class Program
    {
        static async Task Main(string[] args)
        {
            Console.WriteLine("\n=== WithTcs");
            Console.WriteLine("Main Thread: " + Thread.CurrentThread.ManagedThreadId);

            try
            {
                var result = await WithTcs();
                Console.WriteLine("result: "+ result);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
            }


            Console.WriteLine("\n=== WithoutTcs");
            Console.WriteLine("Main Thread: " + Thread.CurrentThread.ManagedThreadId);

            try
            {
                var result = await WithoutTcs();
                Console.WriteLine("result: " + result);
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
            }

            Console.ReadLine();
        }

        public static async Task<int> WithoutTcs()
        {
            Console.WriteLine("Thread start: " + Thread.CurrentThread.ManagedThreadId);
            int value = 42;
            var result = await Task.Run(() =>
            {
                Console.WriteLine("Thread run: " + Thread.CurrentThread.ManagedThreadId);
                return LongRunningSyncOperation(value);
            });
            Console.WriteLine("Thread end: " + Thread.CurrentThread.ManagedThreadId);
            return value;
        }

        public static Task<int> WithTcs()
        {
            Console.WriteLine("Thread start: " + Thread.CurrentThread.ManagedThreadId);
            var tcs = new TaskCompletionSource<int>();
            int value = 42;
            Task.Run(() =>
            {
                Console.WriteLine("Thread run: " + Thread.CurrentThread.ManagedThreadId);
                try
                {
                    var result = LongRunningSyncOperation(value);
                    tcs.SetResult(result);
                }
                catch (Exception ex)
                {
                    tcs.SetException(ex);
                }
            });
            Console.WriteLine("Thread end: " + Thread.CurrentThread.ManagedThreadId);
            return tcs.Task;
        }

        public static int LongRunningSyncOperation(int value)
        {
            Thread.Sleep(2000);
            throw new Exception("Упс");
            Thread.Sleep(2000);
            return value + 100;
        }
    }