PHP计算页面执行时间

run_time.php  Code:
<?php
class runtime
{
var $StartTime = 0;
var $StopTime = 0;
function get_microtime()
{
list($usec, $sec) = explode(' ', microtime());
return ((float)$usec + (float)$sec);
}
function start()
{
$this->StartTime = $this->get_microtime();
}
function stop()
{
$this->StopTime = $this->get_microtime();
}
function spent()
{
return round(($this->StopTime - $this->StartTime) * 1000, 1);
}
}
?>
return_time_test.php  Code:
<?php
include ('run_time.php');
$runtime = new runtime;
$runtime->start();
$a = 0;
for ($i=0;$i&ltrim(1000000);$i++){
$a += $i;
}
$runtime->stop();
echo "页面执行时间：".$runtime->spent()."毫秒!";
?>