From: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
To: Derrick Stolee <stolee@gmail.com>
Cc: Derrick Stolee <dstolee@microsoft.com>,
"git\@vger.kernel.org" <git@vger.kernel.org>
Subject: Re: [PATCH v2 06/11] get_short_oid: sort ambiguous objects by type, then SHA-1
Date: Tue, 01 May 2018 16:10:39 +0200 [thread overview]
Message-ID: <874ljrzctc.fsf@evledraar.gmail.com> (raw)
In-Reply-To: <40868abd-6d2f-3f05-e099-6f0d06cc0683@gmail.com>
On Tue, May 01 2018, Derrick Stolee wrote:
> On 5/1/2018 9:39 AM, Ævar Arnfjörð Bjarmason wrote:
>> On Tue, May 01 2018, Derrick Stolee wrote:
>>
>>> From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
>>>
>>> Here is what I mean by sorting during for_each_abbrev(). This seems to work for
>>> me, so I don't know what the issue is with this one-pass approach.
>>> [...]
>>> +static int sort_ambiguous(const void *a, const void *b)
>>> +{
>>> + int a_type = oid_object_info(a, NULL);
>>> + int b_type = oid_object_info(b, NULL);
>>> + int a_type_sort;
>>> + int b_type_sort;
>>> +
>>> + /*
>>> + * Sorts by hash within the same object type, just as
>>> + * oid_array_for_each_unique() would do.
>>> + */
>>> + if (a_type == b_type)
>>> + return oidcmp(a, b);
>>> +
>>> + /*
>>> + * Between object types show tags, then commits, and finally
>>> + * trees and blobs.
>>> + *
>>> + * The object_type enum is commit, tree, blob, tag, but we
>>> + * want tag, commit, tree blob. Cleverly (perhaps too
>>> + * cleverly) do that with modulus, since the enum assigns 1 to
>>> + * commit, so tag becomes 0.
>>> + */
>>> + a_type_sort = a_type % 4;
>>> + b_type_sort = b_type % 4;
>>> + return a_type_sort > b_type_sort ? 1 : -1;
>>> +}
>>> +
>>> static int get_short_oid(const char *name, int len, struct object_id *oid,
>>> unsigned flags)
>>> {
>>> @@ -451,6 +479,9 @@ int for_each_abbrev(const char *prefix, each_abbrev_fn fn, void *cb_data)
>>> find_short_object_filename(&ds);
>>> find_short_packed_object(&ds);
>>>
>>> + QSORT(collect.oid, collect.nr, sort_ambiguous);
>>> + collect.sorted = 1;
>>> +
>> Yes this works. You're right. I wasn't trying to intentionally omit
>> stuff in my recent 878t93zh60.fsf@evledraar.gmail.com, I'd just written
>> this code some days ago and forgotten why I did what I was doing (and
>> this is hard to test for), but it's all coming back to me now.
>>
>> The actual requirement for oid_array_for_each_unique() working properly
>> is that you've got to feed it in hash order,
>
> To work properly, duplicate entries must be consecutive. Since
> duplicate entries have the same type, our sort satisfies this
> condition.
>
>> but my new sort_ambiguous()
>> still does that (barring any SHA-1 collisions, at which point we have
>> bigger problems), so two passes aren't needed. So yes, this apporoach
>> works and is one-pass.
>>
>> But that's just an implementation detail of the current sort method,
>> when I wrote this I was initially playing with other sort orders,
>> e.g. sorting SHAs regardless of type by the mtime of the file I found
>> them in. With this approach I'd start printing duplicates if I changed
>> the internals of sort_ambiguous() like that.
>
> That makes sense.
>
>> But I think it's extremely implausible that we'll start sorting things
>> like that, so I'll just take this method of doing it and add some
>> comment saying we must hashcmp() the entries in our own sort function
>> for the de-duplication to work, I don't see us ever changing that.
>
> Sounds good.
Actually I'm having second thoughts about that and thinking I might keep
my original approach (with a better explanation).
A few more lines of code seems worthwhile in order to not break the
assumptions a documented API is making, no matter how briefly, so I set
about documenting this case and supporting it, since
e.g. oid_array_lookup() will completely fail with the hack of setting
the .sorted member, and came up with this:
diff --git a/Documentation/technical/api-oid-array.txt b/Documentation/technical/api-oid-array.txt
index b0c11f868d..ff87260220 100644
--- a/Documentation/technical/api-oid-array.txt
+++ b/Documentation/technical/api-oid-array.txt
@@ -16,6 +16,20 @@ Data Structures
the actual data. The `nr` member contains the number of items in
the set. The `alloc` and `sorted` members are used internally,
and should not be needed by API callers.
++
+Both the `oid_array_lookup` and `oid_array_for_each_unique` functions
+rely on the array being sorted. For the former it's an absolute
+requirenment that the internal `oid_array_sort` function has been
+called on it, bu for the latter it's enough that the elements are
+ordered in such a way as to guarantee that identical object IDs are
+adjacent in the array.
++
+This is useful e.g. to print output where commits, tags etc. are
+grouped together (barring a hash collision they won't have the same
+object ID), in such cases the `custom_sorted` member can be set to `1`
+before calling `oid_array_for_each_unique`, and it'll skip its own
+sorting. Once it's been set calling e.g. `oid_array_lookup` without it
+being cleared again will cause an internal panic, so use it carefully.
Functions
---------
diff --git a/sha1-array.c b/sha1-array.c
index 466a926aa3..cbae07ff78 100644
--- a/sha1-array.c
+++ b/sha1-array.c
@@ -18,6 +18,7 @@ static void oid_array_sort(struct oid_array *array)
{
QSORT(array->oid, array->nr, void_hashcmp);
array->sorted = 1;
+ array->custom_sorted = 0;
}
static const unsigned char *sha1_access(size_t index, void *table)
@@ -28,6 +29,13 @@ static const unsigned char *sha1_access(size_t index, void *table)
int oid_array_lookup(struct oid_array *array, const struct object_id *oid)
{
+ if (array->custom_sorted)
+ /*
+ * We could also just clear custom_sorted here, but if
+ * the caller is custom sorting and then calling this
+ * that's likely something they'd like to know about.
+ */
+ BUG("PANIC: Cannot lookup OIDs in arrays with a custom sort!");
if (!array->sorted)
oid_array_sort(array);
return sha1_pos(oid->hash, array->oid, array->nr, sha1_access);
@@ -39,6 +47,7 @@ void oid_array_clear(struct oid_array *array)
array->nr = 0;
array->alloc = 0;
array->sorted = 0;
+ array->custom_sorted = 0;
}
int oid_array_for_each_unique(struct oid_array *array,
@@ -47,7 +56,7 @@ int oid_array_for_each_unique(struct oid_array *array,
{
int i;
- if (!array->sorted)
+ if (!array->sorted && !array->custom_sorted)
oid_array_sort(array);
for (i = 0; i < array->nr; i++) {
diff --git a/sha1-array.h b/sha1-array.h
index 1e1d24b009..bfa77ba1e4 100644
--- a/sha1-array.h
+++ b/sha1-array.h
@@ -6,6 +6,7 @@ struct oid_array {
int nr;
int alloc;
int sorted;
+ int custom_sorted;
};
#define OID_ARRAY_INIT { NULL, 0, 0, 0 }
diff --git a/sha1-name.c b/sha1-name.c
index b81e07adbb..d190800db0 100644
--- a/sha1-name.c
+++ b/sha1-name.c
@@ -490,9 +490,11 @@ int for_each_abbrev(const char *prefix, each_abbrev_fn fn, void *cb_data)
find_short_packed_object(&ds);
QSORT(collect.oid, collect.nr, sort_ambiguous);
- collect.sorted = 1;
+ collect.custom_sorted = 1;
ret = oid_array_for_each_unique(&collect, fn, cb_data);
+ collect.custom_sorted = 0;
+
oid_array_clear(&collect);
return ret;
}
So maybe I should just stop worrying and YOLO it, it just seems wrong to
leave such a fragile setup in place where we set .sorted=1 and some
future refactoring reasonably tries to call oid_array_lookup() on it and
silently fails.
What do you think?
next prev parent reply other threads:[~2018-05-01 14:10 UTC|newest]
Thread overview: 99+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-30 22:07 [PATCH 0/9] get_short_oid UI improvements Ævar Arnfjörð Bjarmason
2018-04-30 22:07 ` [PATCH 1/9] sha1-name.c: remove stray newline Ævar Arnfjörð Bjarmason
2018-04-30 22:07 ` [PATCH 2/9] sha1-array.h: align function arguments Ævar Arnfjörð Bjarmason
2018-04-30 22:07 ` [PATCH 3/9] sha1-name.c: move around the collect_ambiguous() function Ævar Arnfjörð Bjarmason
2018-04-30 22:07 ` [PATCH 4/9] get_short_oid: sort ambiguous objects by type, then SHA-1 Ævar Arnfjörð Bjarmason
2018-05-01 11:11 ` Derrick Stolee
2018-05-01 11:27 ` Ævar Arnfjörð Bjarmason
2018-05-01 12:26 ` Derrick Stolee
2018-05-01 12:36 ` Ævar Arnfjörð Bjarmason
2018-05-01 13:05 ` Derrick Stolee
2018-04-30 22:07 ` [PATCH 5/9] get_short_oid: learn to disambiguate by ^{tag} Ævar Arnfjörð Bjarmason
2018-04-30 22:07 ` [PATCH 6/9] get_short_oid: learn to disambiguate by ^{blob} Ævar Arnfjörð Bjarmason
2018-04-30 22:07 ` [PATCH 7/9] get_short_oid / peel_onion: ^{tree} should mean tree, not treeish Ævar Arnfjörð Bjarmason
2018-05-01 1:13 ` brian m. carlson
2018-04-30 22:07 ` [PATCH 8/9] get_short_oid / peel_onion: ^{tree} should mean commit, not commitish Ævar Arnfjörð Bjarmason
2018-04-30 23:22 ` Eric Sunshine
2018-04-30 22:07 ` [PATCH 9/9] config doc: document core.disambiguate Ævar Arnfjörð Bjarmason
2018-04-30 22:34 ` [PATCH 0/9] get_short_oid UI improvements Stefan Beller
2018-05-01 1:27 ` brian m. carlson
2018-05-01 11:16 ` Derrick Stolee
2018-05-01 12:06 ` [PATCH v2 00/12] " Ævar Arnfjörð Bjarmason
2018-05-01 13:03 ` [PATCH v2 06/11] get_short_oid: sort ambiguous objects by type, then SHA-1 Derrick Stolee
2018-05-01 13:39 ` Ævar Arnfjörð Bjarmason
2018-05-01 13:44 ` Derrick Stolee
2018-05-01 14:10 ` Ævar Arnfjörð Bjarmason [this message]
2018-05-01 14:15 ` Derrick Stolee
2018-05-01 18:40 ` [PATCH v3 00/12] get_short_oid UI improvements Ævar Arnfjörð Bjarmason
2018-05-02 12:42 ` Derrick Stolee
2018-05-02 13:45 ` Derrick Stolee
2018-05-03 6:43 ` Jacob Keller
2018-05-01 18:40 ` [PATCH v3 01/12] sha1-name.c: remove stray newline Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 02/12] sha1-array.h: align function arguments Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 03/12] git-p4: change "commitish" typo to "committish" Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 04/12] cache.h: add comment explaining the order in object_type Ævar Arnfjörð Bjarmason
2018-05-03 5:05 ` Junio C Hamano
2018-05-08 15:35 ` Duy Nguyen
2018-05-08 15:56 ` [PATCH] pack-format.txt: more details on pack file format Nguyễn Thái Ngọc Duy
2018-05-08 17:23 ` Stefan Beller
2018-05-08 18:22 ` Duy Nguyen
2018-05-08 18:58 ` Stefan Beller
2018-05-08 18:21 ` Ævar Arnfjörð Bjarmason
2018-05-08 18:24 ` Duy Nguyen
2018-05-10 15:09 ` [PATCH v2] " Nguyễn Thái Ngọc Duy
2018-05-10 17:06 ` Stefan Beller
2018-05-11 6:41 ` Duy Nguyen
2018-05-11 3:54 ` Junio C Hamano
2018-05-11 6:55 ` [PATCH v3] " Nguyễn Thái Ngọc Duy
2018-05-01 18:40 ` [PATCH v3 05/12] sha1-name.c: move around the collect_ambiguous() function Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 06/12] get_short_oid: sort ambiguous objects by type, then SHA-1 Ævar Arnfjörð Bjarmason
2018-05-03 5:13 ` Junio C Hamano
2018-05-08 14:44 ` Jeff King
2018-05-01 18:40 ` [PATCH v3 07/12] get_short_oid: learn to disambiguate by ^{tag} Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 08/12] get_short_oid: learn to disambiguate by ^{blob} Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 09/12] get_short_oid / peel_onion: ^{tree} should be tree, not treeish Ævar Arnfjörð Bjarmason
2018-05-03 5:28 ` Junio C Hamano
2018-05-03 7:28 ` Ævar Arnfjörð Bjarmason
2018-05-04 2:19 ` Junio C Hamano
2018-05-04 8:42 ` Ævar Arnfjörð Bjarmason
2018-05-07 4:08 ` Junio C Hamano
2018-05-08 14:34 ` Jeff King
2018-05-08 18:53 ` Ævar Arnfjörð Bjarmason
2018-05-09 7:56 ` Jeff King
2018-05-09 10:48 ` Ævar Arnfjörð Bjarmason
2018-05-10 4:21 ` Junio C Hamano
2018-05-10 6:50 ` Jeff King
2018-05-10 12:42 ` [PATCH v4 0/6] get_short_oid UI improvements Ævar Arnfjörð Bjarmason
2018-05-10 16:04 ` Jeff King
2018-05-10 12:42 ` [PATCH v4 1/6] sha1-name.c: remove stray newline Ævar Arnfjörð Bjarmason
2018-05-10 12:42 ` [PATCH v4 2/6] sha1-array.h: align function arguments Ævar Arnfjörð Bjarmason
2018-05-10 15:06 ` Jeff King
2018-05-11 3:07 ` Junio C Hamano
2018-05-11 3:09 ` Junio C Hamano
2018-05-10 12:43 ` [PATCH v4 3/6] git-p4: change "commitish" typo to "committish" Ævar Arnfjörð Bjarmason
2018-05-10 15:00 ` Luke Diamand
2018-05-10 12:43 ` [PATCH v4 4/6] sha1-name.c: move around the collect_ambiguous() function Ævar Arnfjörð Bjarmason
2018-05-10 12:43 ` [PATCH v4 5/6] get_short_oid: sort ambiguous objects by type, then SHA-1 Ævar Arnfjörð Bjarmason
2018-05-10 15:22 ` Jeff King
2018-05-11 5:36 ` Junio C Hamano
2018-05-10 12:43 ` [PATCH v4 6/6] get_short_oid: document & warn if we ignore the type selector Ævar Arnfjörð Bjarmason
2018-05-10 13:15 ` Martin Ågren
2018-05-10 16:03 ` Jeff King
2018-05-10 16:10 ` Jeff King
2018-05-10 16:15 ` Jeff King
2018-05-01 18:40 ` [PATCH v3 10/12] get_short_oid / peel_onion: ^{commit} should be commit, not committish Ævar Arnfjörð Bjarmason
2018-05-01 18:40 ` [PATCH v3 11/12] config doc: document core.disambiguate Ævar Arnfjörð Bjarmason
2018-05-08 14:41 ` Jeff King
2018-05-01 18:40 ` [PATCH v3 12/12] get_short_oid: document & warn if we ignore the type selector Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 01/12] sha1-name.c: remove stray newline Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 02/12] sha1-array.h: align function arguments Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 03/12] git-p4: change "commitish" typo to "committish" Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 04/12] cache.h: add comment explaining the order in object_type Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 05/12] sha1-name.c: move around the collect_ambiguous() function Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 06/12] get_short_oid: sort ambiguous objects by type, then SHA-1 Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 07/12] get_short_oid: learn to disambiguate by ^{tag} Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 08/12] get_short_oid: learn to disambiguate by ^{blob} Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 09/12] get_short_oid / peel_onion: ^{tree} should be tree, not treeish Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 10/12] get_short_oid / peel_onion: ^{commit} should be commit, not committish Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 11/12] config doc: document core.disambiguate Ævar Arnfjörð Bjarmason
2018-05-01 12:06 ` [PATCH v2 12/12] get_short_oid: document & warn if we ignore the type selector Ævar Arnfjörð Bjarmason
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: http://vger.kernel.org/majordomo-info.html
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=874ljrzctc.fsf@evledraar.gmail.com \
--to=avarab@gmail.com \
--cc=dstolee@microsoft.com \
--cc=git@vger.kernel.org \
--cc=stolee@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://80x24.org/mirrors/git.git
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).