Thready safety in Static Variables

StaticThreadySafety.cs

//Interlocked class Provides atomic operations for variables that are shared by multiple threads.

private static string _data;

 public ActionResult Index()
  {
      //Compares two instances of the specified reference type <paramref name="T" /> for equality and, if they are equal, replaces the first one
      if (Interlocked.CompareExchange(ref _data, "test", null) == null)
      {

      }
      ....
  }