fcb8d040e8
Instead of lengthy blurbs, switch to single-line, machine-readable standardized (https://spdx.dev) license identifiers. The Linux kernel switched long ago, so there is strong precedent. Three cases are handled: AGPL-only, Apache-only, and dual licensed. For the latter case, I chose (AGPL-3.0-or-later and Apache-2.0), reasoning that our changes are extensive enough to apply our license. The changes we applied mechanically with a script, except to licenses/README.md. Closes #9937
58 lines
1.8 KiB
C++
58 lines
1.8 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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// 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() {
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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) {
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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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std::ostream& operator<<(std::ostream&, db_clock::time_point);
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