Horton

Use standard SIGHUP and SIGTERM handlers in autoprewarm module

Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>

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From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
To: PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2020-10-05T10:45:49Z
Lists: pgsql-hackers

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Hi,

Autoprewarm module is using it's own SIGHUP(apw_sigterm_handler,
got_sigterm) and SIGTERM(apw_sighup_handler, got_sighup) handlers which are
similar to standard signal handlers(except for a difference [1]). Isn't it
good to remove them and  use standard SignalHandlerForConfigReload and
SignalHandlerForShutdownRequest?

Attaching the patch for the above changes.

Looks like the commit[2] replaced custom handlers with standard handlers.

Thoughts?

[1] apw_sigterm_handler() and apw_sighup_handler() use MyProc->procLatch
if (MyProc)
        SetLatch(&MyProc->procLatch);
where as standard handlers use MyLatch
    SetLatch(MyLatch);
Both MyProc->procLatch and MyLatch point to same, see comment from global.c
/*
 * MyLatch points to the latch that should be used for signal handling by
the
 * current process. It will either point to a process local latch if the
 * current process does not have a PGPROC entry in that moment, or to
 * PGPROC->procLatch if it has.
*Thus it can always be used in signal handlers, * without checking for its
existence.*
 */
struct Latch *MyLatch;

(gdb) p MyProc->procLatch
$6 = {is_set = 0, is_shared = true, owner_pid = 1448807}
(gdb) p MyLatch
*$7 = (struct Latch *) 0x7fcacc6d902c*
(gdb) p &MyProc->procLatch
*$8 = (Latch *) 0x7fcacc6d902c*
(gdb) p *MyLatch
$9 = {is_set = 0, is_shared = true, owner_pid = 1448807}

[2] commit 1e53fe0e70f610c34f4c9e770d108cd94151342c
Author: Robert Haas <rhaas@postgresql.org>
Date:   2019-12-17 13:03:57 -0500

    Use PostgresSigHupHandler in more places.

    There seems to be no reason for every background process to have
    its own flag indicating that a config-file reload is needed.
    Instead, let's just use ConfigFilePending for that purpose
    everywhere.

With Regards,
Bharath Rupireddy.
EnterpriseDB: http://www.enterprisedb.com

Commits

  1. Revert "Get rid of the dedicated latch for signaling the startup process".

  2. Improve log message about termination of background workers.

  3. Use standard SIGTERM signal handler die() in test_shm_mq worker.

  4. Use standard SIGHUP and SIGTERM signal handlers in worker_spi.

  5. Use standard SIGHUP and SIGTERM handlers in walreceiver.

  6. pg_prewarm: make autoprewarm leader use standard SIGHUP and SIGTERM handlers.

  7. Get rid of the dedicated latch for signaling the startup process.

  8. Use standard SIGHUP handler in syslogger.

  9. Use PostgresSigHupHandler in more places.

  10. Fix race condition with unprotected use of a latch pointer variable.

  11. Remove remnants of ImmediateInterruptOK handling.

  12. Introduce Streaming Replication.