bug#56674: [Shepherd] Use of ‘waitpid’, ‘system*’, etc. in service code can cause deadlocks

[Maxime Devos]

On 21-07-2022 17:39, Ludovic Courtès wrote:

> > Alternatively:
> >
> > 4. Do the waitpid in a separate thread (needs work-around for the
> > multi-threaded fork problem, probably C things? Or modifying Guile and
> > maybe glibc to avoid async-unsafe things or make more things
> > async-safe or whatever the appropriate ...-safe is here.)
> >       
> For shepherd, multithreading is not an option due to the semantics of
> fork in the presence of threads.
>

From what I've read, multi-threaded fork is safe as long as you do an exec 'immediately' afterwards, without doing things like taking locks or allocating memory with malloc in-between the fork and exec. I don't think it's possible to do that in Guile code, but that's what the C things are for.

    Greetings,
    Maxime.

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