Scott James Remnant
scott at netsplit.com
Mon Oct 9 18:43:07 BST 2006
On Sun, 2006-10-08 at 11:43 -0400, Sean E. Russell wrote:
> On Sunday 08 October 2006 11:02, you wrote:
> > > Well, Cups was just an example. The Gentoo init scripts are full of
> > > examples of services which have conditional requirements. The idea is
> > > that there's a mechanism for saying "if this service is going to be
> > > started, then wait for it to start. Otherwise, just start now."
> > Could be an interesting problem mapping to an event-driven scenario, how
> > do you know that a service is "going to be started later" ?
> You've got a good point. Since Upstart is an indeterminate system, it is
> possible that a service could be available, but never started because the
> correct event (network/started, say) was never generated.
> There are three cases I can think of:
> 0) A job doesn't exist. This is the simple case -- if there's no job
> in /etc/events.d and another job has it as a conditional dependency, then
> Upstart simply removes the dependency.
> 1) A job fails to start (say, network) and generates a job-failed event. In
> this case, Upstart would "satisfy" the requirement if it is conditional.
> 2) A job goes into a perpetual "wait" state. The only way these could be
> handled is by time-out, but that's a really bad solution.
> #2 is the show-stopper, and may be sufficient to prove that Upstart (or any
> event-driven design) can't be made handle conditional dependencies without
> ugly hacks (timeouts).
Can you provide any actual use cases for #2? I've had a think and can't
actually think of any.
> Finally, would somebody with write access to the main Upstart page please add
> this link to the page? I keep losing it:
Have done so.
Have you ever, ever felt like this?
Had strange things happen? Are you going round the twist?
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