From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: 'guix build' and garbage collection
Date: Sun, 02 Apr 2017 11:30:41 +0200
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In-Reply-To: <878tnjk489.fsf@gmail.com> (Chris Marusich's message of "Sat, 01
	Apr 2017 18:06:30 -0700")
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To: Chris Marusich <cmmarusich@gmail.com>
Cc: guix-devel@gnu.org

Hi Chris,

Chris Marusich <cmmarusich@gmail.com> skribis:

> I saw this in guix/scripts.build.scm:
>
> (and (build-derivations store drv mode)
>      (for-each show-derivation-outputs drv)
>      (for-each (cut register-root store <> <>)
>                (map (lambda (drv)
>                       (map cdr
>                            (derivation->output-paths drv)))
>                     drv)
>                roots))
>
> Here, we build the derivations, and then we add indirect GC roots.  My
> question is: what guarantee is there that the output paths will not be
> garbage collected after we build the derivations but before we add the
> indirect GC roots?

For the duration of the connection to the build daemon, build results
are registered as GC roots, so we=E2=80=99re fine.

You can see it in the =E2=80=98DerivationGoal=E2=80=99 constructor in libst=
ore/build.cc:

    /* Prevent the .chroot directory from being
       garbage-collected. (See isActiveTempFile() in gc.cc.) */
    worker.store.addTempRoot(drvPath);

Likewise in =E2=80=98SubstitutionGoal::init=E2=80=99.

HTH,
Ludo=E2=80=99.