git_async_cat: don't mis-abort replaced process

When a git process gets replaced (e.g. due to new
epochs/alternates), we must be careful and not abort the wrong
one.

I suspect this fixes the problem exacerbated by --batch-command.
It was theoretically possible w/o --batch-command, but it seems
to have made it surface more readily.

This should fix "Failed to retrieve generated blob" errors from
PublicInbox/ViewVCS.pm appearing in syslog

Link: https://public-inbox.org/meta/20230209012932.M934961@dcvr/

1 files changed, 19 insertions, 7 deletions

diff --git a/lib/PublicInbox/GitAsyncCat.pm b/lib/PublicInbox/GitAsyncCat.pm
index c428f6ef..671654b5 100644
--- a/lib/PublicInbox/GitAsyncCat.pm
+++ b/lib/PublicInbox/GitAsyncCat.pm
@@ -14,6 +14,12 @@ use PublicInbox::Git ();
 
 our $GCF2C; # singleton PublicInbox::Gcf2Client
 
+# close w/o aborting another git process
+sub vanish {
+        delete $_[0]->{git};
+        $_[0]->close;
+}
+
 sub close {
         my ($self) = @_;
         if (my $git = delete $self->{git}) {
@@ -22,19 +28,25 @@ sub close {
         $self->SUPER::close; # PublicInbox::DS::close
 }
 
-sub aclose { $_[1]->close } # ignore PID ($_[0])
+sub aclose {
+        my (undef, $self, $f) = @_; # ignore PID ($_[0])
+        if (my $g = $self->{git}) {
+                return vanish($self) if ($g->{$f} // 0) != ($self->{sock} // 1);
+        }
+        $self->close;
+}
 
 sub event_step {
         my ($self) = @_;
         my $git = $self->{git} or return;
-        return $self->close if ($git->{in} // 0) != ($self->{sock} // 1);
+        return vanish($self) if ($git->{in} // 0) != ($self->{sock} // 1);
         my $inflight = $git->{inflight};
         if ($inflight && @$inflight) {
                 $git->cat_async_step($inflight);
 
                 # child death?
                 if (($git->{in} // 0) != ($self->{sock} // 1)) {
-                        $self->close;
+                        vanish($self);
                 } elsif (@$inflight || exists $git->{rbuf}) {
                         # ok, more to do, requeue for fairness
                         $self->requeue;
@@ -48,7 +60,7 @@ sub watch_cat {
                 my $self = bless { git => $git }, __PACKAGE__;
                 $git->{in}->blocking(0);
                 $self->SUPER::new($git->{in}, EPOLLIN|EPOLLET);
-                awaitpid($git->{pid}, \&aclose, $self);
+                awaitpid($git->{pid}, \&aclose, $self, 'in');
                 \undef; # this is a true ref()
         };
 }
@@ -81,7 +93,7 @@ sub async_check ($$$$) {
                 my $self = bless { git => $git }, 'PublicInbox::GitAsyncCheck';
                 $git->{in_c}->blocking(0);
                 $self->SUPER::new($git->{in_c}, EPOLLIN|EPOLLET);
-                awaitpid($git->{pid_c}, \&aclose, $self);
+                awaitpid($git->{pid_c}, \&aclose, $self, 'in_c');
                 \undef; # this is a true ref()
         };
 }
@@ -113,14 +125,14 @@ use PublicInbox::Syscall qw(EPOLLIN EPOLLET);
 sub event_step {
         my ($self) = @_;
         my $git = $self->{git} or return;
-        return $self->close if ($git->{in_c} // 0) != ($self->{sock} // 1);
+        return $self->vanish if ($git->{in_c} // 0) != ($self->{sock} // 1);
         my $inflight = $git->{inflight_c};
         if ($inflight && @$inflight) {
                 $git->check_async_step($inflight);
 
                 # child death?
                 if (($git->{in_c} // 0) != ($self->{sock} // 1)) {
-                        $self->close;
+                        $self->vanish;
                 } elsif (@$inflight || exists $git->{rbuf_c}) {
                         # ok, more to do, requeue for fairness
                         $self->requeue;