Singleton

Singleton is a class that can be instantiated only once to coordinate actions across the system. Below is the simpe implementation of the Singleton class.

class Singleton { private static Singleton instance; // Note: the constructor is protected protected Singleton() { } public static Singleton GetInstance() { //lazy initialization if (instance == null) { instance = new Singleton(); } return instance; } } }

Let’s make multiple calls of the Singleton class and make sure they share the same instance of this class. We can not use the new() keyword since the constructor is protected:

static void Main() { Singleton instance1 = Singleton.GetInstance(); Singleton instance2 = Singleton.GetInstance(); if ( instance1 == instance2 ) { Console.WriteLine("As you may see - I'm the Singleton!"); } Console.Read(); }

As we may expect the execution of this code will return a confirmation from the Singleton class.  The Singleton class requires small modification for making it useable in the multithreading system:

class Singleton { private static Singleton instance; private static object syncLock = new Object(); protected Singleton() { } public static Singleton GetInstance() { lock(syncLock) { if (instance == null) { instance = new Singleton(); } return instance; } return instance; } } }

Apparently the Singleton class may include more methods and instance variables to be shared across the system.