addlistener in legacy based interface

Is it not possible to use 'addlistener' in legacy based programming style? lh = addlistener(Hsource,'EventName',callback) What is 'HSource'? I want to excecute a callback function every 1sec when the data available in the input card exceeds say'5000' points.

[Jan]

What is "legacy based programming style"? What exactly does "data available" mean? When you are talking of a serial connection, a simple callback might be easier.

[jenni]

I am talking about the session based & legacy based interface in data acquisition.I want a function to be called every second when the input data collected by the data acquisition card exceeds some fixed pointsin legacy interface programming.'addlistener' calls a function when 'data available' event occurs. But i dont know its exact usage like what Hsource' means.