[PATCH 3/5] sigfd: call normal Perl %SIG handlers

[Eric Wong <e@80x24.org>]

Instead of storing our own mapping of signal handler callbacks,
rely on the standard %SIG hash table which can be arbitrarily
updated from anywhere.

This makes it easier to allow existing synchronous code (e.g.
NetReader using Mail::IMAPClient or Net::NNTP) to add explicit
points where pending signals can be checked.

Additionally, it allows the `DEFAULT' (SIG_DFL) signal handler
to fire when there's no Perl subroutine to register.

Finally, this also allows us to rely on the OS + Perl itself to
dispatch signal handlers on kevent-based systems (and avoid
redundant dispatch due to our (previous) Linux-centric API).  It
makes Linux signalfd the only system where we'd need to dispatch
%SIG callbacks ourselves.
---
 lib/PublicInbox/DS.pm    | 21 ++++++++++++-------
 lib/PublicInbox/Sigfd.pm | 43 ++++++++++++++++++++++++++------------
 t/sigfd.t                | 45 +++++++++++++++++++++++++---------------
 3 files changed, 71 insertions(+), 38 deletions(-)

diff --git a/lib/PublicInbox/DS.pm b/lib/PublicInbox/DS.pm
index f807c626..bb45ec99 100644
--- a/lib/PublicInbox/DS.pm
+++ b/lib/PublicInbox/DS.pm
@@ -248,7 +248,7 @@ sub sigset_prep ($$$) {
 	my ($sig, $init, $each) = @_; # $sig: { signame => whatever }
 	my $ret = POSIX::SigSet->new;
 	$ret->$init or die "$init: $!";
-	for my $s (keys %$sig) {
+	for my $s (ref($sig) eq 'HASH' ? keys(%$sig) : @$sig) {
 		my $num = $SIGNUM{$s} // POSIX->can("SIG$s")->();
 		$ret->$each($num) or die "$each ($s => $num): $!";
 	}
@@ -259,6 +259,13 @@ sub sigset_prep ($$$) {
 sub allowset ($) { sigset_prep $_[0], 'fillset', 'delset' }
 sub unblockset ($) { sigset_prep $_[0], 'emptyset', 'addset' }
 
+sub allow_sigs (@) {
+	my @signames = @_;
+	my $tmp = allowset(\@signames);
+	sig_setmask($tmp, my $old = POSIX::SigSet->new);
+	on_destroy \&sig_setmask, $old;
+}
+
 # Start processing IO events. In most daemon programs this never exits. See
 # C<post_loop_do> for how to exit the loop.
 sub event_loop (;$$) {
@@ -266,17 +273,15 @@ sub event_loop (;$$) {
 	$Poller //= _InitPoller();
 	require PublicInbox::Sigfd if $sig;
 	my $sigfd = $sig ? PublicInbox::Sigfd->new($sig) : undef;
-	if ($sigfd && $sigfd->{is_kq}) {
-		my $tmp = allowset($sig);
-		local @SIG{keys %$sig} = values(%$sig);
-		sig_setmask($tmp, my $old = POSIX::SigSet->new);
+	local $SIG{PIPE} = 'IGNORE';
+	local @SIG{keys %$sig} = values(%$sig) if $sig;
+	if ($sigfd && $sigfd->{kq_sigs}) {
 		# Unlike Linux signalfd, EVFILT_SIGNAL can't handle
 		# signals received before the filter is created,
 		# so we peek at signals here.
-		sig_setmask($old);
+		my $restore = allow_sigs keys %$sig;
+		select undef, undef, undef, 0; # check sigs
 	}
-	local @SIG{keys %$sig} = values(%$sig) if $sig && !$sigfd;
-	local $SIG{PIPE} = 'IGNORE';
 	if (!$sigfd && $sig) {
 		# wake up every second to accept signals if we don't
 		# have signalfd or IO::KQueue:
diff --git a/lib/PublicInbox/Sigfd.pm b/lib/PublicInbox/Sigfd.pm
index b8a1ddfb..128d933e 100644
--- a/lib/PublicInbox/Sigfd.pm
+++ b/lib/PublicInbox/Sigfd.pm
@@ -8,27 +8,31 @@ use v5.12;
 use parent qw(PublicInbox::DS);
 use PublicInbox::Syscall qw(signalfd EPOLLIN EPOLLET %SIGNUM);
 use POSIX ();
+use autodie qw(kill open);
+my @num2name;
 
 # returns a coderef to unblock signals if neither signalfd or kqueue
 # are available.
 sub new {
 	my ($class, $sig) = @_;
-	my %signo = map {;
-		# $num => [ $cb, $signame ];
-		($SIGNUM{$_} // POSIX->can("SIG$_")->()) => [ $sig->{$_}, $_ ]
-	} keys %$sig;
-	my $self = bless { sig => \%signo }, $class;
+	my @signo;
+	for my $name (keys %$sig) {
+		my $num = $SIGNUM{$name} // POSIX->can("SIG$name")->();
+		push @signo, $num;
+		$num2name[$num] //= $name;
+	}
+	my $self = bless {}, $class;
 	my $io;
-	my $fd = signalfd([keys %signo]);
+	my $fd = signalfd(\@signo);
 	if (defined $fd && $fd >= 0) {
-		open($io, '+<&=', $fd) or die "open: $!";
+		open $io, '+<&=', $fd;
 	} elsif (eval { require PublicInbox::DSKQXS }) {
-		$io = PublicInbox::DSKQXS->signalfd([keys %signo]);
+		$io = PublicInbox::DSKQXS->signalfd(\@signo);
+		$self->{kq_sigs} = [ keys %$sig ];
 	} else {
 		return; # wake up every second to check for signals
 	}
 	$self->SUPER::new($io, EPOLLIN | EPOLLET);
-	$self->{is_kq} = 1 if tied(*$io);
 	$self;
 }
 
@@ -37,13 +41,26 @@ sub wait_once ($) {
 	my ($self) = @_;
 	# 128 == sizeof(struct signalfd_siginfo)
 	my $r = sysread($self->{sock}, my $buf, 128 * 64);
-	if (defined($r)) {
+	if ($self->{kq_sigs}) {
+		# kqueue doesn't consume signals the same way signalfd does,
+		# so the OS + Perl can make calls for us:
+		my $restore = PublicInbox::DS::allow_sigs @{$self->{kq_sigs}};
+		select undef, undef, undef, 0; # checks signals
+	} elsif (defined($r)) { # Linux signalfd
 		my $nr = $r / 128 - 1; # $nr may be -1
 		for my $off (0..$nr) {
 			# the first uint32_t of signalfd_siginfo: ssi_signo
-			my $signo = unpack('L', substr($buf, 128 * $off, 4));
-			my ($cb, $signame) = @{$self->{sig}->{$signo}};
-			$cb->($signame) if $cb ne 'IGNORE';
+			my $num = unpack('L', substr($buf, 128 * $off, 4));
+			my $name = $num2name[$num];
+			my $cb = $SIG{$name} || 'IGNORE';
+			if ($cb eq 'DEFAULT') {
+				my $restore = PublicInbox::DS::allow_sigs $name;
+				kill $name, $$;
+				select undef, undef, undef, 0; # checks signals
+				# $restore fires
+			} elsif (ref $cb) {
+				$cb->($name);
+			} # undef
 		}
 	}
 	$r;
diff --git a/t/sigfd.t b/t/sigfd.t
index 9a7b947d..eab85ed7 100644
--- a/t/sigfd.t
+++ b/t/sigfd.t
@@ -8,6 +8,7 @@ use Errno qw(ENOSYS);
 require_ok 'PublicInbox::Sigfd';
 use PublicInbox::DS;
 my ($linux_sigfd, $has_sigfd);
+use autodie qw(kill);
 
 SKIP: {
 	if ($^O ne 'linux' && !eval { require IO::KQueue }) {
@@ -23,7 +24,7 @@ SKIP: {
 	local $SIG{INT} = sub { $hit->{INT}->{normal}++ };
 	local $SIG{WINCH} = sub { $hit->{WINCH}->{normal}++ };
 	for my $s (qw(USR2 HUP TERM INT WINCH)) {
-		$sig->{$s} = sub { $hit->{$s}->{sigfd}++ };
+		$sig->{$s} = sub { die "SHOULD NOT BE CALLED ($s)" }
 	}
 	kill 'USR2', $$ or die "kill $!";
 	ok(!defined($hit->{USR2}), 'no USR2 yet') or diag explain($hit);
@@ -44,16 +45,13 @@ SKIP: {
 		is(select($rvec, undef, undef, undef), 1, 'select() works');
 		ok($sigfd->wait_once, 'wait_once reported success');
 		for my $s (qw(HUP INT)) {
-			is($hit->{$s}->{sigfd}, 1, "sigfd fired $s");
-			is($hit->{$s}->{normal}, undef,
-				"normal \$SIG{$s} not fired");
+			is($hit->{$s}->{normal}, 1, "sigfd fired $s");
 		}
 		SKIP: {
 			skip 'Linux sigfd-only behavior', 1 if !$linux_sigfd;
-			is($hit->{USR2}->{sigfd}, 1,
+			is($hit->{USR2}->{normal}, 1,
 				'USR2 sent before signalfd created received');
 		}
-		ok(!$hit->{USR2}->{normal}, 'USR2 not fired normally');
 		PublicInbox::DS->Reset;
 		$sigfd = undef;
 
@@ -64,26 +62,39 @@ SKIP: {
 		kill('HUP', $$) or die "kill $!";
 		local @PublicInbox::DS::post_loop_do = (sub {}); # loop once
 		PublicInbox::DS::event_loop();
-		is($hit->{HUP}->{sigfd}, 2, 'HUP sigfd fired in event loop') or
+		is($hit->{HUP}->{normal}, 2, 'HUP sigfd fired in event loop') or
 			diag explain($hit); # sometimes fails on FreeBSD 11.x
 		kill('TERM', $$) or die "kill $!";
 		kill('HUP', $$) or die "kill $!";
 		PublicInbox::DS::event_loop();
 		PublicInbox::DS->Reset;
-		is($hit->{TERM}->{sigfd}, 1, 'TERM sigfd fired in event loop');
-		is($hit->{HUP}->{sigfd}, 3, 'HUP sigfd fired in event loop');
-		ok($hit->{WINCH}->{sigfd}, 'WINCH sigfd fired in event loop');
+		is($hit->{TERM}->{normal}, 1, 'TERM sigfd fired in event loop');
+		is($hit->{HUP}->{normal}, 3, 'HUP sigfd fired in event loop');
+		ok($hit->{WINCH}->{normal}, 'WINCH sigfd fired in event loop');
+
+		my $restore = PublicInbox::DS::allow_sigs 'HUP';
+		kill 'HUP', $$;
+		select undef, undef, undef, 0;
+		is $hit->{HUP}->{normal}, 4, 'HUP sigfd fired after allow_sigs';
+
+		undef $restore;
+		kill 'HUP', $$;
+		vec($rvec = '', fileno($nbsig->{sock}), 1) = 1;
+		ok select($rvec, undef, undef, 1),
+			'select reports sigfd readiness';
+		is $hit->{HUP}->{normal}, 4, 'HUP not fired when sigs blocked';
+		$nbsig->event_step;
+		is $hit->{HUP}->{normal}, 5, 'HUP fires only on ->event_step';
+
+		kill 'HUP', $$;
+		is $hit->{HUP}->{normal}, 5, 'HUP not fired, yet';
+		$restore = PublicInbox::DS::allow_sigs 'HUP';
+		select(undef, undef, undef, 0);
+		is $hit->{HUP}->{normal}, 6, 'HUP fires from allow_sigs';
 	} else {
 		skip('signalfd disabled?', 10);
 	}
-	ok(!$hit->{USR2}->{normal}, 'USR2 still not fired normally');
 	PublicInbox::DS::sig_setmask($old);
-	SKIP: {
-		($has_sigfd && !$linux_sigfd) or
-			skip 'EVFILT_SIGNAL-only behavior check', 1;
-		is($hit->{USR2}->{normal}, 1,
-			"USR2 fired normally after unblocking on $^O");
-	}
 }
 
 done_testing;