ShutdownProcess event does not work from TimerAction

[jacobperron]

Bug report

Required Info:

• Operating System:
  • Ubuntu 20.04
• Installation type:
  • from source
• Version or commit hash:
  • 0.15.0

Steps to reproduce issue

launch file (repro.launch.py):

import launch
from launch.actions import ExecuteProcess
from launch.actions import EmitEvent
from launch.actions import TimerAction
from launch.events.process import ShutdownProcess
from launch.events import matches_action


def generate_launch_description():
    execute_proc = ExecuteProcess(
        cmd=['./test.sh'],
        name='my_test',
        output='screen',
    )
    kill_proc_event = EmitEvent(
        event=ShutdownProcess(
            process_matcher=matches_action(execute_proc)
        )
    )
    return launch.LaunchDescription([
        execute_proc,
        TimerAction(period=0.5, actions=[kill_proc_event]),
        # replacing the timer above with the following line works as expected (but without the time delay)
        # kill_proc_event
    ])

test process test.sh:

#!/usr/bin/env bash

echo "Test!"
sleep 1
echo "One"
sleep 1
echo "Two"
sleep 1
echo "Three"

launch command:

ros2 launch repro.launch.py

Expected behavior

After the timer expires, the ExecuteProcess action is shutdown.

Actual behavior

We see a SIGINT being sent to the process, but it is not shutdown.

Additional information

If we remove TimerAction, and emit the shutdown signal directly (see commented line in example), then the launch script behaves as expected: the test process is immediately shutdown.

[jacobperron]

If I increase the delays in test.sh, eventually launch gives up on the SIGINT and sends a SIGTERM. This successfully kills the process:

[ERROR] [my_test-1]: process[my_test-1] failed to terminate '5' seconds after receiving 'SIGINT', escalating to 'SIGTERM'

[jacobperron]

@hidmic I know you where dealing with signal handlers and launch recently, any ideas? Note, this doesn't look like a regression, just something that never worked.

[hidmic]

I may be wrong, but this doesn't seem like a problem in launch. launch sends signals to your test process, but your test process does not forward signals to its child processes. Ctrl+C on a terminal with job control is not the same as SIGINT'ing the process. This blog talks about it briefly.

[jacobperron]

You're right, launch is working as expected. I was not understanding how the terminal was interacting differently than sending a SIGINT. TIL. Thanks!

Handling the interrupt with trap or swapping in a Python script works as expected.