using System;

using System.Threading.Tasks;

using System.Collections.Generic;

​

public class Program

{

    public async static Task Main()

    {

        var tasks = new List<Task>();

        var vasyan = new Account(1, "vasyan", 2000.0);

        var tolyan = new Account(2, "tolyan", 1000.0);

        var t1 = Task.Run(()=>

        Parallel.For(0, 30, i =>

        {

            Send(vasyan, tolyan, 50.0);

        })

                 );

        var t2 = Task.Run(()=> {        lock (vasyan)

        {

            lock (tolyan)

            {

                vasyan.Amount += 50;

                tolyan.Amount -= 50;

            }

        }});

        await Task.WhenAll(new []{t1, t2});

​

        Console.WriteLine(vasyan.Amount);

        Console.WriteLine(tolyan.Amount);

    }

​

    public class Account

    {

        public Account(int userId, string name, double amount)

        {

            UserId = userId;

            UserName = name;

            Amount = amount;

        }

​

        public int UserId;

        public string UserName;

        public double Amount;

    }

​

    public static void Send(Account a, Account b, double amount)

    {

        lock (a)

        {

            lock (b)

            {

                a.Amount += amount;

                b.Amount -= amount;

            }

        }

    }

}