gc_clock.hh

/*
 * Copyright (C) 2015 ScyllaDB
 */

/*
 * This file is part of Scylla.
 *
 * Scylla is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Affero General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Scylla is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Scylla.  If not, see <http://www.gnu.org/licenses/>.
 */

#pragma once

#include "clocks-impl.hh"

#include <seastar/core/lowres_clock.hh>

#include <chrono>
#include <experimental/optional>

// FIXME: wraps around in 2038
class gc_clock final {
public:
    using base = seastar::lowres_system_clock;
    using rep = int32_t;
    using period = std::ratio<1, 1>; // seconds
    using duration = std::chrono::duration<rep, period>;
    using time_point = std::chrono::time_point<gc_clock, duration>;

    static constexpr auto is_steady = base::is_steady;

    static constexpr std::time_t to_time_t(time_point t) {
        return std::chrono::duration_cast<std::chrono::seconds>(t.time_since_epoch()).count();
    }

    static constexpr time_point from_time_t(std::time_t t) {
        return time_point(std::chrono::duration_cast<duration>(std::chrono::seconds(t)));
    }

    static time_point now() {
        return time_point(std::chrono::duration_cast<duration>(base::now().time_since_epoch())) + get_clocks_offset();
    }
};

using expiry_opt = std::experimental::optional<gc_clock::time_point>;
using ttl_opt = std::experimental::optional<gc_clock::duration>;

// 20 years in seconds
static constexpr gc_clock::duration max_ttl = gc_clock::duration{20 * 365 * 24 * 60 * 60};