Daemon mode to speed up startup

[seeM]

There've been ongoing discussions in various channels about adding a daemon mode to execnb. Although this is probably a longer-term thing, I thought an issue could be a good place to store useful notes and important decisions made along the way.

What is a daemon mode?

@jph00's thread sums it up well:

Python scripts can be slow to start because the imports can take a long time. I have lots of scripts that read/write stdin/out. I'd like to replace them with something with identical behavior, but which behind the scenes auto-launches a little server. [...] The idea is that the overhead of starting the script only happens once. This is useful for stuff like git hook scripts.

References

• PEP 3143 – Standard daemon process library
• python-daemon: reference implementation for PEP 3143
• Rules that daemons are meant to follow
• daemonize: a library for writing system daemons in Python (unmaintained)
• Discussion on a daemon mode for Python

cc @hamelsmu