/** condition to manage thread wakeups when we have nothing to do */
boost::condition _empty_condition;
/** condition to manage thread wakeups when we have too much to do */
boost::condition _full_condition;
/** condition to manage thread wakeups when we have nothing to do */
boost::condition _empty_condition;
/** condition to manage thread wakeups when we have too much to do */
boost::condition _full_condition;