code: public function start()
      {
          if ($this->isProfiling) {
              return false;
          }
          $backtrace = \debug_backtrace(DEBUG_BACKTRACE_IGNORE_ARGS);
          $backtrace = $this->backtraceRemoveInternal($backtrace);
          foreach ($backtrace as $frame) {
              $class = isset($frame['class']) ? $frame['class'].'::' : '';
              $this->rootStack[] = $class.$frame['function'];
          }
          \register_tick_function(array($this, 'tickFunction'));
          $this->isProfiling = true;
          $this->timeLastTick = \microtime(true);
          return true;
      }
docs: Set initial stack info
  
  @return boolean