CopiaCartelle(),  CancellationToken.None, TaskCreationOptions.None, TaskScheduler.Default))

你要进入GeneraListaCartelleCompletata在UI线程上的延续，它正在调度UI线程上的任务-放置TaskScheduler。默认情况下，它会在自己的线程中运行。

Answer 2

@NDJ发布的内容是正确的，我已经做了一个快速的示例来展示正在发生的事情。

首先，方法:

private static void TaskGestioneCartelle()
{            
    Task.Factory.StartNew(() => GeneraListaCartelle())
        .ContinueWith(t => GeneraListaCartelleCompletata()
        , CancellationToken.None
        , TaskContinuationOptions.None
        , TaskScheduler.FromCurrentSynchronizationContext());
}
private static void GeneraListaCartelle()
{
    //No sleep could block the thread UI because the task is being executed on a different Thread
    Debug.WriteLine("GeneraListaCartelle " + Thread.CurrentThread.ManagedThreadId);
    Thread.Sleep(4000);            
    mainForm.Invoke(new Action(() => bla.Text = "uno due tre, Genera Lista!"));            
}
private static void GeneraListaCartelleCompletata()
{
    //This is begin executed on the UI thread
    Debug.WriteLine("GeneraListaCartelleCompletata " + Thread.CurrentThread.ManagedThreadId);
    Task.Factory.StartNew(() => CopiaCartelle())
        .ContinueWith(t => CopiaCartelleCompletato()
        , CancellationToken.None
        , TaskContinuationOptions.None
        , TaskScheduler.FromCurrentSynchronizationContext());
}
private static void CopiaCartelle()
{
    //This is begin executed on the UI thread (doesn't even show in the form 'cause the thread is blocked)
    Debug.WriteLine("CopiaCartelle " + Thread.CurrentThread.ManagedThreadId);
    Thread.Sleep(4000);   
    mainForm.Invoke(new Action(() => bla.Text = "Copia Cartelle \o"));            
}
private static void CopiaCartelleCompletato()
{
    //This is begin executed on the UI thread
    Debug.WriteLine("CopiaCartelleCompletato " + Thread.CurrentThread.ManagedThreadId);
    Thread.Sleep(4000);   
    mainForm.Invoke(new Action(() => bla.Text = "Completato!"));
    //Stops blocking the UI thread
}

现在是表单和组件

    static Label bla = new Label()
    {
        Text = "Mama Mia, Gestione Cartelle!",
        Left = 100,
        Top = 100,
        Width=300
    };
    static Label hangOn = new Label()
    {
        Text="Hang loose"
    };
    static Form mainForm = new Form()
    {
        Width = 600,
        Height = 600
    };
[STAThread]
static void Main(string[] args)
{
    mainForm.Controls.Add(bla);
    mainForm.Controls.Add(hangOn);
    mainForm.MouseMove += (o, e) => { hangOn.Left = e.X; hangOn.Top = e.Y; };
    Debug.WriteLine("UI Thread: "+ Thread.CurrentThread.ManagedThreadId);
    TaskGestioneCartelle();
    Application.Run(mainForm);
}

首先，运行应用程序并继续移动鼠标。您将注意到，当Hang Loose Label停止跟随鼠标时，UI线程被阻塞。

现在，如果您从Debug中检查Output，您将看到类似这样的内容:

UI Thread: 10
GeneraListaCartelle 6
GeneraListaCartelleCompletata 10
CopiaCartelle 10
CopiaCartelleCompletato 10

看到了

?它使用UI线程来运行你的任务，因此挂起你的UI。

现在，把TaskScheduler.FormCurrentSynchronizationContext()改成TaskScheduler.Default

的大作:

UI Thread: 8
GeneraListaCartelle 9
GeneraListaCartelleCompletata 10
CopiaCartelle 10
CopiaCartelleCompletato 11

值得注意的是，我使用mainForm.Invoke来调用要在UI Thread中执行的操作，例如更改标签文本。

如果你有任何疑问，请随意评论。