Hi Maxim! Maxim Cournoyer <maxim.courno...@gmail.com> skribis:
>> The goal is to make shepherd (the daemon) use Fibers¹ for concurrency. > > Very exciting work! I can't wait to have my 5 min boot reduced (mostly > busy-waiting on the child-hurd VM to start) ;-). Same here! The childhurd service will need some help as it’s currently written in a way that would block. > Interesting; in a (unmerged) patch I had made to mcron, I had extended > the select loop in a way that it'd detect available output and use a > suspendable port to accomplish this; perhaps Fibers would be a > cleaner/more straightforward way to accomplish this. Also, I was > particularly happy about how flexible the timestamp/metadata prefixed to > each line could be configured by a user; you may want to steal ideas > from it! [0] > > [0] https://lists.gnu.org/archive/html/bug-mcron/2021-08/msg00008.html Oh nice! I hope that patch will eventually make it into mcron (or we could use our own version!). For the timestamp format there’s currently a parameter, which is not exposed, and defaults to syslog style. > I see. I was puzzle by this configure.ac check: > > +dnl Check for extra dependencies. > +GUILE_MODULE_AVAILABLE([have_fibers], [(fibers)]) > +if test "x$have_fibers" != "xyes"; then > + AC_MSG_ERROR([Fibers is missing; please install it.]) > +fi > + > +dnl Make sure Fibers does not create POSIX threads: since shepherd > +dnl forks, it must be single-threaded. > +AC_CACHE_CHECK([whether Fibers might create POSIX threads], > + [ac_cv_fibers_creates_pthreads], > + [GUILE_CHECK([retval], > + [(use-modules (fibers)) > + (set! (@ (ice-9 threads) call-with-new-thread) > + (lambda _ (throw 'new-thread!))) > + (run-fibers (lambda () (spawn-fiber (lambda () 1))) > + #:parallelism 1 #:hz 0)]) > + if test "$retval" = 0; then > + ac_cv_fibers_creates_pthreads="no" > + else > + ac_cv_fibers_creates_pthreads="yes" > + fi]) > +if test "x$ac_cv_fibers_creates_pthreads" = "xyes"; then > + AC_MSG_ERROR([Fibers creates POSIX threads behind our back; aborting.]) > +fi > > > In which scenario would Fibers create unwanted POSIX threads? It shouldn’t happen with #:parallelism 1 #:hz 0. Here I’m just being super defensive: it’s PID 1 after all, and if future Fibers versions break that assumption for some reason, I’d rather detect it early. > 1. In fae59fb * build: Capture the source and object directories of > Fibers. > > Why must we even capture the Fibers source/compiled objects directories? We don’t have to, but if we don’t do it here, then the ‘shepherd’ package definition will have to use ‘wrap-program’ to do it for us. Since there’s just one dependency, I thought we might as well do it upstream. > 2. nitpick; in "service: 'read-pid-file' no longer blocks": > > -;; Copyright (C) 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021 > Ludovic Courtès <l...@gnu.org> > +;; Copyright (C) 2013-2022 Ludovic Courtès <l...@gnu.org> > > While I agree this reads better, I've recently stumbled in info > '(maintain) Copyright Notices' on: > > You can use a range (‘2008-2010’) instead of listing individual years > (‘2008, 2009, 2010’) if and only if: 1) every year in the range, > inclusive, really is a “copyrightable” year that would be listed > individually; _and_ 2) you make an explicit statement in a ‘README’ file > about this usage. > > So you'd want to add an explicit statement in the README about it. Yes, will do (it’s typical FSF pedantry; I remember the time it took before this anecdotal-looking paragraph would end up in that document, as if software freedom was at stake :-)). > 3. I was a bit skeptical about the ability to configure the encoding of > the log file; in which situation would switching it to something else > than UTF-8 be useful? I agree; the log files produced by shepherd are always UTF-8. What’s configurable is the encoding of the data produced by daemons. It’s probably rarely useful, but if you have a daemon that writes, say, ISO-8859-1 strings, you can say so. That way, the output of that daemon is properly decoded as ISO-8859-1; the log file produced by shepherd remains UTF-8 no matter what. Thanks for taking a look! Since that initial message I added support for inetd-style service startup. Among the services I use, it could be use for sshd (OpenSSH), bitlbee, and dicod. More on that later… Ludo’.
