From 10bf54305da8422d9ece6b809996092c1c4b1786 Mon Sep 17 00:00:00 2001
From: Eric Wong <e@80x24.org>
Date: Sat, 26 Dec 2020 09:34:39 +0000
Subject: inboxidle: avoid needless syscalls on refresh

We don't have to replace a bunch of existing watches
with identical new ones.  On Linux with Linux::Inotify2
installed, this avoids a storm of inotify_add_watch(2)
and inotify_rm_watch(2) syscalls on SIGHUP with -imapd
and "-extindex --watch"
---
 lib/PublicInbox/InboxIdle.pm | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

(limited to 'lib')

diff --git a/lib/PublicInbox/InboxIdle.pm b/lib/PublicInbox/InboxIdle.pm
index 84b6d26f..508007d7 100644
--- a/lib/PublicInbox/InboxIdle.pm
+++ b/lib/PublicInbox/InboxIdle.pm
@@ -24,17 +24,26 @@ sub in2_arm ($$) { # PublicInbox::Config::each_inbox callback
 	my $dir = $ibx->{inboxdir};
 	my $inot = $self->{inot};
 	my $cur = $self->{pathmap}->{$dir} //= [];
+	my $lock = "$dir/".($ibx->version >= 2 ? 'inbox.lock' : 'ssoma.lock');
 
 	# transfer old subscriptions to the current inbox, cancel the old watch
-	if (my $old_ibx = $cur->[0]) {
+	my $old_ibx = $cur->[0];
+	$cur->[0] = $ibx;
+	if ($old_ibx) {
 		$ibx->{unlock_subs} and
 			die "BUG: $dir->{unlock_subs} should not exist";
 		$ibx->{unlock_subs} = $old_ibx->{unlock_subs};
+
+		# Linux::Inotify2::Watch::name matches if watches are the
+		# same, no point in replacing a watch of the same name
+		if ($cur->[1]->name eq $lock) {
+			$self->{on_unlock}->{$lock} = $ibx;
+			return;
+		}
+		# rare, name changed (v1 inbox converted to v2)
 		$cur->[1]->cancel; # Linux::Inotify2::Watch::cancel
 	}
-	$cur->[0] = $ibx;
 
-	my $lock = "$dir/".($ibx->version >= 2 ? 'inbox.lock' : 'ssoma.lock');
 	if (my $w = $cur->[1] = $inot->watch($lock, $IN_MODIFY)) {
 		$self->{on_unlock}->{$w->name} = $ibx;
 	} else {
-- 
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