Backoff.h

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// Honeycomb, Copyright (C) 2015 NewGamePlus Inc.  Distributed under the Boost Software License v1.0.
#pragma once

#include "Honey/Thread/Thread.h"

namespace honey { namespace lockfree
{

class Backoff
{
public:

    Backoff(bool spin = true, Nanosec timeMin = 100_ns, Nanosec timeMax = 100_us, int tickThresh = 5) :
        _spin(spin),
        _timeMin(timeMin),
        _timeMax(timeMax),
        _tickThresh(tickThresh)
    {}

    void inc(int ticks = 1)
    {
        Local& l = _l;
        for (l.tick += ticks; l.tick >= _tickThresh; l.tick -= _tickThresh)
        {
            //Deactivate spin
            if (l.spin) { l.spin = false; continue; }
            //Grow sleep time
            l.time = l.time*2 + 1_ns;
            if (l.time > _timeMax) l.time = _timeMax;
        }
    }

    void dec(int ticks = 1)
    {
        Local& l = _l;
        for (l.tick -= ticks; l.tick <= -_tickThresh; l.tick += _tickThresh)
        {
            //Activate spin
            if (l.time == _timeMin) { l.spin = _spin; continue; }
            //Shrink sleep time
            l.time = l.time/2;
            if (l.time < _timeMin) l.time = _timeMin;
        }
    }

    void wait()                             { Local& l = _l; if (l.spin) thread::current::pause(); else thread::current::sleep(l.time); }

    void reset()                            { Local& l = _l; l.spin = _spin; l.time = _timeMin; l.tick = 0; }

private:

    struct Local
    {
        bool                spin;
        Nanosec             time;
        int                 tick;
    };

    bool                    _spin;
    Nanosec                 _timeMin;
    Nanosec                 _timeMax;
    int                     _tickThresh;
    thread::Local<Local>    _l;
};

} }