PHP debugging or performance Hook

Question

In an interpreted language like PHP it is possible in theory to set up some sort of callback function that would be run indiscriminately after every line of code. I am wondering if such a thing exists in PHP or if such a thing could be accomplished in any way? Such a feature could be useful for diagnostics or performance tests. Does anyone know of such a mechanism in PHP?

Answer 1

http://php.net/manual/en/function.register-tick-function.php

Answer 2

I am not that familiar with that but you can check out zend-studio and xdebug