From: Junio C Hamano <gitster@pobox•com>
To: Jeff King <peff@peff•net>
Cc: Jonathan Tan <jonathantanmy@google•com>, git@vger•kernel.org
Subject: Re: [PATCH v4 7/8] sha1_file: do not access pack if unneeded
Date: Sat, 24 Jun 2017 11:41:39 -0700 [thread overview]
Message-ID: <xmqq7f019qjg.fsf@gitster.mtv.corp.google.com> (raw)
In-Reply-To: <20170624124813.wajhxkrqhw4xoee4@sigill.intra.peff.net> (Jeff King's message of "Sat, 24 Jun 2017 08:48:14 -0400")
Jeff King <peff@peff•net> writes:
> On Wed, Jun 21, 2017 at 11:15:01AM -0700, Junio C Hamano wrote:
>
>> > + if (!oi->typep && !oi->sizep && !oi->disk_sizep &&
>> > + !oi->delta_base_sha1 && !oi->typename && !oi->contentp &&
>> > + !oi->populate_u) {
>> > + oi->whence = OI_PACKED;
>> > + return 0;
>> > + }
>> > +
>>
>> ... this "if" statement feels like a maintenance nightmare. The
>> intent of the guard, I think, is "when the call wants absolutely
>> nothing but whence", but the implementation of the guard will not
>> stay true to the intent whenever somebody adds a new field to oi.
>>
>> I wonder if it makes more sense to have a new field "whence_only",
>> which is set only by such a specialized caller, which this guard
>> checks (and no other fields).
>
> The other nice thing about whence_only is that it flips the logic. So
> any existing callers which depend on filling the union automatically
> will not be affected (though I would be surprised if there are any such
> callers; most of that information isn't actually that interesting).
Hmph, but the solution does not scale. When a caller wants whence
and something else that cannot be asked for or ignored by being a
"pointer to a result" field, such a request cannot be expressed. We
either need to make all fields in oi request to "pointer to a
result, if the result is needed, or NULL when the result is not of
interest", or give a bit for each non-pointer field to allow the
caller to express "I am not interested in the value of this field".
In the usecase Jonathan has, the caller's wish is a very narrow "I
am interested in nothing; just checking if the object is there", and
passing NULL for oi works fine. So I'm inclined to suggest that we
take that approach now and worry about a more generic and scalable
"how would one tell the machinery that the value for a field is
uninteresting when the field is not a pointer to result?" mechanism
until a real need arises.
Thanks.
next prev parent reply other threads:[~2017-06-24 18:41 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-09 19:23 [RFC PATCH 0/4] Improvements to sha1_file Jonathan Tan
2017-06-09 19:23 ` [RFC PATCH 1/4] sha1_file: teach packed_object_info about typename Jonathan Tan
2017-06-12 20:55 ` Junio C Hamano
2017-06-09 19:23 ` [RFC PATCH 2/4] sha1_file: extract type and size from object_info Jonathan Tan
2017-06-10 7:01 ` Jeff King
2017-06-12 19:52 ` Jonathan Tan
2017-06-12 21:13 ` Jeff King
2017-06-09 19:23 ` [RFC PATCH 3/4] sha1_file: consolidate storage-agnostic object fns Jonathan Tan
2017-06-09 19:23 ` [RFC PATCH 4/4] sha1_file, fsck: add missing blob support Jonathan Tan
2017-06-13 21:05 ` [PATCH v2 0/4] Improvements to sha1_file Jonathan Tan
2017-06-13 21:05 ` [PATCH v2 1/4] sha1_file: teach packed_object_info about typename Jonathan Tan
2017-06-13 21:05 ` [PATCH v2 2/4] sha1_file: move delta base cache code up Jonathan Tan
2017-06-15 17:00 ` Junio C Hamano
2017-06-13 21:05 ` [PATCH v2 3/4] sha1_file: consolidate storage-agnostic object fns Jonathan Tan
2017-06-15 17:50 ` Junio C Hamano
2017-06-15 18:14 ` Jonathan Tan
2017-06-17 12:19 ` Jeff King
2017-06-19 4:18 ` Junio C Hamano
2017-06-13 21:06 ` [PATCH v2 4/4] sha1_file, fsck: add missing blob support Jonathan Tan
2017-06-15 18:34 ` Junio C Hamano
2017-06-15 20:31 ` Jonathan Tan
2017-06-15 20:52 ` Junio C Hamano
2017-06-15 20:39 ` [PATCH v3 0/4] Improvements to sha1_file Jonathan Tan
2017-06-15 20:39 ` [PATCH v3 1/4] sha1_file: teach packed_object_info about typename Jonathan Tan
2017-06-15 20:39 ` [PATCH v3 2/4] sha1_file: move delta base cache code up Jonathan Tan
2017-06-15 20:39 ` [PATCH v3 3/4] sha1_file: consolidate storage-agnostic object fns Jonathan Tan
2017-06-15 20:39 ` [PATCH v3 4/4] sha1_file, fsck: add missing blob support Jonathan Tan
2017-06-20 1:03 ` [PATCH v4 0/8] Improvements to sha1_file Jonathan Tan
2017-06-20 1:03 ` [PATCH v4 1/8] sha1_file: teach packed_object_info about typename Jonathan Tan
2017-06-20 1:03 ` [PATCH v4 2/8] sha1_file: rename LOOKUP_UNKNOWN_OBJECT Jonathan Tan
2017-06-21 17:22 ` Junio C Hamano
2017-06-21 17:34 ` Jonathan Tan
2017-06-20 1:03 ` [PATCH v4 3/8] sha1_file: rename LOOKUP_REPLACE_OBJECT Jonathan Tan
2017-06-21 17:33 ` Junio C Hamano
2017-06-20 1:03 ` [PATCH v4 4/8] sha1_file: move delta base cache code up Jonathan Tan
2017-06-20 1:03 ` [PATCH v4 5/8] sha1_file: refactor read_object Jonathan Tan
2017-06-21 17:58 ` Junio C Hamano
2017-06-20 1:03 ` [PATCH v4 6/8] sha1_file: improve sha1_object_info_extended Jonathan Tan
2017-06-24 12:45 ` Jeff King
2017-06-26 16:45 ` Jonathan Tan
2017-06-26 17:28 ` Junio C Hamano
2017-06-26 17:35 ` Jonathan Tan
2017-06-26 17:26 ` Junio C Hamano
2017-06-20 1:03 ` [PATCH v4 7/8] sha1_file: do not access pack if unneeded Jonathan Tan
2017-06-21 18:15 ` Junio C Hamano
2017-06-24 12:48 ` Jeff King
2017-06-24 18:41 ` Junio C Hamano [this message]
2017-06-24 20:39 ` Jeff King
2017-06-26 16:28 ` Jonathan Tan
2017-06-20 1:03 ` [PATCH v4 8/8] sha1_file: refactor has_sha1_file_with_flags Jonathan Tan
2017-06-21 18:18 ` [PATCH v4 0/8] Improvements to sha1_file Junio C Hamano
2017-06-24 12:51 ` Jeff King
2017-06-22 0:40 ` [PATCH v5 " Jonathan Tan
2017-06-22 0:40 ` [PATCH v5 1/8] sha1_file: teach packed_object_info about typename Jonathan Tan
2017-06-22 0:40 ` [PATCH v5 2/8] sha1_file: rename LOOKUP_UNKNOWN_OBJECT Jonathan Tan
2017-06-22 0:40 ` [PATCH v5 3/8] sha1_file: rename LOOKUP_REPLACE_OBJECT Jonathan Tan
2017-06-22 0:40 ` [PATCH v5 4/8] sha1_file: move delta base cache code up Jonathan Tan
2017-06-22 0:40 ` [PATCH v5 5/8] sha1_file: refactor read_object Jonathan Tan
2017-06-22 0:40 ` [PATCH v5 6/8] sha1_file: improve sha1_object_info_extended Jonathan Tan
2017-06-22 0:40 ` [PATCH v5 7/8] sha1_file: do not access pack if unneeded Jonathan Tan
2017-06-22 0:40 ` [PATCH v5 8/8] sha1_file: refactor has_sha1_file_with_flags Jonathan Tan
2017-07-18 10:30 ` Christian Couder
2017-07-18 16:39 ` Jonathan Tan
2017-07-19 12:52 ` Johannes Schindelin
2017-07-19 17:12 ` [PATCH] sha1_file: use access(), not lstat(), if possible Jonathan Tan
2017-07-20 21:48 ` Junio C Hamano
2017-07-22 11:16 ` Johannes Schindelin
2017-07-22 16:15 ` Junio C Hamano
2017-07-25 10:19 ` Johannes Schindelin
2017-06-22 1:40 ` [PATCH v5 0/8] Improvements to sha1_file Junio C Hamano
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