SnowMaker .Net library for Azure

Question

I am using the above library in my vb.net web app. The person who developed snowmaker said that you shouldn't create a new instance every time you want an ID, you should use a basic singleton.

I know what singletons are, but have never used them. I have come across this on stack overflow

Public NotInheritable Class MySingleton
    Private Shared ReadOnly _instance As New Lazy(Of MySingleton)(Function() New
        MySingleton(), System.Threading.LazyThreadSafetyMode.ExecutionAndPublication)

    Private Sub New()
    End Sub

    Public Shared ReadOnly Property Instance() As MySingleton
        Get
            Return _instance.Value
        End Get
    End Property
End Class

Here is the code I'm using to generate the ID's

Dim storageAccount As CloudStorageAccount = CloudStorageAccount.Parse(ConfigurationManager.ConnectionStrings("blobStorage").ConnectionString)
Dim ds As New BlobOptimisticDataStore(storageAccount, "container-name")

Dim generator = New UniqueIdGenerator(ds)
Dim ret = generator.NextId(table)

which works, but how do I incorporate that into the singleton class so that I only call it once from my web app?

Answer 1

A singleton is a static object that you can call as many times as you want and be assured that it will only run one call at a time.

You don't instantiate a singleton, it is like a class level or global object that you just call. You havent included the code for UniqueIdGenerator, but your code might look something like this:

Imports SnowMaker
Imports Microsoft.WindowsAzure.Storage

Module Module1

    Sub Main()
        Dim storageAccount = CloudStorageAccount.Parse("xxxxxxxxxxxxxxxxxxxxxxxxxxxxx")
        Dim ds As New BlobOptimisticDataStore(storageAccount, "vhds")

        MySingleton.Instance.DataSource = ds
        MySingleton.Instance.Table = "table"
        Dim myid = MySingleton.Instance.NextId
        Dim myid2 = MySingleton.Instance.NextId
        Dim myid3 = MySingleton.Instance.NextId
        Dim myid4 = MySingleton.Instance.NextId

    End Sub

End Module

Then your singleton code would call your generator

Imports SnowMaker

Public NotInheritable Class MySingleton
    Private Shared ReadOnly _instance = New Lazy(Of MySingleton)(Function() New MySingleton(), System.Threading.LazyThreadSafetyMode.ExecutionAndPublication)
    Private _generator As UniqueIdGenerator

    Private Sub New()
    End Sub

    Public Shared ReadOnly Property Instance() As MySingleton
        Get
            Return _instance.Value
        End Get
    End Property

    Private _ds As BlobOptimisticDataStore
    Public Property DataSource() As BlobOptimisticDataStore
        Get
            Return _ds
        End Get
        Set(ByVal value As BlobOptimisticDataStore)
            _ds = value
        End Set
    End Property

    Private _tableName As String
    Public Property Table() As String
        Get
            Return _tableName
        End Get
        Set(ByVal value As String)
            _tableName = value
        End Set
    End Property

    Private _Id As Integer
    Public ReadOnly Property NextId() As Integer
        Get
            If _generator Is Nothing Then
                _generator = New UniqueIdGenerator(_ds)
            End If
            Return _generator.NextId(_tableName)
        End Get
    End Property

End Class