From: Jonathan Nieder <jrnieder@gmail.com>
To: Jeff King <peff@peff.net>
Cc: "René Scharfe" <l.s.r@web.de>,
"Derrick Stolee" <stolee@gmail.com>,
"Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>,
git@vger.kernel.org, "Junio C Hamano" <gitster@pobox.com>,
"Derrick Stolee" <dstolee@microsoft.com>
Subject: Re: [PATCH 15/16] commit-reach: make can_all_from_reach... linear
Date: Tue, 17 Nov 2020 18:16:05 -0800 [thread overview]
Message-ID: <20201118021605.GB360414@google.com> (raw)
In-Reply-To: <20181017083340.GB31932@sigill.intra.peff.net>
Hi,
Jeff King wrote:
> On Sun, Oct 14, 2018 at 04:29:06PM +0200, René Scharfe wrote:
>> Anyway, drove the generative approach a bit further, and came up with
>> the new DEFINE_SORT below. I'm unsure about the name; perhaps it should
>> be called DEFINE_SORT_BY_COMPARE_FUNCTION_BODY, but that's a bit long.
>> It handles casts and const attributes behind the scenes and avoids
>> repetition, but looks a bit weird, as it is placed where a function
>> signature would go.
>>
>> Apart from that the macro is simple and doesn't use any tricks or
>> added checks. It just sets up boilerplate functions to offer type-safe
>> sorting.
>>
>> diffcore-rename.c and refs/packed-backend.c receive special treatment in
>> the patch because their compare functions are used outside of sorting as
>> well. I made them take typed pointers nevertheless and used them from
>> DEFINE_SORT; the wrapper generated by that macro is supposed to be
>> private. Given that such reuse is rare and I think we don't need a way
>> to make it public.
>>
>> What do y'all think about this direction?
>
> I think it's the best we're likely to do, and is an improvement on the
> status quo.
>
> The patch looks overall sane to me. I think DEFINE_SORT() is a fine
> name.
Since this came up in [1], I took a glance at this.
I also think it looks reasonable, though it's possible to do better if
we're willing to (1) cast between pointers to function with different
signatures, which is portable in practice but I don't believe the C
standard speaks to and (2) conditionally make use of gcc extensions,
for typechecking.
For example, CCAN's asort[2] does typechecking on the arrays passed in
and the callback cookie parameter to qsort_r, with no extra
boilerplate or run-time overhead involved[3].
(The core of that macro is ccan's typesafe_cb_cast[4]:
/* CC0 (Public domain) - see LICENSE file for details */
#if HAVE_TYPEOF && HAVE_BUILTIN_CHOOSE_EXPR && HAVE_BUILTIN_TYPES_COMPATIBLE_P
/**
* typesafe_cb_cast - only cast an expression if it matches a given type
* @desttype: the type to cast to
* @oktype: the type we allow
* @expr: the expression to cast
*
* This macro is used to create functions which allow multiple types.
* The result of this macro is used somewhere that a @desttype type is
* expected: if @expr is exactly of type @oktype, then it will be
* cast to @desttype type, otherwise left alone.
*
* This macro can be used in static initializers.
*
* This is merely useful for warnings: if the compiler does not
* support the primitives required for typesafe_cb_cast(), it becomes an
* unconditional cast, and the @oktype argument is not used. In
* particular, this means that @oktype can be a type which uses the
* "typeof": it will not be evaluated if typeof is not supported.
*
* Example:
* // We can take either an unsigned long or a void *.
* void _set_some_value(void *val);
* #define set_some_value(e) \
* _set_some_value(typesafe_cb_cast(void *, unsigned long, (e)))
*/
#define typesafe_cb_cast(desttype, oktype, expr) \
__builtin_choose_expr( \
__builtin_types_compatible_p(__typeof__(0?(expr):(expr)), \
oktype), \
(desttype)(expr), (expr))
#else
#define typesafe_cb_cast(desttype, oktype, expr) ((desttype)(expr))
#endif
)
Thanks,
Jonathan
[1] https://lore.kernel.org/git/20201117223011.GA642234@coredump.intra.peff.net/
[2] https://git.ozlabs.org/?p=ccan;a=blob;f=ccan/asort/asort.h;hb=HEAD
[3] https://ccodearchive.net/info/asort.html
[4] https://git.ozlabs.org/?p=ccan;a=blob;f=ccan/typesafe_cb/typesafe_cb.h;hb=HEAD
next prev parent reply other threads:[~2020-11-18 2:17 UTC|newest]
Thread overview: 118+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-16 13:00 [PATCH 00/16] Consolidate reachability logic Derrick Stolee via GitGitGadget
2018-06-19 20:25 ` [PATCH 04/16] upload-pack: make reachable() more generic Derrick Stolee via GitGitGadget
2018-06-19 20:35 ` [PATCH 05/16] upload-pack: refactor ok_to_give_up() Derrick Stolee via GitGitGadget
2018-06-25 17:16 ` [PATCH 01/16] commit-reach: move walk methods from commit.c Derrick Stolee via GitGitGadget
2018-07-16 18:57 ` Stefan Beller
2018-07-16 21:31 ` Jonathan Tan
2018-06-25 17:35 ` [PATCH 02/16] commit-reach: move ref_newer from remote.c Derrick Stolee via GitGitGadget
2018-07-16 19:10 ` Stefan Beller
2018-06-25 18:01 ` [PATCH 03/16] commit-reach: move commit_contains from ref-filter Derrick Stolee via GitGitGadget
2018-07-16 19:14 ` Stefan Beller
2018-06-28 12:31 ` [PATCH 15/16] commit-reach: make can_all_from_reach... linear Derrick Stolee via GitGitGadget
2018-07-16 22:37 ` Stefan Beller
2018-07-17 1:16 ` Jonathan Tan
2018-10-01 19:16 ` René Scharfe
2018-10-01 19:26 ` Derrick Stolee
2018-10-01 20:37 ` René Scharfe
2018-10-04 22:59 ` René Scharfe
2018-10-05 12:15 ` Derrick Stolee
2018-10-05 16:51 ` Jeff King
2018-10-05 18:48 ` René Scharfe
2018-10-05 19:08 ` Jeff King
2018-10-05 19:36 ` René Scharfe
2018-10-05 19:42 ` Jeff King
2018-10-14 14:29 ` René Scharfe
2018-10-15 15:31 ` Derrick Stolee
2018-10-15 16:26 ` René Scharfe
2018-10-16 23:09 ` Junio C Hamano
2018-10-17 8:33 ` Jeff King
2020-11-18 2:16 ` Jonathan Nieder [this message]
2020-11-18 6:54 ` Jeff King
2020-11-18 17:47 ` René Scharfe
2018-10-05 19:12 ` Ævar Arnfjörð Bjarmason
2018-10-05 19:28 ` Jeff King
2018-10-05 19:42 ` Ævar Arnfjörð Bjarmason
2018-10-05 19:44 ` Jeff King
2018-07-12 20:47 ` [PATCH 06/16] upload-pack: generalize commit date cutoff Derrick Stolee via GitGitGadget
2018-07-16 19:38 ` Stefan Beller
2018-07-18 16:04 ` Derrick Stolee
2018-07-12 20:52 ` [PATCH 07/16] commit-reach: move can_all_from_reach_with_flags Derrick Stolee via GitGitGadget
2018-07-16 22:37 ` Jonathan Tan
2018-07-13 14:06 ` [PATCH 08/16] test-reach: create new test tool for ref_newer Derrick Stolee via GitGitGadget
2018-07-16 23:00 ` Jonathan Tan
2018-07-18 16:14 ` Derrick Stolee
2018-07-13 14:28 ` [PATCH 09/16] test-reach: test in_merge_bases Derrick Stolee via GitGitGadget
2018-07-13 14:38 ` [PATCH 10/16] test-reach: test is_descendant_of Derrick Stolee via GitGitGadget
2018-07-13 14:51 ` [PATCH 11/16] test-reach: test get_merge_bases_many Derrick Stolee via GitGitGadget
2018-07-16 21:24 ` Stefan Beller
2018-07-16 23:08 ` Jonathan Tan
2018-07-13 16:51 ` [PATCH 12/16] test-reach: test reduce_heads Derrick Stolee via GitGitGadget
2018-07-16 21:30 ` Stefan Beller
2018-07-16 21:59 ` Eric Sunshine
2018-07-13 17:22 ` [PATCH 13/16] test-reach: test can_all_from_reach_with_flags Derrick Stolee via GitGitGadget
2018-07-16 21:54 ` Stefan Beller
2018-07-18 16:54 ` Derrick Stolee
2018-07-17 0:10 ` Jonathan Tan
2018-07-13 18:37 ` [PATCH 14/16] commit-reach: replace ref_newer logic Derrick Stolee via GitGitGadget
2018-07-16 22:16 ` Stefan Beller
2018-07-13 19:25 ` [PATCH 16/16] commit-reach: use can_all_from_reach Derrick Stolee via GitGitGadget
2018-07-16 22:47 ` Stefan Beller
2018-07-16 13:54 ` [PATCH 00/16] Consolidate reachability logic Ramsay Jones
2018-07-16 16:18 ` Jeff King
2018-07-16 18:40 ` Eric Sunshine
2018-07-16 18:56 ` Jeff King
2018-07-16 18:59 ` Eric Sunshine
2018-07-18 12:32 ` Johannes Schindelin
2018-07-18 12:23 ` Johannes Schindelin
2018-07-18 19:21 ` Jeff King
2018-07-19 16:34 ` Johannes Schindelin
2018-07-16 17:26 ` Stefan Beller
2018-07-16 18:44 ` Eric Sunshine
2018-07-16 18:47 ` Derrick Stolee
2018-07-18 12:28 ` Johannes Schindelin
2018-07-18 15:01 ` Duy Nguyen
2018-07-18 17:01 ` Junio C Hamano
2018-07-18 17:11 ` Derrick Stolee
2018-07-19 16:37 ` Johannes Schindelin
2018-07-19 16:32 ` Johannes Schindelin
2018-07-20 16:33 ` [PATCH v2 00/18] " Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 01/18] commit-reach: move walk methods from commit.c Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 02/18] commit.h: remove method declarations Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 03/18] commit-reach: move ref_newer from remote.c Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 04/18] commit-reach: move commit_contains from ref-filter Derrick Stolee
2018-08-28 21:24 ` Jonathan Nieder
2018-08-28 21:33 ` Derrick Stolee
2018-08-28 21:36 ` [PATCH] commit-reach: correct accidental #include of C file Jonathan Nieder
2018-08-28 21:39 ` Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 05/18] upload-pack: make reachable() more generic Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 06/18] upload-pack: refactor ok_to_give_up() Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 07/18] upload-pack: generalize commit date cutoff Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 08/18] commit-reach: move can_all_from_reach_with_flags Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 09/18] test-reach: create new test tool for ref_newer Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 10/18] test-reach: test in_merge_bases Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 11/18] test-reach: test is_descendant_of Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 12/18] test-reach: test get_merge_bases_many Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 13/18] test-reach: test reduce_heads Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 14/18] test-reach: test can_all_from_reach_with_flags Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 15/18] test-reach: test commit_contains Derrick Stolee
2018-07-23 20:35 ` Jonathan Tan
2018-07-25 18:08 ` Junio C Hamano
2018-07-25 18:30 ` Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 16/18] commit-reach: replace ref_newer logic Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 17/18] commit-reach: make can_all_from_reach... linear Derrick Stolee
2018-07-23 20:41 ` Jonathan Tan
2018-08-01 20:41 ` Derrick Stolee
2018-09-12 4:14 ` Jeff King
2018-09-12 4:29 ` Jeff King
2018-09-12 13:08 ` Derrick Stolee
2018-07-20 16:33 ` [PATCH v2 18/18] commit-reach: use can_all_from_reach Derrick Stolee
2018-07-20 17:10 ` [PATCH v2 00/18] Consolidate reachability logic Stefan Beller
2018-07-20 17:15 ` Derrick Stolee
2018-07-20 22:16 ` Stefan Beller
2018-08-01 20:33 ` Derrick Stolee
2018-07-20 17:18 ` Derrick Stolee
2018-07-20 18:09 ` Eric Sunshine
2018-07-20 19:14 ` Derrick Stolee
2018-07-20 17:41 ` Duy Nguyen
2018-07-20 19:09 ` Derrick Stolee
2018-07-20 22:45 ` Junio C Hamano
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