Click here to Skip to main content
11,711,750 members (62,605 online)
Click here to Skip to main content

Tagged as

Singletons in C#, Static Constructor vs Static Initialization

, 1 Jul 2010 CPOL 28K 17
Rate this:
Please Sign up or sign in to vote.
In C#, you can implement a thread safe singleton where the complexity is hidden in the .NET Framework, you do not even need an if statement!

Not a long time ago, I posted an article about how to implement a static constructor. As an example, I used a singleton to show how the static constructor works and how it is implemented. The result was a discussion about singletons, what they are good for and how it can be implemented in C#. There is the standard way (how it is normally done) and also a lot easier way for C# with a static constructor or a static initialization.

The Classic Singleton

public sealed class Singleton
{
   private static volatile Singleton instance;
   private static object syncRoot = new Object();

   private Singleton() {}

   public static Singleton Instance
   {
      get 
      {
         if (instance == null) 
         {
            lock (syncRoot) 
            {
               if (instance == null) 
                  instance = new Singleton();
            }
         }

         return instance;
      }
   }
}

In every object oriented language (or those I know), a Singleton looks nearly (more or less) like the code above. The Singleton restricts the instantiation of a class to one object. This is provided by a static field which holds the instance. If the instance which is stored in the static field is still null, a new object will be created and assigned to the static variable. The code which does the instantiation is locked so it also works in a multi threaded environment (double check locking). Too much code for you? 

Singleton with Static Initialization

public sealed class Singleton
{
   private static readonly Singleton instance = new Singleton();
   
   private Singleton(){}

   public static Singleton Instance
   {
      get 
      {
         return instance; 
      }
   }
}

C# allows you to initialize the static field directly (and it also works properly)! The instantiation does occur when instance property is called the first time, so it is some sort of lazy instantiation. .NET takes control that it also works in multi threaded environments, so you have nothing to do with it. But you will still have a problem with that solution if you want to execute custom code before instantiation! With a static constructor, you can solve this problem!

Singleton with Static Constructor

public sealed class Singleton
{
   private static readonly Singleton instance;
   
   private Singleton() { }

   static Singleton()
   {
      instance = new Singleton()
   }

   public static Singleton Instance
   {
      get 
      {
         return instance; 
      }
   }
}

It allows you to execute custom code before the singleton is instantiated. But the complexity is still handled by the .NET Framework, so you don't have to implement a double check locking also when you work in multi threaded environments. The static constructor is only executed when the instance property is called the first time. So both variations allow you to implement a thread safe singleton where the complexity is hidden in the .NET Framework. You do not even need an if statement!

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Share

About the Author

Mattia Baldinger
Software Developer
Switzerland Switzerland
No Biography provided

You may also be interested in...

Comments and Discussions

 
QuestionFor better understanding Pin
vicvis16-Dec-14 23:46
membervicvis16-Dec-14 23:46 
GeneralMy vote of 5 Pin
abhi.shrotriya31-Oct-14 22:24
memberabhi.shrotriya31-Oct-14 22:24 
Generalnice one Pin
Pranay Rana21-Dec-10 21:41
memberPranay Rana21-Dec-10 21:41 
GeneralCalss per singleton Pin
Asher Barak11-Jul-10 1:14
memberAsher Barak11-Jul-10 1:14 
GeneralI'm missing an attribution to John Skeet Pin
jeroenp8-Jul-10 9:59
memberjeroenp8-Jul-10 9:59 
GeneralMy vote of 4 Pin
johannesnestler7-Jul-10 3:33
memberjohannesnestler7-Jul-10 3:33 
GeneralMy vote of 1 Pin
mavric2126-Jul-10 19:17
membermavric2126-Jul-10 19:17 
GeneralJeffrey Richter CLR via C# (second edition) Chapter "The Famous Double-Check Locking Technique" page 642-641 Pin
romgun5-Jul-10 19:37
memberromgun5-Jul-10 19:37 
GeneralMaybe old wine in new sacs Pin
Rozis2-Jul-10 9:30
memberRozis2-Jul-10 9:30 
GeneralRe: Maybe old wine in new sacs Pin
woric5-Jul-10 14:44
memberworic5-Jul-10 14:44 
GeneralRe: Maybe old wine in new sacs Pin
Jason Christian5-Jul-10 20:14
memberJason Christian5-Jul-10 20:14 
GeneralRe: Maybe old wine in new sacs Pin
Rozis6-Jul-10 4:57
memberRozis6-Jul-10 4:57 
GeneralRe: Maybe old wine in new sacs [modified] Pin
johannesnestler7-Jul-10 3:20
memberjohannesnestler7-Jul-10 3:20 
GeneralRe: Maybe old wine in new sacs Pin
johannesnestler7-Jul-10 3:29
memberjohannesnestler7-Jul-10 3:29 

General General    News News    Suggestion Suggestion    Question Question    Bug Bug    Answer Answer    Joke Joke    Rant Rant    Admin Admin   

Use Ctrl+Left/Right to switch messages, Ctrl+Up/Down to switch threads, Ctrl+Shift+Left/Right to switch pages.

| Advertise | Privacy | Terms of Use | Mobile
Web01 | 2.8.150819.1 | Last Updated 2 Jul 2010
Article Copyright 2010 by Mattia Baldinger
Everything else Copyright © CodeProject, 1999-2015
Layout: fixed | fluid