Understanding actions
I've been using ROS services to ask a node to perform a long running (a few seconds) task and I want to switch to using ROS actions as recommended on http://wiki.ros.org/actionlib . The task is a call to a path-planning library that blocks until a path is found.
The documentation has me confused when it comes to blocking on the action server side in the goal callback. The fibonnacti example stays in the callback until the action is complete.
The under-the-hood description says:
Any actions taken in a callback received for a new goal should not be long running. The user may, of course, signal another thread to do work, but should not block.
1) Isn't that exactly the point of actions, that they are long running? Does that mean that the fibonnaci example is actually bad practice?
The under-the-hood description continues to say:
Upon construction of the simple action server, the user decides whether or not to spin up an extra thread to allow for taking long running actions in a goal callback.
2) I don't see this in the SimpleActionServer constructor. It has a boolean to choose autostarting, but nothing about spinning a separate thread.
This is an option in the SimpleActionClient, but its use is discouraged anyway.
3) So what is the recommended approach?
Should I only check for the legality of the goal and then setAccepted in the goal callback and then do the real work in my main thread (while(ros::ok() { ... }))? *
Or should/can I do the work in the goal callback (as the fibonnaci example does)? If I do that, will my feedback be sent and will I receive preemptions?
Thanks
EDIT:
* I just noticed that setAccepted is not a member function of SimpleActionServer. This raises the question: Can I and do I have to mark a goal as accepted or is this done automatically when entering the goal callback with that goal?
