VB InvokeRequired doesn't appear to detect different threads - vb.net

Question

I have a logging function that get called from different threads. The logging function uses InvokeRequired to determine if the caller is in the same thread as the textbox was created in. If all the code is put into the same class it works fine. But when separated out InvokeRequired always returns false.
Imports System.Threading
Public Class Test_Main
Dim tt_object As Test_Thread = Test_Thread.Get_Test_Thread_Class()
Private Shared logger_lock As New Object
Delegate Sub WriteLogMessage_Callback(text As String)
Private Sub btn_start_Click(sender As Object, e As EventArgs) Handles btn_start.Click
WriteLogMessage("From - btn_start_Click")
tt_object.Start_Threads()
End Sub
Public Sub WriteLogMessage(ByVal message As String)
If (Me.InvokeRequired) Then
Dim d As New WriteLogMessage_Callback(AddressOf WriteLogMessage)
Me.Invoke(d, New Object() {[message]})
Else
SyncLock logger_lock
log_box.Text += System.DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff") & " " & message & vbCrLf
log_box.SelectionStart = log_box.Text.Length
log_box.ScrollToCaret()
End SyncLock
End If
Application.DoEvents()
End Sub
End Class
Public Class Test_Thread
Private Shared _thisInstance As Test_Thread = Nothing
Private t_1 As Thread
Private t_2 As Thread
Protected Sub New() 'Class constructor
t_1 = New Thread(AddressOf Thread_1)
t_2 = New Thread(AddressOf Thread_2)
End Sub
Public Shared Function Get_Test_Thread_Class() As Test_Thread
If _thisInstance Is Nothing Then 'Initialize object if it hasn't laready been done
_thisInstance = New Test_Thread()
End If
Return _thisInstance 'Return the object instance
End Function
Public Sub Start_Threads()
Dim counter As Integer = 0
Test_Main.WriteLogMessage("BEGIN - Start_Threads")
t_1.Start()
t_2.Start()
Do While counter < 50
Application.DoEvents()
Thread.Sleep(500)
counter += 1
Loop
t_1.Abort()
t_2.Abort()
Test_Main.WriteLogMessage("END - Start_Threads")
End Sub
Public Sub Thread_1()
Dim counter As Integer = 0
Test_Main.WriteLogMessage("BEGIN - Thread_1")
Do While True
Test_Main.WriteLogMessage("Thread_1: " & counter)
counter += 1
Thread.Sleep(1000)
Loop
End Sub
Public Sub Thread_2()
Dim counter As Integer = 0
Test_Main.WriteLogMessage("BEGIN - Thread_2")
Do While True
Test_Main.WriteLogMessage("Thread_2: " & counter)
counter += 1
Thread.Sleep(1500)
Loop
End Sub
End Class

Answer 1

I solve it with the following code! Thanks for all the help.
Imports System.Threading
Public Class Test_Main
Private Sub btn_start_Click(sender As Object, e As EventArgs) Handles btn_start.Click
Dim log_object As Logger = Logger.Get_Logger_Class(log_box)
Dim tt_object As Test_Thread = Test_Thread.Get_Test_Thread_Class(log_object)
log_object.WriteLogMessage("From - btn_start_Click")
tt_object.Start_Threads()
End Sub
End Class
Public Class Logger
Private Shared _thisInstance As Logger = Nothing
Private log_box As TextBox
Delegate Sub WriteLogMessage_Callback(text As String)
Private Shared logger_lock As New Object
Public Shared Function Get_Logger_Class(log_box_addr As TextBox) As Logger
If _thisInstance Is Nothing Then 'Initialize object if it hasn't laready been done
_thisInstance = New Logger()
_thisInstance.log_box = log_box_addr
End If
Return _thisInstance 'Return the object instance
End Function
Public Sub WriteLogMessage(ByVal message As String)
If (log_box.InvokeRequired) Then
Dim d As New WriteLogMessage_Callback(AddressOf WriteLogMessage)
log_box.Invoke(d, New Object() {[message]})
Else
SyncLock logger_lock
Me.log_box.Text += System.DateTime.Now.ToString("yyyy/MM/dd HH:mm:ss.fff") & " " & message & vbCrLf
Me.log_box.SelectionStart = log_box.Text.Length
Me.log_box.ScrollToCaret()
End SyncLock
End If
Application.DoEvents()
End Sub
End Class
Public Class Test_Thread
Private Shared _thisInstance As Test_Thread = Nothing
Private log_addr As Logger
Public t_1 As Thread
Public t_2 As Thread
Protected Sub New() 'Class constructor
t_1 = New Thread(AddressOf Thread_1)
t_2 = New Thread(AddressOf Thread_2)
End Sub
Public Shared Function Get_Test_Thread_Class(logger_addr As Logger) As Test_Thread
If _thisInstance Is Nothing Then 'Initialize object if it hasn't laready been done
_thisInstance = New Test_Thread()
_thisInstance.log_addr = logger_addr
End If
Return _thisInstance 'Return the object instance
End Function
Public Sub Start_Threads()
Dim counter As Integer = 0
log_addr.WriteLogMessage("BEGIN - Start_Threads")
t_1.Start()
t_2.Start()
Do While counter < 50
Application.DoEvents()
Thread.Sleep(500)
counter += 1
Loop
t_1.Abort()
t_2.Abort()
log_addr.WriteLogMessage("END - Start_Threads")
End Sub
Public Sub Thread_1()
Dim counter As Integer = 0
log_addr.WriteLogMessage("BEGIN - Thread_1")
Do While True
log_addr.WriteLogMessage("Thread_1: " & counter)
counter += 1
Thread.Sleep(1000)
Loop
End Sub
Public Sub Thread_2()
Dim counter As Integer = 0
log_addr.WriteLogMessage("BEGIN - Thread_2")
Do While True
log_addr.WriteLogMessage("Thread_2: " & counter)
counter += 1
Thread.Sleep(1500)
Loop
End Sub
End Class