SimpleActionClient callbacks

edit

Hello, I m sending goals to move_base action server using SimpleActionClient. I have TaskControl class methods for action client callback functions. I m confused about callbacks of actions.. My question is; if these callbacks are running as a seperate thread from main or is it the same thread with main and blocking my code while running callbacks..

actionlib::SimpleActionClient<move_base_msgs::MoveBaseAction> nav_ac("move_base", true);
nav_ac.sendGoal(
          nav_goal,
          boost::bind(
              &TaskControl::doneCB<move_base_msgs::MoveBaseResultConstPtr>,
              this, _1, _2),
          boost::bind(&TaskControl::activeCB, this),
          boost::bind(&TaskControl::navFeedbackCB, this, _1));

Thanx Best Regards