Re: pgsql: Use SIGURG rather than SIGUSR1 for latches.

On Sat, Apr 17, 2021 at 8:49 AM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> (I would've thought that a SIG_IGN'd signal would be dropped
> immediately even if blocked; that's the behavior that dummy_handler
> is designed to prevent, and I'm pretty sure that that code is there
> because we saw it actually behaving that way on some platforms.
> But apparently not on Linux?)

Yeah, it's a point of variation between platforms.

POSIX: "If the action associated with a blocked signal is to ignore
the signal and if that signal is generated for the process, it is
unspecified whether the signal is discarded immediately upon
generation or remains pending."
Linux: "Blocked signals are never ignored, since the signal handler
may change by the time it is unblocked."
BSDs, Darwin: "If the signal is being ignored, then we forget about it
immediately."