lei_mirror: forkgroups use `git fetch --multiple'

This offloads network parallelization and safety off to git
itself while reducing the amount of unnecessary process spawning
we do.  This also improves readability of pack-refs invocations
and reduces the need for them.

To prevent heavily-forked repos from hitting system command-line
size limits, we group refs to be updated in the "fgrptmp" group.

1 files changed, 108 insertions, 52 deletions

diff --git a/lib/PublicInbox/LeiMirror.pm b/lib/PublicInbox/LeiMirror.pm
index 00732128..8b55a7da 100644
--- a/lib/PublicInbox/LeiMirror.pm
+++ b/lib/PublicInbox/LeiMirror.pm
@@ -316,7 +316,7 @@ sub fgrp_update {
         }
         close($w) or warn "E: close(update-ref --stdin): $! (need git 1.8.5+)\n";
         $LIVE->{$pid} = [ \&reap_cmd, $fgrp, $cmd ];
-        do_reap($fgrp);
+        pack_refs($fgrp, $fgrp->{cur_dst});
 }
 
 sub pack_refs {
@@ -324,49 +324,101 @@ sub pack_refs {
         do_reap($self);
         my $cmd = [ 'git', "--git-dir=$git_dir", qw(pack-refs --all --prune) ];
         $self->{lei}->qerr("# @$cmd");
+        return if $self->{dry_run};
         my $opt = { 1 => $self->{lei}->{1}, 2 => $self->{lei}->{2} };
         $LIVE->{spawn($cmd, undef, $opt)} = [ \&reap_cmd, $self, $cmd ];
 }
 
-sub fgrp_fetched {
-        my ($fgrp) = @_;
-        return if $fgrp->{dry_run} || !$LIVE;
-        my $rn = $fgrp->{-remote};
-        my %opt = map { $_ => $fgrp->{lei}->{$_} } (0..2);
-        pack_refs($fgrp, $fgrp->{-osdir}); # objstore refs always packed
-
-        my $update_ref = PublicInbox::OnDestroy->new($$, \&fgrp_update, $fgrp);
-
-        my $src = [ 'git', "--git-dir=$fgrp->{-osdir}", 'for-each-ref',
-                "--format=refs/%(refname:lstrip=3)%00%(objectname)",
-                "refs/remotes/$rn/" ];
-        do_reap($fgrp);
-        open($fgrp->{srcfh}, '+>', undef) or die "open(src): $!";
-        $fgrp->{lei}->qerr("# @$src >SRC");
-        my $pid = spawn($src, undef, { %opt, 1 => $fgrp->{srcfh} });
-        $LIVE->{$pid} = [ \&reap_cmd, $fgrp, $src, $update_ref ];
-
-        my $dst = [ 'git', "--git-dir=$fgrp->{cur_dst}", 'for-each-ref',
-                '--format=%(refname)%00%(objectname)' ];
-        do_reap($fgrp);
-        open($fgrp->{dstfh}, '+>', undef) or die "open(dst): $!";
-        $fgrp->{lei}->qerr("# @$dst >DST");
-        $pid = spawn($dst, undef, { %opt, 1 => $fgrp->{dstfh} });
-        $LIVE->{$pid} = [ \&reap_cmd, $fgrp, $dst, $update_ref ];
-}
-
-sub fgrp_fetch {
-        my ($fgrp, $fini) = @_;
-        my $cmd = [ @{$fgrp->{-torsocks}}, 'git', "--git-dir=$fgrp->{-osdir}",
-                        fetch_args($fgrp->{lei}, my $opt = {}), '--no-tags',
-                        $fgrp->{-remote} ];
-        $fgrp->{-fini} = $fini;
-        do_reap($fgrp);
-        $fgrp->{lei}->qerr("# @$cmd");
-        return if $fgrp->{dry_run};
-        my $fgrp_fini = PublicInbox::OnDestroy->new($$, \&fgrp_fetched, $fgrp);
-        my $pid = spawn($cmd, undef, $opt);
-        $LIVE->{$pid} = [ \&reap_cmd, $fgrp, $cmd, $fgrp_fini ];
+sub fgrpv_done {
+        my ($fgrpv) = @_;
+        return if !$LIVE;
+        my $pid;
+        my $first = $fgrpv->[0] // die 'BUG: no fgrpv->[0]';
+        pack_refs($first, $first->{-osdir}); # objstore refs always packed
+        for my $fgrp (@$fgrpv) {
+                my $rn = $fgrp->{-remote};
+                my %opt = map { $_ => $fgrp->{lei}->{$_} } (0..2);
+
+                my $update_ref = $fgrp->{dry_run} ? undef :
+                        PublicInbox::OnDestroy->new($$, \&fgrp_update, $fgrp);
+
+                my $src = [ 'git', "--git-dir=$fgrp->{-osdir}", 'for-each-ref',
+                        "--format=refs/%(refname:lstrip=3)%00%(objectname)",
+                        "refs/remotes/$rn/" ];
+                do_reap($fgrp);
+                $fgrp->{lei}->qerr("# @$src >SRC");
+                if ($update_ref) {
+                        open(my $fh, '+>', undef) or die "open(src): $!";
+                        $pid = spawn($src, undef, { %opt, 1 => $fh });
+                        $fgrp->{srcfh} = $fh;
+                        $LIVE->{$pid} = [ \&reap_cmd, $fgrp, $src, $update_ref ]
+                }
+                my $dst = [ 'git', "--git-dir=$fgrp->{cur_dst}", 'for-each-ref',
+                        '--format=%(refname)%00%(objectname)' ];
+                do_reap($fgrp);
+                $fgrp->{lei}->qerr("# @$dst >DST");
+                if ($update_ref) {
+                        open(my $fh, '+>', undef) or die "open(dst): $!";
+                        $pid = spawn($dst, undef, { %opt, 1 => $fh });
+                        $fgrp->{dstfh} = $fh;
+                        $LIVE->{$pid} = [ \&reap_cmd, $fgrp, $dst, $update_ref ]
+                }
+        }
+}
+
+sub fgrp_fetch_all {
+        my ($self) = @_;
+        my $todo = delete $self->{fgrp_todo} or return;
+        keys(%$todo) or return;
+
+        # Rely on the fgrptmp remote groups in the config file rather
+        # than listing all remotes since the remote name list may exceed
+        # system argv limits:
+        my $grp = 'fgrptmp';
+
+        my @git = (@{$self->{-torsocks}}, 'git');
+        my $j = $self->{lei}->{opt}->{jobs};
+        my $opt = {};
+        my @fetch = do {
+                local $self->{lei}->{opt}->{jobs} = 1;
+                (fetch_args($self->{lei}, $opt),
+                        qw(--no-tags --multiple));
+        };
+        push(@fetch, "-j$j") if $j;
+        my $pid;
+        while (my ($osdir, $fgrpv) = each %$todo) {
+                my $f = "$osdir/config";
+
+                # clobber group from previous run atomically
+                my $cmd = ['git', "--git-dir=$osdir", qw(config -f),
+                                $f, '--unset-all', "remotes.$grp"];
+                $self->{lei}->qerr("# @$cmd");
+                if (!$self->{dry_run}) {
+                        $pid = spawn($cmd);
+                        waitpid($pid, 0) // die "waitpid: $!";
+                        die "E: @$cmd: \$?=$?" if ($? && ($? >> 8) != 5);
+
+                        # update the config atomically via O_APPEND while
+                        # respecting git-config locking
+                        sysopen(my $lk, "$f.lock", O_CREAT|O_EXCL|O_WRONLY)
+                                or die "open($f.lock): $!";
+                        open my $fh, '>>', $f or die "open(>>$f): $!";
+                        $fh->autoflush(1);
+                        my $buf = join('', "[remotes]\n",
+                                map { "\t$grp = $_->{-remote}\n" } @$fgrpv);
+                        print $fh $buf or die "print($f): $!";
+                        close $fh or die "close($f): $!";
+                        unlink("$f.lock") or die "unlink($f.lock): $!";
+                }
+
+                $cmd = [ @git, "--git-dir=$osdir", @fetch, $grp ];
+                do_reap($self);
+                $self->{lei}->qerr("# @$cmd");
+                my $end = PublicInbox::OnDestroy->new($$, \&fgrpv_done, $fgrpv);
+                return if $self->{dry_run};
+                $pid = spawn($cmd, undef, $opt);
+                $LIVE->{$pid} = [ \&reap_cmd, $self, $cmd, $end ];
+        }
 }
 
 # keep this idempotent for future use by public-inbox-fetch
@@ -400,7 +452,6 @@ sub forkgroup_prep {
                         run_die([@cmd, @kv], undef, $opt);
                 }
         }
-        $self->{-do_pack_refs} = 1; # likely coderepo
         if (!-d $self->{cur_dst} && !$self->{dry_run}) {
                 my $alt = File::Spec->rel2abs("$dir/objects");
                 PublicInbox::Import::init_bare($self->{cur_dst});
@@ -440,18 +491,21 @@ sub clone_v1 {
         $self->{-torsocks} //= $curl->torsocks($lei, $uri) or return;
         my $dst = $self->{cur_dst} // $self->{dst};
         my $fini = PublicInbox::OnDestroy->new($$, \&v1_done, $self);
-        my $cmd = [ @{$self->{-torsocks}}, clone_cmd($lei, my $opt = {}),
-                "$uri", $dst ];
-        my $fgrp = forkgroup_prep($self, $uri);
-        if (!defined($fgrp) && defined($self->{-ent})) {
-                if (defined(my $ref = $self->{-ent}->{reference})) {
-                        -e "$self->{dst}$ref" and
-                                push @$cmd, '--reference', "$self->{dst}$ref";
+        if (my $fgrp = forkgroup_prep($self, $uri)) {
+                $fgrp->{-fini} = $fini;
+                push @{$self->{fgrp_todo}->{$fgrp->{-osdir}}}, $fgrp;
+        } else { # normal fetch
+                my $cmd = [ @{$self->{-torsocks}},
+                                clone_cmd($lei, my $opt = {}), "$uri", $dst ];
+                if (defined($self->{-ent})) {
+                        if (defined(my $ref = $self->{-ent}->{reference})) {
+                                -e "$self->{dst}$ref" and
+                                        push @$cmd, '--reference',
+                                                "$self->{dst}$ref";
+                        }
                 }
-        }
-        $fgrp ? fgrp_fetch($fgrp, $fini) :
                 start_clone($self, $cmd, $opt, $fini);
-
+        }
         if (!$self->{-is_epoch} && $lei->{opt}->{'inbox-config'} =~
                                 /\A(?:always|v1)\z/s) {
                 _get_txt_start($self, '_/text/config/raw', $fini);
@@ -576,7 +630,6 @@ sub v1_done { # called via OnDestroy
                         ft_rename($ft, $fn, 0666, $fh);
                 }
         }
-        pack_refs($self, $dst) if delete $self->{-do_pack_refs};
         eval { set_description($self) };
         warn $@ if $@;
         return if ($self->{-is_epoch} ||
@@ -770,6 +823,7 @@ EOM
                         last; # restart %$todo iteration
                 }
         }
+        fgrp_fetch_all($self);
         do_reap($self, 1);
 }
 
@@ -793,6 +847,7 @@ sub try_manifest {
         my $uri = URI->new($self->{src});
         my $lei = $self->{lei};
         my $curl = $self->{curl} //= PublicInbox::LeiCurl->new($lei) or return;
+        $self->{-torsocks} //= $curl->torsocks($lei, $uri) or return;
         my $path = $uri->path;
         chop($path) eq '/' or die "BUG: $uri not canonicalized";
         $uri->path($path . '/manifest.js.gz');
@@ -814,6 +869,7 @@ sub try_manifest {
         return $lei->child_error(1, $multi) if !ref($multi);
         my $v2 = delete $multi->{v2};
         local $self->{todo} = {};
+        local $self->{fgrp_todo} = {}; # { objstore_dir => [fgrp, ...] }
         if ($v2) {
                 for my $name (sort keys %$v2) {
                         my $epochs = delete $v2->{$name};