Horton

Re: stopgap fix for signal handling during restore_command

Nathan Bossart <nathandbossart@gmail.com>

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From: Nathan Bossart <nathandbossart@gmail.com>
To: Andres Freund <andres@anarazel.de>
Cc: Thomas Munro <thomas.munro@gmail.com>, Michael Paquier <michael@paquier.xyz>, Robert Haas <robertmhaas@gmail.com>, Tom Lane <tgl@sss.pgh.pa.us>, Fujii Masao <fujii@postgresql.org>, Postgres hackers <pgsql-hackers@lists.postgresql.org>
Date: 2023-03-01T22:47:51Z
Lists: pgsql-hackers

Attachments

On Tue, Feb 28, 2023 at 08:36:03PM -0800, Nathan Bossart wrote:
> On Sun, Feb 26, 2023 at 12:12:27PM -0800, Andres Freund wrote:
>> Partially I just want something that can easily be searched for, that can have
>> comments attached to it documenting why what it is doing is safe.
>> 
>> It'd not be a huge amount of work to have a slow and restricted string
>> interpolation support, to make it easier to write messages. Converting floats
>> is probably too hard to do safely, and I'm not sure %m can safely be
>> supported. But basic things like %d would be pretty simple.
>> 
>> Basically a loop around the format string that directly writes to stderr using
>> write(), and only supports a signal safe subset of normal format strings.
> 
> Got it, thanks.  I will try to put something together along these lines,
> although I don't know if I'll pick up the interpolation support in this
> thread.

Here is an attempt at adding a signal safe function for writing to STDERR.

I didn't add support for format strings, but looking ahead, I think one
challenge will be avoiding va_start() and friends.  In any case, IMO format
string support probably deserves its own thread.

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

Commits

  1. windows: msvc: Define STDIN/OUT/ERR_FILENO.

  2. Avoid calling proc_exit() in processes forked by system().

  3. Move extra code out of the Pre/PostRestoreCommand() section.