rclpy should provide a method to check if initialized

[wjwwood]

Feature request

Feature description

rclpy should provide a method to indicate if rclpy.init() has been called since the program started or since the last time rclpy.shutdown() was called.

Implementation considerations

This could also be served by provided a specific exception to raise when called too many times, currently it raises a generic RuntimeError, but I think a func to tell without raising an exception would also be good to have.

Should work after calling rclpy.shutdown() after originally calling rclpy.init() the first time.

[hemantku]

I can help on this. Do you want to assign this to me?

[sloretz]

Thanks @hemantku

I'm not able to assign you to the ticket, but go ahead and start on it anyways. I would be happy to answer questions you may have if you encounter issues.

[hemantku]

#224

[hemantku]

@sloretz : Is there an reference architecture doc for rclpy just like launch: https://github.com/ros2/launch/blob/master/launch/doc/source/architecture.rst ? For example, How is the state stored in each node, using the lifecycle node? or is it something else

[sloretz]

Is there an reference architecture doc for rclpy just like launch

Not that I know of. There are slides about the architecture leading up to rclpy py starting at slide 30 here: https://roscon.ros.org/2016/presentations/ROSCon%202016%20-%20ROS%202%20Update.pdf

For example, How is the state stored in each node, using the lifecycle node

What kind of state? There is a pycapsule holding a pointer to an rcl_node_t on node._handle.

[suab321321]

I would like to help on this @sloretz

[pr-db]

@wjwwood Hello, I'm new to open source and love working with ros. How can I approach this issue?

[wjwwood]

Sorry @pr-db, this got lost. If you, or anyone else, wants to work on this...

We need a function to check if rclpy is already initialized or not, or perhaps just a more specific exception being raise. You can see from here:

https://github.com/ros2/launch/pull/75#discussion_r195281980

That we're catching a generic exception and comparing the error string to see if it is the already initialized error, which is very fragile.

[sloretz]

I think this feature already exists as rclpy.ok()

https://github.com/ros2/rclpy/blob/77949d2c54b8104e48a94d0ea83c7049e18a8809/rclpy/rclpy/init.py#L55

Implementation

https://github.com/ros2/rclpy/blob/77949d2c54b8104e48a94d0ea83c7049e18a8809/rclpy/rclpy/utilities.py#L49-L52

[EricCousineau-TRI]

Yeah, I think @sloretz is right - worth closing this issue now?

[fujitatomoya]

@EricCousineau-TRI it would be appreciated if you could review https://github.com/ros2/rclpy/pull/1198

[sloretz]

Closing this issue as complete