Introducing simple-launch

[johnwason]

@Levi-Armstrong @marip8 @robinsonmm @marip8 @wolfv @traversaro @Tobias-Fischer @gavanderhoorn

simple-launch it a lightweight launch tool (process orchestractor). It has similar goals to roslaunch, but is intended to be a lot simpler and not require ROS. It has the following major benefits:

• Lightweight, single file Python program with minimal dependencies
• Does not require ROS and can run any program necessary
• Various parameters available to control program execution including arguments, working directory, environment, restart, auto quit, etc.
• Better Windows support, using Jobs and Windows Messages to provide graceful shutdown and avoid hanging programs
• A simple GUI that can be displayed to the user with a "Stop All" button, useful for when a launch is done interactively
• A companion "simple-launch-process" library used to catch signals and windows messages, to provide a graceful shutdown signal. The companion libraries are available for Python and C++

https://github.com/johnwason/simple-launch-process
https://github.com/johnwason/simple-launch-process-cpp

[gavanderhoorn]

Nice project.

Would it perhaps make sense not to call it simple-launch? For anyone not familiar with roslaunch -- which you imply is not simple -- it doesn't necessarily mean anything this is simple launch.

Also: you may end up adding more features which would take it away from its simple roots, at which point the name may no longer be appropriate.

Better Windows support, using Jobs and Windows Messages to provide graceful shutdown and avoid hanging programs

might be nice to contribute upstream?

[johnwason]

I am open to renaming the project. I couldn't think of a better name...

might be nice to contribute upstream?

roslaunch is pretty complicated. If one of the maintainers is interested I can explain how to incorporate better Windows support. Unfortunately it does require some changes to the applications running on Windows because there isn't an equivalent of signal in Windows, it requires some work by the programs. The companion libraries implement this functionality here.

[gavanderhoorn]

I wasn't necessarily thinking of roslaunch. ros2/launch is also supposed to be ROS-agnostic, is also written in Python and supports Windows as well.

Unfortunately it does require some changes to the applications running on Windows because there isn't an equivalent of signal in Windows, it requires some work by the programs.

hm, that complicates things.

[johnwason]

This project is extracted from the PyRI teach pendant launcher (https://github.com/pyri-project/pyri-core) and modified to be standalone. I did look at ros2/launch, but didn't like the way that threading and signaling was handled. This project is designed to be importable as a module, so it may be easier to wrap it than backport the improvements.

I did a short writeup on Windows signaling here: https://github.com/johnwason/simple-launch-process#shutdown-signal-explanation TL;DR windows processes that don't have a main window need to listen for "Windows Messages" and "Console Control Events" to reliably receive a graceful shutdown signal. The companion libraries use a hidden "message only" window to receive the events.

[johnwason]

See also #4 about Linux cgroup support. cgroup is necessary to make sure that all processes terminate correctly in the event of a crash, but require root access unless specially configured.

[johnwason]

I added support for Jinja2 templates and pushed to pypi.org. This should make it easier to work with Conda environments.

[johnwason]

What do you guys think of the name drakkar or drekar instead of simple-launch? It is a type of Viking longboat. Idea came from all rowing together as a team...

[johnwason]

Rename to drekar-launch is complete