Re: incorrect xlog.c coverage report

On Thu, Nov 22, 2018 at 10:43 AM Thomas Munro
<thomas(dot)munro(at)enterprisedb(dot)com> wrote:
>
> On Thu, Nov 22, 2018 at 2:22 PM Michael Paquier <michael(at)paquier(dot)xyz> wrote:
> > On Wed, Nov 21, 2018 at 01:20:48PM -0500, Tom Lane wrote:
> > > Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> writes:
> > >> I think we should change all calls of ->teardown_node to ->stop(),
> > >> except the one in the END block, and look for places which are currently
> > >> relying too much on END (i.e. add more ->stop() calls where needed).
> > >
> > > Hm. We probably don't want to have zero coverage of immediate stop mode,
> > > though I agree we could cut it way back.
> >
> > The root of the issue is that gcov is not able to write out the gcda
> > file when Postgres is stopped in immediate mode? There are some code
> > paths in the recovery tests where teardown_node is used on purpose (see
> > for example 009_twophase.pl).
>
> So the issue is that quickdie() uses _exit(), so the GCOV atexit()
> handler (or whatever similar mechanism they use for that) doesn't run,
> right?

I think so too. Since gcov uses atexit(3) handler the exiting by
exit(3) or from main() is required.

> Presumably you could add your own call to __gcov_flush() in
> quickdie(), so that we get GCOV data but no other atexit()-like stuff.
> I see that some people advocate doing that in signal handlers, but I
> don't know if it's really safe. If that is somehow magically OK,
> you'd probably also need the chdir() hack from proc_exit() to get
> per-pid files.

That's probably a good idea, I'm also not sure if it's really safe
though. An alternative approach could be that we can do $node->restart
after recovered from $node->teardown_node() to write gcda file surely,
although it would make the tests hard to read.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center