From 94ae705673cb03045a109041eec9a6704b8a735b Mon Sep 17 00:00:00 2001
From: Eric Wong <e@yhbt.net>
Date: Mon, 31 Aug 2020 04:41:34 +0000
Subject: [PATCH] watch: avoid unnecessary spawning on spam removals

This should further mitigate lock contention problems
when -watch is configured to watch on a Maildir for spam
while performing a large NNTP import.

There is now a small risk a message won't get removed because if
it's in the current (uncommitted) fast-import batch, but
unlikely given the batch size is now only 10 messages.

If a that small window is hit, flipping the \Seen flag
(e.g. marking it unread, and then read again) will trigger
another removal attempt via IMAP or Maildir.
---
 lib/PublicInbox/Import.pm     |  3 +++
 lib/PublicInbox/V2Writable.pm |  3 +++
 lib/PublicInbox/Watch.pm      | 31 +++++++++++++++++++++++++------
 3 files changed, 31 insertions(+), 6 deletions(-)

diff --git a/lib/PublicInbox/Import.pm b/lib/PublicInbox/Import.pm
index 700b4026..ee5ca2ea 100644
--- a/lib/PublicInbox/Import.pm
+++ b/lib/PublicInbox/Import.pm
@@ -461,6 +461,9 @@ sub init_bare {
 	}
 }
 
+# true if locked and active
+sub active { !!$_[0]->{out} }
+
 sub done {
 	my ($self) = @_;
 	my $w = delete $self->{out} or return;
diff --git a/lib/PublicInbox/V2Writable.pm b/lib/PublicInbox/V2Writable.pm
index f2288904..553dd839 100644
--- a/lib/PublicInbox/V2Writable.pm
+++ b/lib/PublicInbox/V2Writable.pm
@@ -655,6 +655,9 @@ sub checkpoint ($;$) {
 # public
 sub barrier { checkpoint($_[0], 1) };
 
+# true if locked and active
+sub active { !!$_[0]->{im} }
+
 # public
 sub done {
 	my ($self) = @_;
diff --git a/lib/PublicInbox/Watch.pm b/lib/PublicInbox/Watch.pm
index 5f786139..0bb92d0a 100644
--- a/lib/PublicInbox/Watch.pm
+++ b/lib/PublicInbox/Watch.pm
@@ -134,15 +134,34 @@ sub _done_for_now {
 sub remove_eml_i { # each_inbox callback
 	my ($ibx, $arg) = @_;
 	my ($self, $eml, $loc) = @$arg;
+
 	eval {
-		my $im = _importer_for($self, $ibx);
-		$im->remove($eml, 'spam');
-		if (my $scrub = $ibx->filter($im)) {
-			my $scrubbed = $scrub->scrub($eml, 1);
-			if ($scrubbed && $scrubbed != REJECT) {
-				$im->remove($scrubbed, 'spam');
+		# try to avoid taking a lock or unnecessary spawning
+		my $im = $self->{importers}->{"$ibx"};
+		my $scrubbed;
+		if ((!$im || !$im->active) && $ibx->over) {
+			if (content_exists($ibx, $eml)) {
+				# continue
+			} elsif (my $scrub = $ibx->filter($im)) {
+				$scrubbed = $scrub->scrub($eml, 1);
+				if ($scrubbed && $scrubbed != REJECT &&
+					  !content_exists($ibx, $scrubbed)) {
+					return;
+				}
+			} else {
+				return;
 			}
 		}
+
+		$im //= _importer_for($self, $ibx); # may spawn fast-import
+		$im->remove($eml, 'spam');
+		$scrubbed //= do {
+			my $scrub = $ibx->filter($im);
+			$scrub ? $scrub->scrub($eml, 1) : undef;
+		};
+		if ($scrubbed && $scrubbed != REJECT) {
+			$im->remove($scrubbed, 'spam');
+		}
 	};
 	if ($@) {
 		warn "error removing spam at: $loc from $ibx->{name}: $@\n";
-- 
2.44.0