VB.NET best way to check if index is out of bounds in array

I should clarify, I'm having a strange issue with this piece of a function that uses an array of a custom structure:

For x = 1 To UBound(PrivateMessageQ)
  PMQt = PrivateMessageQ(x)
  ...
Next

I'm getting the first chance exception in the line: PMQt = PrivateMessageQ(x)

This function is in a shared module & is being called by other threads... I believe that something is happening simultaneously & changing the array size before the loop has completed.

Does this sound right? Is there a way to lock functions like this until they are completed so I can avoid this?

Oops, the function is in a Class that is used multiple times however the "PrivateMessageQ" array is a public array...

"Is there a way to lock functions like this until they are completed so I can avoid this?"

Use SyncLock...you need an Object that all threads can access:

    Public Class Sync
        Public Shared SyncObject As New Object
    End Class

Then you utitlize it like this:

    SyncLock Sync.SyncObject
        For x = 1 To UBound(PrivateMessageQ)
            PMQt = PrivateMessageQ(x)
            ...
        Next
    End SyncLock

ahhhh ok that makes sense, what about if i have some type of Try Catch exception or Exit Sub / Exit Function in the code...

Do I need to call End SyncLock in this event as well?

Example:

Public Sub Something()
    SyncLock Sync.SyncObject

    Try
            For x = 1 To UBound(PrivateMessageQ)
                PMQt = PrivateMessageQ(x)
                ...
            Next
    Catch
           Debug.Writeline("error")
           End SyncLock
    End Try

    End SyncLock
End Sub

or

Public Sub Something()
    SyncLock Sync.SyncObject

            For x = 1 To UBound(PrivateMessageQ)
                PMQt = PrivateMessageQ(x)

                If a = b Then
                    End SyncLock
                    Exit Sub
                End If
            Next

    End SyncLock
End Sub

yeah, it looks like i can't

thanks for the help, its working smoothly so far!