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Sequential processing of asynchronous tasks

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旧时难觅i
旧时难觅i 2020-12-08 02:53

Assume the following synchronous code:

try
{
    Foo();
    Bar();
    Fubar();
    Console.WriteLine(\"All done\");
}
catch(Exception e) // For illustration
5条回答
  • 抹茶落季
    抹茶落季 (楼主)
    2020-12-08 03:14

    Here's how it would work with async:

    try
{
    await FooAsync();
    await BarAsync();
    await FubarAsync();
    Console.WriteLine("All done");
}
catch(Exception e) // For illustration purposes only. Catch specific exceptions!
{
    Console.WriteLine(e);
}

    This would work on .NET 4.0 if you installed the (prerelease) Microsoft.Bcl.Async package.

    Since you're stuck on VS2010, you can use a variant of Stephen Toub's Then:

    public static Task Then(this Task first, Func next)
{
  var tcs = new TaskCompletionSource();
  first.ContinueWith(_ =>
  {
    if (first.IsFaulted) tcs.TrySetException(first.Exception.InnerExceptions);
    else if (first.IsCanceled) tcs.TrySetCanceled();
    else
    {
      try
      {
        next().ContinueWith(t =>
        {
          if (t.IsFaulted) tcs.TrySetException(t.Exception.InnerExceptions);
          else if (t.IsCanceled) tcs.TrySetCanceled();
          else tcs.TrySetResult(null);
        }, TaskContinuationOptions.ExecuteSynchronously);
      }
      catch (Exception exc) { tcs.TrySetException(exc); }
    }
  }, TaskContinuationOptions.ExecuteSynchronously);
  return tcs.Task; 
}



    You can use it as such:
    


    var task = FooAsync().Then(() => BarAsync()).Then(() => FubarAsync());
task.ContinueWith(t =>
{
  if (t.IsFaulted || t.IsCanceled)
  {
    var e = t.Exception.InnerException;
    // exception handling
  }
  else
  {
    Console.WriteLine("All done");
  }
}, TaskContinuationOptions.ExcecuteSynchronously);

    


    


    Using Rx, it would look like this (assuming you don't have the async methods already exposed as IObservable):
    


    FooAsync().ToObservable()
    .SelectMany(_ => BarAsync().ToObservable())
    .SelectMany(_ => FubarAsync().ToObservable())
    .Subscribe(_ => { Console.WriteLine("All done"); },
        e => { Console.WriteLine(e); });

    


    I think. I'm not an Rx master, by any means. :)
    
    
    
             
    
                                                        
    
            
            
    
              
                
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