On 2014-03-07 14:14:17 -0500, Tom Lane wrote:
> Andres Freund <andres@2ndquadrant.com> writes:
> > On 2014-03-07 13:54:42 -0500, Tom Lane wrote:
> >> The big picture here is that in the scenario being debated in the other
> >> thread, exit() in a child process forked from a backend will execute that
> >> backend's on_detach actions *even if the code had done on_exit_reset after
> >> the fork*.
>
> > Hm, aren't those actions called via shmem_exit() calling
> > dsm_backend_shutdown() et al? I think that should be cleared by
> > on_shmem_exit()?
>
> But dsm_backend_shutdown gets called whether or not any shmem_exit
> actions are registered.
Yikes. I thought on_exit_reset() disarmed the atexit callback, but
indeed, it does not...
> > I think you're misunderstanding me. I am saying we *should* defend
> > against it. Our opinions just seem to differ on what to do when the
> > scenario is detected. I am saying we should scream bloody murder (which
> > admittedly is a hard in a child), you want to essentially declare it
> > supported.
>
> And if we scream bloody murder, what will happen? Absolutely nothing
> except we'll annoy our users. They won't have control over the
> third-party libraries that are doing what you want to complain about.
If the third party library is suitably careful it will only use fork()
and then exec() or _exit(), otherwise there are other things that'll be
broken (e.g. stdio). In that case everything was and is fine. If not,
the library's user can then fix or file a bug against the library.
Both perl and glibc seem to do just that in system() btw...
Greetings,
Andres Freund
-- Andres Freund http://www.2ndQuadrant.com/PostgreSQL Development, 24x7 Support, Training &
Services
