Bug report

Required Info:

• Operating System:
  • Ubuntu Bionic 18.04 (as in Nvidia OpenGL Docker image)
• Installation type:
  • Binaries
• Version or commit hash:
  • Crystal pre-release (updated 14-12-2018; version 0.6.1)
• DDS implementation:
  • Checked with FastRTPS and connext_cpp
• Client library (if applicable):
  • rclcpp

Steps to reproduce issue

Start top in a terminal to monitor CPU usage.

Then, from another terminal, run minimal_action_server:

ros2 run examples_rclcpp_minimal_action_server action_server_not_composable

Finally, run minimal_action_client with cancel:

ros2 run examples_rclcpp_minimal_action_client action_client_not_composable_with_cancel

Expected behavior

Action is canceled, everything exits gracefully.

Actual behavior

Action is canceled, but in some cases a CPU thread keeps working at 100% until the server is shut down.

Additional information

This doesn't happen every time the action client is launched, but it's not too hard to reproduce either by launching it a few times. It seems to happen ~50% of the times.
This might be related to ros2/rcl#354.