Re: Hack the (init) system!

[ludo@gnu.org (Ludovic Courtès)]

Mark H Weaver <mhw@netris.org> skribis:

> ludo@gnu.org (Ludovic Courtès) writes:

[...]

>> I’m tempted to just commit that.  There are shortcomings: (1) the REPL
>> server runs in a thread and threads + fork don’t go together well
>> (although in practice dmd only does fork followed by exec, so it’s OK),
>
> Unfortunately, it's only okay if the code between fork and exec in the
> child process is carefully written to execute only "async-signal-safe"
> operations.

Right (I was not suggesting that the hack is robus, rather that it’s
kinda OK “in practice”, notably because I would only start it once all
the ‘fork’ calls have been made.)

> So, I think we have two choices:
>
> 1. Avoid threads in dmd, i.e. either refrain from adding this REPL
>    server feature, or re-implement it in a way that avoids threads.
>
> 2. Avoid 'primitive-fork' in dmd, which means reimplementing
>    'fork+exec-command' in C; reimplementing the code where we currently
>    use 'primitive-fork' within various guix service definitions; and
>    documenting that users should never use 'primitive-fork' in their
>    services.  If we choose this route, we should probably disable
>    'primitive-fork' somehow, or at least have it issue a stern warning.
>
> I don't think that we should add a set of features to dmd that will make
> it fundamentally unreliable in a way that cannot be fixed.
>
> What do you think?

Agreed, of course.  I think #1 is the way to go.

Thanks,
Ludo’.