[ros-users] Nodelets

[Patrick Bouffard]

I'm trying to consolidate a number of separate nodes into a single
process using nodelets. I think I worked out the changes necessary to
go from ordinary nodes to nodelets that can be run standalone. But
when I try to take those same nodelets and load them all into a
nodelet manager, things start to break. I think this might have
something to do with threading/callback queues or something to that
effect.

One of the things that my node(let)s do at startup is to wait for a
service to be advertised. The node that advertises that service is now
one of the nodelets, and I notice that when I load the nodelets that
are the service clients into the nodelet manager, the service doesn't
ever seem to start. I suspect this might be because when I call
ros::service::waitForService(), it's blocking all of the nodelets,
including the one that would be advertising the service--does that
make sense? What is the Right Thing to do here to get the illusion of
having multiple nodes but with them running in the same process to
take advantage of zero-copy message passing etc.?

Initially I thought perhaps I just need to add ros::spin() in the
onInit method in each nodelet, but I saw in another thread (no pun
intended :-) that this is not correct. I'm guessing the answer lies in
threading but I'm not quite sure where to start. Is there anywhere in
the ROS ecosystem a package that has a similar structure to what I'm
trying to do, that I could look at as an example?

Also, I'm wondering what the distinction between ROS_INFO and
NODELET_INFO is; should I always be using the latter in nodelets?

Thanks,
Pat