Respawn in ROS2

dheera · June 15, 2021, 11:28pm

I need respawn functionality in ROS2. How do I do this? I searched all over the web and the only thing I found is “respawn” is no longer supported attribute.

But none of the docs explain: What is the ROS2 way to achieve the same thing?

flynneva · June 15, 2021, 11:52pm

I think you should be able to do this with a Lifecycle node

Just start up the node again on the shutdown event and I think you’d get a “respawn” effect.

wjwwood · June 16, 2021, 12:23am

I think this is an ideal question for answers.ros.org. But I’ll try to answer it anyway, but please consider posting the question and answer there too.

I think the documentation is out of date, because it says here you cannot use respawn any longer:

http://docs.ros.org/en/rolling/Guides/Launch-files-migration-guide.html?highlight=respawn#node

But looking at the api you can ask it to respawn an executable if it crashes or exits (which what I assume you’re asking about):

github.com

ros2/launch/blob/e519deaa9e8c739257b6321b09e03ea0749dd1ee/launch/launch/actions/execute_process.py#L204

    
      
              Overridden externally by the OVERRIDE_LAUNCH_PROCESS_OUTPUT envvar value.
              See `launch.logging.get_output_loggers()` documentation for further
              reference on all available options.
          :param: output_format for logging each output line, supporting `str.format()`
              substitutions with the following keys in scope: `line` to reference the raw
              output line and `this` to reference this action instance.
          :param: log_cmd if True, prints the final cmd before executing the
              process, which is useful for debugging when substitutions are
              involved.
          :param: on_exit list of actions to execute upon process exit.
          :param: respawn if 'True', relaunch the process that abnormally died.
              Defaults to 'False'.
          :param: respawn_delay a delay time to relaunch the died process if respawn is 'True'.
          """
          super().__init__(**kwargs)
          self.__cmd = [normalize_to_list_of_substitutions(x) for x in cmd]
          self.__name = name if name is None else normalize_to_list_of_substitutions(name)
          self.__cwd = cwd if cwd is None else normalize_to_list_of_substitutions(cwd)
          self.__env = None  # type: Optional[List[Tuple[List[Substitution], List[Substitution]]]]
          if env is not None:
              self.__env = []

The “node” action inherits from the executable action, so when defining a node in launch with either python or xml you should be able to specify this argument.

Post to answers and I’ll make a more concrete answer with examples.

JWaynee · July 2, 2021, 12:19pm

I don’t fully understand how to use the respawn parameter. Can you please give an concrete example using a python launch file? (I’m using foxy).

Thanks a lot
Jeremy

tomoyafujita · July 2, 2021, 11:23pm

Here is an example. we just need to enable respawn argument.

github.com

ros2/launch/blob/d0f7a68cab058e3395b7b9b57b8bd3c869c4d3b9/launch/test/launch/test_execute_process.py#L156

    
      
          
          
respawn_delay = 2.0
          shutdown_time = 3.0   # to shutdown the launch service, so that the process only respawn once
          expected_called_count = 2   # normal exit and respawn exit
          
          
def generate_launch_description():
              return LaunchDescription([
          
          
        ExecuteProcess(
                      cmd=[sys.executable, '-c', "print('action')"],
                      respawn=True, respawn_delay=respawn_delay, on_exit=on_exit_callback
                  ),
          
          
        TimerAction(
                      period=shutdown_time,
                      actions=[
                          Shutdown(reason='Timer expired')
                      ]
                  )
              ])

please post the further question on http://answers.ros.org/ to aggregate the Q&A for the community thanks!

JWaynee · July 8, 2021, 2:37pm

Thanks for the help! I posted a follow up question on https://answers.ros.org/question/382043/ros2-respawn/.

asherikov · July 13, 2021, 8:30pm

If somebody is looking for a more generic solution: I did some experiments with dinit service manager in ROS1 context (GitHub - asherikov/cdinit). The goal is to get systemd-like behavior in userspace – service dependencies, startup ordering, restarts, manual starting/stopping, and complement or replace roslaunch. Overall seems to be a plausible approach, should also be transferrable to ROS2. It is of low priority for me, but if somebody is interested I can try to push it forward.

Topic		Replies	Views
Changing default parameters for node in LaunchDescription General ros2	1	326	June 18, 2022
Sequentially starting launch files using ROS 2 Python when a specific log message is detected General	3	3227	April 30, 2023
ROS2 Logging Next Generation ROS ros2	35	12605	April 21, 2020
Do we have Event Handling in ROS2 launch files written in XML? General event , ros2 , lifecycle , launch	1	702	February 18, 2022
Regarding Migration of Launch File from ROS1 -> ROS2 ros2	2	940	December 12, 2018

Respawn in ROS2

Related topics