how to write async function

Question

what i need to learn for it?

Answer 1

Without knowing more about your specific requirement I would consider the notifications facilities available with Cocoa

Answer 2

As ennuikiller point out, you need to provide more information about what kind of async function do you want, its hard to give you more info.

A common async function will be the callback functions in javascript, for example in mootools javascript:

window.addEvent('domready', function() {
   alert("ready to rock");
});

Here you attach a function to the DOM ready event, its async because the function will only execute when the DOM is ready, not like conventional procedure function - execute expressions line after another line(it doesn't need to wait).

A pretty good slide about non-blocking:

http://www.slideshare.net/simon/evented-io-based-web-servers-explained-using-bunnies

If you want to write async function in python, there is framework called twisted which help you write async(non-blocking) functions, for ruby, there is eventmachine framework. If you want to write non-blocking/async on server side there is node.js.