Catch Multiple Async Task Exceptions

// -----------------------------------------------------------------------------
// Task Extension To Collect Multiple Task Exceptions
//
// A cleaner way of reacting to a task’s status, we don’t just try to fetch the
// result and catch any exceptions; we handle each status individually.
//
// MORE SOPHISTICATED (BUT LOSSY) EXCEPTION HANDLING
// http://codeblog.jonskeet.uk/2011/06/22/eduasync-part-11-more-sophisticated-but-lossy-exception-handling/
// -----------------------------------------------------------------------------

public static Task<T> WithAllExceptions<T>(this Task<T> task)
{
    TaskCompletionSource<T> tcs = new TaskCompletionSource<T>();

    task.ContinueWith(ignored =>
    {
        switch (task.Status)
        {
            case TaskStatus.Canceled:
                tcs.SetCanceled();
                break;
            case TaskStatus.RanToCompletion:
                tcs.SetResult(task.Result);
                break;
            case TaskStatus.Faulted:
                // SetException will automatically wrap the original AggregateException
                // in another one. The new wrapper will be removed in TaskAwaiter, leaving
                // the original intact.
                tcs.SetException(task.Exception);
                break;
            default:
                tcs.SetException(new InvalidOperationException("Continuation called illegally."));
                break;
        }
    });

    return tcs.Task;
}

// -------
// Example
// -------

private static async Task<int> AwaitMultipleFailures()
{
    try
    {
        await CauseMultipleFailures().WithAllExceptions();
    }
    catch (AggregateException e)
    {
        Console.WriteLine("Caught arbitrary exception: {0}", e);
        return e.InnerExceptions.Count;
    }

    // Nothing went wrong, remarkably!
    return 0;
}

private static Task<int> CauseMultipleFailures()
{
    // Simplest way of inducing multiple exceptions
    Exception[] exceptions = { new IOException(), new ArgumentException() };
    TaskCompletionSource<int> tcs = new TaskCompletionSource<int>();
    tcs.SetException(exceptions);

    return tcs.Task;
}