class TimeCost
{

 private $cost = array();
 private $record = array();
 private $scale = 6;
 public function __construct($scale = 6)
 {
 $this->cost = array();
 $this->record = array();
 $this->scale = $scale;
 }

 public function __toString()
 {
 return $this->getString();
 }

 /**
 * start to cal time.
 *
 * @param mixed $key
 */
 public function addCost($key)
 {
 $this->cost[$key] = microtime(true);
 }

 /**
 * stop to cal time.
 *
 * @param mixed $key
 */
 public function closeCost($key)
 {
 $cost = bcsub(microtime(true), $this->cost[$key], $this->scale);

 if (in_array($key, array_keys($this->record))) {
  $this->record[$key] = bcadd($cost, $this->record[$key], $this->scale);
 } else {
  $this->record[$key] = $cost;
 }
 return $cost;
 }

 
 public function getString($key = null)
 {
 if ($key) {
  return "{$key}[{$this->record[$key]}]";
 }

 $str = '';
 foreach ($this->record as $k => $v) {
  $str .= "{$k}[{$v}]";
 }
 return $str;
 }
}

$obj = new TimeCost();
$token = 'test_a';
$obj->addCost($token);
some_code();

$obj->closeCost($token);
$reslut = $obj->getString($token);