Race condition in MultiThreadedExecutor #1393
Description
Bug report
Required Info:
- Operating System:
- Ubuntu 24.04.1
- Installation type:
- Binaries
- Version or commit hash:
rollingviaros-tooling/action-ros-ci@v0.3GitHub action
- DDS implementation:
- unknown
- Client library (if applicable):
- rclpy
Steps to reproduce the issue
Documented here: felixdivo/ros2-easy-test#45. It is not 100% reproducible, yet it occurs frequently in my repo.
Expected behavior
No exception is raised.
Actual behavior
self = <rclpy.executors.MultiThreadedExecutor object at 0x7fb80c2f32f0>
timeout_sec = <rclpy.executors.TimeoutObject object at 0x7fb80c41cb90>
wait_condition = <bound method Future.done of <rclpy.task.Task object at 0x7fb80c2f30b0>>
def _spin_once_impl(
self,
timeout_sec: Optional[Union[float, TimeoutObject]] = None,
wait_condition: Callable[[], bool] = lambda: False
) -> None:
try:
handler, entity, node = self.wait_for_ready_callbacks(
timeout_sec, None, wait_condition)
except ExternalShutdownException:
pass
except ShutdownException:
pass
except TimeoutException:
pass
except ConditionReachedException:
pass
else:
self._executor.submit(handler)
self._futures.append(handler)
# make a copy of the list that we iterate over while modifying it
# (https://stackoverflow.com/q/1207406/3753684)
for future in self._futures[:]:
if future.done():
> self._futures.remove(future)
E ValueError: list.remove(x): x not in list
/opt/ros/rolling/lib/python3.12/site-packages/rclpy/executors.py:895: ValueError
Additional information
Previously, I had similar issues caused by race conditions reported in #1129. This again appears to be caused by multiple threads simultaneously acting on the executor. Is there some unintended usage by me?
Possible solution
If not, I suggest going with the it is "Easier to ask for forgiveness than permission" and just wrap the self._futures.remove(future) in a try-except block catching and ValueErrors. I can also do that if you confirm it is a reasonable path forward.