The following are examples of the results of running php_who.d.
Tracing... Hit Ctrl-C to end.
^C
PID UID FUNCS FILE
158525 80 7 /opt/coolstack/apache2/htdocs/php/func_abc.php
Running the php_who.d while the func_abc.php program runs, we can see that
while func_abc.php was running, it called seven functions.