Retrieving out variables from procedure

[David .]

Hello!

As I have understood it you can either return a resultset from the procedure (SELECT out_variable1, out_variable2, out_variable3 inside the procedure) or access the OUT variables.

I want to know which is (if it any) the preferred way to access OUT varables from a procedure into PHP.

Also I have some issues with my code, which I'm not sure is correct. It works but executes with a warning:
PHP Warning: mysqli_free_result() expects parameter 1 to be mysqli_result, boolean given in ... (@ the first mysqli_free_result($result)).

I'm not sure if I just can remove mysqli_free_result: Also I don't want to ignore this warning since it will arise in every procedure I want to retrive varaibles from. How will a proper retrival of the OUT variables look (that is fast and not produces warnings)?

MY CODE:

$query_procedure = "CALL GET_PROCEDURE($in_variable, @out_variable1, @out_variable2, @out_variable3);SELECT @out_variable1, @out_variable2, @out_variable3";


if(mysqli_multi_query($mysql_connection, $query_procedure))
{
$result = mysqli_use_result($mysql_connection);
mysqli_free_result($result);
mysqli_next_result($mysql_connection);
$result = mysqli_use_result($mysql_connection);
$row = mysqli_fetch_assoc($result);
mysqli_free_result($result);
}

$result1 = $row['@out_variable1'];
$result2 = $row['@out_variable2'];
$result3 = $row['@out_variable3'];