Waiting until threads finish before executing next step - vb.net

Question

I, at most, have two threads running at any single time. How do I wait for these threads to finish before executing my next step?
If I don't wait for them, I get a NullReferenceException when I check the values because they haven't been set yet due to the threads still running.

Answer 1

I would go with the Async / Await pattern on this. It gives you excellent flow control and won't lock up your UI.
Here is a great example from MSDN:
Public Class Form1
Public Async Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
Dim tasks As New List(Of Task)()
tasks.Add(Task.Run(addressof Task1))
tasks.Add(Task.Run(addressof Task2))
Await Task.WhenAll(tasks)
MsgBox("Done!")
End Sub
Private Async Function Task1() As Task 'Takes 5 seconds to complete
'Do some long running operating here. Task.Delay simulates the work, don't use it in your real code
Await Task.Delay(5000)
End Function
Private Async Function Task2() As Task 'Takes 10 seconds to complete
'Do some long running operating here. Task.Delay simulates the work, don't use it in your real code
Await Task.Delay(10000)
End Function
End Class
The basic idea is to create an array of Task (these can point to functions that return Task also). This queues up the "threads" wrapped in task objects that get run when you call Task.WhenAll, which will execute all the tasks in the array and continue after they all complete. Code after that will run once every tasks completes, but it won't block the UI thread.

Answer 2

If you call join the main Thread will be wait that the other thread finished. I think the code bellow will be good to understand the idea.
Sub Main()
thread = New System.Threading.Thread(AddressOf countup)
thread.Start()
thread2 = New System.Threading.Thread(AddressOf countup2)
thread2.Start()
thread.Join() 'wait thread to finish
thread2.Join() 'wait thread2 to finish
Console.WriteLine("All finished ")
Console.ReadKey()
End Sub
See the links:
General;
WinForms