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From: Eric Wong <e@80x24.org>
To: meta@public-inbox.org
Subject: [RFC] lei: address lifetime problems from Linux::Inotify2
Date: Wed, 28 Jul 2021 12:34:33 +0000
Message-Id: <20210728123433.30248-1-e@80x24.org>
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Linux::Inotify2 doesn't supply an explicit close() wrapper,
and Linux::Inotify2::Event objects maintain a reference to the
parent Linux::Inotify2 object, so we were leaking inotify FDs
into the "lei note-event" worker processes.

This delays the fork()-ing code paths into the next tick of the
event loop to ensure the inotify FD is closed when $dir_idle
is undef'ed in ->_lei_atfork_child.

Note: I'm not sure if I want to keep this, since
The correct fix would be to have a way to close inotify FDs,
but the current Linux::Inotify2 API doesn't make it easy.
And leaking an inotify FD isn't the worst thing in the world,
since it won't hang other processes.  So maybe the cure
is worse than the disease, in this case.
---
 lib/PublicInbox/LEI.pm | 31 ++++++++++++++++++++++---------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/lib/PublicInbox/LEI.pm b/lib/PublicInbox/LEI.pm
index d9fd40fd..b81f95c9 100644
--- a/lib/PublicInbox/LEI.pm
+++ b/lib/PublicInbox/LEI.pm
@@ -28,8 +28,8 @@ use Time::HiRes qw(stat); # ctime comparisons for config cache
 use File::Path qw(mkpath);
 use File::Spec;
 our $quit = \&CORE::exit;
-our ($current_lei, $errors_log, $listener, $oldset, $dir_idle,
-	$recv_cmd, $send_cmd);
+our ($current_lei, $errors_log, $listener, $oldset,
+	$dir_idle, $lne_nxt, $lne_q, $recv_cmd, $send_cmd);
 my $GLP = Getopt::Long::Parser->new;
 $GLP->configure(qw(gnu_getopt no_ignore_case auto_abbrev));
 my $GLP_PASS = Getopt::Long::Parser->new;
@@ -557,6 +557,8 @@ sub _lei_atfork_child {
 	close $listener if $listener;
 	undef $listener;
 	undef $dir_idle;
+	undef $lne_nxt;
+	undef $lne_q;
 	%PATH2CFG = ();
 	$MDIR2CFGPATH = {};
 	eval 'no warnings; undef $PublicInbox::LeiNoteEvent::to_flush';
@@ -1153,6 +1155,21 @@ sub cfg2lei ($) {
 	$lei;
 }
 
+sub lne_task { # requeue, runs without dir_idle stuff on stack
+	undef $lne_nxt;
+	my $q = $lne_q // return;
+	$lne_q = undef;
+
+	while (my ($loc, $nc, $bn, $fn, $cfg) = splice(@$q, 0, 5)) {
+		eval {
+			local %ENV = %{$cfg->{-env}};
+			my $lei = cfg2lei($cfg);
+			$lei->dispatch('note-event', $loc, $nc, $bn, $fn);
+		};
+		warn "E note-event $cfg->{-f}: $@\n" if $@;
+	}
+}
+
 sub dir_idle_handler ($) { # PublicInbox::DirIdle callback
 	my ($ev) = @_; # Linux::Inotify2::Event or duck type
 	my $fn = $ev->fullname;
@@ -1161,14 +1178,9 @@ sub dir_idle_handler ($) { # PublicInbox::DirIdle callback
 		$nc = '' if $ev->IN_DELETE;
 		for my $f (keys %{$MDIR2CFGPATH->{$mdir} // {}}) {
 			my $cfg = $PATH2CFG{$f} // next;
-			eval {
-				local %ENV = %{$cfg->{-env}};
-				my $lei = cfg2lei($cfg);
-				$lei->dispatch('note-event',
-						"maildir:$mdir", $nc, $bn, $fn);
-			};
-			warn "E note-event $f: $@\n" if $@;
+			push @$lne_q, "maildir:$mdir", $nc, $bn, $fn, $cfg;
 		}
+		$lne_nxt //= PublicInbox::DS::requeue(\&lne_task) if $lne_q;
 	}
 	if ($ev->can('cancel') && ($ev->IN_IGNORE || $ev->IN_UNMOUNT)) {
 		$ev->cancel;
@@ -1261,6 +1273,7 @@ sub lazy_start {
 	undef $sig;
 	local $SIG{PIPE} = 'IGNORE';
 	require PublicInbox::DirIdle;
+	local ($lne_q, $lne_nxt);
 	local $dir_idle = PublicInbox::DirIdle->new([$sock_dir], sub {
 		# just rely on wakeup to hit PostLoopCallback set below
 		dir_idle_handler($_[0]) if $_[0]->fullname ne $path;