extmsg: prevent cross-inbox matches from hogging event loop

With many inboxes, checking multiple SQLite repos will be slow
and time-consuming, so ensure we can schedule it fairly between
multiple inboxes.

1 files changed, 70 insertions, 31 deletions

diff --git a/lib/PublicInbox/ExtMsg.pm b/lib/PublicInbox/ExtMsg.pm
index 929737f1..ce1a47bb 100644
--- a/lib/PublicInbox/ExtMsg.pm
+++ b/lib/PublicInbox/ExtMsg.pm
@@ -74,69 +74,106 @@ sub search_partial ($$) {
 }
 
 sub ext_msg_i {
-        my ($other, $cur, $mid, $ibxs, $found) = @_;
+        my ($other, $ctx) = @_;
 
-        return if $other->{name} eq $cur->{name} || !$other->base_url;
+        return if $other->{name} eq $ctx->{-inbox}->{name} || !$other->base_url;
 
         my $mm = $other->mm or return;
 
         # try to find the URL with Msgmap to avoid forking
-        my $num = $mm->num_for($mid);
+        my $num = $mm->num_for($ctx->{mid});
         if (defined $num) {
-                push @$found, $other;
+                push @{$ctx->{found}}, $other;
         } else {
                 # no point in trying the fork fallback if we
                 # know Xapian is up-to-date but missing the
                 # message in the current repo
-                push @$ibxs, $other;
+                push @{$ctx->{again}}, $other;
+        }
+}
+
+sub ext_msg_step {
+        my ($pi_cfg, $section, $ctx) = @_;
+        if (defined($section)) {
+                return if $section !~ m!\Apublicinbox\.([^/]+)\z!;
+                my $ibx = $pi_cfg->lookup_name($1) or return;
+                ext_msg_i($ibx, $ctx);
+        } else { # undef == "EOF"
+                finalize_exact($ctx);
         }
 }
 
 sub ext_msg {
         my ($ctx) = @_;
-        my $cur = $ctx->{-inbox};
-        my $mid = $ctx->{mid};
+        sub {
+                $ctx->{-wcb} = $_[0]; # HTTP server write callback
+
+                if ($ctx->{env}->{'pi-httpd.async'}) {
+                        require PublicInbox::ConfigIter;
+                        my $iter = PublicInbox::ConfigIter->new(
+                                                $ctx->{www}->{pi_config},
+                                                \&ext_msg_step, $ctx);
+                        $iter->event_step;
+                } else {
+                        $ctx->{www}->{pi_config}->each_inbox(\&ext_msg_i, $ctx);
+                        finalize_exact($ctx);
+                }
+        };
+}
 
-        eval { require PublicInbox::Msgmap };
-        my $ibxs = [];
-        my $found = [];
+# called via PublicInbox::DS->EventLoop
+sub event_step {
+        my ($ctx, $sync) = @_;
+        # can't find a partial match in current inbox, try the others:
+        my $ibx = shift @{$ctx->{again}} or goto \&finalize_partial;
+        my $mids = search_partial($ibx, $ctx->{mid}) or
+                        return ($sync ? undef : PublicInbox::DS::requeue($ctx));
+        $ctx->{n_partial} += scalar(@$mids);
+        push @{$ctx->{partial}}, [ $ibx, $mids ];
+        $ctx->{n_partial} >= PARTIAL_MAX ? goto(\&finalize_partial)
+                        : ($sync ? undef : PublicInbox::DS::requeue($ctx));
+}
 
-        $ctx->{www}->{pi_config}->each_inbox(\&ext_msg_i,
-                                                $cur, $mid, $ibxs, $found);
+sub finalize_exact {
+        my ($ctx) = @_;
 
-        return exact($ctx, $found, $mid) if @$found;
+        return $ctx->{-wcb}->(exact($ctx)) if $ctx->{found};
 
         # fall back to partial MID matching
-        my @partial;
-        my $n_partial = 0;
+        my $mid = $ctx->{mid};
+        my $cur = $ctx->{-inbox};
         my $mids = search_partial($cur, $mid);
         if ($mids) {
-                $n_partial = scalar(@$mids);
-                push @partial, [ $cur, $mids ];
-        }
-
-        # can't find a partial match in current inbox, try the others:
-        if (!$n_partial && length($mid) >= $MIN_PARTIAL_LEN) {
-                foreach my $ibx (@$ibxs) {
-                        $mids = search_partial($ibx, $mid) or next;
-                        $n_partial += scalar(@$mids);
-                        push @partial, [ $ibx, $mids];
-                        last if $n_partial >= PARTIAL_MAX;
+                $ctx->{n_partial} = scalar(@$mids);
+                push @{$ctx->{partial}}, [ $cur, $mids ];
+        } elsif ($ctx->{again} && length($mid) >= $MIN_PARTIAL_LEN) {
+                bless $ctx, __PACKAGE__;
+                if ($ctx->{env}->{'pi-httpd.async'}) {
+                        $ctx->event_step;
+                        return;
                 }
+
+                # synchronous fall-through
+                $ctx->event_step while @{$ctx->{again}};
         }
+        goto \&finalize_partial;
+}
 
+sub finalize_partial {
+        my ($ctx) = @_;
+        my $mid = $ctx->{mid};
         my $code = 404;
         my $href = mid_href($mid);
         my $html = ascii_html($mid);
         my $title = "<$html> not found";
         my $s = "<pre>Message-ID &lt;$html&gt;\nnot found\n";
-        if ($n_partial) {
+        if (my $n_partial = $ctx->{n_partial}) {
                 $code = 300;
                 my $es = $n_partial == 1 ? '' : 'es';
                 $n_partial .= '+' if ($n_partial == PARTIAL_MAX);
                 $s .= "\n$n_partial partial match$es found:\n\n";
-                my $cur_name = $cur->{name};
-                foreach my $pair (@partial) {
+                my $cur_name = $ctx->{-inbox}->{name};
+                foreach my $pair (@{$ctx->{partial}}) {
                         my ($ibx, $res) = @$pair;
                         my $env = $ctx->{env} if $ibx->{name} eq $cur_name;
                         my $u = $ibx->base_url($env) or next;
@@ -155,7 +192,7 @@ sub ext_msg {
         $ctx->{-html_tip} = $s .= '</pre>';
         $ctx->{-title_html} = $title;
         $ctx->{-upfx} = '../';
-        html_oneshot($ctx, $code);
+        $ctx->{-wcb}->(html_oneshot($ctx, $code));
 }
 
 sub ext_urls {
@@ -177,7 +214,9 @@ sub ext_urls {
 }
 
 sub exact {
-        my ($ctx, $found, $mid) = @_;
+        my ($ctx) = @_;
+        my $mid = $ctx->{mid};
+        my $found = $ctx->{found};
         my $href = mid_href($mid);
         my $html = ascii_html($mid);
         my $title = "&lt;$html&gt; found in ";