class Something {
    function a() {
        sleep(2); echo "a()"; return TRUE;
    }
    function b() {
        sleep(2); echo "b()"; return TRUE;
    }
    function c() {
        sleep(2); echo "c()"; return TRUE;
    }
}

$something = new Something();
if($something->a()) {
    if($something->b()) {
        if($something->c()) {
            echo "everything completed!!";
        }
    }
}

a()b()c()everything completed!!

<?php
header( 'Content-Type: text/html; charset=utf-8' );

class Something {
    function a() {
        echo "a()" . str_repeat(' ', 1024);
        ob_flush(); flush();
        sleep(2); return TRUE;
    }
    function b() {
        echo "b()" . str_repeat(' ', 1024);
        ob_flush(); flush();
        sleep(2); return TRUE;
    }
    function c() {
        echo "c()" . str_repeat(' ', 1024);
        ob_flush(); flush();
        sleep(2); return TRUE;
    }
}

$something = new Something();
if($something->a()) {
    if($something->b()) {
        if($something->c()) {
            echo "everything completed!!";
        }
    }
}

$something = new Something();
if($something->a()) {
    if($something->b()) {
        if($something->c()) {
            echo "everything completed!!";
            a();
        }
    }
}