using System;

using System.Threading;

public class Program

{

    public static double Add(ref double location1, double value)

    {

        double newCurrentValue = location1; // non-volatile read, so may be stale

        while (true)

        {

            double currentValue = newCurrentValue;

            double newValue = currentValue + value;

            newCurrentValue = Interlocked.CompareExchange(ref location1, newValue, currentValue);

            if (newCurrentValue == currentValue)

                return newValue;

        }

    }

    public static void Main()

    {

        double d1 = Double.NaN;

        Console.WriteLine(Add(ref d1, 2));

    }

}