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Retry a task multiple times based on user input in case of an exception in task

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甜味超标
甜味超标 2020-11-27 05:29

All the service calls in my application are implemented as tasks.When ever a task is faulted ,I need to present the user with a dialog box to retry the last operation failed

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  • 生来不讨喜
    生来不讨喜 (楼主)
    2020-11-27 06:15

    When at the high level, I find it helps to make a function signature from what you have and what you want.

    You have:

    • A function that gives you a task (Func). We'll use the function because tasks themselves are not retryable in general.
    • A function that determines if the overall task is completed or should be retried (Func)

    You want:

    • An overall Task

    So you'll have a function like:

    Task Retry(Func action, Func shouldRetry);

    Extending the practice inside the function, tasks pretty much have 2 operations to do with them, read their state and ContinueWith. To make your own tasks, TaskCompletionSource is a good starting point. A first try might look something like:

    //error checking
var result = new TaskCompletionSource();
action().ContinueWith((t) => 
  {
    if (shouldRetry(t))
        action();
    else
    {
        if (t.IsFaulted)
            result.TrySetException(t.Exception);
        //and similar for Canceled and RunToCompletion
    }
  });



    The obvious problem here is that only 1 retry will ever happen.  To get around that, you need to make a way for the function to call itself.  The usual way to do this with lambdas is something like this:
    


    //error checking
var result = new TaskCompletionSource();

Func retryRec = null; //declare, then assign
retryRec = (t) => { if (shouldRetry(t))
                        return action().ContinueWith(retryRec).Unwrap();
                    else
                    {
                        if (t.IsFaulted) 
                            result.TrySetException(t.Exception);
                        //and so on
                        return result.Task; //need to return something
                     }
                  };
 action().ContinueWith(retryRec);
 return result.Task;

    
    
             
    
                                                        
    
            
            
    
              
                
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