Php synchronized log system error after request for Codeigniter 2

php_error_log_collect_hook.php

<?php if (!defined('BASEPATH')) exit('No direct script access allowed');
/**
 * php synchronized log system error after request
 * WARNING : only suitable for runing FastCGI model by PHP
 * @reference: http://huoding.com/2011/04/12/63
 */
class Php_error_log_collect_hook extends MY_Log {

    public static $level = array(
        E_ERROR              =>  'Error',
        E_WARNING            =>  'Warning',
        E_PARSE              =>  'Parsing Error',
        E_NOTICE             =>  'Notice',
        E_CORE_ERROR         =>  'Core Error',
        E_CORE_WARNING       =>  'Core Warning',
        E_COMPILE_ERROR      =>  'Compile Error',
        E_COMPILE_WARNING    =>  'Compile Warning',
        E_USER_ERROR         =>  'User Error',
        E_USER_WARNING       =>  'User Warning',
        E_USER_NOTICE        =>  'User Notice',
        E_STRICT             =>  'Runtime Notice'
    );

    public static $level_mapping = array(
        E_ERROR              =>  'ERROR',
        E_WARNING            =>  'WARN',
        E_PARSE              =>  'ERROR',
        E_NOTICE             =>  'INFO',
        E_CORE_ERROR         =>  'ERROR',
        E_CORE_WARNING       =>  'WARN',
        E_COMPILE_ERROR      =>  'ERROR',
        E_COMPILE_WARNING    =>  'WARN',
        E_USER_ERROR         =>  'ERROR',
        E_USER_WARNING       =>  'WARN',
        E_USER_NOTICE        =>  'INFO',
        E_STRICT             =>  'INFO'
    );

    public function __construct() {
        parent::__construct();
    }

    public function callback() {
        register_shutdown_function(array($this, 'handle_fatal_error'));
    }

    public function handle_fatal_error() {
        if ($last_error = error_get_last()) {
            $error_no = $last_error['type'];
            if (isset(self::$level_mapping[$error_no]) && self::$level_mapping[$error_no] === 'ERROR') {
                $log_info = "PHP Fatal Error: " . $last_error['message'] . " " . $last_error['file'] . " in line " . $last_error['line'];
                $this -> write_log("ERROR", $log_info);
            }
        }
    }

}