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.

diff --git a/lib/PublicInbox/DS.pm b/lib/PublicInbox/DS.pm
index b2f59983f0a50214cae967d70abf366007fda840..a82360239f43a79e86eaf97f7afcbf0149f29858 100644 (file)
--- a/lib/PublicInbox/DS.pm
+++ b/lib/PublicInbox/DS.pm
@@ -571,12 +571,6 @@ sub epwait ($$) {
     0;
 }
 
-sub watch ($$) {
-    my ($self, $ev) = @_;
-    my $sock = $self->{sock} or return;
-    epwait($sock, $ev);
-}
-
 # return true if complete, false if incomplete (or failure)
 sub accept_tls_step ($) {
     my ($self) = @_;

diff --git a/lib/PublicInbox/HTTP.pm b/lib/PublicInbox/HTTP.pm
index 680be72b15a28c9b208ba62db33dd11e1c9b0563..5546ac465570d123d19498ef285b385b3b1ba913 100644 (file)
--- a/lib/PublicInbox/HTTP.pm
+++ b/lib/PublicInbox/HTTP.pm
@@ -467,11 +467,4 @@ sub busy () {
        ($self->{rbuf} || $self->{env} || $self->{wbuf});
 }
 
-# fires after pending writes are complete:
-sub restart_pass ($) {
-       $_[0]->{forward}->restart_read; # see PublicInbox::HTTPD::Async
-}
-
-sub enqueue_restart_pass ($) { $_[0]->write(\&restart_pass) }
-
 1;

diff --git a/lib/PublicInbox/HTTPD/Async.pm b/lib/PublicInbox/HTTPD/Async.pm
index 35d171506cd52b3253456aca2728d4a68685b30b..1ffc2565a01c5902030732a351d3269a96b3612c 100644 (file)
--- 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];