Signals in a BGW

From: Chapman Flack <chap(at)anastigmatix(dot)net>
To: PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Signals in a BGW
Date: 2017-12-04 16:40:37
Message-ID: a8080882-bac7-e539-05a9-eb6cd3d628d6@anastigmatix.net
Views: Raw Message | Whole Thread | Download mbox
Thread:
Lists: pgsql-hackers

I'm curious about handling signals in a background worker.

As I understand it, these are blocked when the BGW is born, until
enabled with BackgroundWorkerUnblockSignals() after possible
customization.

Is there a known, default behavior that some signals will
have, if I simply BackgroundWorkerUnblockSignals() without customizing?
Will SIGINT and SIGTERM, for example, have default handlers that
interact with the volatile flags in miscadmin.h that are used by
CHECK_FOR_INTERRUPTS, and set the process latch?

I notice that the worker_spi example code customizes SIGHUP
and SIGTERM, giving them handlers that set a (different, local
to the module) volatile flag, and set the process latch.

The example code does call CHECK_FOR_INTERRUPTS, though I assume
this won't detect ProcDie at all, now that the custom SIGTERM
handler is setting a different, local flag. Perhaps it still
does something useful with QueryCancel?

Does this use of a custom SIGTERM handler, setting a custom flag,
setting the process latch, and then checked in custom code,
accomplish something important that would not be accomplished
by a generic handler and CHECK_FOR_INTERRUPTS ?

I'm just not clearly grasping the reason it's customized here.

-Chap

Responses

Browse pgsql-hackers by date

  From Date Subject
Next Message Alvaro Herrera 2017-12-04 16:44:37 Re: [HACKERS] Secondary index access optimizations
Previous Message Konstantin Knizhnik 2017-12-04 16:14:57 Re: [HACKERS] Secondary index access optimizations