Re: RFC: subcommand to pause/resume builds

["Ludovic Courtès" <ludo@gnu.org>]

Hi,

John Soo <jsoo1@asu.edu> skribis:

> I was looking to pause a long build today and asked on IRC how to
> accomplish pause/resume.  It seems this is possible already with the
> following:
>
> kill --signal SIGSTOP|SIGCONT {pids-of-build-process-tree}
>
> There is already a command to list the processes associated to guix
> commands: guix processes.  Perhaps pause/resume can be a subcommand or
> set of flags to guix processes. The following is the first thing that
> comes to mind:
>
> guix processes --pause package-name ... --resume package-name ...
>
> What do you think?

First, note that the daemon is unaware of “packages”, it only knows
about “derivations”.

Second, ‘guix processes’ is nice but it uses low-level heuristics to
determine what daemon sessions are open, what their clients are, and
what they’re building; it resorts to heuristics because the daemon as it
stands doesn’t have a way to communicate its current state.  It works
well in practice, but still I wouldn’t go too far building around it.

Last, you’d need to send SIGTSTP to the whole process group of the
build, like so (I think, haven’t tried):

  sudo kill -TSTP -123

where 123 is the “SessionPID” shown by ‘guix processes’.  However, doing
so may affect build results: processes in the build environment might
handle SIGTSTP specially, which can have side effects.  It’s an
observable action.

Conclusion: I don’t think we can implement this reliably.

HTH!

Ludo’.