How Can I Best Handle AggregateExceptions When Using `await`?

Problems in handling AggregateException in asynchronous programming

In the world of asynchronous programming, the await keyword provides an elegant way to pause execution until a task is completed. However, await introduces a subtle problem when handling erroneous tasks: it rethrows the first exception in AggregateException, potentially losing valuable error information.

To solve this problem, developers are faced with a difficult problem. They might resort to some inelegant solution, or try to use a custom awaiter. However, best practices for handling await cleanly within AggregateException remain elusive.

Answer to the question

Contrary to the suggestion in the title, the default behavior of await is often beneficial in this situation. In most cases, just knowing about an exception is enough. The real challenge is to handle AggregateException in a way that allows selective exception handling.

To achieve this, the following extension method provides a neat solution:

<code class="language-csharp">public static async Task WithAggregateException(this Task source)
{
  try
  {
    await source.ConfigureAwait(false);
  }
  catch (Exception ex)
  {
    // source.Exception 可能为 null，如果任务被取消。
    if (source.Exception == null)
      throw ex; // 抛出原始异常，例如取消异常

    // EDI 保留原始异常的堆栈跟踪，如果有的话。
    ExceptionDispatchInfo.Capture(source.Exception).Throw();
  }
}</code>

By encapsulating the await operation in a try-catch block, this method allows developers to access the AggregateException and rethrow it using ExceptionDispatchInfo.Capture. This preserves the stack trace of the original exception, allowing developers to handle errors appropriately. The modified code handles task cancellation cases more completely.

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