Executor spin_once must check wait_for_ready_callbacks returns None

• Operating System:
  • Ubuntu 18.04
• Installation type:
  • ubuntu packages
• Version or commit hash:
  • Dashing
• Client library (if applicable):
  • rclpy

When developping a node that has a timer and Action clients, and having a MultiThreadExecutor manage the callbacks, I encoutered the following issue when trying to shutdown the executor from the timer callback:

File "/home/lesire/Work/MUST/ros2_ws/build/oara/oara/actor.py", line 40, in run
    self._executor.spin()
  File "/opt/ros/dashing/lib/python3.6/site-packages/rclpy/executors.py", line 273, in spin
    self.spin_once()
  File "/opt/ros/dashing/lib/python3.6/site-packages/rclpy/executors.py", line 695, in spin_once
    handler, entity, node = self.wait_for_ready_callbacks(timeout_sec=timeout_sec)
TypeError: 'NoneType' object is not iterable

[ivanpauno]

@ivanpauno Are you sure that we need to backport #574 to Dashing? The backport won’t be trivial, as I noted in #574 (comment): the fix breaks tests in Eloquent (#584) and doesn’t merge cleanly into Dashing. I suspect we will see at least the same test failures as we did in Eloquent after addressing the merge conflicts in Dashing.

What I mean is that this is still a bug in Dashing (where the bug is being reported). We can either fix it, add it to known bugs, or mark the issue as help wanted.

But I don’t think that marking the ticket as solved is correct. This is still a bug in the distribution it was reported, and backporting the fix applied on master doesn’t seem trivial.

[sloretz]

Dashing is EOL. Closing.