Re: on_exit_reset fails to clear DSM-related exit actions

Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> On Fri, Mar 7, 2014 at 10:04 AM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> I just noticed that the DSM patch has introduced a whole new class of
>> failures related to the bug #9464 issue: to wit, any on_detach
>> actions registered in a parent process will also be performed when a
>> child process exits, because nothing has been added to on_exit_reset
>> to prevent that. It seems likely that this is undesirable.

> I don't think this can actually happen. There are quite a number of
> things that would go belly-up if you tried to use dynamic shared
> memory from the postmaster, which is why dsm_create() and dsm_attach()
> both Assert(IsUnderPostmaster).

Nonetheless it seems like a good idea to make on_exit_reset drop any
such queued actions.

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*. So whether or not you buy Andres' argument that it's not
necessary for atexit_callback to defend against this scenario, there's
actually no other defense possible given the way things work in HEAD.

regards, tom lane