TimeKeeper.h

//------------------------------------------------------------------------------
/*
    This file is part of rippled: https://github.com/ripple/rippled
    Copyright (c) 2012, 2013 Ripple Labs Inc.
 
    Permission to use, copy, modify, and/or distribute this software for any
    purpose  with  or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.
 
    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
//==============================================================================
 
#ifndef RIPPLE_CORE_TIMEKEEPER_H_INCLUDED
#define RIPPLE_CORE_TIMEKEEPER_H_INCLUDED
 
#include <ripple/basics/chrono.h>
#include <ripple/beast/clock/abstract_clock.h>
 
#include <atomic>
 
namespace ripple {
 
class TimeKeeper : public beast::abstract_clock<NetClock>
{
private:
    std::atomic<std::chrono::seconds> closeOffset_{};
 
    // Adjust system_clock::time_point for NetClock epoch
    static constexpr time_point
    adjust(std::chrono::system_clock::time_point when)
    {
        return time_point(std::chrono::duration_cast<duration>(
            when.time_since_epoch() - epoch_offset));
    }
 
public:
    virtual ~TimeKeeper() = default;
 
    [[nodiscard]] time_point
    now() const override
    {
        return adjust(std::chrono::system_clock::now());
    }
 
    [[nodiscard]] time_point
    closeTime() const
    {
        return now() + closeOffset_.load();
    }
 
    // This may return a negative value
    [[nodiscard]] std::chrono::seconds
    closeOffset() const
    {
        return closeOffset_.load();
    }
 
    std::chrono::seconds
    adjustCloseTime(std::chrono::seconds by)
    {
        using namespace std::chrono_literals;
 
        auto offset = closeOffset_.load();
 
        if (by == 0s && offset == 0s)
            return offset;
 
        // The close time adjustment is serialized externally to this
        // code. The compare/exchange only serves as a weak check and
        // should not fail. Even if it does, it's safe to simply just
        // skip the adjustment.
        closeOffset_.compare_exchange_strong(offset, [by, offset]() {
            // Ignore small offsets and push the close time
            // towards our wall time.
            if (by > 1s)
                return offset + ((by + 3s) / 4);
 
            if (by < -1s)
                return offset + ((by - 3s) / 4);
 
            return (offset * 3) / 4;
        }());
 
        return closeOffset_.load();
    }
};
 
}  // namespace ripple
 
#endif