using System;

using System.Threading;

using System.Threading.Tasks;

using System.Linq;

public class Program

{

    public static async Task Main()

    {

        Console.WriteLine($"Thread # {Thread.CurrentThread.ManagedThreadId} is running the program.");

        await Task.WhenAll(Enumerable.Range(0, 10).Select(async _ => {

            var dal = new DAL();

            var result = await dal.GetValue();

        }));

        var dal = new DAL();

        var result = await dal.GetValue();

        Console.WriteLine($"Current value is {result}");

    }

    public class DAL {

        private static object _lock = new object();

        private static DateTime _refreshTime = DateTime.MinValue;

        private static bool isBeingRefreshed = false;

        private static int currentValue = 0;

        public async Task<int> GetValue() 

        {

            bool isCurrentThreadRefreshing = false;

            lock(_lock) {

                if (!isBeingRefreshed && _refreshTime < DateTime.Now.AddSeconds(-5)) {

                    isBeingRefreshed = true;

                    isCurrentThreadRefreshing = true;

                }

            }

            if (isCurrentThreadRefreshing) {

                await Task.Delay(500);

                currentValue += 1;

                isBeingRefreshed = false;

                _refreshTime = DateTime.Now;

                Console.WriteLine($"Thread # {Thread.CurrentThread.ManagedThreadId} refreshed the value.");

            }

            return currentValue;

        }

    }

}