code: public function stream_flush()
      {
          if (!$this->handle) {
              return false;
          }
          self::restorePrev();
          $success = \fflush($this->handle);
          self::register();
          return $success;
      }
docs: Flush the output
  
  @return boolean
  
  @see http://php.net/manual/en/streamwrapper.stream-flush.php