multiple threads selecting the same listbox item

[jmcilhinney]

Put the objects into a queue first and then let each thread dequeue an item to use. If you were using .NET 4.0 or later, the obvious choice would be the ConcurrentQueue(Of T), which is inherently thread-safe. As you're using .NET 3.5 or earlier, you should use a Queue(Of T) and synchronise the dequeuing yourself, e.g.

Private ReadOnly items As New Queue(Of Object)

Private ReadOnly syncRoot As New Object

Private Function GetNextItem() As Object
    SyncLock syncRoot
        Return items.Dequeue()
    End SyncLock
End Function