MANIFEST                       |  1 +
 lib/PublicInbox/Git.pm         | 10 +++++-----
 lib/PublicInbox/GitAsyncCat.pm | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 lib/PublicInbox/IMAP.pm        | 49 ++++++++++++++++++++++++++-----------------------
 lib/PublicInbox/Inbox.pm       | 16 ++++++++++++----
 t/git.t                        |  1 -
 xt/cmp-msgstr.t                |  1 -
 xt/cmp-msgview.t               |  1 -
 xt/eml_check_limits.t          |  1 -
 xt/git_async_cmp.t             |  1 -
 xt/msgtime_cmp.t               |  1 -
 xt/perf-msgview.t              |  1 -

diff --git a/MANIFEST b/MANIFEST
index 2e4ec915412f592ea9c38d24daf93cd63a8c7d8c..82f047f36232dd67e548f65a1c0cd84a07ad3c7c 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 54c163e8c2f5151b0122c998936c94f72507e801..c5a3fa4642c23cdb008fbf39200a34f3755cf393 100644
--- a/lib/PublicInbox/Git.pm
+++ b/lib/PublicInbox/Git.pm
@@ -156,7 +156,7 @@ 		return defined($r) ? '' : undef; # EOF or error
 	}
 }
 
-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 @@
 # 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 ($$$;$) {
 	my ($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 $oid;
diff --git a/lib/PublicInbox/GitAsyncCat.pm b/lib/PublicInbox/GitAsyncCat.pm
new file mode 100644
index 0000000000000000000000000000000000000000..f168169f68d605a28ff4b6baf4ea578a304f5321
--- /dev/null
+++ b/lib/PublicInbox/GitAsyncCat.pm
@@ -0,0 +1,49 @@
+# Copyright (C) 2020 all contributors <meta@public-inbox.org>
+# License: AGPL-3.0+ <https://www.gnu.org/licenses/agpl-3.0.txt>
+#
+# internal class used by PublicInbox::Git + Danga::Socket
+# This parses the output pipe of "git cat-file --batch"
+#
+# Note: this does NOT set the non-blocking flag, we expect `git cat-file'
+# to be a local process, and git won't start writing a blob until it's
+# fully read.  So minimize context switching and read as much as possible
+# and avoid holding a buffer in our heap any longer than it has to live.
+package PublicInbox::GitAsyncCat;
+use strict;
+use parent qw(PublicInbox::DS Exporter);
+use fields qw(git);
+use PublicInbox::Syscall qw(EPOLLIN EPOLLET);
+our @EXPORT = qw(git_async_msg);
+
+sub new {
+	my ($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 3966719908016c0c9f4c64b67a9d88908a652b25..2282e3ce78c6be097b289d04f68ce9c9b0e0842b 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 @@ 	if (my $partial = $want->{-partial}) {
 		partial_emit($self, $partial, $eml);
 	}
 	$self->msg_more(")\r\n");
+	requeue_once($self);
 }
 
 sub uid_fetch_m { # long_response
@@ -432,11 +451,7 @@ 			return;
 		}
 		$$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 @@ 	}
 	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 @@ 		$self->close;
 	} elsif ($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 b250bef33d3de8e890ed61223f2919dcda03cfe8..407751c30637c7b3988b051140bbdc16a385cf0c 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 @@ 				delete $ibx->{$f};
 				# 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 @@ 	return if $self->version < 2;
 	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 b05ac123bec6a342204726b838a235253799cfb1..0b2089ba701293c5f6e528d66064400a1bbee8b7 100644
--- a/t/git.t
+++ b/t/git.t
@@ -40,7 +40,6 @@ 	my $oid = $x[0];
 	my $arg = { 'foo' => 'bar' };
 	my $res = [];
 	my $missing = [];
-	$gcf->cat_async_begin;
 	$gcf->cat_async($oid, sub {
 		my ($bref, $oid_hex, $type, $size, $arg) = @_;
 		$res = [ @_ ];
diff --git a/xt/cmp-msgstr.t b/xt/cmp-msgstr.t
index 6bae0f66e83f6b1a55c25dee568f84dfa2409df7..0276f8454b01d1d37948e60d7d21d14ca98dd89d 100644
--- a/xt/cmp-msgstr.t
+++ b/xt/cmp-msgstr.t
@@ -93,7 +93,6 @@ 		# using `git diff', diff(1) may not be installed
 		diag xqx([qw(git diff), "$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 66fb467eb1af12b333855099a4cc23e5d76b436f..5bd7aa174df0c786fcd16978a022e3d72e1728bb 100644
--- a/xt/cmp-msgview.t
+++ b/xt/cmp-msgview.t
@@ -77,7 +77,6 @@ 		diag Dumper([ $oid, eml => $eml_cmp, mime =>$mime_cmp ]);
 		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 39de047645b378de92d4d0d706790fe857323714..2d632799956730bbb124b1795921259d3e490fce 100644
--- a/xt/eml_check_limits.t
+++ b/xt/eml_check_limits.t
@@ -55,7 +55,6 @@ 	$max_size = [ $size, $oid ] if $size > $max_size->[0];
 };
 
 my $t = timeit(1, sub {
-	$git->cat_async_begin;
 	my ($blob, $type);
 	while (<$fh>) {
 		($blob, $type) = split / /;
diff --git a/xt/git_async_cmp.t b/xt/git_async_cmp.t
index 46d27b26bed57de872b21dd0de361d55fea860d9..8f8d1cf4d01e12e21740e3c1de2a5f560052ace2 100644
--- a/xt/git_async_cmp.t
+++ b/xt/git_async_cmp.t
@@ -25,7 +25,6 @@ 		my ($bref) = @_;
 		$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 95d7c64bec67a337eaccf44d5b4227d1925a2fad..0ce3c042217ddbf74dab648cd31b235265d347aa 100644
--- a/xt/msgtime_cmp.t
+++ b/xt/msgtime_cmp.t
@@ -59,7 +59,6 @@ 	quiet_is_deeply(\@cur, \@old, 'timestamp', $oid, $hdr);
 }
 
 my $fh = $git->popen(@cat);
-$git->cat_async_begin;
 while (<$fh>) {
 	my ($oid, $type) = split / /;
 	next if $type ne 'blob';
diff --git a/xt/perf-msgview.t b/xt/perf-msgview.t
index 30fc07dcbc87ad812de8da9d41bb3df0bc1883e3..d99101a30de67d4ac7a28ba93c981a7a672823a2 100644
--- a/xt/perf-msgview.t
+++ b/xt/perf-msgview.t
@@ -44,7 +44,6 @@ 	++$m;
 	$obuf = '';
 };
 
-$git->cat_async_begin;
 my $t = timeit(1, sub {
 	$ctx->{obuf} = \$obuf;
 	$ctx->{mhref} = '../';