Re: Should svwaitup/down be built again, or how to make sv do this?

[Stefan Karrmann <S.Karrmann@web.de>]

Dear all,

due to racing conditions, you cannot guarantee that a service is active.

E.g. regard:
#! /bin/sh
svwaitup /service/foo
exec baz

After svwaitup returns with success, the service foo can crash before the
shell starts the command exec.

If foo crashes you can hope that runsv restarts it. It would be worse if
foo is in a deadlock.

Even if the control of foo is in baz or foo offers a control socket which
reports the activity of foo the racing can happen in baz itself.

Most of the time you ignore the racing conditions in Un*x.
The only formal solution is the usage of timeouts in baz together with
error handlers.

> So, it sounds like you're saying that the functionality of checking for a 
> service to be running, and waiting until that service is running before 
> continuing no longer exists in runit as it is presently built.  Is this 
> correct?

Kind regards,
-- 
Stefan Karrmann

Computer programmers never die, they just get lost in the processing.