[PATCH] searchthread: reduce indirection by removing container

[PATCH] searchthread: reduce indirection by removing container

[Eric Wong]

We can rid ourselves of a layer of indirection by subclassing
PublicInbox::Smsg instead of using a container object to hold
each $smsg.  Furthermore, the `{id}' vs. `{mid}' field name
confusion is eliminated.

This reduces the size of the $rootset passed to walk_thread by
around 15%, that is over 50K memory when rendering a /$INBOX/
landing page.
---
 Documentation/technical/data_structures.txt |  8 +--
 lib/PublicInbox/SearchThread.pm             | 67 ++++++++++++---------
 lib/PublicInbox/SearchView.pm               |  4 +-
 lib/PublicInbox/View.pm                     | 55 +++++++++--------
 t/thread-cycle.t                            |  5 +-
 5 files changed, 75 insertions(+), 64 deletions(-)

diff --git a/Documentation/technical/data_structures.txt b/Documentation/technical/data_structures.txt
index 08dfc7ac..46d5acff 100644
--- a/Documentation/technical/data_structures.txt
+++ b/Documentation/technical/data_structures.txt
@@ -61,15 +61,13 @@ Per-message classes
   There may be hundreds or thousands of these objects in memory
   at-a-time, so fields are pruned if unneeded.
 
-* PublicInbox::SearchThread::Msg - container for message threading
+* PublicInbox::SearchThread::Msg - subclass of Smsg
   Common abbreviation: $cont or $node
   Used by: PublicInbox::WWW
 
-  The container we use for a non-recursive[1] variant of
+  The structure we use for a non-recursive[1] variant of
   JWZ's algorithm: <https://www.jwz.org/doc/threading.html>.
-  This holds a $smsg and is only used for message threading.
-  This wrapper class may go away in the future and handled
-  directly by PublicInbox::Smsg to save memory.
+  Nowadays, this is a re-blessed $smsg with additional fields.
 
   As with $smsg objects, there may be hundreds or thousands
   of these objects in memory at-a-time.
diff --git a/lib/PublicInbox/SearchThread.pm b/lib/PublicInbox/SearchThread.pm
index 38d1aa6e..60f692b2 100644
--- a/lib/PublicInbox/SearchThread.pm
+++ b/lib/PublicInbox/SearchThread.pm
@@ -24,7 +24,16 @@ use PublicInbox::MID qw($MID_EXTRACT);
 
 sub thread {
 	my ($msgs, $ordersub, $ctx) = @_;
-	my $id_table = {};
+
+	# A. put all current $msgs (non-ghosts) into %id_table
+	my %id_table = map {;
+		# this delete saves around 4K across 1K messages
+		# TODO: move this to a more appropriate place, breaks tests
+		# if we do it during psgi_cull
+		delete $_->{num};
+
+		$_->{mid} => PublicInbox::SearchThread::Msg::cast($_);
+	} @$msgs;
 
 	# Sadly, we sort here anyways since the fill-in-the-blanks References:
 	# can be shakier if somebody used In-Reply-To with multiple, disparate
@@ -32,36 +41,21 @@ sub thread {
 	# always determine ordering when somebody uses multiple In-Reply-To.
 	# We'll trust the client Date: header here instead of the Received:
 	# time since this is for display (and not retrieval)
-	_add_message($id_table, $_) for sort { $a->{ds} <=> $b->{ds} } @$msgs;
+	_set_parent(\%id_table, $_) for sort { $a->{ds} <=> $b->{ds} } @$msgs;
 	my $ibx = $ctx->{-inbox};
 	my $rootset = [ grep {
 			!delete($_->{parent}) && $_->visible($ibx)
-		} values %$id_table ];
-	$id_table = undef;
+		} values %id_table ];
 	$rootset = $ordersub->($rootset);
 	$_->order_children($ordersub, $ctx) for @$rootset;
 	$rootset;
 }
 
-sub _get_cont_for_id ($$) {
-	my ($id_table, $mid) = @_;
-	$id_table->{$mid} ||= PublicInbox::SearchThread::Msg->new($mid);
-}
-
-sub _add_message ($$) {
-	my ($id_table, $smsg) = @_;
-
-	# A. if id_table...
-	my $this = _get_cont_for_id($id_table, $smsg->{mid});
-	$this->{smsg} = $smsg;
-
-	# saves around 4K across 1K messages
-	# TODO: move this to a more appropriate place, breaks tests
-	# if we do it during psgi_cull
-	delete $smsg->{num};
+sub _set_parent ($$) {
+	my ($id_table, $this) = @_;
 
 	# B. For each element in the message's References field:
-	defined(my $refs = $smsg->{references}) or return;
+	defined(my $refs = $this->{references}) or return;
 
 	# This loop exists to help fill in gaps left from missing
 	# messages.  It is not needed in a perfect world where
@@ -70,7 +64,8 @@ sub _add_message ($$) {
 	my $prev;
 	foreach my $ref ($refs =~ m/$MID_EXTRACT/go) {
 		# Find a Container object for the given Message-ID
-		my $cont = _get_cont_for_id($id_table, $ref);
+		my $cont = $id_table->{$ref} //=
+			PublicInbox::SearchThread::Msg::ghost($ref);
 
 		# Link the References field's Containers together in
 		# the order implied by the References header
@@ -96,22 +91,31 @@ sub _add_message ($$) {
 }
 
 package PublicInbox::SearchThread::Msg;
+use base qw(PublicInbox::Smsg);
 use strict;
 use warnings;
 use Carp qw(croak);
 
-sub new {
+# declare a ghost smsg (determined by absence of {blob})
+sub ghost {
 	bless {
-		id => $_[1],
+		mid => $_[0],
 		children => {}, # becomes an array when sorted by ->order(...)
-	}, $_[0];
+	}, __PACKAGE__;
+}
+
+# give a existing smsg the methods of this class
+sub cast {
+	my ($smsg) = @_;
+	$smsg->{children} = {};
+	bless $smsg, __PACKAGE__;
 }
 
 sub topmost {
 	my ($self) = @_;
 	my @q = ($self);
 	while (my $cont = shift @q) {
-		return $cont if $cont->{smsg};
+		return $cont if $cont->{blob};
 		push @q, values %{$cont->{children}};
 	}
 	undef;
@@ -122,7 +126,7 @@ sub add_child {
 	croak "Cowardly refusing to become my own parent: $self"
 	  if $self == $child;
 
-	my $cid = $child->{id};
+	my $cid = $child->{mid};
 
 	# reparenting:
 	if (defined(my $parent = $child->{parent})) {
@@ -148,8 +152,13 @@ sub has_descendent {
 # being folded/mangled by a MUA, and not a missing message.
 sub visible ($$) {
 	my ($self, $ibx) = @_;
-	($self->{smsg} ||= eval { $ibx->smsg_by_mid($self->{id}) }) ||
-	 (scalar values %{$self->{children}});
+	return 1 if $self->{blob};
+	if (my $by_mid = $ibx->smsg_by_mid($self->{mid})) {
+		%$self = (%$self, %$by_mid);
+		1;
+	} else {
+		(scalar values %{$self->{children}});
+	}
 }
 
 sub order_children {
diff --git a/lib/PublicInbox/SearchView.pm b/lib/PublicInbox/SearchView.pm
index 4fbf59ef..4336e4d9 100644
--- a/lib/PublicInbox/SearchView.pm
+++ b/lib/PublicInbox/SearchView.pm
@@ -243,8 +243,8 @@ sub search_nav_bot {
 
 sub sort_relevance {
 	[ sort {
-		(eval { $b->topmost->{smsg}->{pct} } // 0) <=>
-		(eval { $a->topmost->{smsg}->{pct} } // 0)
+		(eval { $b->topmost->{pct} } // 0) <=>
+		(eval { $a->topmost->{pct} } // 0)
 	} @{$_[0]} ]
 }
 
diff --git a/lib/PublicInbox/View.pm b/lib/PublicInbox/View.pm
index b6d7acaf..9b62ed3c 100644
--- a/lib/PublicInbox/View.pm
+++ b/lib/PublicInbox/View.pm
@@ -297,11 +297,9 @@ sub _th_index_lite {
 	my $nr_c = scalar @$children;
 	my $nr_s = 0;
 	my $siblings;
-	if (my $smsg = $node->{smsg}) {
-		# delete saves about 200KB on a 1K message thread
-		if (my $refs = delete $smsg->{references}) {
-			($$irt) = ($refs =~ m/$MID_EXTRACT\z/o);
-		}
+	# delete saves about 200KB on a 1K message thread
+	if (my $refs = delete $node->{references}) {
+		($$irt) = ($refs =~ m/$MID_EXTRACT\z/o);
 	}
 	my $irt_map = $mapping->{$$irt} if defined $$irt;
 	if (defined $irt_map) {
@@ -310,12 +308,12 @@ sub _th_index_lite {
 		$rv .= $pad . $irt_map->[0];
 		if ($idx > 0) {
 			my $prev = $siblings->[$idx - 1];
-			my $pmid = $prev->{id};
+			my $pmid = $prev->{mid};
 			if ($idx > 2) {
 				my $s = ($idx - 1). ' preceding siblings ...';
 				$rv .= pad_link($pmid, $level, $s);
 			} elsif ($idx == 2) {
-				my $ppmid = $siblings->[0]->{id};
+				my $ppmid = $siblings->[0]->{mid};
 				$rv .= $pad . $mapping->{$ppmid}->[0];
 			}
 			$rv .= $pad . $mapping->{$pmid}->[0];
@@ -328,26 +326,26 @@ sub _th_index_lite {
 	$attr =~ s!<a\nhref=[^>]+>([^<]+)</a>!$1!s; # no point linking to self
 	$rv .= "<b>@ $attr";
 	if ($nr_c) {
-		my $cmid = $children->[0]->{id};
+		my $cmid = $children->[0]->{mid};
 		$rv .= $pad . $mapping->{$cmid}->[0];
 		if ($nr_c > 2) {
 			my $s = ($nr_c - 1). ' more replies';
 			$rv .= pad_link($cmid, $level + 1, $s);
 		} elsif (my $cn = $children->[1]) {
-			$rv .= $pad . $mapping->{$cn->{id}}->[0];
+			$rv .= $pad . $mapping->{$cn->{mid}}->[0];
 		}
 	}
 
 	my $next = $siblings->[$idx+1] if $siblings && $idx >= 0;
 	if ($next) {
-		my $nmid = $next->{id};
+		my $nmid = $next->{mid};
 		$rv .= $pad . $mapping->{$nmid}->[0];
 		my $nnext = $nr_s - $idx;
 		if ($nnext > 2) {
 			my $s = ($nnext - 1).' subsequent siblings';
 			$rv .= pad_link($nmid, $level, $s);
 		} elsif (my $nn = $siblings->[$idx + 2]) {
-			$rv .= $pad . $mapping->{$nn->{id}}->[0];
+			$rv .= $pad . $mapping->{$nn->{mid}}->[0];
 		}
 	}
 	$rv .= $pad ."<a\nhref=#r$id>$s_s, $s_c; $ctx->{s_nr}</a>\n";
@@ -369,7 +367,7 @@ sub walk_thread ($$$) {
 
 sub pre_thread  { # walk_thread callback
 	my ($ctx, $level, $node, $idx) = @_;
-	$ctx->{mapping}->{$node->{id}} = [ '', $node, $idx, $level ];
+	$ctx->{mapping}->{$node->{mid}} = [ '', $node, $idx, $level ];
 	skel_dump($ctx, $level, $node);
 }
 
@@ -388,8 +386,8 @@ sub stream_thread_i { # PublicInbox::WwwStream::getline callback
 		my $node = shift @$q or next;
 		my $cl = $level + 1;
 		unshift @$q, map { ($cl, $_) } @{$node->{children}};
-		if (my $smsg = $ctx->{-inbox}->smsg_mime($node->{smsg})) {
-			return thread_index_entry($ctx, $level, $smsg);
+		if ($ctx->{-inbox}->smsg_mime($node)) {
+			return thread_index_entry($ctx, $level, $node);
 		} else {
 			return ghost_index_entry($ctx, $level, $node);
 		}
@@ -407,7 +405,7 @@ sub stream_thread ($$) {
 		my $node = shift @q or next;
 		my $cl = $level + 1;
 		unshift @q, map { ($cl, $_) } @{$node->{children}};
-		$smsg = $ibx->smsg_mime($node->{smsg}) and last;
+		$smsg = $ibx->smsg_mime($node) and last;
 	}
 	return missing_thread($ctx) unless $smsg;
 
@@ -825,7 +823,7 @@ sub indent_for {
 sub find_mid_root {
 	my ($ctx, $level, $node, $idx) = @_;
 	++$ctx->{root_idx} if $level == 0;
-	if ($node->{id} eq $ctx->{mid}) {
+	if ($node->{mid} eq $ctx->{mid}) {
 		$ctx->{found_mid_at} = $ctx->{root_idx};
 		return 0;
 	}
@@ -899,8 +897,8 @@ sub dedupe_subject {
 }
 
 sub skel_dump { # walk_thread callback
-	my ($ctx, $level, $node) = @_;
-	my $smsg = $node->{smsg} or return _skel_ghost($ctx, $level, $node);
+	my ($ctx, $level, $smsg) = @_;
+	$smsg->{blob} or return _skel_ghost($ctx, $level, $smsg);
 
 	my $skel = $ctx->{skel};
 	my $cur = $ctx->{cur};
@@ -983,7 +981,7 @@ sub skel_dump { # walk_thread callback
 sub _skel_ghost {
 	my ($ctx, $level, $node) = @_;
 
-	my $mid = $node->{id};
+	my $mid = $node->{mid};
 	my $d = '     [not found] ';
 	$d .= '    '  if exists $ctx->{searchview};
 	$d .= indent_for($level) . th_pfx($level);
@@ -1006,18 +1004,23 @@ sub _skel_ghost {
 
 sub sort_ds {
 	[ sort {
-		(eval { $a->topmost->{smsg}->{ds} } || 0) <=>
-		(eval { $b->topmost->{smsg}->{ds} } || 0)
+		(eval { $a->topmost->{ds} } || 0) <=>
+		(eval { $b->topmost->{ds} } || 0)
 	} @{$_[0]} ];
 }
 
 # accumulate recent topics if search is supported
 # returns 200 if done, 404 if not
 sub acc_topic { # walk_thread callback
-	my ($ctx, $level, $node) = @_;
-	my $mid = $node->{id};
-	my $smsg = $node->{smsg} // $ctx->{-inbox}->smsg_by_mid($mid);
-	if ($smsg) {
+	my ($ctx, $level, $smsg) = @_;
+	my $mid = $smsg->{mid};
+	my $has_blob = $smsg->{blob} // do {
+		if (my $by_mid = $ctx->{-inbox}->smsg_by_mid($mid)) {
+			%$smsg = (%$smsg, %$by_mid);
+			1;
+		}
+	};
+	if ($has_blob) {
 		my $subj = subject_normalized($smsg->{subject});
 		$subj = '(no subject)' if $subj eq '';
 		my $ds = $smsg->{ds};
@@ -1208,7 +1211,7 @@ sub thread_adj_level {
 sub ghost_index_entry {
 	my ($ctx, $level, $node) = @_;
 	my ($beg, $end) = thread_adj_level($ctx,  $level);
-	$beg . '<pre>'. ghost_parent($ctx->{-upfx}, $node->{id})
+	$beg . '<pre>'. ghost_parent($ctx->{-upfx}, $node->{mid})
 		. '</pre>' . $end;
 }
 
diff --git a/t/thread-cycle.t b/t/thread-cycle.t
index e9ea0a27..d6545c6d 100644
--- a/t/thread-cycle.t
+++ b/t/thread-cycle.t
@@ -19,6 +19,7 @@ sub make_objs {
 		my $msg = $_;
 		$msg->{ds} ||= ++$n;
 		$msg->{references} =~ s/\s+/ /sg if $msg->{references};
+		$msg->{blob} = '0'x40; # any dummy value will do, here
 		my $simple = Email::Simple->create(header => [
 			'Message-ID' => "<$msg->{mid}>",
 			'References' => $msg->{references},
@@ -100,13 +101,13 @@ done_testing();
 sub thread_to_s {
 	my ($msgs) = @_;
 	my $rootset = PublicInbox::SearchThread::thread($msgs, sub {
-		[ sort { $a->{id} cmp $b->{id} } @{$_[0]} ] });
+		[ sort { $a->{mid} cmp $b->{mid} } @{$_[0]} ] });
 	my $st = '';
 	my @q = map { (0, $_) } @$rootset;
 	while (@q) {
 		my $level = shift @q;
 		my $node = shift @q or next;
-		$st .= (" "x$level). "$node->{id}\n";
+		$st .= (" "x$level). "$node->{mid}\n";
 		my $cl = $level + 1;
 		unshift @q, map { ($cl, $_) } @{$node->{children}};
 	}