69 lines
2.3 KiB
C++
69 lines
2.3 KiB
C++
/*
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* Copyright (C) 2015 ScyllaDB
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*/
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/*
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* This file is part of Scylla.
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*
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* Scylla is free software: you can redistribute it and/or modify
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* it under the terms of the GNU Affero General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* Scylla is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with Scylla. If not, see <http://www.gnu.org/licenses/>.
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*/
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#pragma once
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#include <atomic>
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#include <chrono>
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#include <experimental/optional>
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extern std::atomic<int64_t> clocks_offset;
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static inline std::chrono::seconds get_clocks_offset()
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{
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auto off = clocks_offset.load(std::memory_order_relaxed);
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return std::chrono::seconds(off);
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}
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// FIXME: wraps around in 2038
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class gc_clock {
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public:
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using base = std::chrono::system_clock;
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using rep = int32_t;
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using period = std::ratio<1, 1>; // seconds
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using duration = std::chrono::duration<rep, period>;
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using time_point = std::chrono::time_point<gc_clock, duration>;
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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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// Returns a time point which is earlier from t by d, or minimum time point if it cannot be represented.
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template<typename Clock, typename Duration, typename Rep, typename Period>
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inline
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auto saturating_subtract(std::chrono::time_point<Clock, Duration> t, std::chrono::duration<Rep, Period> d) -> decltype(t) {
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return std::max(t, decltype(t)::min() + d) - d;
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}
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using expiry_opt = std::experimental::optional<gc_clock::time_point>;
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using ttl_opt = std::experimental::optional<gc_clock::duration>;
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// 20 years in seconds
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static constexpr gc_clock::duration max_ttl = gc_clock::duration{20 * 365 * 24 * 60 * 60};
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template<typename Duration>
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static inline void forward_jump_clocks(Duration delta)
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{
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auto d = std::chrono::duration_cast<std::chrono::seconds>(delta).count();
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clocks_offset.fetch_add(d, std::memory_order_relaxed);
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}
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