On Dec 5, 2010, at 12:31 AM, Tully Foote wrote:
> 
> 
> I am trying to move some computer vision code to nodelets. The idea is to have one camera nodelet serving frames, and everybody else grabbing and processing them.
> 
> That is one of the goals of the nodelet design.  You can see my other ros-users post about how to add an nodelet::Loader class to your node and then you can just load into that manager.  http://code.ros.org/lurker/message/20101205.074703.0991b0ae.en.html
>  

Tully, I have been playing around with this approach, trying to get it to work. I have been having some trouble. The nodelets are loaded, onInit() is called, but callbacks aren't called on the nodelets. Is there something about ros::spinOnce() that doesn't do the right thing for nodelets?

Below is a detailed example, if it helps. 

--Nick 

===========

I set up something similar to this example, but that also  publishes a message:

{{{
int main(int argc, char** argv)
{	
	ros::init(argc, argv, "VisionNodeletManager");
	ros::NodeHandle n;
	nodelet::Loader l; //This is what we need to be a nodelet manager
	
	ros::Publisher pub = n.advertise<std_msgs::Bool>("camera_display_disable", 1000);
	
	ros::Rate loop_rate(1);

	while (ros::ok()) {	
		std_msgs::Bool msg; 
		msg.data = 0; 
		pub.publish(msg); 
		ROS_INFO_STREAM("Published frame."); 
		ros::spinOnce();
		loop_rate.sleep(); 
	}
	
	return 0;
}
}}}

I then set up a listener nodelet: 

{{{
namespace vision_nodelets
{
	
	class CameraDisplayNodelet : public nodelet::Nodelet
	{
	public:
		CameraDisplayNodelet() : 
		disabled_(0), 
		{}
		
	private:
		virtual void onInit()
		{
			ROS_INFO_STREAM("Calling onInit() for CameraDisplayNodelet"); 
			ros::NodeHandle& private_nh = getPrivateNodeHandle();
			private_nh.getParam("disabled", disabled_);
			ROS_INFO_STREAM("Parameters: disabled=" << disabled_ ); 
			sub = private_nh.subscribe("camera_display_disable", 1000, &CameraDisplayNodelet::callback, this);
			ROS_INFO_STREAM("Finished onInit()"); 
		}

		
		void callback(const std_msgs::Bool::ConstPtr& input)
		{
			ROS_INFO_STREAM("Received message: camera_display_disable=" << input->data); 
			disabled_ = input->data;
		}
		int disabled_; 
		ros::Subscriber sub;
		
	};
	
	PLUGINLIB_DECLARE_CLASS(vision_nodelets, CameraDisplayNodelet, vision_nodelets::CameraDisplayNodelet, nodelet::Nodelet);
}

}}}

In Terminal A, I run 

{{{
rosrun vision_nodelets vision_nodelet_manager 
}}}

In Terminal B, I run 

{{{
rosrun nodelet nodelet load vision_nodelets/CameraDisplayNodelet VisionNodeletManager
}}}

In Terminal C, I run

{{{
rostopic echo /camera_display_disable
}}}

The following behavior is observed: 

In Terminal A I see unexpected outpt:
Every second I see the message "Published Frame". When the nodelet is started in Terminal B, I see "Calling onInit()"... I never see "Received message."

In Terminal B I see expected output:
{{{
[ INFO] [1291578492.136581000]: Loading nodelet /vision_nodelets_CameraDisplayNodelet of type vision_nodelets/CameraDisplayNodelet to manager VisionNodeletManager with the following remappings:
}}}

In Terminal C I see expected output: 
Once every second I see
{{{
---
data: False
}}}