168ade72f8
in in {fmt} before v10, it provides the specialization of `fmt::formatter<..>`
for `std::string_view` as well as the specialization of `fmt::formatter<..>`
for `fmt::string_view` which is an implementation builtin in {fmt} for
compatibility of pre-C++17. and this type is used even if the code is
compiled with C++ stadandard greater or equal to C++17. also, before v10,
the `fmt::formatter<std::string_view>::format()` is defined so it accepts
`std::string_view`. after v10, `fmt::formatter<std::string_view>` still
exists, but it is now defined using `format_as()` machinery, so it's
`format()` method does not actually accept `std::string_view`, it
accepts `fmt::string_view`, as the former can be converted to
`fmt::string_view`.
this is why we can inherit from `fmt::formatter<std::string_view>` and
use `formatter<std::string_view>::format(foo, ctx);` to implement the
`format()` method with {fmt} v9, but we cannot do this with {fmt} v10,
and we would have following compilation failure:
```
FAILED: service/CMakeFiles/service.dir/RelWithDebInfo/topology_state_machine.cc.o
/home/kefu/.local/bin/clang++ -DFMT_DEPRECATED_OSTREAM -DFMT_SHARED -DSCYLLA_BUILD_MODE=release -DSEASTAR_API_LEVEL=7 -DSEASTAR_LOGGER_COMPILE_TIME_FMT -DSEASTAR_LOGGER_TYPE_STDOUT -DSEASTAR_SCHEDULING_GROUPS_COUNT=16 -DSEASTAR_SSTRING -DXXH_PRIVATE_API -DCMAKE_INTDIR=\"RelWithDebInfo\" -I/home/kefu/dev/scylladb -I/home/kefu/dev/scylladb/build/gen -I/home/kefu/dev/scylladb/seastar/include -I/home/kefu/dev/scylladb/build/seastar/gen/include -I/home/kefu/dev/scylladb/build/seastar/gen/src -ffunction-sections -fdata-sections -O3 -g -gz -std=gnu++20 -fvisibility=hidden -Wall -Werror -Wextra -Wno-error=deprecated-declarations -Wimplicit-fallthrough -Wno-c++11-narrowing -Wno-deprecated-copy -Wno-mismatched-tags -Wno-missing-field-initializers -Wno-overloaded-virtual -Wno-unsupported-friend -Wno-enum-constexpr-conversion -Wno-unused-parameter -ffile-prefix-map=/home/kefu/dev/scylladb=. -march=westmere -mllvm -inline-threshold=2500 -fno-slp-vectorize -U_FORTIFY_SOURCE -Werror=unused-result -MD -MT service/CMakeFiles/service.dir/RelWithDebInfo/topology_state_machine.cc.o -MF service/CMakeFiles/service.dir/RelWithDebInfo/topology_state_machine.cc.o.d -o service/CMakeFiles/service.dir/RelWithDebInfo/topology_state_machine.cc.o -c /home/kefu/dev/scylladb/service/topology_state_machine.cc
/home/kefu/dev/scylladb/service/topology_state_machine.cc:254:41: error: no matching member function for call to 'format'
254 | return formatter<std::string_view>::format(it->second, ctx);
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
/usr/include/fmt/core.h:2759:22: note: candidate function template not viable: no known conversion from 'seastar::basic_sstring<char, unsigned int, 15>' to 'const fmt::basic_string_view<char>' for 1st argument
2759 | FMT_CONSTEXPR auto format(const T& val, FormatContext& ctx) const
| ^ ~~~~~~~~~~~~
```
because the inherited `format()` method actually comes from
`fmt::formatter<fmt::string_view>`. to reduce the confusion, in this
change, we just inherit from `fmt::format<string_view>`, where
`string_view` is actually `fmt::string_view`. this follows
the document at
https://fmt.dev/latest/api.html#formatting-user-defined-types,
and since there is less indirection under the hood -- we do not
use the specialization created by `FMT_FORMAT_AS` which inherit
from `formatter<fmt::string_view>`, hopefully this can improve
the compilation speed a little bit. also, this change addresses
the build failure with {fmt} v10.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closes scylladb/scylladb#18299
66 lines
2.1 KiB
C++
66 lines
2.1 KiB
C++
/*
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* Copyright (C) 2014-present ScyllaDB
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*/
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/*
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* SPDX-License-Identifier: AGPL-3.0-or-later
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*/
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#pragma once
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#include "clocks-impl.hh"
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#include "gc_clock.hh"
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#include <chrono>
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#include <cstdint>
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#include <ratio>
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#include <type_traits>
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#include <fmt/chrono.h>
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// the database clock follows Java - 1ms granularity, 64-bit counter, 1970 epoch
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class db_clock final {
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public:
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using base = std::chrono::system_clock;
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using rep = int64_t;
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using period = std::ratio<1, 1000>; // milliseconds
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using duration = std::chrono::duration<rep, period>;
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using time_point = std::chrono::time_point<db_clock, duration>;
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static constexpr bool is_steady = base::is_steady;
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static constexpr std::time_t to_time_t(time_point t) {
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return std::chrono::duration_cast<std::chrono::seconds>(t.time_since_epoch()).count();
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}
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static constexpr time_point from_time_t(std::time_t t) {
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return time_point(std::chrono::duration_cast<duration>(std::chrono::seconds(t)));
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}
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static time_point now() noexcept {
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return time_point(std::chrono::duration_cast<duration>(base::now().time_since_epoch())) + get_clocks_offset();
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}
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};
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static inline
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gc_clock::time_point to_gc_clock(db_clock::time_point tp) noexcept {
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// Converting time points through `std::time_t` means that we don't have to make any assumptions about the epochs
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// of `gc_clock` and `db_clock`, though we require that that the period of `gc_clock` is also 1 s like
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// `std::time_t` to avoid loss of information.
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{
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using second = std::ratio<1, 1>;
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static_assert(
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std::is_same<gc_clock::period, second>::value,
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"Conversion via std::time_t would lose information.");
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}
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return gc_clock::from_time_t(db_clock::to_time_t(tp));
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}
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/* For debugging and log messages. */
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template <>
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struct fmt::formatter<db_clock::time_point> : fmt::formatter<string_view> {
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template <typename FormatContext>
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auto format(const db_clock::time_point& tp, FormatContext& ctx) const {
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auto t = db_clock::to_time_t(tp);
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return fmt::format_to(ctx.out(), "{:%Y/%m/%d %T}", fmt::gmtime(t));
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}
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};
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