[RESOLVED] Threading best practices...help!

[BigPhil]

Hello everyone! I have a couple of questions about some threading best practices. Here is some of the code I have written that spawns some threadpool threads and each threadpool thread opens a log file on processes it (still dont know if its any faster than a single thread at this point) >

Imports System.IO
Imports System.Data.SqlClient
Imports System.Threading

Public Class Form1
    Dim SqlDataConn As New SqlClient.SqlConnection(My.Settings.SqlDataConn)
    Dim CustomSql As New SqlDataRetrieve.SqlReadOrChange
    Dim LogsScanned, MaxThreads, PlaceHolder, AvailableThreads As Integer
    Dim TempLogsDir As String = "TempLogs"
    Dim SqlLock As New Object

    Private Sub ButtonReadLogs_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ButtonReadLogs.Click
        WriteToLogFile(Now.ToString() + " -Process started")
        SqlDataConn.Open()
        My.Computer.FileSystem.CreateDirectory(TempLogsDir)
        For Each LogFile As String In My.Computer.FileSystem.GetFiles(Me.TextBoxLogPath.Text, FileIO.SearchOption.SearchTopLevelOnly)
            Dim LogFileInfo As New FileInfo(LogFile)
            If Not My.Computer.FileSystem.FileExists(TempLogsDir + "\" + LogFileInfo.Name) Then
                My.Computer.FileSystem.CopyFile(LogFile, TempLogsDir + "\" + LogFileInfo.Name)
            End If
            LogFile = Nothing
            LogFileInfo = Nothing
        Next LogFile

        For Each CopiedLogFile In My.Computer.FileSystem.GetFiles(TempLogsDir)
            ThreadPool.QueueUserWorkItem(New WaitCallback(AddressOf ReadLogFile), CopiedLogFile)
            LogsScanned += 1
            CopiedLogFile = Nothing
        Next CopiedLogFile

        ThreadPool.GetMaxThreads(MaxThreads, PlaceHolder)
        ThreadPool.GetAvailableThreads(AvailableThreads, PlaceHolder)
        Do While MaxThreads <> AvailableThreads
            ThreadPool.GetMaxThreads(MaxThreads, PlaceHolder)
            ThreadPool.GetAvailableThreads(AvailableThreads, PlaceHolder)
            Thread.Sleep(5000)
        Loop
        WriteToLogFile(Now.ToString() + " -Process Finished")
        MessageBox.Show("Finished!")
    End Sub

    Private Sub ReadLogFile(ByVal state As Object)
        Dim LogFilePath As String = DirectCast(state, String)
        Dim MyCommand As New SqlCommand
        Dim oRead As System.IO.StreamReader
        Try
            oRead = File.OpenText(LogFilePath)
            While oRead.Peek <> -1
                Try
                    Dim LogFileLine As String = oRead.ReadLine.Replace("'", "`")
                    If Not LogFileLine.StartsWith("#") Then
                        If Not LogFileLine.Contains("EVJournaling") Then
                            LogFileLine = LogFileLine.Replace(",", "','")
                            LogFileLine = LogFileLine.Insert(0, "'")
                            LogFileLine = LogFileLine + "'"
                            MyCommand.CommandText = ("sp_InsertMailEvent " + LogFileLine)
                            SyncLock SqlLock
                                CustomSql.InsertUpdateDelete(SqlDataConn, MyCommand)
                            End SyncLock
                            LogFileLine = String.Empty
                            MyCommand.CommandText = String.Empty
                        Else
                            LogFileLine = String.Empty
                        End If

                    End If
                Catch ex As Exception

                End Try
            End While
            oRead.Close()
            oRead.Dispose()
        Catch ex As Exception
         
        End Try
        MyCommand.Dispose()
        LogFilePath = Nothing
        state = Nothing
    End Sub

    Private Sub WriteToLogFile(ByVal Text As String)
       File.AppendAllText("ExchangeServerMT_" & DateString & ".log", Text & ControlChars.CrLf)
        Text = Nothing
       End Sub

End Class

Here is the code in the CustomSql library >

Imports System.Data.SqlClient

Public NotInheritable Class SqlReadOrChange

    ''' <summary>
    ''' Connects to a SQL database, executes a SqlCommand, and returns the number of rows affected.
    ''' </summary>
    ''' <param name="MyConnection">The connection used to open the SQL Server database</param>
    ''' <param name="MyCommand">The SqlCommand to run against the connection</param>
    ''' <param name="KeepConnectionOpen">Determines whether or not to keep the connection to the database open. Default is True.</param>
    ''' <remarks></remarks>
    Public Function InsertUpdateDelete(ByRef MyConnection As SqlConnection, ByVal MyCommand As SqlCommand, Optional ByVal KeepConnectionOpen As Boolean = True) As Integer
        Try
            MyCommand.Connection = MyConnection
            If MyConnection.State <> ConnectionState.Open Then
                MyConnection.Open()
            End If
            InsertUpdateDelete = MyCommand.ExecuteNonQuery()
            If KeepConnectionOpen = False Then
                If MyConnection.State <> ConnectionState.Closed Then
                    MyConnection.Close()
                End If
            End If
        Catch ex As Exception
            InsertUpdateDelete = Nothing
        End Try
        MyCommand.Dispose()
    End Function
End Class

My question is this; Is it necessary to use some sort of synchronizing (ie: im using SyncLock in the ReadLogFile sub) when making the insert call into the CustomSql class? If I dont use it, I get some strange NullException errors in the CustomSql class. I'm still a bit confused on WHEN I should use some sort of synchronizing when working with multi threading. Like when each threadpool thread gets called, does each one keep track of all its own variables in the ReadLogFile sub, so there is no contamination of values between the threads? I understand the simple use of synchronizing like this article multithreading, but would like some more help understanding using it in more complicated code. Thanks in advance for any help you can give me!