What are the real world applications of the singleton pattern?

Question

Duplicate

On design patterns: When should I use the singleton?

class Singleton
{
    private static Singleton instance;

    private Singleton() {}

             


        

Answer 1

Assuming your question is in the title:

I once worked with a COM object that could only have one instance per server. We exposed it to the entire ASP.NET application through a singleton.

Answer 2

This is not a singleton as a singleton provides the thread safety with readonly keywords.

For example,

public sealed class Singleton
{
    // private static Singleton instance; (instead of this, it should be like this, see below)
    private static readonly Singleton instance = new Singleton();

    static Singleton(){}

    private Singleton() {}

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

By using this it will provide the tread safety and proper singleton pattern (that is how it is different from a static class). Your code for the singleton were not thread safe.

For more about singleton, check these links:

• http://csharpindepth.com/articles/general/singleton.aspx
• http://aspalliance.com/70_Session_Based_Singleton_Object

Answer 3

In my project we created a logger component which is getting used for logging in the application to different sources (e.g. text file, XML, and database, based on configurations). So there is a log manager which creates the only one instance of the logger class across the application for logging the message, errors, etc.

Answer 4

You should use a Singleton when there should only be one instance of an object. However, Misko Hevery has some thoughts on why Singletons are bad!