Remove all signals from a signal_set.
asio::error_code & ec);
This function removes all signals from the set. It has no effect if the
set is already empty.
Set to indicate what error occurred, if any.
Removes all queued notifications.
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)