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I am creating a Windows Service in VB.NET that will loop over a set of functions indefinitely, so threading is necessary. You can't just run your loop in OnStart(); it has to return to the Service Controller.

My program completely crashes after New DataContext with no exceptions or anything.

I have removed a lot of code that seems irrelevant to me, so that you can see the main problem code better. I have removed all Try blocks and changed my Meter types to Object types, so you can copy and paste mostly working code.

I know this is a problem with DataContext and threading that I don't understand. Here's a summary of MultiThreading and DataContext concerns. What specifically am I doing wrong? 

Public Class Molly
    Dim stopping As Boolean = False
    Dim stoppedEvent As Threading.ManualResetEvent

    Protected Overrides Sub OnStart(ByVal args() As String)

        'vv~~~~ If these two are uncommented, my code fails at an indeterminate place AFTER the New ConfigInterpreter below.
        'Dim Example1 As New LocalDBDataContext
        'Dim Example2 As New ConfigInterpreter

        Threading.ThreadPool.QueueUserWorkItem(New Threading.WaitCallback(AddressOf ThreadWorker))
    End Sub

    Protected Overrides Sub OnStop()
        stopping = True
        stoppedEvent.WaitOne()
    End Sub

    Private Sub ThreadWorker()
        Dim MyCI As New ConfigInterpreter '<~~~~ 'My program fails here every time, 
                                                 'unless the two lines above are uncommented,
                                                 'then it fails at a random point after this.

        Dim ListOfMeters as List(Of Meter) = MyCI.CompileListOfMeters()

        While stopping = False
                For Each mtr In ListOfMeters()
                    mtr.Read()
                Next

                Threading.Thread.Sleep(My.Settings.CheckIntervalMS)
        End While

        stoppedEvent.Set()
    End Sub
End Class 'Molly

Public Class ConfigInterpreter
    Public Sub New()
        Try

            Dim LocalDB As New LocalDBDataContext '<~~~~~~~ My program typically crashes here.

        Catch ex As Exception '<~~~~ No exception is thrown.

        End Try
    End Sub

    Public Function CompileListOfMeters() As List(Of Object)
        Dim LocalDB As New LocalDBDataContext
        Dim qMeters As IQueryable(Of tblMeter) = From ff In LocalDB.tblMeters
                                             Select ff

        Dim ReturnList As New List(Of Object) 
        For Each mtr In qMeters
            ReturnList.Add(mtr)
        Next

        Return ReturnList
    End Function
End Class 'ConfigInterpreter
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  • Check if it works if you have just one global dbDataContext that you are reusing. – Archlight Jul 23 '14 at 07:01
  • If there are no exceptions, how do you know it "crashes"? Have you tried attaching the debugger and stepping through it? Is there anything in the Windows Application Event Log? – Chris Dunaway Jul 23 '14 at 14:24
  • @Archlight I rewrote it so that a single `LocalDB` is being passed through `New()`'s parameters. Now it makes it as far as the `ForEach` line in `CompileListOfMeters()`. When I hover over `qMeters`, it says _Type Molly.tblMeter is not defined_. I have deleted and re-inserted all the table into the .dbml, so I know my schemas match up. – Z_AHK Jul 23 '14 at 16:05

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