Re: On-demand running query plans using auto_explain and signals

On Sat, Aug 29, 2015 at 5:44 PM, Andres Freund <andres(at)anarazel(dot)de> wrote:

> On 2015-08-29 17:33:22 +0200, Shulgin, Oleksandr wrote:
> > Probably using SIGUSR2 would be more appropriate, but I'm not sure if
> there
> > are other extensions out there that might be already using it for some
> > other reason (well, I do not know that for SIGUSR1 either). Looking at
> the
> > current state of affairs in procsignal_sigusr1_handler() makes me believe
> > it should be pretty safe to catch the signal like I do. Or is that not
> the
> > case?
>
> You can catch signals, but you're not allowed to do a lot from
> them. Anything allocating memory, acquiring locks, etc. is out - these
> functions aren't reentrant. If you can guarantee that you're not
> interrupting any relevant code you can bend those rules, but that's
> obviously not the case here.
>
> Check out the list of async-signal-safe functions at
> http://man7.org/linux/man-pages/man7/signal.7.html

Good point. There's still hope to set a flag and process it later on.
Will have to check if it's possible to stay in the scope of a loaded module
though.