git: decouple cat_async_retry from POSIX pipe semantics

While pipes guarantee writes of <= 512 bytes to be atomic,
Unix stream sockets (or TCP sockets) have no such guarantees.
Removing the pipe assumption will make it possible for us to
switch to bidirectional Unix stream sockets and save FDs with
`git cat-file' processes as we have with Gcf2Client.  The
performance benefit of larger pipe buffers over stream sockets
isn't irrelevant when interacting with git as it is with
SearchIdx shards.

diff --git a/lib/PublicInbox/Git.pm b/lib/PublicInbox/Git.pm
index eb88aa48987ddfff6f3119b577c0497f7c94e6ba..8ac40d2b9bd13498e9003f2a22dd72263d6b843d 100644 (file)
--- a/lib/PublicInbox/Git.pm
+++ b/lib/PublicInbox/Git.pm
@@ -223,25 +223,21 @@ sub my_readline ($$) {
 }
 
 sub cat_async_retry ($$) {
-       my ($self, $inflight) = @_;
+       my ($self, $old_inflight) = @_;
 
        # {inflight} may be non-existent, but if it isn't we delete it
        # here to prevent cleanup() from waiting:
        delete $self->{inflight};
        cleanup($self);
+       batch_prepare($self, my $new_inflight = []);
 
-       batch_prepare($self, $inflight);
-       my $buf = '';
-       for (my $i = 0; $i < @$inflight; $i += 3) {
-               $buf .= "$inflight->[$i]\n";
+       while (my ($oid, $cb, $arg) = splice(@$old_inflight, 0, 3)) {
+               write_all($self, $self->{out}, $oid."\n",
+                               \&cat_async_step, $new_inflight);
+               $oid = \$oid if !@$new_inflight; # to indicate oid retried
+               push @$new_inflight, $oid, $cb, $arg;
        }
-       $self->{out}->blocking(1); # brand new pipe, should never block
-       print { $self->{out} } $buf or $self->fail("write error: $!");
-       $self->{out}->blocking(0);
-       my $req = shift @$inflight;
-       unshift(@$inflight, \$req); # \$ref to indicate retried
-
-       cat_async_step($self, $inflight); # take one step
+       cat_async_step($self, $new_inflight); # take one step
 }
 
 # returns true if prefetch is successful