// In software engineering, the singleton pattern is a design pattern used to implement the mathematical 
// concept of a singleton, by restricting the instantiation of a class to one object. This is useful when 
// exactly one object is needed to coordinate actions across the system. The concept is sometimes generalized 
// to systems that operate more efficiently when only one object exists, or that restrict the instantiation 
// to a certain number of objects.

public sealed class MySingleton
{
	private static MySingleton instance;
	private static readonly Object sync = new object();

	private MySingleton()
	{
		// initialize members here
	}

	public static MySingleton Instance
	{
		get
		{
			if (instance == null)
			{
				lock (sync)
				{
					if (instance == null)
						instance = new MySingleton();
				}
			}

			return instance;
		}
	}
	
	public void SayHello()
	{
		Console.WriteLine("Hello!");
	}
	
}