Construct a signal set without adding any signals.
template< typename ExecutionContext> basic_signal_set( ExecutionContext & context, typename enable_if< is_convertible< ExecutionContext &, execution_context & >::value >::type * = 0);
This constructor creates a signal set without registering for any signals.
An execution context which provides the I/O executor that the signal set will use, by default, to dispatch handlers for any asynchronous operations performed on the signal set.