Private Sub New()

End Sub

Imports System.Threading

Imports System.Data.SqlClient

Private ConnectionCounter As Integer

Private ConnectionString As String

Private Shared CMS As Hashtable = New Hashtable

Private Sub New()

    ConnectionCounter = 0

    ConnectionString = _

          "server=Server;database=DB;uid=UID;pwd=PWD"

End Sub

Public Shared ReadOnly Property Instance() As ConnectionManager

    Get

       If (Not CMS.Contains(Thread.CurrentThread)) Then

           CMS.Add(Thread.CurrentThread, New ConnectionManager)

       End If

       Return CType(CMS(Thread.CurrentThread), ConnectionManager)

    End Get

End Property

Public Function GetConnection() As SqlConnection

    ConnectionCounter += 1

    If (ConnectionCounter = 1) Then

        Connection = New SqlConnection(ConnectionString)

        Connection.Open()

    End If

    Return Connection

End Function

Public Function ReleaseConnection() As SqlConnection

    ConnectionCounter -= 1

    If (ConnectionCounter = 0) Then

        Connection.Close()

        Connection = Nothing

    End If

End Function

ConnectionManager.Instance.GetConnection()

ConnectionManager.Instance.ReleaseConnection()