ROS Timer: difference between types of NodeHandles?

Question

Dear all,

a student approached me a day back with a question that I just couldn't answer: "Should a ROS timer be on a a private NodeHandle, or on a global one?" (or any other, obviously...)

We usually do something like the following:

ros::NodeHandle nh_         = ros::NodeHandle(""); // for subscribers/publishers/...
ros::NodeHandle private_nh_ = ros::NodeHandle("~"); // for parameters

For parameters, subscribers etc. there is a clear difference which NodeHandle is used to access/initialize them.

Is there any for Timers?

Thank you for your insights!

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Originally posted by mgruhler on ROS Answers with karma: 12390 on 2016-04-29

Post score: 2

Answer 1

A ROS timer does not have an associated ROS graph name, so the namespace of the nodehandle doesn't affect how the timer functions.

I believe (though I'm not entirely certain), that if your NodeHandles have different callback queues, then the timer callback will get called on queue of the associated NodeHandle. This is a fairly advanced use case and it requires explicit setup, so it's probably not something that most students will encounter.

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Originally posted by ahendrix with karma: 47576 on 2016-05-05

This answer was ACCEPTED on the original site

Post score: 2

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Original comments

Comment by mgruhler on 2016-05-09:
@ahendrix thanks. This sounds reasonable. And this is actually something nobody could answer here. :-)