Re: Fix signal handler in pgpool main

Hi Emond,

> I got a bug report regarding pgpool main process from Emond Papegaaij:
> its exit/reload signal handler uses non signal safe functions, and it
> could lead to a crash of the process.
>
> Attached is the patch from him generated by Claude Code, with slight
> modifications by me.
>
> Basically it changes the signal handler to async-signal-safe calls
> only: capture the signal number into a new volatile sig_atomic_t
> main_exit_request, write one byte to the existing self-pipe to wake
> the main loop, restore errno, and return. The actual shutdown is
> performed synchronously by a new do_shutdown() function called from
> the pgpol main loop at the top of every iteration (via
> check_requests()) and also right after the inner pool_pause() returns,
> so a signal arriving during the 2-second select() sleep is acted on
> without an extra tick of latency.
>
> I think this patch is important and worth to apply to all supported
> branches.
>
> However, since it touches one of the most critical part of pgpool, I
> would like to apply to master branch first and see how our build-farm
> acts before back patching (it will take a few days).
>
> Comments?

Patch pushed to v4.4.

Peng and Koshino reviewed the patch off-list. No change was necessary.
I just removed some non-ASCII characters in comments (probably I
mistakenly brought them in by copy-and-paste). I tried to back-patch
to v4.3 but it seems it needs invasive changes and I gave up it. So I
decided to back patch through v4.4.

Thank you!
--
Tatsuo Ishii
SRA OSS K.K.
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