Thread-Safe Lazy Singleton Implementation in .NET 4
It has been a while since I needed to develop a singleton in .NET, and now that I am working in .NET 4, I thought it was a good time to revisit the implementation and take advantage of new language features.
So without much fanfare, here it is:
1Public NotInheritable Class MySingleton
2
3#Region " Thread-Safe Lazy Singleton "
4
5 Private Shared _instance As Lazy(Of MySingleton) = New Lazy(Of MySingleton)(Function() New MySingleton())
6
7 ''' <summary>
8 ''' Hide the constructor
9 ''' </summary>
10 ''' <remarks></remarks>
11 Private Sub New()
12 ' nothing to do
13 End Sub
14
15 ''' <summary>
16 ''' Singleton instance
17 ''' </summary>
18 ''' <value></value>
19 ''' <returns></returns>
20 ''' <remarks></remarks>
21 Public Shared ReadOnly Property Instance As MySingleton
22 Get
23 Return _instance.Value
24 End Get
25 End Property
26
27#End Region
28
29End Class
The .NET 4 Lazy class by default ensures that the singleton is thread-safe.
If you use the Lazy class and do not pass in any parameters, it will construct the type automatically for you… which means that the class must have a public constructor method with no parameters. By passing a value factory delegate into the constructor of the Lazy class, we can keep our constructor private and thereby force others to use our Instance property and truly make a Singleton.