Re: [PATCH] midx: use buffered I/O to talk to pack-objects

["René Scharfe" <l.s.r@web.de>]

Am 04.08.20 um 00:27 schrieb René Scharfe:
> Am 03.08.20 um 20:10 schrieb Johannes Sixt:
>> Am 02.08.20 um 18:11 schrieb Chris Torek:
>>> On Sun, Aug 2, 2020 at 7:40 AM René Scharfe <l.s.r@web.de> wrote:
>>>> @@ -1443,10 +1446,15 @@ int midx_repack(struct repository *r, const char *object_dir, size_t batch_size,
>>>>                         continue;
>>>>
>>>>                 nth_midxed_object_oid(&oid, m, i);
>>>> -               xwrite(cmd.in, oid_to_hex(&oid), the_hash_algo->hexsz);
>>>> -               xwrite(cmd.in, "\n", 1);
>>>> +               fprintf(cmd_in, "%s\n", oid_to_hex(&oid));
>>>> +       }
>>>> +
>>>> +       if (fclose(cmd_in)) {
>>>> +               error_errno(_("could not close stdin of pack-objects"));
>>>> +               result = 1;
>>>> +               finish_command(&cmd);
>>>> +               goto cleanup;
>>>>         }
>>>> -       close(cmd.in);
>>>>
>>>>         if (finish_command(&cmd)) {
>>>>                 error(_("could not finish pack-objects"));
>>>> --
>>>> 2.28.0

>> We need this explicit test after each fprintf anyway because SIGPIPE may
>> be ignored, and then writing fails with EPIPE. On Windows, this is
>> doubly important because we do not have SIGPIPE at all (and always see
>> EPIPE), but we see EPIPE only on the first failed write; subsequent
>> writes produce EINVAL.
>
> Why is this important?  The current code doesn't care about it, at
> least.  It does care about EINTR, though.

Ah, that's the point, right?  You want to *ignore* EPIPE, because the
failed pack-objects process at the other end will have died with a
(hopefully) useful error message already.

OK, so we also need a fprintf() wrapper that retries on EINTR, ignores
EPIPE and exits early if the error indicator is set?

Somehow staying with write(2) and its friends and just adding strbuf
based buffering looks attractive to me now. :-/

René