SQL Queries and Threading - mysql

Question

I have to execute several SQL queries and I want to use Threads for this, because this queries have to be executed every 1 second to update or get some different values of the database.
When I try to execute my code, I get the following Error:
WindowsApplication1.vshost.exe Error: 0 : There is already an open
DataReader associated with this Connection which must be closed first.
I have read on stackoverflow, that the Connection should ALWAYS be opened as late as possible and be closed as fast as possible.
Is there any solution for this Problem?
Here is my code:
Imports MySql.Data.MySqlClient
Imports System.Threading
Public Class Form1
Private server As String = Nothing
Private pass As String = Nothing
Private user As String = Nothing
Private port As String = Nothing
Private db As String = Nothing
Dim Thread1 As Thread
Dim Thread2 As Thread
Dim con As New MySqlConnection
Dim cmd As New MySqlCommand
Dim reader As MySqlDataReader
Public Sub New()
Me.server = "localhost"
Me.user = "root"
Me.pass = ""
Me.port = "3306"
Me.db = "diagnosedb"
cmd.Connection = con
con.ConnectionString = "Server = " & Me.server & ";
Port = " & Me.port & ";
Database = " & Me.db & ";
Uid = " & Me.user & ";
Pwd = " & Me.pass & ";"
Thread1 = New Thread(AddressOf Querie1)
Thread2 = New Thread(AddressOf Querie2)
Thread1.Start()
Thread2.Start()
End Sub
Private Sub Querie1()
cmd.CommandText = "UPDATE teileliste
SET verschleis = 500
WHERE ID = 1;"
Try
con.Open()
cmd.ExecuteNonQuery()
Catch ex As Exception
MsgBox(ex.Message)
Finally
con.Close()
End Try
End Sub
Private Sub Querie2()
cmd.CommandText = "UPDATE teileliste
SET verschleis = 0
WHERE ID = 20;"
Try
con.Open()
cmd.ExecuteNonQuery()
Catch ex As Exception
MsgBox(ex.Message)
Finally
con.Close()
End Try
End Sub
End Class

Answer 1

Create and close a new connection within the Querie1 and Querie2 methods. You can't have multiple concurrent operations going on with one connection. (Even if you could, you're closing the connection in both methods. One method might try to close it while the other is using it.)
The .NET Framework is good at managing connections. While you're opening and closing them in your code, behind the scenes it's actually keeping connections open for a brief period. This is called thread pooling. When you close a connection, it's actually kept open temporarily. When you open a new connection, it might actually give you the same one.
Most of the time we don't need to pay attention to that. All we do is create a new connection as close as possible to when we're going to open and use it, and then close (dispose) it as soon as possible.