Future::privateCall PHP 메소드

    private function privateCall($callback, $next, $x)
    {
        try {
            $r = call_user_func($callback, $x);
            $next->resolve($r);
        } catch (UncatchableException $e) {
            throw $e->getPrevious();
        } catch (Exception $e) {
            $next->reject($e);
        } catch (Throwable $e) {
            $next->reject($e);
        }
    }