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From: "Serge E. Hallyn" <serge@hallyn.com>
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Subject: Re: Readiness notification exemplars
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To: Laurent Bercot <ska-supervision@skarnet.org>
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On Wed, Apr 01, 2020 at 05:13:06PM +0000, Laurent Bercot wrote:
> 
> > There are pros and cons, but you are arguing for parsing stdout for a
> > text message and/or using pidfiles (written to an fd).
> 
>  I'm arguing for none of these things.
>  I'm arguing for daemons to write a newline to a fd of their choice,
> which is hardly anything difficult. And hardly anything difficult for
> a supervisor to implement (if you're going to say that it's "parsing

Sorry, the week got away from me and I never replied.

So the API would be - the thing that starts the daemon opens an fd N,
the daemon accepts an argument "--ready-fd=N", daemon writes something
to fd N when ready or just closes it, and the thing checking whether
daemon is ready sees fd activity and starts things depending on the
daemon?

It does sound good.