[PATCH 11/34] watch: use signalfd for Maildir watching

[Eric Wong <e@yhbt.net>]

We can get rid of the janky wannabe
self-using-a-directory-instead-of-pipe thing we needed to
workaround Filesys::Notify::Simple being blocking.

For existing Maildir users, this should be more robust and
immune to missed wakeups for to signalfd and kqueue-enabled
systems; as well as being immune to BOFHs clearing $TMPDIR
and preventing notifications from firing.

The IMAP IDLE code still uses normal Perl signals, so it's still
vulnerable to missed wakeups.  That will be addressed in future
commits.
---
 lib/PublicInbox/Daemon.pm       | 19 ++++------
 lib/PublicInbox/Sigfd.pm        | 12 +++++-
 lib/PublicInbox/WatchMaildir.pm | 67 ++++++++++++++++++---------------
 script/public-inbox-watch       | 24 +++++++++---
 t/watch_maildir.t               |  4 +-
 5 files changed, 75 insertions(+), 51 deletions(-)

diff --git a/lib/PublicInbox/Daemon.pm b/lib/PublicInbox/Daemon.pm
index 2f63bd73b4a..ab0c2226e40 100644
--- a/lib/PublicInbox/Daemon.pm
+++ b/lib/PublicInbox/Daemon.pm
@@ -18,9 +18,9 @@ use PublicInbox::DS qw(now);
 use PublicInbox::Syscall qw(SFD_NONBLOCK);
 require PublicInbox::Listener;
 require PublicInbox::ParentPipe;
-require PublicInbox::Sigfd;
+use PublicInbox::Sigfd;
 my @CMD;
-my ($set_user, $oldset, $newset);
+my ($set_user, $oldset);
 my (@cfg_listen, $stdout, $stderr, $group, $user, $pid_file, $daemonize);
 my $worker_processes = 1;
 my @listeners;
@@ -72,15 +72,10 @@ sub accept_tls_opt ($) {
 	{ SSL_server => 1, SSL_startHandshake => 0, SSL_reuse_ctx => $ctx };
 }
 
-sub sig_setmask { sigprocmask(SIG_SETMASK, @_) or die "sigprocmask: $!" }
-
 sub daemon_prepare ($) {
 	my ($default_listen) = @_;
 	my $listener_names = {}; # sockname => IO::Handle
-	$oldset = POSIX::SigSet->new();
-	$newset = POSIX::SigSet->new();
-	$newset->fillset or die "fillset: $!";
-	sig_setmask($newset, $oldset);
+	my $oldset = PublicInbox::Sigfd::block_signals();
 	@CMD = ($0, @ARGV);
 	my %opts = (
 		'l|listen=s' => \@cfg_listen,
@@ -515,7 +510,7 @@ EOF
 	};
 	my $sigfd = PublicInbox::Sigfd->new($sig, 0);
 	local %SIG = (%SIG, %$sig) if !$sigfd;
-	sig_setmask($oldset) if !$sigfd;
+	PublicInbox::restore_signals($oldset) if !$sigfd;
 	while (1) { # main loop
 		my $n = scalar keys %pids;
 		unless (@listeners) {
@@ -531,7 +526,7 @@ EOF
 		}
 		my $want = $worker_processes - 1;
 		if ($n <= $want) {
-			sig_setmask($newset) if !$sigfd;
+			PublicInbox::Sigfd::block_signals() if !$sigfd;
 			for my $i ($n..$want) {
 				my $pid = fork;
 				if (!defined $pid) {
@@ -544,7 +539,7 @@ EOF
 					$pids{$pid} = $i;
 				}
 			}
-			sig_setmask($oldset) if !$sigfd;
+			PubliInbox::Sigfd::set_sigmask($oldset) if !$sigfd;
 		}
 
 		if ($sigfd) { # Linux and IO::KQueue users:
@@ -632,7 +627,7 @@ sub daemon_loop ($$$$) {
 	if (!$sigfd) {
 		# wake up every second to accept signals if we don't
 		# have signalfd or IO::KQueue:
-		sig_setmask($oldset);
+		PublicInbox::Sigfd::set_sigmask($oldset);
 		PublicInbox::DS->SetLoopTimeout(1000);
 	}
 	PublicInbox::DS->EventLoop;
diff --git a/lib/PublicInbox/Sigfd.pm b/lib/PublicInbox/Sigfd.pm
index f500902ea67..17456592a7e 100644
--- a/lib/PublicInbox/Sigfd.pm
+++ b/lib/PublicInbox/Sigfd.pm
@@ -5,7 +5,7 @@ use strict;
 use parent qw(PublicInbox::DS);
 use fields qw(sig); # hashref similar to %SIG, but signal numbers as keys
 use PublicInbox::Syscall qw(signalfd EPOLLIN EPOLLET SFD_NONBLOCK);
-use POSIX ();
+use POSIX qw(:signal_h);
 use IO::Handle ();
 
 # returns a coderef to unblock signals if neither signalfd or kqueue
@@ -62,4 +62,14 @@ sub event_step {
 	while (wait_once($_[0])) {} # non-blocking
 }
 
+sub sig_setmask { sigprocmask(SIG_SETMASK, @_) or die "sigprocmask: $!" }
+
+sub block_signals () {
+	my $oldset = POSIX::SigSet->new;
+	my $newset = POSIX::SigSet->new;
+	$newset->fillset or die "fillset: $!";
+	sig_setmask($newset, $oldset);
+	$oldset;
+}
+
 1;
diff --git a/lib/PublicInbox/WatchMaildir.pm b/lib/PublicInbox/WatchMaildir.pm
index 22f190366a4..4d3cd032e5a 100644
--- a/lib/PublicInbox/WatchMaildir.pm
+++ b/lib/PublicInbox/WatchMaildir.pm
@@ -8,9 +8,9 @@ use strict;
 use warnings;
 use PublicInbox::Eml;
 use PublicInbox::InboxWritable;
-use File::Temp 0.19 (); # 0.19 for ->newdir
 use PublicInbox::Filter::Base qw(REJECT);
 use PublicInbox::Spamcheck;
+use PublicInbox::Sigfd;
 use PublicInbox::DS qw(now);
 use POSIX qw(_exit WNOHANG);
 *mime_from_path = \&PublicInbox::InboxWritable::mime_from_path;
@@ -108,6 +108,7 @@ sub new {
 		imap => scalar keys %imap ? \%imap : undef,
 		importers => {},
 		opendirs => {}, # dirname => dirhandle (in progress scans)
+		ops => [], # 'quit', 'full'
 	}, $class;
 }
 
@@ -195,7 +196,9 @@ sub _try_path {
 
 sub quit {
 	my ($self) = @_;
-	trigger_scan($self, 'quit') or $self->{quit} = 1;
+	$self->{quit} = 1;
+	%{$self->{opendirs}} = ();
+	_done_for_now($self);
 	if (my $imap_pid = $self->{-imap_pid}) {
 		kill('QUIT', $imap_pid);
 	}
@@ -213,24 +216,15 @@ sub quit {
 sub watch_fs {
 	my ($self) = @_;
 	require PublicInbox::DirIdle;
-	my $scan = File::Temp->newdir("public-inbox-watch.$$.scan.XXXXXX",
-					TMPDIR => 1);
-	my $scandir = $self->{scandir} = $scan->dirname;
-	my $scan_re = qr!\A$scandir/!;
 	my $done = sub {
 		delete $self->{done_timer};
 		_done_for_now($self);
 	};
 	my $cb = sub {
-		my $path = $_[0]->fullname;
-		if ($path =~ $scan_re) {
-			scan($self, $path);
-		} else {
-			_try_path($self, $path);
-		}
+		_try_path($self, $_[0]->fullname);
 		$self->{done_timer} //= PublicInbox::DS::requeue($done);
 	};
-	my $di = PublicInbox::DirIdle->new([@{$self->{mdir}}, $scandir], $cb);
+	my $di = PublicInbox::DirIdle->new($self->{mdir}, $cb);
 	PublicInbox::DS->SetPostLoopCallback(sub { !$self->{quit} });
 	PublicInbox::DS->EventLoop;
 	_done_for_now($self);
@@ -485,6 +479,12 @@ sub watch_imap_idle_1 ($$$) {
 	}
 }
 
+sub watch_atfork_child ($) {
+	my ($self) = @_;
+	PublicInbox::Sigfd::sig_setmask($self->{oldset});
+	%SIG = (%SIG, %{$self->{sig}});
+}
+
 sub watch_imap_idle_all ($$) {
 	my ($self, $idle) = @_; # $idle = [[ uri1, intvl1 ], [ uri2, intvl2 ]]
 	$self->{mics} = {}; # going to be forking, so disconnect
@@ -494,6 +494,7 @@ sub watch_imap_idle_all ($$) {
 			my ($uri, $intvl) = @$uri_intvl;
 			defined(my $pid = fork) or die "fork: $!";
 			if ($pid == 0) {
+				watch_atfork_child($self);
 				delete $self->{idle_pids};
 				watch_imap_idle_1($self, $uri, $intvl);
 				_exit(0);
@@ -564,15 +565,20 @@ sub watch_imap ($) {
 }
 
 sub watch {
-	my ($self) = @_;
+	my ($self, $sig, $oldset) = @_;
+	$self->{oldset} = $oldset;
+	$self->{sig} = $sig;
 	if ($self->{mdre} && $self->{imap}) {
 		defined(my $pid = fork) or die "fork: $!";
 		if ($pid == 0) {
+			watch_atfork_child($self);
 			imap_start($self);
 			goto &watch_imap;
 		}
 		$self->{-imap_pid} = $pid;
 	} elsif ($self->{imap}) {
+		# not a child process, but no signalfd, yet:
+		watch_atfork_child($self);
 		imap_start($self);
 		goto &watch_imap;
 	}
@@ -580,23 +586,18 @@ sub watch {
 }
 
 sub trigger_scan {
-	my ($self, $base) = @_;
-	my $dir = $self->{scandir} or return;
-	open my $fh, '>', "$dir/$base" or die "open $dir/$base failed: $!\n";
-	close $fh or die "close $dir/$base failed: $!\n";
+	my ($self, $op) = @_;
+	push @{$self->{ops}}, $op;
+	PublicInbox::DS::requeue($self);
 }
 
-sub scan {
-	my ($self, $path) = @_;
-	if ($path =~ /quit\z/) {
-		%{$self->{opendirs}} = ();
-		_done_for_now($self);
-		delete $self->{scandir};
-		$self->{quit} = 1;
-		return;
-	}
-	# else: $path =~ /(cont|full)\z/
+# called directly, and by PublicInbox::DS
+sub event_step ($) {
+	my ($self) = @_;
 	return if $self->{quit};
+	my $op = shift @{$self->{ops}};
+
+	# continue existing scan
 	my $max = 10;
 	my $opendirs = $self->{opendirs};
 	my @dirnames = keys %$opendirs;
@@ -609,7 +610,7 @@ sub scan {
 		}
 		$opendirs->{$dir} = $dh if $n < 0;
 	}
-	if ($path =~ /full\z/) {
+	if ($op && $op eq 'full') {
 		foreach my $dir (@{$self->{mdir}}) {
 			next if $opendirs->{$dir}; # already in progress
 			my $ok = opendir(my $dh, $dir);
@@ -627,7 +628,13 @@ sub scan {
 	}
 	_done_for_now($self);
 	# do we have more work to do?
-	trigger_scan($self, 'cont') if keys %$opendirs;
+	PublicInbox::DS::requeue($self) if keys %$opendirs;
+}
+
+sub scan {
+	my ($self, $op) = @_;
+	push @{$self->{ops}}, $op;
+	goto &event_step;
 }
 
 sub _importer_for {
diff --git a/script/public-inbox-watch b/script/public-inbox-watch
index 2057066a2a9..b6d545adad7 100755
--- a/script/public-inbox-watch
+++ b/script/public-inbox-watch
@@ -5,6 +5,10 @@ use strict;
 use warnings;
 use PublicInbox::WatchMaildir;
 use PublicInbox::Config;
+use PublicInbox::DS;
+use PublicInbox::Sigfd;
+use PublicInbox::Syscall qw(SFD_NONBLOCK);
+my $oldset = PublicInbox::Sigfd::block_signals();
 my ($config, $watch_md);
 my $reload = sub {
 	$config = PublicInbox::Config->new;
@@ -14,14 +18,22 @@ my $reload = sub {
 $reload->();
 if ($watch_md) {
 	my $scan = sub { $watch_md->trigger_scan('full') if $watch_md };
-	$SIG{HUP} = $reload;
-	$SIG{USR1} = $scan;
-	$SIG{ALRM} = sub { $SIG{ALRM} = 'DEFAULT'; $scan->() };
-	$SIG{QUIT} = $SIG{TERM} = $SIG{INT} = sub {
+	my $quit = sub {
 		$watch_md->quit if $watch_md;
 		$watch_md = undef;
 	};
+	my $sig = { HUP => $reload, USR1 => $scan };
+	$sig->{QUIT} = $sig->{TERM} = $sig->{INT} = $quit;
+
 	# --no-scan is only intended for testing atm, undocumented.
-	alarm(1) unless (grep(/\A--no-scan\z/, @ARGV));
-	$watch_md->watch while ($watch_md);
+	unless (grep(/\A--no-scan\z/, @ARGV)) {
+		PublicInbox::DS::requeue($scan);
+	}
+	my $sigfd = PublicInbox::Sigfd->new($sig, SFD_NONBLOCK);
+	local %SIG = (%SIG, %$sig) if !$sigfd;
+	if (!$sigfd) {
+		PublicInbox::Sigfd::set_sigmask($oldset);
+		PublicInbox::DS->SetLoopTimeout(1000);
+	}
+	$watch_md->watch($sig, $oldset) while ($watch_md);
 }
diff --git a/t/watch_maildir.t b/t/watch_maildir.t
index a2c09b0351b..c8658140cf2 100644
--- a/t/watch_maildir.t
+++ b/t/watch_maildir.t
@@ -184,10 +184,10 @@ More majordomo info at  http://vger.kernel.org/majordomo-info.html\n);
 			my $ino_fdinfo = "/proc/$wm->{pid}/fdinfo/$ino_fd";
 			while (time < $end && open(my $fh, '<', $ino_fdinfo)) {
 				@ino_info = grep(/^inotify wd:/, <$fh>);
-				last if @ino_info >= 4;
+				last if @ino_info >= 3;
 				tick;
 			}
-			$sleep = undef if @ino_info >= 4;
+			$sleep = undef if @ino_info >= 3;
 		}
 	}
 	if ($sleep) {