<?php  if ( ! defined("BASEPATH")) exit("No direct script access allowed");
/**
 * CodeIgniter
 *
 * An open source application development framework for PHP 5.1.6 or newer
 *
 * @package		CodeIgniter
 * @author		ExpressionEngine Dev Team
 * @copyright	Copyright (c) 2008 - 2011, EllisLab, Inc.
 * @license		http://codeigniter.com/user_guide/license.html
 * @link		http://codeigniter.com
 * @since		Version 1.0
 * @filesource
 */

// ------------------------------------------------------------------------

/**
 * CodeIgniter Benchmark Class
 *
 * This class enables 能够 you to mark points and calculate 计算 the time difference 差异
 * between them.  Memory consumption can also be displayed.
 *
 * @package		CodeIgniter
 * @subpackage	Libraries
 * @category	Libraries
 * @author		ExpressionEngine Dev Team
 * @link		http://codeigniter.com/user_guide/libraries/benchmark.html
 */
class CI_Benchmark {

	/**
	 * List of all benchmark markers and when they were added
	 * 用来存储基准测试类标记的数组
	 * @var array
	 */
	var $marker = array();

	// --------------------------------------------------------------------

	/**
	 * Set a benchmark marker
	 * 设置一个标记点
	 * Multiple calls to this function can be made so that several
	 * execution points can be timed
	 *
	 * @access	public
	 * @param	string	$name	name of the marker
	 * @return	void
	 */
	function mark($name)
	{
		// 在程序的任意地方调用方法时，会记录当前的时间点。
		$this->marker[$name] = microtime();
	}

	// --------------------------------------------------------------------

	/**
	 * Calculates the time difference between two marked points.
	 * 计算出两个时间点之间的时间。
	 * If the first parameter is empty this function instead returns the
	 * {elapsed_time} pseudo-variable 虚假变量. This permits 许可 the full system
	 * execution time to be shown in a template. The output class will
	 * swap the real value for this variable.
	 *
	 * @access	public
	 * @param	string	a particular marked point
	 * @param	string	a particular marked point
	 * @param	integer	the number of decimal places
	 * @return	mixed
	 */
	function elapsed_time($point1 = "", $point2 = "", $decimals = 4)
	{
		/* 
		 * 如果没有给出明确的时间点，那么会计算出整个程序运行的时间。
		 * 怎么可以做到计算出整个程序的运行时间的呢？其实执行此计算的是Output组件。
		 * 而调用Benchmark::elapsed_time();（无参数）的时候，实质上先返回的并不是
		 * 整个程序运行的时间，也不可能做到，实质返回的是一个{elapsed_time}标签，然后
		 * Output在处理输出的时候，再计算出整个程序运行时间，因为处理输出阶段程序可以视
		 * 为处于最后阶段，于是可以近似计算出总时间，然后把输出中的{elapsed_time}替换掉。
		 * 下面的memory_usage()原理相同。
		 */
		if ($point1 == "")
		{
			return "{elapsed_time}";
		}

		if ( ! isset($this->marker[$point1]))
		{
			return "";
		}

		if ( ! isset($this->marker[$point2]))
		{
			$this->marker[$point2] = microtime();
		}

		//这里为什么要用到list，是因为microtime();返回值是“msec sec”的格式。
		list($sm, $ss) = explode(" ", $this->marker[$point1]);
		list($em, $es) = explode(" ", $this->marker[$point2]);

		return number_format(($em + $es) - ($sm + $ss), $decimals);
	}

	// --------------------------------------------------------------------

	/**
	 * Memory Usage 
	 *
	 * This function returns the {memory_usage} pseudo-variable.
	 * This permits it to be put it anywhere in a template
	 * without the memory being calculated until the end.
	 * The output class will swap the real value for this variable.
	 *
	 * @access	public
	 * @return	string
	 */
	function memory_usage()
	{
		return "{memory_usage}";
	}

}

// END CI_Benchmark class

/* End of file Benchmark.php */
/* Location: ./system/core/Benchmark.php */