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

Question

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

Answer 1

Here's a riffed version of Panagiotis Kanavos's excellent answer which I've tested and am using in production.

It addresses some things that were important to me:

• Want to be able to decide whether to retry based on number of preceding attempts and exception from current attempt
• Don't want to rely on async (less environment constraints)
• Want to have the resulting Exception in the case of failure include details from each attempt

static Task RetryWhile(
    Func> func, 
    Func shouldRetry )
{
    return RetryWhile( func, shouldRetry, new TaskCompletionSource(), 0, Enumerable.Empty() );
}

static Task RetryWhile( 
    Func> func, 
    Func shouldRetry, 
    TaskCompletionSource tcs, 
    int previousAttempts, IEnumerable previousExceptions )
{
    func( previousAttempts ).ContinueWith( antecedent =>
    {
        if ( antecedent.IsFaulted )
        {
            var antecedentException = antecedent.Exception;
            var allSoFar = previousExceptions
                .Concat( antecedentException.Flatten().InnerExceptions );
            if ( shouldRetry( antecedentException, previousAttempts ) )
                RetryWhile( func,shouldRetry,previousAttempts+1, tcs, allSoFar);
            else
                tcs.SetException( allLoggedExceptions );
        }
        else
            tcs.SetResult( antecedent.Result );
    }, TaskContinuationOptions.ExecuteSynchronously );
    return tcs.Task;
}