ros2
rclpy Context.on_shutdown callbacks are not called when Ctrl-C is pressed
The on_shutdown doesn't get triggered unless the user explicitly catches the Ctrl-C and then calls shutdown themselves.
#!/usr/bin/env python3
import rclpy
class TestShutdown():
def on_shutdown_method(self):
print("on shutdown method called")
def main(args=None):
rclpy.init(args=args)
ros_node = rclpy.create_node('test_node')
test_class = TestShutdown()
rclpy.get_default_context().on_shutdown(test_class.on_shutdown_method)
rclpy.spin(ros_node)
# Shutdown
print("exiting")
rclpy.shutdown()
if __name__ == '__main__':
main()
If you put a try catch around the spin it will work. But otherwise you get no on_shutdown which could be useful for cleaning up a hardware driver etc.
test_shutdown.py
^CTraceback (most recent call last):
File "/home/tfoote/work/tdk/test_shutdown.py", line 25, in <module>
main()
File "/home/tfoote/work/tdk/test_shutdown.py", line 17, in main
rclpy.spin(ros_node)
File "/home/tfoote/work/workspaces/rclpy/install/rclpy/lib/python3.6/site-packages/rclpy/__init__.py", line 190, in spin
executor.spin_once()
File "/home/tfoote/work/workspaces/rclpy/install/rclpy/lib/python3.6/site-packages/rclpy/executors.py", line 676, in spin_once
handler, entity, node = self.wait_for_ready_callbacks(timeout_sec=timeout_sec)
File "/home/tfoote/work/workspaces/rclpy/install/rclpy/lib/python3.6/site-packages/rclpy/executors.py", line 662, in wait_for_ready_callbacks
return next(self._cb_iter)
File "/home/tfoote/work/workspaces/rclpy/install/rclpy/lib/python3.6/site-packages/rclpy/executors.py", line 560, in _wait_for_ready_callbacks
_rclpy.rclpy_wait(wait_set, timeout_nsec)
KeyboardInterrupt
Letting the Ctrl-C bubble up is probably still correct, but the Context could use a ContextManager or other mechanism to make sure that the shutdown occurs for this and other unexpected exits otherwise the on_shutdown callback is not particularly useful.
The workaround in the short term is to simply put a try catch around the spin and catch the KeyboardInterrupt exception.
According to the latest codes (77949d2c54b8104e48a94d0ea83c7049e18a8809), this problem also exists.
After receiving SIGINT/SIGTERM, this thread will be awaked and call rclpy::shutdown_contexts() which call rcl_shutdown.
https://github.com/ros2/rclpy/blob/77949d2c54b8104e48a94d0ea83c7049e18a8809/rclpy/src/rclpy/signal_handler.cpp#L137-L146
For user codes
...
try:
rclpy.spin(node)
except KeyboardInterrupt:
pass
except ExternalShutdownException:
sys.exit(1)
finally:
rclpy.try_shutdown()
node.destroy_node()
It will call rclpy.try_shutdown(). Since rcl_shutdown has been called, self.__context.ok() is always false.
It leads shutdown callback never is called.
https://github.com/ros2/rclpy/blob/77949d2c54b8104e48a94d0ea83c7049e18a8809/rclpy/rclpy/context.py#L105-L113
Maybe we can use setting shutdown flag instead of calling rclpy::shutdown_contexts() in signal handling thread (signal_handler.cpp).
At line 591, check above shutdown flag.
https://github.com/ros2/rclpy/blob/77949d2c54b8104e48a94d0ea83c7049e18a8809/rclpy/rclpy/executors.py#L588-L592
Of course, this may introduce new issues. @ivanpauno do you have any opinions ?
Maybe we can use setting shutdown flag instead of calling rclpy::shutdown_contexts() in signal handling thread (signal_handler.cpp).
I don't understand how that would work. Could you expand the idea?
Maybe rclpy::shutdown_contexts() should also call the shutdown callbacks, though that might not be simple to implement.
Could you expand the idea?
My rough idea is
At context.cpp, add 2 functions.
void requst_shutdown()
{
Set a global shutdown flag
}
bool check_shutdown_request()
{
return global shutdown flag
}
At signal_handler.cpp
setup_deferred_signal_handler()
{
...
rclpy::requst_shutdown() // call new function
trigger_guard_conditions();
// rclpy::shutdown_contexts(); // comment this line
}
At executors.py
def _wait_for_ready_callbacks()
...
# Wait for something to become ready
wait_set.wait(timeout_nsec)
if self._is_shutdown:
raise ShutdownException()
if _rclpy.check_shutdown_request or not self._context.ok(): # Check if shutdown is requested.
raise ExternalShutdownException()
User app take charge of calling shutdown.
...
try:
rclpy.spin(node)
except KeyboardInterrupt:
pass
except ExternalShutdownException:
pass
finally:
rclpy.try_shutdown()
That would only be effective if there's an executor spinning, if that's not the case shutdown() would never get called.
That would only be effective if there's an executor spinning, if that's not the case
shutdown()would never get called.
Yes. I missed this case.
As I read this issue to be only related to SIGINT (Ctrl+C) just the note for whoever is also wondering:
A callback registered via on_shutdown is never called if the program was closed/interrupted via a signal. I tested:
SIGINT, SIGTERM, SIGQUIT
