Re: Support to define custom wait events for extensions

On Fri, Jun 23, 2023 at 05:56:26PM +0900, Masahiro Ikeda wrote:
> I updated the patches to handle the warning mentioned
> by PostgreSQL Patch Tester, and removed unnecessary spaces.

I have begun hacking on that, and the API layer inspired from the
LWLocks is sound.  I have been playing with it in my own extensions
and it is nice to be able to plug in custom wait events into
pg_stat_activity, particularly for bgworkers.  Finally.

The patch needed a rebase after the recent commit that introduced the
automatic generation of docs and code for wait events.  It requires
two tweaks in generate-wait_event_types.pl, feel free to double-check
them.

Some of the new structures and routine names don't quite reflect the
fact that we have wait events for extensions, so I have taken a stab
at that.

Note that the test module test_custom_wait_events would crash if
attempting to launch a worker when not loaded in
shared_preload_libraries, so we'd better have some protection in
wait_worker_launch() (this function should be renamed as well).

Attached is a rebased patch that I have begun tweaking here and
there.  For now, the patch is moved as waiting on author.  I have
merged the test module with the main patch for the moment, for
simplicity.  A split is straight-forward as the code paths touched are
different.

Another and *very* important thing is that we are going to require
some documentation in xfunc.sgml to explain how to use these routines
and what to expect from them.  Ikeda-san, could you write some?  You
could look at the part about shmem and LWLock to get some
inspiration.
--
Michael