异步/等待具有进度/取消的长时间运行的API方法

Question

编辑 我认为强制等待异步调用worker的正确方法是使用Task.Run,​​如下所示:

await Task.Run(() => builder.Build(dlg.FileName, cts.Token, new Progress(ReportProgress)));

从http://blogs.msdn.com/b/pfxteam/archive/2012/04/12/10293335.aspx获得了一些启示.

---

这应该很容易,但我是async/await的新手,所以请耐心等待.我正在构建一个类库,通过一些长时间运行的操作公开API.在过去,我使用BackgroundWorker来处理进度报告和取消,就像在这个简化的代码片段中一样:

public void DoSomething(object sender, DoWorkEventArgs e)
{
            BackgroundWorker bw = (BackgroundWorker)sender;
            // e.Argument is any object as passed by consumer via RunWorkerAsync...

            do
            {
                // ... do something ...

                // abort if requested
                if (bw.CancellationPending)
                {
                    e.Cancel = true;
                    break;
                } //eif

                // notify progress
                bw.ReportProgress(nPercent);
            }
}

客户端代码如下:

BackgroundWorker worker = new BackgroundWorker
{ WorkerReportsProgress = true,
    WorkerSupportsCancellation = true
};
worker.DoWork += new DoWorkEventHandler(_myWorkerClass.DoSomething);
worker.ProgressChanged += WorkerProgressChanged;
worker.RunWorkerCompleted += WorkerCompleted;
worker.RunWorkerAsync(someparam);

现在我想利用新的异步模式.所以,首先我要在API中编写一个简单的长期运行方法; 在这里,我只是逐行阅读一个文件,只是为了模拟一个真实世界的过程,我必须通过一些处理来转换文件格式:

public async Task DoSomething(string sInputFileName, CancellationToken? cancel, IProgress progress)
{
    using (StreamReader reader = new StreamReader(sInputFileName))
    {
        int nLine = 0;
        int nTotalLines = CountLines(sInputFileName);

        while ((sLine = reader.ReadLine()) != null)
        {
            nLine++;
            // do something here...
      if ((cancel.HasValue) && (cancel.Value.IsCancellationRequested)) break;
      if (progress != null) progress.Report(nLine * 100 / nTotalLines);
        }
        return nLine;
    }
}

为了这个示例,请说这是DummyWorker类的方法.现在,这是我的客户端代码(WPF测试应用程序):

private void ReportProgress(int n)
{
    Dispatcher.BeginInvoke((Action)(() => { _progress.Value = n; }));
}

private async void OnDoSomethingClick(object sender, RoutedEventArgs e)
{
    OpenFileDialog dlg = new OpenFileDialog { Filter = "Text Files (*.txt)|*.txt" };
    if (dlg.ShowDialog() == false) return;

        // show the job progress UI...

    CancellationTokenSource cts = new CancellationTokenSource();
    DummyWorker worker = new DummyWorker();
    await builder.Build(dlg.FileName, cts.Token, new Progress(ReportProgress));

    // hide the progress UI...
}

IProgress界面的实现来自http://blog.stephencleary.com/2010/06/reporting-progress-from-tasks.html,因此您可以参考该URL.无论如何,在这个使用测试中,UI被有效阻止,我看不到任何进展.那么,参考消费代码,这种情景的全貌是什么？

Answer 1

正如该博客文章顶部所述,该帖子中的信息已过时.您应该使用IProgress<T>.NET 4.5中提供的新API.

如果您正在使用阻止I/O,那么请阻止您的核心方法:

public void Build(string sInputFileName, CancellationToken cancel, IProgress<int> progress)
{
  using (StreamReader reader = new StreamReader(sInputFileName))
  {
    int nLine = 0;
    int nTotalLines = CountLines(sInputFileName);

    while ((sLine = reader.ReadLine()) != null)
    {
      nLine++;
      // do something here...
      cancel.ThrowIfCancellationRequested();
      if (progress != null) progress.Report(nLine * 100 / nTotalLines);
    }

    return nLine;
  }
}

然后在Task.Run调用它时将其包装:

private async void OnDoSomethingClick(object sender, RoutedEventArgs e)
{
  OpenFileDialog dlg = new OpenFileDialog { Filter = "Text Files (*.txt)|*.txt" };
  if (dlg.ShowDialog() == false) return;

  // show the job progress UI...

  CancellationTokenSource cts = new CancellationTokenSource();
  DummyWorker worker = new DummyWorker();
  var progress = new Progress<int>((_, value) => { _progress.Value = value; });
  await Task.Run(() => builder.Build(dlg.FileName, cts.Token, progress);

  // hide the progress UI...
}

或者,您可以重写Build以使用异步API,然后直接从事件处理程序中调用它而不将其包装Task.Run.