[ros-users] RFC: warning for (lacking) queue_size for python publishers in Indigo?

[Austin Hendrix]

+1 to option a

-Austin

On Mar 5, 2014, at 5:58 PM, Dirk Thomas <dthomas at osrfoundation.org> wrote:

> We are looking for feedback from ROS users on a very specific question for rospy in Indigo.
> 
> In the past rospy publishers sent the messages synchronously to each connection.
> That becomes a problem when one of the underlying network buffers runs full (which implies that it blocks).
> This commonly happens when e.g. using a connection over wlan and the connectivity is lost.
> The client code would then block on the publish() call for an undetermined amount of time (potentially forever).
> 
> Therefore in Hydro an optional keyword argument was introduced to the rospy.Publisher constructor: queue_size=None (see [1])
> 
> The default value of `None` maintains the previous behavior (synchronous behavior, no queuing).
> When an integer value is passed a queue with the maximum size of N is used to queue published messages which are then send to each connection from separate threads.
> (A size of zero means an infinite queue, which can be dangerous.)
> 
> The implementation follows the existing roscpp implementation - except that in roscpp that argument is required.
> It is definitely not possible to make the argument in Python required as well since that would imply breaking every existing Python publisher.
> 
> Therefore we have two options how to handle this in Indigo:
> 
> a) The constructor could output a warning when the queue_size argument is missing in order to notify users / developers to update the code and actually provide a reasonable queue_size.
>   The warning would be printed using the Python warnings module and can therefore be omitted by setting an environment variable (see [2]).
> 
> b) We keep the code as it is in Hydro meaning messages are by default published synchronously.
>   Users can use the optional keyword but are not given any indication from the code at runtime.
> 
> The tutorials as well as Indigo migration guide will mention whatever option will finally be used.
> 
> Which option would you prefer for Indigo?
> 
> Thank you for your feedback,
> - Dirk
> 
> 
> [1] http://wiki.ros.org/rospy/Overview/Publishers%20and%20Subscribers
> [2] https://github.com/ros/ros_comm/pull/372
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