FuncUtils.cs

using System;
using System.Threading;
using System.Threading.Tasks;

namespace BSSConsumer.Core
{
    public static class FuncUtils
    {
        public static readonly IRetryPolicy DefaultRetryPolicy = new FibonacciRetryPolicy();

        public static Task<T> Retry<T>(this Func<Task<T>> func, int maxNumOfRetries, CancellationToken token)
        {
            return RetryFunc(func, 0, maxNumOfRetries, token, DefaultRetryPolicy);
        }

        public static Task<T> Retry<T>(this Func<Task<T>> func, int maxNumOfRetries, CancellationToken token, IRetryPolicy retryPolicy)
        {
            return RetryFunc(func, 0, maxNumOfRetries, token, retryPolicy);
        }

        public interface IRetryPolicy
        {
            int GetWaitTime(int currentRetryNum);
        }

        private class FibonacciRetryPolicy : IRetryPolicy
        {
            public int GetWaitTime(int n)
            {
                if (n <= 1) return n;
                else return GetWaitTime(n - 1) + GetWaitTime(n - 2);
            }
        }

        #region Main

        private async static Task<T> RetryFunc<T>(Func<Task<T>> func, int currentRetryNum, int maxNumOfRetries, CancellationToken token, IRetryPolicy retryPolicy)
        {
            try
            {
                int waitTime = (retryPolicy.GetWaitTime(currentRetryNum) * 1000);
                await Task.Delay(waitTime, token);
                return await func.Invoke();
            }
            catch (Exception ex)
            {
                if (currentRetryNum < maxNumOfRetries && !token.IsCancellationRequested)
                {
                    return await RetryFunc(func, ++currentRetryNum, maxNumOfRetries, token, retryPolicy);
                }
                else
                {
                    throw ex;
                }
            }
        }

        #endregion
    }
}