Hello,

yes the callback's are queued .. they come in over the windows messaging system ..

here's a small async sample with the help of a timer object ..

&& server objects (compile into COM-Exe)

DEFINE CLASS oTestServer AS Session OLEPUBLIC

    loCallback = .NULL. && saves reference to callback object
    lAdvised = .F. && is callbackobject set?
    HIDDEN loTimer
		
    FUNCTION Init
	DECLARE INTEGER Sleep IN WIN32API INTEGER		
	THIS.loTimer = CREATEOBJECT('dirTimer',THIS)
    ENDFUNC

    FUNCTION Destroy
	THIS.loTimer = NULL
	CLEAR DLLS	
   ENDFUNC

   FUNCTION FireEvent AS VOID
      LPARAMETERS lcSomeValue
      IF THIS.lAdvised
         THIS.loCallBack.EventMethod(lcSomeValue)
      ENDIF
   ENDFUNC

   FUNCTION Advise AS VOID
      LPARAMETERS loObj
      THIS.loCallback = loObj
      THIS.lAdvised = .T.
   ENDFUNC

   FUNCTION UnAdvise AS VOID
      THIS.loCallback = .NULL.
      THIS.lAdvised = .F.
   ENDFUNC

   FUNCTION SomeMethodThatFiresEvents AS Boolean
        && prepare something
        THIS.FireEvent('Task startet .. ')
        Sleep(5000)
        THIS.FireEvent('Task finished X percent ..')
        Sleep(5000)
        && do more
        THIS.FireEvent('Task fineshied XX percent ..')
        && ..
    ENDFUNC
    
    FUNCTION DoSomeAsynWork AS Boolean
    	THIS.loTimer.Interval = 1
	RETURN .T.
    ENDFUNC

ENDDEFINE

DEFINE CLASS dirTimer AS Timer

	Interval = 0
	loParent = NULL
	
	FUNCTION Init
		LPARAMETERS loObj
		THIS.loParent = loObj
	ENDFUNC
	
	FUNCTION Destroy
		THIS.loParent = NULL
	ENDFUNC
	
	FUNCTION Timer
		THIS.Interval = 0
                && do some work
                Sleep(1000) && sleep to simulate some work ..
		THIS.loParent.FireEvent('Timer Fired')
	ENDFUNC

ENDDEFINE

&& client testprogram
startprocess.prg:

PUBLIC loFoxServer, loEventhandler

loFoxServer = CREATEOBJECT('testcom1.oTestServer')
loEventHandler = CREATEOBJECT('oTestCallback')

loFoxServer.Advise(loEventHandler)

DEFINE CLASS oTestCallback AS Session OLEPUBLIC

    FUNCTION EventMethod
        LPARAMETERS lcSomeParam
        ? lcSomeParam
    ENDFUNC

ENDDEFINE

startasyn.prg:

?loFoxServer.DoSomeAsynWork() && returns immediately .. 

&& simulate block situation
DECLARE INTEGER Sleep IN WIN32API INTEGER
Sleep(15000) && the event of ther server is fired when this runs


endprocess.prg:

loFoxServer.Unadvise()
loFoxServer = NULL
loEventhandler = NULL

Regards

Christian