private static readonly SpinLock _lock = new SpinLock();

        private static int _value = 0;

        private static void Increment()
        {
            bool ok = false;
            try
            {
                _lock.Enter(ref ok);

                _value++;

                // ...
            }
            finally
            {
                if (_lock.IsHeld)
                    _lock.Exit(true);
            }
        }

        static void Main(string[] args)
        {
            Parallel.For(0, 100000, i => Increment());
            Console.WriteLine($"Actual: {_value};");

            Console.WriteLine("Done.");
            Console.ReadKey();
        }