Thread: pgsql: Use latch instead of select() in walreceiver

Use latch instead of select() in walreceiver

Replace use of poll()/select() by WaitLatchOrSocket(), which is more
portable and flexible.

Also change walreceiver to use its procLatch instead of a custom latch.

From: Petr Jelinek <petr@2ndquadrant.com>

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/597a87ccc9a6fa8af7f3cf280b1e24e41807d555

Modified Files
--------------
src/backend/postmaster/pgstat.c                    |   3 +
.../libpqwalreceiver/libpqwalreceiver.c            | 101 +++++----------------
src/backend/replication/walreceiver.c              |  18 ++--
src/backend/replication/walreceiverfuncs.c         |   6 +-
src/include/pgstat.h                               |   1 +
src/include/replication/walreceiver.h              |   3 +-
6 files changed, 43 insertions(+), 89 deletions(-)

On Fri, Dec 2, 2016 at 10:29 AM, Peter Eisentraut <peter_e@gmx.net> wrote:
> Use latch instead of select() in walreceiver
>
> Replace use of poll()/select() by WaitLatchOrSocket(), which is more
> portable and flexible.
>
> Also change walreceiver to use its procLatch instead of a custom latch.
>
> From: Petr Jelinek <petr@2ndquadrant.com>

+           ResetLatch(&MyProc->procLatch);
+           rc = WaitLatchOrSocket(&MyProc->procLatch,
+                                  WL_POSTMASTER_DEATH | WL_SOCKET_READABLE |
+                                  WL_LATCH_SET,
+                                  PQsocket(streamConn),
+                                  0,
+                                  WAIT_EVENT_LIBPQWALRECEIVER_READ);
+           if (rc & WL_POSTMASTER_DEATH)
+               exit(1);
Hmm. We have always been very careful about not leaving immediately
from libpqwalreceiver.c which is an independent shared library so as
the WAL receiver can take cleanup actions. See here for more details:
https://www.postgresql.org/message-id/CAEepm=0hg_FX7kdUhosTpJ_kPsUZw6k-7nuQNy-dGAOaetn_tA@mail.gmail.com
--
Michael