httpd|nntpd: avoid missed signal wakeups

Our attempt at using a self-pipe in signal handlers was
ineffective, since pure Perl code execution is deferred
and Perl doesn't use an internal self-pipe/eventfd.  In
retrospect, I actually prefer the simplicity of Perl in
this regard...

We can use sigprocmask() from Perl, so we can introduce
signalfd(2) and EVFILT_SIGNAL support on Linux and *BSD-based
systems, respectively.  These OS primitives allow us to avoid a
race where Perl checks for signals right before epoll_wait() or
kevent() puts the process to sleep.

The (few) systems nowadays without signalfd(2) or IO::KQueue
will now see wakeups every second to avoid missed signals.

1 files changed, 28 insertions, 0 deletions

diff --git a/t/ds-kqxs.t b/t/ds-kqxs.t
index 785570c3..43b6333f 100644
--- a/t/ds-kqxs.t
+++ b/t/ds-kqxs.t
@@ -10,5 +10,33 @@ unless (eval { require IO::KQueue }) {
                                 : "no IO::KQueue, skipping $0: $@";
         plan skip_all => $m;
 }
+
+if ('ensure nested kqueue works for signalfd emulation') {
+        require POSIX;
+        my $new = POSIX::SigSet->new(POSIX::SIGHUP());
+        my $old = POSIX::SigSet->new;
+        my $hup = 0;
+        local $SIG{HUP} = sub { $hup++ };
+        POSIX::sigprocmask(POSIX::SIG_SETMASK(), $new, $old) or die;
+        my $kqs = IO::KQueue->new or die;
+        $kqs->EV_SET(POSIX::SIGHUP(), IO::KQueue::EVFILT_SIGNAL(),
+                        IO::KQueue::EV_ADD());
+        kill('HUP', $$) or die;
+        my @events = $kqs->kevent(3000);
+        is(scalar(@events), 1, 'got one event');
+        is($events[0]->[0], POSIX::SIGHUP(), 'got SIGHUP');
+        my $parent = IO::KQueue->new or die;
+        my $kqfd = $$kqs;
+        $parent->EV_SET($kqfd, IO::KQueue::EVFILT_READ(), IO::KQueue::EV_ADD());
+        kill('HUP', $$) or die;
+        @events = $parent->kevent(3000);
+        is(scalar(@events), 1, 'got one event');
+        is($events[0]->[0], $kqfd, 'got kqfd');
+        is($hup, 0, '$SIG{HUP} did not fire');
+        POSIX::sigprocmask(POSIX::SIG_SETMASK(), $old) or die;
+        defined(POSIX::close($kqfd)) or die;
+        defined(POSIX::close($$parent)) or die;
+}
+
 local $ENV{TEST_IOPOLLER} = 'PublicInbox::DSKQXS';
 require './t/ds-poll.t';