From 21a539a2df0cbbc929aecec88f9fd6879e20f466 Mon Sep 17 00:00:00 2001
From: Eric Wong <e@80x24.org>
Date: Fri, 28 Jun 2019 18:58:36 +0000
Subject: httpd/async: switch to buffering-as-fast-as-possible

With DS buffering to a temporary file nowadays, applying
backpressure to git-http-backend(1) hurts overall memory
usage of the system.  Instead, try to get git-http-backend(1)
to finish as quickly as possible and use edge-triggered
notifications to reduce wakeups on our end.
---
 lib/PublicInbox/HTTPD/Async.pm | 40 +++++++++++++++++-----------------------
 1 file changed, 17 insertions(+), 23 deletions(-)

(limited to 'lib/PublicInbox/HTTPD/Async.pm')

diff --git a/lib/PublicInbox/HTTPD/Async.pm b/lib/PublicInbox/HTTPD/Async.pm
index 35d17150..1ffc2565 100644
--- a/lib/PublicInbox/HTTPD/Async.pm
+++ b/lib/PublicInbox/HTTPD/Async.pm
@@ -4,14 +4,15 @@
 # XXX This is a totally unstable API for public-inbox internal use only
 # This is exposed via the 'pi-httpd.async' key in the PSGI env hash.
 # The name of this key is not even stable!
-# Currently is is intended for use with read-only pipes.
+# Currently intended for use with read-only pipes with expensive
+# processes such as git-http-backend(1), cgit(1)
 package PublicInbox::HTTPD::Async;
 use strict;
 use warnings;
 use base qw(PublicInbox::DS);
 use fields qw(cb cleanup);
-require PublicInbox::EvCleanup;
 use Errno qw(EAGAIN);
+use PublicInbox::Syscall qw(EPOLLIN EPOLLET);
 
 sub new {
 	my ($class, $io, $cb, $cleanup) = @_;
@@ -26,14 +27,12 @@ sub new {
 
 	my $self = fields::new($class);
 	IO::Handle::blocking($io, 0);
-	$self->SUPER::new($io, PublicInbox::DS::EPOLLIN());
+	$self->SUPER::new($io, EPOLLIN | EPOLLET);
 	$self->{cb} = $cb;
 	$self->{cleanup} = $cleanup;
 	$self;
 }
 
-sub restart_read ($) { $_[0]->watch(PublicInbox::DS::EPOLLIN()) }
-
 sub main_cb ($$$) {
 	my ($http, $fh, $bref) = @_;
 	sub {
@@ -41,25 +40,15 @@ sub main_cb ($$$) {
 		my $r = sysread($self->{sock}, $$bref, 8192);
 		if ($r) {
 			$fh->write($$bref); # may call $http->close
-
 			if ($http->{sock}) { # !closed
-				if ($http->{wbuf}) {
-					# HTTP client could not keep up, so
-					# stop reading and buffering.
-					$self->watch(0);
-
-					# Tell the HTTP socket to restart us
-					# when HTTP client is done draining
-					# $http->{wbuf}:
-					$http->enqueue_restart_pass;
-				}
-				# stay in EPOLLIN, but let other clients
-				# get some work done, too.
+				$self->requeue;
+				# let other clients get some work done, too
 				return;
 			}
-			# fall through to close below...
-		} elsif (!defined $r) {
-			return restart_read($self) if $! == EAGAIN;
+
+			# else: fall through to close below...
+		} elsif (!defined $r && $! == EAGAIN) {
+			return; # EPOLLET means we'll be notified
 		}
 
 		# Done! Error handling will happen in $fh->close
@@ -75,10 +64,15 @@ sub async_pass {
 	# will automatically close this ($self) object.
 	$http->{forward} = $self;
 	$fh->write($$bref); # PublicInbox:HTTP::{chunked,identity}_wcb
-	$self->{cb} = main_cb($http, $fh, $bref);
+	my $cb = $self->{cb} = main_cb($http, $fh, $bref);
+	$cb->($self); # either hit EAGAIN or ->requeue to keep EPOLLET happy
 }
 
-sub event_step { $_[0]->{cb}->(@_) }
+sub event_step {
+	# {cb} may be undef after ->requeue due to $http->close happening
+	my $cb = $_[0]->{cb} or return;
+	$cb->(@_);
+}
 
 sub close {
 	my $self = $_[0];
-- 
cgit v1.2.3-24-ge0c7