Asp.net Vb.net , access control concurrency - asp.net

Question

Hello guys I am trying to make restriction on my WebApp that runs on VB.net with framework Asp.net. In another words, how can I Control the permitted number of sessions.
The WebApp works perfectly and now I want to add "How many users can access the WebApp" if Number of users "Sessions" exceeded the new coming users will be redirected to a site.
I have been working on this for few weeks... tried Cookies and Seasons and neither is working
Scenario: Maximum users can access the WebApp is 1
when I launch the second Browser and start new session the UserNumber will be incremented by 1 hence will be redirected to "ServerBusy" page...
However, If the second Browser opened new tab and accessed the WebApp that will bypass the Condition at Session_Start and will access the WebApp .
Thank you.
here is the Code
Imports System.Web
Public Class Global_asax
Inherits System.Web.HttpApplication
Public Shared maxUsersAllowance As Integer = 1 'Total number of users can enter the server
Public Shared UserNumber As Integer = 0 ' the current number of users
Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
' Fires when the application is started
End Sub
Sub Session_Start(ByVal sender As Object, ByVal e As EventArgs)
UserNumber = UserNumber + 1
Dim myCookie As New HttpCookie("UserNumber")
Dim myCookie2 As New HttpCookie("Access")
myCookie.Value = UserNumber
myCookie2.Value = True
Response.Cookies.Add(myCookie)
Response.Cookies.Add(myCookie2)
If (Request.Cookies("UserNumber") IsNot Nothing) Then
If (Request.Cookies("UserNumber").Value > 1) Then
If (Request.Cookies("Access").Value) Then
Response.Redirect("~/ServerBusy.aspx")
End If
End If
End If
End Sub
Sub Application_BeginRequest(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Sub Application_AuthenticateRequest(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Sub Application_Error(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Sub Session_End(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Sub Application_End(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Sub Application_Init(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Sub Application_Dispose(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Sub Application_Unload(ByVal sender As Object, ByVal e As EventArgs)
End Sub
End Class
After Reading Article https://stackoverflow.com/a/6218525/1260204 and Updating the code, the Issue still exist which is that the User Can get into the WebApp if he open new Tab on the browser and connected
Imports System.Web
Public Class Global_asax
Inherits System.Web.HttpApplication
Sub Application_Start(ByVal sender As Object, ByVal e As EventArgs)
' Fires when the application is started
Application("ActiveSessions") = 0
End Sub
Sub Session_Start(ByVal sender As Object, ByVal e As EventArgs)
Try
Application.Lock()
Dim activeSessions As Integer = CInt(Application("ActiveSessions")) + 1
Dim allowedSessions As Integer = 1
' retrieve the threshold here instead
Application("ActiveSessions") = activeSessions
If activeSessions > allowedSessions Then
System.Web.HttpContext.Current.Response.Redirect("~/ServerBusy.aspx", False)
End If
Finally
Application.UnLock()
End Try
End Sub
Sub Application_BeginRequest(ByVal sender As Object, ByVal e As EventArgs)
Dim LiveSessionsCount As Integer = CInt(Application("LiveSessionsCount"))
End Sub
Sub Application_AuthenticateRequest(ByVal sender As Object, ByVal e As EventArgs)
End Sub
Sub Session_End(ByVal sender As Object, ByVal e As EventArgs)
Application.Lock()
Application("ActiveSessions") = CInt(Application("ActiveSessions")) - 1
Application.UnLock()
End Sub
End Class
Update, I have solved the Issue with the Tabs. by adding
Session.Abandon()
In my redirected page. However that is half solution as far as i can get to... the other half is , if the user closes his browser by the X , I do need to wait 20 minutes until the session ends ... is there a away to terminate the session once the user exit/kill the page?