Re: sqlite memory allocation and async signal safety

[Eli Zaretskii <eliz@gnu.org>]

> From: Po Lu <luangruo@yahoo.com>
> Cc: emacs-devel@gnu.org
> Date: Thu, 24 Mar 2022 18:21:29 +0800
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > I think we used to block input around function calls that could
> > allocate memory because our signal handlers, and in particular SIGIO
> > handler, did non-trivial stuff.  Nowadays our signal handlers just set
> > a flag and return, so I'm not sure this is needed anymore.  Especially
> > when system library malloc is called, which AFAIU is mostly async-safe
> > nowadays on modern platforms.
> >
> > Am I missing something?
> 
> Unfortunately, most system malloc implementations are still not
> async-signal safe, but if all that happens is a flag being set, then I
> don't think calling block_input is required anymore.
> 
> Which flag is that, and where is it tested?

It depends on the signal.  Look at the signal handlers we install.
For SIGIO, this is the handler:

  void
  handle_input_available_signal (int sig)
  {
    pending_signals = true;

    if (input_available_clear_time)
      *input_available_clear_time = make_timespec (0, 0);
  }

and the flag is pending_signals.