pgsql: Use latch instead of select() in walreceiver

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

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On 12/1/16 8:50 PM, Michael Paquier wrote:

+           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

walreceiver.c does the same thing. The message you pointed out is not
exactly clear why that would be wrong.

--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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