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Posted Nov 22, 2014 16:10 UTC (Sat) by smurf (subscriber, #17840)
In reply to: Thanks by mjg59
Parent article: Today's Debian technical committee resignation: Ian Jackson

To summarize: While an event-based init system seemed like a good idea at the time, upstart quickly ran into a whole lot of corner cases which are basically unsolvable without adding job state as separate concepts. Upstart has tried working around this by adding even more events (like "starting to start" and "finished starting") but they don't help in general.

Given this fact, a dependency-based system which uses events just to change the units' state simplifies the whole system and affords easier debugging, as it's statically introspectable – meaning you don't need an event history to figure out what's wrong, just the current job states and the dependency graph.

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Thanks

Posted Nov 22, 2014 21:14 UTC (Sat) by mgb (guest, #3226) [Link] (4 responses)

Forgy invented http://en.wikipedia.org/wiki/Rete_algorithm in the 70's and it was widely adopted in the early 80's.

Sad to see the wheel painfully being reinvented again.

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Posted Nov 22, 2014 21:46 UTC (Sat) by smurf (subscriber, #17840) [Link] (1 responses)

Dependency resolution in an init system doesn't need anything remotely this elaborate. We don't even need alternates (what for?).

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Posted Nov 22, 2014 22:08 UTC (Sat) by mgb (guest, #3226) [Link]

> Dependency resolution in an init system doesn't need anything remotely this elaborate.

Rete is not elaborate. It is a clean elegant modular algorithm.

> We don't even need alternates (what for?).

Alternate networks. Sometimes alternate data stores. Alternate entropy sources - you want sshd ASAP but maybe not until you have some entropy. "If I can't get any entropy bring up sshd only on the private LAN and if that doesn't work fall back to telnetd on the private LAN."

As the "new" init systems try to invade serious servers they will keep on running into problems and adding more keywords and reliving the 70's until they eventually relearn the lessons of the early 80's.

Thanks

Posted Nov 22, 2014 23:33 UTC (Sat) by mjg59 (subscriber, #23239) [Link] (1 responses)

How would you apply this to an event-based init system?

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Posted Nov 23, 2014 0:15 UTC (Sun) by mgb (guest, #3226) [Link]

> How would you apply this to an event-based init system?

Your own http://lwn.net/Articles/622742/ answers that.

If you want functionality beyond inittab, an event-based init system is even worse than an ad-hoc dependency-based init system that has to keep adding keywords like RequiresMountsFor.