rclpy Context.on_shutdown callbacks are not called when Ctrl-C is pressed

[tfoote]

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.

[Barry-Xu-2018]

According to the latest codes (77949d2), this problem also exists.

After receiving SIGINT/SIGTERM, this thread will be awaked and call rclpy::shutdown_contexts() which call rcl_shutdown.

rclpy/rclpy/src/rclpy/signal_handler.cpp

Lines 137 to 146 in 77949d2

	g_deferred_signal_handling_thread = std::thread(
	[]() {
	while (g_signal_handler_installed.load()) {
	wait_for_signal();
	if (g_signal_handler_installed.load()) {
	trigger_guard_conditions();
	rclpy::shutdown_contexts();
	}
	}
	});

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.

rclpy/rclpy/rclpy/context.py

Lines 105 to 113 in 77949d2

	def try_shutdown(self):
	"""Shutdown this context, if not already shutdown."""
	if self.__context is None:
	return
	with self.__context, self._lock:
	if self.__context.ok():
	self.__context.shutdown()
	self._call_on_shutdown_callbacks()
	self._logging_fini()

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.

rclpy/rclpy/rclpy/executors.py

Lines 588 to 592 in 77949d2

	wait_set.wait(timeout_nsec)
	if self._is_shutdown:
	raise ShutdownException()
	if not self._context.ok():
	raise ExternalShutdownException()

Of course, this may introduce new issues. @ivanpauno do you have any opinions ?

[ivanpauno]

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.

[Barry-Xu-2018]

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()

[ivanpauno]

That would only be effective if there's an executor spinning, if that's not the case shutdown() would never get called.

[Barry-Xu-2018]

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.

[firesurfer]

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