From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp59.i.mail.ru (smtp59.i.mail.ru [217.69.128.39]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dev.tarantool.org (Postfix) with ESMTPS id 14290469710 for ; Thu, 14 May 2020 01:10:33 +0300 (MSK) References: <22a830fb9d2dbc3883b9710d36ab88c638101002.1589240704.git.v.shpilevoy@tarantool.org> <20200513123145.GA16814@tarantool.org> From: Vladislav Shpilevoy Message-ID: <06c4d5d9-db84-4043-0d7a-81c0320b6663@tarantool.org> Date: Thu, 14 May 2020 00:10:29 +0200 MIME-Version: 1.0 In-Reply-To: <20200513123145.GA16814@tarantool.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Subject: Re: [Tarantool-patches] [PATCH 4/5] error: provide MP_ERROR extension serializer List-Id: Tarantool development patches List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Nikita Pettik Cc: tarantool-patches@dev.tarantool.org Thanks for the review! On 13/05/2020 14:31, Nikita Pettik wrote: > On 12 May 01:45, Vladislav Shpilevoy wrote: >> src/box/mp_error.h | 29 ++++ >> test/unit/mp_error.cc | 270 +++++++++++++++++++++++++++++++++++++- >> test/unit/mp_error.result | 72 +++++++++- >> 4 files changed, 529 insertions(+), 3 deletions(-) >> + >> +#define MP_ERROR_PRINT_DEFINITION >> +#define MP_PRINT_FUNC snprintf >> +#define MP_PRINT_SUFFIX snprint >> +#define MP_PRINT_2(total, func, ...) \ >> + SNPRINT(total, func, buf, size, __VA_ARGS__) >> +#define MP_PRINT_ARGS_DECL char *buf, int size >> +#include __FILE__ >> + >> +#define MP_ERROR_PRINT_DEFINITION >> +#define MP_PRINT_FUNC fprintf >> +#define MP_PRINT_SUFFIX fprint >> +#define MP_PRINT_2(total, func, ...) do { \ >> + int bytes = func(file, __VA_ARGS__); \ >> + if (bytes < 0) \ >> + return -1; \ >> + total += bytes; \ >> +} while (0) >> +#define MP_PRINT_ARGS_DECL FILE *file >> +#include __FILE__ > > I've failed to understand how this is supposed to work. > Why do you have to include file itself? Why do you have to do it twice? > This macro related part definitely lacks some comments. This is not supposed to work. It works already. Was a surprise even for me. I wasn't sure this needs more explanation that I gave below: > /** > * MP_ERROR extension string serializer. > * There are two applications for string serialization - into a > * buffer, and into a file. Structure of both is exactly the same > * except for the copying/writing itself. To avoid code > * duplication the code is templated and expects some macros to do > * the actual output. > */ This is basically a C template. The same as bps tree, rb tree, mhash. But located in the same source file which needs it. Since this is not a common enough feature to move it to a separate place. I include self with pre-declared macros MP_ERROR_PRINT_DEFINITION. When it is defined, the file skips everything except the 3 functions in the end: mp_print_error_one(), mp_print_error_stack(), mp_print_error(). The skip uses mere #ifdef MP_ERROR_PRINT_DEFINITION to understand, that currently the file is being included into self to customize the error printers. So all is skipped except them. I include the file twice, but with different parameters. Like if I would customize one template with two parameter sets in C++. First inclusion turns mp_print_error_one(), mp_print_error_stack(), mp_print_error() into mp_snprint_error_one(), mp_snprint_error_stack(), mp_snprint_error() and snprintf() calls inside. The second inclusion turns the functions into mp_fprint_error_one(), mp_fprint_error_stack(), mp_fprint_error() and fprintf() calls inside. I tried to extend the comment. ==================== diff --git a/src/box/mp_error.cc b/src/box/mp_error.cc index 0b5e6bc96..a4a4ccaca 100644 --- a/src/box/mp_error.cc +++ b/src/box/mp_error.cc @@ -587,6 +587,21 @@ error_unpack_unsafe(const char **data) * except for the copying/writing itself. To avoid code * duplication the code is templated and expects some macros to do * the actual output. + * + * Templates are defined similarly to the usual C trick, when all + * the code is in one file and relies on some external macros to + * define customizable types, functions, parameters. Then other + * code can include this file with the macros defined. Even + * multiple times, in case structure and function names also are + * customizable. + * + * The tricky thing here is that the templates are defined in the + * same file, which needs them. So the file needs to include + * *self* with a few macros defined beforehand. That allows to + * hide this template from any external access, use mp_error + * internal functions, and keep all the code in one place without + * necessity to split it into different files just to be able to + * turn it into a template. */