From 08b543eb6c67cc19ea8e86afe6b9494df79e2fea Mon Sep 17 00:00:00 2001
From: Eric Wong <e@80x24.org>
Date: Sat, 23 Oct 2021 18:20:44 -0600
Subject: [PATCH] thread: avoid Perl5 internal scratchpad target cache

The use of array-returning built-ins such as `grep' inside
arrayref declarations appears to result in permanently allocated
scratchpad space for caching according to my malloc inspector.

Thread skeletons get discarded every response, but multiple
skeletons can exist in memory at once, so do what we can to
prevent long-lived allocations from being made, here.

In other words, replacing constructs such as:

	my $foo = [ grep(...) ];

with:

	my @foo = grep(...);

Seems to ensure the mortality of the underlying array.
---
 lib/PublicInbox/SearchThread.pm | 22 +++++++++++-----------
 lib/PublicInbox/SearchView.pm   |  4 ++--
 lib/PublicInbox/View.pm         |  4 ++--
 t/thread-cycle.t                |  4 ++--
 4 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/lib/PublicInbox/SearchThread.pm b/lib/PublicInbox/SearchThread.pm
index 507f25ba..f07dd696 100644
--- a/lib/PublicInbox/SearchThread.pm
+++ b/lib/PublicInbox/SearchThread.pm
@@ -83,15 +83,15 @@ sub thread {
 		}
 	}
 	my $ibx = $ctx->{ibx};
-	my $rootset = [ grep { # n.b.: delete prevents cyclic refs
+	my @rootset = grep { # n.b.: delete prevents cyclic refs
 			!delete($_->{parent}) && $_->visible($ibx)
-		} values %id_table ];
-	$rootset = $ordersub->($rootset);
-	$_->order_children($ordersub, $ctx) for @$rootset;
+		} values %id_table;
+	$ordersub->(\@rootset);
+	$_->order_children($ordersub, $ctx) for @rootset;
 
 	# parent imposter messages with reused Message-IDs
 	unshift(@{$id_table{$_->{mid}}->{children}}, $_) for @imposters;
-	$rootset;
+	\@rootset;
 }
 
 package PublicInbox::SearchThread::Msg;
@@ -172,12 +172,12 @@ sub order_children {
 	my @q = ($cur);
 	my $ibx = $ctx->{ibx};
 	while (defined($cur = shift @q)) {
-		my $c = $cur->{children}; # The hashref here...
-
-		$c = [ grep { !$seen{$_}++ && visible($_, $ibx) } values %$c ];
-		$c = $ordersub->($c) if scalar @$c > 1;
-		$cur->{children} = $c; # ...becomes an arrayref
-		push @q, @$c;
+		# the {children} hashref here...
+		my @c = grep { !$seen{$_}++ && visible($_, $ibx) }
+			values %{$cur->{children}};
+		$ordersub->(\@c) if scalar(@c) > 1;
+		$cur->{children} = \@c; # ...becomes an arrayref
+		push @q, @c;
 	}
 }
 
diff --git a/lib/PublicInbox/SearchView.pm b/lib/PublicInbox/SearchView.pm
index a42867c5..b1cdb480 100644
--- a/lib/PublicInbox/SearchView.pm
+++ b/lib/PublicInbox/SearchView.pm
@@ -274,10 +274,10 @@ sub search_nav_bot { # also used by WwwListing for searching extindex miscidx
 }
 
 sub sort_relevance {
-	[ sort {
+	@{$_[0]} = sort {
 		(eval { $b->topmost->{pct} } // 0) <=>
 		(eval { $a->topmost->{pct} } // 0)
-	} @{$_[0]} ]
+	} @{$_[0]};
 }
 
 sub mset_thread {
diff --git a/lib/PublicInbox/View.pm b/lib/PublicInbox/View.pm
index 116aa641..2e9cf705 100644
--- a/lib/PublicInbox/View.pm
+++ b/lib/PublicInbox/View.pm
@@ -1073,10 +1073,10 @@ sub _skel_ghost {
 }
 
 sub sort_ds {
-	[ sort {
+	@{$_[0]} = sort {
 		(eval { $a->topmost->{ds} } || 0) <=>
 		(eval { $b->topmost->{ds} } || 0)
-	} @{$_[0]} ];
+	} @{$_[0]};
 }
 
 # accumulate recent topics if search is supported
diff --git a/t/thread-cycle.t b/t/thread-cycle.t
index e89b1846..1e5dfb51 100644
--- a/t/thread-cycle.t
+++ b/t/thread-cycle.t
@@ -108,7 +108,7 @@ SKIP: {
 	eval 'package EmptyInbox; sub smsg_by_mid { undef }';
 	my $ctx = { ibx => bless {}, 'EmptyInbox' };
 	my $rootset = PublicInbox::SearchThread::thread($smsgs, sub {
-		[ sort { $a->{mid} cmp $b->{mid} } @{$_[0]} ] }, $ctx);
+		@{$_[0]} = sort { $a->{mid} cmp $b->{mid} } @{$_[0]} }, $ctx);
 	my $oldout = select $fh;
 	find_cycle($rootset);
 	select $oldout;
@@ -120,7 +120,7 @@ done_testing;
 sub thread_to_s {
 	my ($msgs) = @_;
 	my $rootset = PublicInbox::SearchThread::thread($msgs, sub {
-		[ sort { $a->{mid} cmp $b->{mid} } @{$_[0]} ] });
+		@{$_[0]} = sort { $a->{mid} cmp $b->{mid} } @{$_[0]} });
 	my $st = '';
 	my @q = map { (0, $_) } @$rootset;
 	while (@q) {
-- 
2.44.0