watch: use signalfd for Maildir watching

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 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.

1 files changed, 18 insertions, 6 deletions

diff --git a/script/public-inbox-watch b/script/public-inbox-watch
index 2057066a..b6d545ad 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);
 }