From bb8a6a435a4b7707e9fb0329c49671f495262016 Mon Sep 17 00:00:00 2001
From: Eric Wong <e@80x24.org>
Date: Sat, 16 Oct 2021 01:01:03 +0000
Subject: [PATCH] httpd/async: switch to level-triggered epoll

We'll save ourselves some code here and let the kernel do more
work, instead.
---
 Documentation/technical/ds.txt |  3 +--
 lib/PublicInbox/HTTPD/Async.pm | 16 +++++-----------
 lib/PublicInbox/Qspawn.pm      |  1 -
 3 files changed, 6 insertions(+), 14 deletions(-)

diff --git a/Documentation/technical/ds.txt b/Documentation/technical/ds.txt
index 7bc1ad79..5a1655a1 100644
--- a/Documentation/technical/ds.txt
+++ b/Documentation/technical/ds.txt
@@ -77,8 +77,7 @@ New features
   which (if any) events it's interested in for the next loop iteration.
 
 * Edge-triggering available via EPOLLET or EV_CLEAR.  These reduce wakeups
-  for unidirectional classes (e.g. PublicInbox::Listener sockets,
-  and pipes via PublicInbox::HTTPD::Async).
+  for unidirectional classes when throughput is more important than fairness.
 
 * IO::Socket::SSL support (for NNTPS, STARTTLS+NNTP, HTTPS)
 
diff --git a/lib/PublicInbox/HTTPD/Async.pm b/lib/PublicInbox/HTTPD/Async.pm
index 7238650a..1651da88 100644
--- a/lib/PublicInbox/HTTPD/Async.pm
+++ b/lib/PublicInbox/HTTPD/Async.pm
@@ -17,7 +17,7 @@ package PublicInbox::HTTPD::Async;
 use strict;
 use parent qw(PublicInbox::DS);
 use Errno qw(EAGAIN);
-use PublicInbox::Syscall qw(EPOLLIN EPOLLET);
+use PublicInbox::Syscall qw(EPOLLIN);
 
 # This is called via: $env->{'pi-httpd.async'}->()
 # $io is a read-only pipe ($rpipe) for now, but may be a
@@ -39,7 +39,7 @@ sub new {
 	}, $class;
 	my $pp = tied *$io;
 	$pp->{fh}->blocking(0) // die "$io->blocking(0): $!";
-	$self->SUPER::new($io, EPOLLIN | EPOLLET);
+	$self->SUPER::new($io, EPOLLIN);
 }
 
 sub event_step {
@@ -54,15 +54,12 @@ sub event_step {
 		my $r = sysread($sock, my $buf, 65536);
 		if ($r) {
 			$self->{fh}->write($buf); # may call $http->close
-			if ($http->{sock}) { # !closed
-				$self->requeue;
-				# let other clients get some work done, too
-				return;
-			}
+			# let other clients get some work done, too
+			return if $http->{sock}; # !closed
 
 			# else: fall through to close below...
 		} elsif (!defined $r && $! == EAGAIN) {
-			return; # EPOLLET means we'll be notified
+			return; # EPOLLIN means we'll be notified
 		}
 
 		# Done! Error handling will happen in $self->{fh}->close
@@ -89,9 +86,6 @@ sub async_pass {
 
 	$self->{http} = $http;
 	$self->{fh} = $fh;
-
-	# either hit EAGAIN or ->requeue to keep EPOLLET happy
-	event_step($self);
 }
 
 # may be called as $forward->close in PublicInbox::HTTP or EOF (event_step)
diff --git a/lib/PublicInbox/Qspawn.pm b/lib/PublicInbox/Qspawn.pm
index a1ff65b6..53d0ad55 100644
--- a/lib/PublicInbox/Qspawn.pm
+++ b/lib/PublicInbox/Qspawn.pm
@@ -192,7 +192,6 @@ sub event_step {
 sub rd_hdr ($) {
 	my ($self) = @_;
 	# typically used for reading CGI headers
-	# we must loop until EAGAIN for EPOLLET in HTTPD/Async.pm
 	# We also need to check EINTR for generic PSGI servers.
 	my $ret;
 	my $total_rd = 0;
-- 
2.44.0