Called by program which desires to manipulate this actuator, when it is activated.

def activate_program(self, program):
        """
            Called by program which desires to manipulate this actuator, when it is activated.
        """
        self.logger.debug("activate_program %s", program)
        if program in self.program_stack:
            return

        with self._program_lock:
            self.logger.debug("activate_program got through %s", program)
            self.program_stack.append(program)
            self._update_program_stack()