Hi,

2014-02-18 9:42 GMT+01:00 Ingo Lütkebohle <iluetkeb@gmail.com>:
> I know that many people feel otherwise, but in my personal opinion,
services are a bad idea anyway,
> and what we really want is something more like (though not necessarily
exactly the same) what actionlib
> offers. That is, something which *explicitly* acknowledges that there are
always packets/messages
> underneath, that there is asynchronicity, and that there may be
impossibility to act *in the protocol*.

Just to make sure there is no misunderstanding: I did not want to advocate
the use of services (actually we are fully in the event-driven camp).
Instead, I wanted to point out that this is an additional issue that needs
consideration when switching ROS transport over to DDS as I suppose that
there exist a number of components that rely on the service API.

Still, users will most likely expect (a)synchronous remote procedure call /
query / task patterns with or without feedback that are well supported.
Conceptually, the realization of these patterns in event-based
architectures are well documented in the literature, cf. [1] for an intro.
From my perspective, the question is rather how to realize these in a
usable, efficient and possibly standardized way without complicating the
user-level API.

In any case, it would be good if future implementations of these patterns
support recording through tools such as rosbag, cf. also [2], which should
be easily possible if it is realized in an event-based manner.

Best,

Sebastian

[1] Faison, Ted ; Hassel, J. (ed.): Event-Based Programming: Taking Events
to the Limit. Berkeley, CA. Chapter 9: Event-based Interactions. Apress,
2006
[2] https://github.com/ros/ros_comm/issues/250