Eric Wong <e@80x24.org> writes:

> Do you know which pipes are which?  "lsof -p $PID +E" can help
> with connectivity checking, as can script/dtas-graph in
> https://80x24.org/dtas.git if you have Graph::Easy

Yes.  I'm attaching my lsof output and a typescript.

The processes of interest here are 4849 public-inbox-convert and 4879
git cat-file.
PID 4849's FD 11 is the write end of a pipe, with 4879's stdin as the
read end.
PID 4849's FD 12 is the read end of a pipe, with 4879's stdout as the
write end.  At the point of the hang, 4849 is trying to write a SHA1 to
FD 11, while 4879 is writing an email message to its stdout.

> Some shots in the dark:
>
> 2. Tweak $PIPE_BUFSIZ and/or MAX_INFLIGHT to smaller values.  e.g.
>
> diff --git a/lib/PublicInbox/Git.pm b/lib/PublicInbox/Git.pm
> index 882a9a4a..ec40edd7 100644
> --- a/lib/PublicInbox/Git.pm
> +++ b/lib/PublicInbox/Git.pm
> @@ -23,13 +23,12 @@ use Carp qw(croak carp);
>  use Digest::SHA ();
>  use PublicInbox::DS qw(dwaitpid);
>  our @EXPORT_OK = qw(git_unquote git_quote);
> -our $PIPE_BUFSIZ = 65536; # Linux default
> +our $PIPE_BUFSIZ = 4096; # Linux default
>  our $in_cleanup;
>  our $RDTIMEO = 60_000; # milliseconds
>  our $async_warn; # true in read-only daemons
>  
> -use constant MAX_INFLIGHT => (POSIX::PIPE_BUF * 3) /
> -	65; # SHA-256 hex size + "\n" in preparation for git using non-SHA1
> +use constant MAX_INFLIGHT => 4;
>  
>  my %GIT_ESC = (
>  	a => "\a",
>

This right here seems to have fixed it, when testing locally.

PS.  Thank you for that lsof command.  I've never used lsof in that way;
I'll have to add that to my *nix debugging toolbelt.

-- Chris