[PATCH] Cygwin: signa: Redesign signal queue handling

[Corinna Vinschen]

On Mar  9 13:28, Christian Franke wrote:
> Takashi Yano wrote:
> > ...
> > With this patch prevents all signals from that issues by redesigning
> > the signal queue, Only the exception is the case that the process is
> > in the PID_STOPPED state. In this case, SIGCONT/SIGKILL should be
> > processed prior to the other signals in the queue.
> > 
> > Addresses: https://cygwin.com/pipermail/cygwin/2025-March/257582.html
> > Fixes: 7ac6173643b1 ("(pending_signals): New class.")
> > Reported by: Christian Franke <Christian.Franke@t-online.de>
> > Reviewed-by:
> > Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
> > ...
> >   void
> >   pending_signals::add (sigpacket& pack)
> >   {
> > ...
> > +  if (q->si.si_signo == pack.si.si_signo)
> > +    q->usecount++;
> > ...
> > 
> 
> This should possibly also compare the si.si_sigval fields. Otherwise values
> would be lost if the same real-time signal is issued multiple times with
> different value parameters.

Looks like this doesn't only affect RT signals.  I just read POSIX.1-2024
on sigaction,
https://pubs.opengroup.org/onlinepubs/9799919799/functions/sigaction.html
and this is what it has to say in terms of queuing:

  If SA_SIGINFO is not set in sa_flags, then the disposition of
  subsequent occurrences of sig when it is already pending is
  implementation-defined; the signal-catching function shall be invoked
  with a single argument. If SA_SIGINFO is set in sa_flags, then
  subsequent occurrences of sig generated by sigqueue() or as a result
  of any signal-generating function that supports the specification of
  an application-defined value (when sig is already pending) shall be
  queued in FIFO order until delivered or accepted;

This isn't quite what the Linux man pages describe.  Signal(7) says:

  Standard signals do not queue.  If multiple instances of a standard
  signal are generated while that signal is blocked, then only one
  instance of the signal is marked as pending (and the signal will be
  delivered just once when it is unblocked).  In the case where a
  standard signal is already pending, the siginfo_t structure (see
  sigaction(2)) associated with that signal is not overwritten on
  arrival of subsequent instances of the same signal.  Thus, the process
  will receive the information associated with the first instance of the
  signal.

Am I just confused or do these two description not match?


Corinna