Task.Run vs BackgroundWorker: Conclusion

In this series on Task.Run vs BackgroundWorker, we’ve looked at the most common aspects of running background tasks. As a recap, here’s the full list of posts in chronological order:

• Introduction - we’re only contrasting Task.Run with BackgroundWorker for situations that BackgroundWorker was designed for.
• Round 1: Basics - how to run code on a background thread and receive a completion notification marshaled back to the UI thread. The Task.Run code is shorter and simpler with less “ceremony code”.
• Round 2: Errors - how to handle exceptions from the background thread code. The Task.Run code uses the more natural and less error-prone try/catch blocks, and has less error-prone exception propagation.
• Round 3: Results - how to retrieve a result value from the background thread. The Task.Run code uses the more natural return statement and the result value is strongly-typed.
• Round 4: Cancellation - how to cancel the background thread. The Task.Run code uses the common cancellation framework, which is simpler, less error-prone, and interoperates more cleanly with other cancellation-aware APIs.
• Round 5: Progress Reports - how to support progress updates from the background thread. The Task.Run code uses a strongly-typed progress report type.

What I am not planning to cover in this series are more complex situations, which is actually where Task.Run really outperforms BackgroundWorker. For example, nesting one background operation within another is easier with Task.Run. Also, anything like waiting for two separate background operations to complete before doing something else is much easier with Task.Run. Pretty much any time you have to coordinate background operations, Task.Run code is going to be much simpler!

I hope that this series is sufficient to convince you that BackgroundWorker is a type that should not be used in new code. Everything it can do, Task.Run can do better; and Task.Run can do a lot of things that BackgroundWorker can’t!

I’ll leave you with a “combined” example. The code below starts a cancelable background operation that reports progress, and will either throw an exception or return a value. These are all the basic operations of BackgroundWorker. One of these uses BackgroundWorker and the other uses Task.Run. Don’t just look at the length of the code; consider all the little nuances of how it works (type safety, how easily the API can be misused, etc). Then ask yourself: which code would I rather maintain?

private BackgroundWorker _bgw;
private void button1_Click(object sender, EventArgs e)
{
  var fail = checkBox1.Checked;
  _bgw = new BackgroundWorker();
  var bgw = _bgw;
  bgw.WorkerSupportsCancellation = true;
  bgw.WorkerReportsProgress = true;
  bgw.DoWork += (_, args) =>
  {
    for (int i = 0; i != 100; ++i)
    {
      bgw.ReportProgress(0, i + "%");
      if (bgw.CancellationPending)
      {
        args.Cancel = true;
        return;
      }
      Thread.Sleep(100);
    }
    if (fail)
      throw new InvalidOperationException("Requested to fail.");
    args.Result = 13;
  };
  bgw.ProgressChanged += (_, args) =>
  {
    label1.Text = (string)args.UserState;
  };
  bgw.RunWorkerCompleted += (_, args) =>
  {
    if (args.Cancelled)
    {
      label1.Text = "Cancelled.";
    }
    else if (args.Error == null)
    {
      var result = (int)args.Result;
      label1.Text = "Completed: " + result;
    }
    else
    {
      label1.Text = args.Error.GetType().Name + ": " + args.Error.Message;
    }
  };
  bgw.RunWorkerAsync();
}
private void cancelButton1_Click(object sender, EventArgs e)
{
  if (_bgw != null)
    _bgw.CancelAsync();
}

private CancellationTokenSource _cts;
private async void button2_Click(object sender, EventArgs e)
{
  var fail = checkBox1.Checked;
  _cts = new CancellationTokenSource();
  var token = _cts.Token;
  var progressHandler = new Progress<string>(value =>
  {
    label2.Text = value;
  });
  var progress = progressHandler as IProgress<string>;
  try
  {
    var result = await Task.Run(() =>
    {
      for (int i = 0; i != 100; ++i)
      {
        if (progress != null)
          progress.Report(i + "%");
        token.ThrowIfCancellationRequested();
        Thread.Sleep(100);
      }
      if (fail)
        throw new InvalidOperationException("Requested to fail.");
      return 13;
    });
    label2.Text = "Completed: " + result;
  }
  catch (OperationCanceledException)
  {
    label2.Text = "Cancelled.";
  }
  catch (Exception ex)
  {
    label2.Text = ex.GetType().Name + ": " + ex.Message;
  }
}
private void cancelButton2_Click(object sender, EventArgs e)
{
  if (_cts != null)
    _cts.Cancel();
}