imap: use git-cat-file asynchronously

This ought to improve overall performance with multiple clients.
Single client performance suffers a tiny bit due to extra
syscall overhead from epoll.

This also makes the existing async interface easier-to-use,
since calling cat_async_begin is no longer required.

12 files changed, 93 insertions, 39 deletions

diff --git a/MANIFEST b/MANIFEST
index 2e4ec915..82f047f3 100644
--- a/MANIFEST
+++ b/MANIFEST
@@ -119,6 +119,7 @@ lib/PublicInbox/Filter/SubjectTag.pm
 lib/PublicInbox/Filter/Vger.pm
 lib/PublicInbox/GetlineBody.pm
 lib/PublicInbox/Git.pm
+lib/PublicInbox/GitAsyncCat.pm
 lib/PublicInbox/GitHTTPBackend.pm
 lib/PublicInbox/GzipFilter.pm
 lib/PublicInbox/HTTP.pm
diff --git a/lib/PublicInbox/Git.pm b/lib/PublicInbox/Git.pm
index 54c163e8..c5a3fa46 100644
--- a/lib/PublicInbox/Git.pm
+++ b/lib/PublicInbox/Git.pm
@@ -156,7 +156,7 @@ sub my_readline ($$) {
         }
 }
 
-sub _cat_async_step ($$) {
+sub cat_async_step ($$) {
         my ($self, $inflight) = @_;
         die 'BUG: inflight empty or odd' if scalar(@$inflight) < 2;
         my ($cb, $arg) = splice(@$inflight, 0, 2);
@@ -178,7 +178,7 @@ sub cat_async_wait ($) {
         my ($self) = @_;
         my $inflight = delete $self->{inflight} or return;
         while (scalar(@$inflight)) {
-                _cat_async_step($self, $inflight);
+                cat_async_step($self, $inflight);
         }
 }
 
@@ -277,6 +277,7 @@ sub qx {
 # returns true if there are pending "git cat-file" processes
 sub cleanup {
         my ($self) = @_;
+        cat_async_wait($self);
         _destroy($self, qw(--batch in out pid));
         _destroy($self, qw(--batch-check in_c out_c pid_c err_c));
         !!($self->{pid} || $self->{pid_c});
@@ -334,9 +335,9 @@ sub cat_async_begin {
 
 sub cat_async ($$$;$) {
         my ($self, $oid, $cb, $arg) = @_;
-        my $inflight = $self->{inflight} or die 'BUG: not in async';
+        my $inflight = $self->{inflight} // cat_async_begin($self);
         if (scalar(@$inflight) >= MAX_INFLIGHT) {
-                _cat_async_step($self, $inflight);
+                cat_async_step($self, $inflight);
         }
 
         print { $self->{out} } $oid, "\n" or fail($self, "write error: $!");
@@ -358,7 +359,6 @@ sub modified ($) {
         my ($self) = @_;
         my $modified = 0;
         my $fh = popen($self, qw(rev-parse --branches));
-        cat_async_begin($self);
         local $/ = "\n";
         while (my $oid = <$fh>) {
                 chomp $oid;
diff --git a/lib/PublicInbox/GitAsyncCat.pm b/lib/PublicInbox/GitAsyncCat.pm
new file mode 100644
index 00000000..f168169f
--- /dev/null
+++ b/lib/PublicInbox/GitAsyncCat.pm
@@ -0,0 +1,49 @@
+# Copyright (C) 2020 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+#
+# internal class used by PublicInbox::Git + Danga::Socket
+# This parses the output pipe of "git cat-file --batch"
+#
+# Note: this does NOT set the non-blocking flag, we expect `git cat-file'
+# to be a local process, and git won't start writing a blob until it's
+# fully read.  So minimize context switching and read as much as possible
+# and avoid holding a buffer in our heap any longer than it has to live.
+package PublicInbox::GitAsyncCat;
+use strict;
+use parent qw(PublicInbox::DS Exporter);
+use fields qw(git);
+use PublicInbox::Syscall qw(EPOLLIN EPOLLET);
+our @EXPORT = qw(git_async_msg);
+
+sub new {
+        my ($class, $git) = @_;
+        my $self = fields::new($class);
+        $git->batch_prepare;
+        $self->SUPER::new($git->{in}, EPOLLIN|EPOLLET);
+        $self->{git} = $git;
+        $self;
+}
+
+sub event_step {
+        my ($self) = @_;
+        my $git = $self->{git} or return; # ->close-ed
+        my $inflight = $git->{inflight};
+        if (@$inflight) {
+                $git->cat_async_step($inflight);
+                $self->requeue if @$inflight || length(${$git->{'--batch'}});
+        }
+}
+
+sub close {
+        my ($self) = @_;
+        delete $self->{git};
+        $self->SUPER::close; # PublicInbox::DS::close
+}
+
+sub git_async_msg ($$$$) {
+        my ($ibx, $smsg, $cb, $arg) = @_;
+        $ibx->git->cat_async($smsg->{blob}, $cb, $arg);
+        $ibx->{async_cat} //= new(__PACKAGE__, $ibx->{git});
+}
+
+1;
diff --git a/lib/PublicInbox/IMAP.pm b/lib/PublicInbox/IMAP.pm
index 39667199..2282e3ce 100644
--- a/lib/PublicInbox/IMAP.pm
+++ b/lib/PublicInbox/IMAP.pm
@@ -21,8 +21,10 @@ use PublicInbox::Eml;
 use PublicInbox::EmlContentFoo qw(parse_content_disposition);
 use PublicInbox::DS qw(now);
 use PublicInbox::Syscall qw(EPOLLIN EPOLLONESHOT);
+use PublicInbox::GitAsyncCat;
 use Text::ParseWords qw(parse_line);
 use Errno qw(EAGAIN);
+
 my $Address;
 for my $mod (qw(Email::Address::XS Mail::Address)) {
         eval "require $mod" or next;
@@ -367,14 +369,30 @@ EOF
         \$ret;
 }
 
-sub uid_fetch_cb { # called by git->cat_async
+sub requeue_once ($) {
+        my ($self) = @_;
+        # COMPRESS users all share the same DEFLATE context.
+        # Flush it here to ensure clients don't see
+        # each other's data
+        $self->zflush;
+
+        # no recursion, schedule another call ASAP,
+        # but only after all pending writes are done.
+        # autovivify wbuf:
+        my $new_size = push(@{$self->{wbuf}}, \&long_step);
+
+        # wbuf may be populated by $cb, no need to rearm if so:
+        $self->requeue if $new_size == 1;
+}
+
+sub uid_fetch_cb { # called by git->cat_async via git_async_msg
         my ($bref, $oid, $type, $size, $fetch_m_arg) = @_;
         my ($self, undef, $ibx, undef, undef, $msgs, $want) = @$fetch_m_arg;
         my $smsg = shift @$msgs or die 'BUG: no smsg';
         if (!defined($oid)) {
                 # it's possible to have TOCTOU if an admin runs
                 # public-inbox-(edit|purge), just move onto the next message
-                return unless defined $want->{-seqno};
+                return requeue_once($self) unless defined $want->{-seqno};
                 $bref = dummy_message($smsg->{num}, $ibx);
         } else {
                 $smsg->{blob} eq $oid or die "BUG: $smsg->{blob} != $oid";
@@ -420,6 +438,7 @@ sub uid_fetch_cb { # called by git->cat_async
                 partial_emit($self, $partial, $eml);
         }
         $self->msg_more(")\r\n");
+        requeue_once($self);
 }
 
 sub uid_fetch_m { # long_response
@@ -432,11 +451,7 @@ sub uid_fetch_m { # long_response
                 }
                 $$beg = $msgs->[-1]->{num} + 1;
         }
-        my $git = $ibx->git;
-        $git->cat_async_begin; # TODO: actually make async
-        $git->cat_async($msgs->[0]->{blob}, \&uid_fetch_cb, \@_);
-        $git->cat_async_wait;
-        1;
+        git_async_msg($ibx, $msgs->[0], \&uid_fetch_cb, \@_);
 }
 
 sub cmd_status ($$$;@) {
@@ -677,20 +692,17 @@ sub seq_fetch_m { # long_response
         my $seq = $want->{-seqno}++;
         my $cur_num = $msgs->[0]->{num};
         if ($cur_num == $seq) { # as expected
-                my $git = $ibx->git;
-                $git->cat_async_begin; # TODO: actually make async
-                $git->cat_async($msgs->[0]->{blob}, \&uid_fetch_cb, \@_);
-                $git->cat_async_wait;
+                git_async_msg($ibx, $msgs->[0], \&uid_fetch_cb, \@_);
         } elsif ($cur_num > $seq) {
                 # send dummy messages until $seq catches up to $cur_num
                 my $smsg = bless { num => $seq, ts => 0 }, 'PublicInbox::Smsg';
                 unshift @$msgs, $smsg;
                 my $bref = dummy_message($seq, $ibx);
                 uid_fetch_cb($bref, undef, undef, undef, \@_);
+                $smsg; # blessed response since uid_fetch_cb requeues
         } else { # should not happen
                 die "BUG: cur_num=$cur_num < seq=$seq";
         }
-        1; # more messages on the way
 }
 
 sub cmd_fetch ($$$;@) {
@@ -810,17 +822,8 @@ sub long_step {
         } elsif ($more) { # $self->{wbuf}:
                 $self->update_idle_time;
 
-                # COMPRESS users all share the same DEFLATE context.
-                # Flush it here to ensure clients don't see
-                # each other's data
-                $self->zflush;
-
-                # no recursion, schedule another call ASAP, but only after
-                # all pending writes are done.  autovivify wbuf:
-                my $new_size = push(@{$self->{wbuf}}, \&long_step);
-
-                # wbuf may be populated by $cb, no need to rearm if so:
-                $self->requeue if $new_size == 1;
+                # control passed to $more may be a GitAsyncCat object
+                requeue_once($self) if !ref($more);
         } else { # all done!
                 delete $self->{long_cb};
                 my $elapsed = now() - $t0;
diff --git a/lib/PublicInbox/Inbox.pm b/lib/PublicInbox/Inbox.pm
index b250bef3..407751c3 100644
--- a/lib/PublicInbox/Inbox.pm
+++ b/lib/PublicInbox/Inbox.pm
@@ -18,6 +18,16 @@ my $cleanup_timer;
 my $cleanup_avail = -1; # 0, or 1
 my $have_devel_peek;
 my $CLEANUP = {}; # string(inbox) -> inbox
+
+sub git_cleanup ($) {
+        my ($self) = @_;
+        my $git = $self->{git} or return;
+        if (my $async_cat = delete $self->{async_cat}) {
+                $async_cat->close;
+        }
+        $git->cleanup;
+}
+
 sub cleanup_task () {
         $cleanup_timer = undef;
         my $next = {};
@@ -32,9 +42,7 @@ sub cleanup_task () {
                                 # refcnt is zero when tmp is out-of-scope
                         }
                 }
-                if (my $git = $ibx->{git}) {
-                        $again = $git->cleanup;
-                }
+                git_cleanup($ibx);
                 if (my $gits = $ibx->{-repo_objs}) {
                         foreach my $git (@$gits) {
                                 $again = 1 if $git->cleanup;
@@ -157,7 +165,7 @@ sub max_git_epoch {
         my $cur = $self->{-max_git_epoch};
         my $changed = git($self)->alternates_changed;
         if (!defined($cur) || $changed) {
-                $self->git->cleanup if $changed;
+                git_cleanup($self) if $changed;
                 my $gits = "$self->{inboxdir}/git";
                 if (opendir my $dh, $gits) {
                         my $max = -1;
diff --git a/t/git.t b/t/git.t
index b05ac123..0b2089ba 100644
--- a/t/git.t
+++ b/t/git.t
@@ -40,7 +40,6 @@ use_ok 'PublicInbox::Git';
         my $arg = { 'foo' => 'bar' };
         my $res = [];
         my $missing = [];
-        $gcf->cat_async_begin;
         $gcf->cat_async($oid, sub {
                 my ($bref, $oid_hex, $type, $size, $arg) = @_;
                 $res = [ @_ ];
diff --git a/xt/cmp-msgstr.t b/xt/cmp-msgstr.t
index 6bae0f66..0276f845 100644
--- a/xt/cmp-msgstr.t
+++ b/xt/cmp-msgstr.t
@@ -93,7 +93,6 @@ my $git_cb = sub {
                 diag xqx([qw(git diff), "$tmpdir/mime", "$tmpdir/eml"]);
         }
 };
-$git->cat_async_begin;
 my $t = timeit(1, sub {
         while (<$fh>) {
                 my ($oid, $type) = split / /;
diff --git a/xt/cmp-msgview.t b/xt/cmp-msgview.t
index 66fb467e..5bd7aa17 100644
--- a/xt/cmp-msgview.t
+++ b/xt/cmp-msgview.t
@@ -77,7 +77,6 @@ my $git_cb = sub {
                 is_deeply($eml_cmp, $mime_cmp, "$inboxdir $oid match");
         }
 };
-$git->cat_async_begin;
 my $t = timeit(1, sub {
         while (<$fh>) {
                 my ($oid, $type) = split / /;
diff --git a/xt/eml_check_limits.t b/xt/eml_check_limits.t
index 39de0476..2d632799 100644
--- a/xt/eml_check_limits.t
+++ b/xt/eml_check_limits.t
@@ -55,7 +55,6 @@ my $cat_cb = sub {
 };
 
 my $t = timeit(1, sub {
-        $git->cat_async_begin;
         my ($blob, $type);
         while (<$fh>) {
                 ($blob, $type) = split / /;
diff --git a/xt/git_async_cmp.t b/xt/git_async_cmp.t
index 46d27b26..8f8d1cf4 100644
--- a/xt/git_async_cmp.t
+++ b/xt/git_async_cmp.t
@@ -25,7 +25,6 @@ my $async = timeit($nr, sub {
                 $dig->add($$bref);
         };
         my $cat = $git->popen(@cat);
-        $git->cat_async_begin;
 
         while (<$cat>) {
                 my ($oid, undef, undef) = split(/ /);
diff --git a/xt/msgtime_cmp.t b/xt/msgtime_cmp.t
index 95d7c64b..0ce3c042 100644
--- a/xt/msgtime_cmp.t
+++ b/xt/msgtime_cmp.t
@@ -59,7 +59,6 @@ sub compare {
 }
 
 my $fh = $git->popen(@cat);
-$git->cat_async_begin;
 while (<$fh>) {
         my ($oid, $type) = split / /;
         next if $type ne 'blob';
diff --git a/xt/perf-msgview.t b/xt/perf-msgview.t
index 30fc07dc..d99101a3 100644
--- a/xt/perf-msgview.t
+++ b/xt/perf-msgview.t
@@ -44,7 +44,6 @@ my $cb = sub {
         $obuf = '';
 };
 
-$git->cat_async_begin;
 my $t = timeit(1, sub {
         $ctx->{obuf} = \$obuf;
         $ctx->{mhref} = '../';