Instruments Hooks for a Page of WordPress. Outputs during the Shutdown Hook after add get-params: ?instrument=hooks

wp-hooks-filter.php

<?php
/*
Plugin Name: Instrument Hooks for WordPress
Plugin URI: http://bueltge.de/
Description: Instruments Hooks for a Page. Outputs during the Shutdown Hook after add get-params <code>?instrument=hooks</code>.
Version: 0.0.1
Author: Frank B&uuml;ltge
Author URI: http://bueltge.de/
*/

if ( isset( $_GET['instrument'] ) && $_GET['instrument'] == 'hooks' ) {

	function instrument_hooks() {
		global $wpdb;
		
		$hooks  = $wpdb->get_results("SELECT * FROM wp_hook_list ORDER BY first_call");
		$html   = array();
		$html[] = '<style>#instrumented-hook-list table,#instrumented-hook-list th,#instrumented-hook-list td {border:1px solid gray;padding:2px 5px;}</style>
<div align="center" id="instrumented-hook-list">
	<table>
		<tr>
		<th>First Call</th>
		<th>Hook Name</th>
		<th>Hook Type</th>
		<th>Arg Count</th>
		<th>Called By</th>
		<th>Line #</th>
		<th>File Name</th>
		</tr>';
		
		foreach($hooks as $hook) {
			$html[] = "<tr>
			<td>{$hook->first_call}</td>
			<td>{$hook->hook_name}</td>
			<td>{$hook->hook_type}</td>
			<td>{$hook->arg_count}</td>
			<td>{$hook->called_by}</td>
			<td>{$hook->line_num}</td>
			<td>{$hook->file_name}</td>
			</tr>";
		}
		
		$html[] = '</table></div>';
		echo implode("\n", $html);
	}
	
	function record_hook_usage($hook){
		global $wpdb;
		
		static $in_hook = FALSE;
		static $first_call = 1;
		static $doc_root;
		
		$callstack = debug_backtrace();
		
		if ( !$in_hook ) {
			$in_hook = TRUE;
			
			if ($first_call == 1) {
				
				$doc_root = $_SERVER['DOCUMENT_ROOT'];
				$results = $wpdb->get_results("SHOW TABLE STATUS LIKE 'wp_hook_list'");
				
				if ( count($results) == 1 ) {
					$wpdb->query("TRUNCATE TABLE wp_hook_list");
				} else {
					$wpdb->query(
						"CREATE TABLE wp_hook_list (
						called_by varchar(96) NOT NULL,
						hook_name varchar(96) NOT NULL,
						hook_type varchar(15) NOT NULL,
						first_call int(11) NOT NULL,
						arg_count tinyint(4) NOT NULL,
						file_name varchar(128) NOT NULL,
						line_num smallint NOT NULL,
						PRIMARY KEY (first_call,hook_name))"
					);
				}
				
			}
			
			$args = func_get_args();
			$arg_count = count($args) -1;
			$hook_type = str_replace( 'do_', '',
				str_replace( 'apply_filters',
					'filter',
					str_replace( '_ref_array', '[]', $callstack[3]['function'] )
				)
			);
			
			$file_name = addslashes( str_replace( $doc_root, '', $callstack[3]['file'] ) );
			$line_num = $callstack[3]['line'];
			
			if ( isset($callstack[4]['function']) )
				$called_by = $callstack[4]['function'];
			else
				$called_by = '';
				
			$wpdb->query("
				INSERT wp_hook_list
				( first_call, called_by, hook_name, hook_type, arg_count, file_name, line_num )
				VALUES ( $first_call, '$called_by()', '$hook', '$hook_type', $arg_count, '$file_name', $line_num)
			");
			
			$first_call++;
			$in_hook = FALSE;
		}
	}
	
	add_action('shutdown', 'instrument_hooks');
	add_action('all', 'record_hook_usage');
}

@bueltge what does this hook do exactly

@hoshomoh putting this functions into your active theme's functions.php file, it will allow you to register all called hooks and display the calls at the end of a request if you put ?instrument=hooks at the end of the URL