; Check if the script is already running
; Note: The recommended approach is to use _Singleton from Misc.au3

#include <MsgBoxConstants.au3>

Local $sMyAutoItTitle = "ThisIsSomeUniqueStringThatOtherWindowsWontHave"

If WinExists($sMyAutoItTitle) Then
    ; The script is already running

    MsgBox($MB_SYSTEMMODAL, Default, "The script is already running." & @CRLF & @CRLF & _
            "It's PID is: " & WinGetProcess($sMyAutoItTitle))
Else
    ; This is the first instance of the script.

    ; Set the autoit window title
    AutoItWinSetTitle($sMyAutoItTitle)

    ; Run this script again.
    If @Compiled Then
        Run('"' & @ScriptFullPath & '"')
    Else
        Run('"' & @AutoItExe & '" "' & @ScriptFullPath & '"')
    EndIf

    MsgBox($MB_SYSTEMMODAL, Default, "This is the first instance." & @CRLF & @CRLF & _
            "My PID is: " & @AutoItPID)
EndIf

#include <GUIConstantsEx.au3>

Example()

Func Example()
    ; Set the title of the AutoIt Hidden Window.
    AutoItWinSetTitle("My AutoIt Window")

    ; Display AutoIt's Hidden Window.
    AutoItWinShow()

    While 1
        Switch GUIGetMsg()
            Case $GUI_EVENT_CLOSE
                ExitLoop
        EndSwitch
    WEnd
EndFunc   ;==>Example

; Display AutoIt's Hidden Window. Returns the handle of the window.
Func AutoItWinShow()
    Local $hWnd = WinGetHandle(AutoItWinGetTitle()) ; Get the handle of the AutoIt Hidden Window by finding out the title of the AutoIt Hidden Window.
    WinMove($hWnd, "", (@DesktopWidth / 2) - 250, (@DesktopHeight / 2) - 250, 500, 500) ; Move the AutoIt Hidden Window and re-size for a better view.
    WinSetState($hWnd, "", @SW_SHOW) ; Show the AutoIt Hidden Window, normally this is hidden, but in the interest of this example I"m displaying it.
    Return $hWnd
EndFunc   ;==>AutoItWinShow