AuroraRuntime/Source/Threading/AuWaitFor.hpp

/***
    Copyright (C) 2021 J Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: WaitFor.hpp
    Date: 2021-6-12
    Author: Reece
***/
#pragma once

namespace Aurora::Threading
{
    // the original idea:
    // It's not insane to expect slow linux kernels to run at 250 jiffies a second, so, 4ms
    // It's also not insane to expect a complete context swap/rescheduled yield on windows to last 15ms  
    // -> if sleep time greater than 15ms, yield to nt Sleep 
    // -> if sleep time greater than 4ms, yield to linux kernel 
    // -> if sleep time greater than 2ms (?), yield to SwitchToThread 
    // -> SPIIIIIN

    static const AuUInt64 kPredictedLinuxKernelJiffies = 250; // some kernel builds go up to 1000
    static const AuUInt64 kPredictedLinuxKernelTimeMilli = (1000 / kPredictedLinuxKernelJiffies);
    static const AuUInt64 kPredictedLinuxKernelTimeMicro = kPredictedLinuxKernelTimeMilli * 1000;
    static const AuUInt64 kPredictedLinuxKernelTimeNano = kPredictedLinuxKernelTimeMilli * 1000000;
    static const AuUInt64 kLinuxYieldTimeNano = 1e+6 / 150; // completely arbitrary
    static const AuUInt64 kLinuxYieldTimeThresNano = 1e+6 / 25; // completely arbitrary
    static const AuUInt64 kPredictedLinuxKernelTimeRTNano = (kLinuxYieldTimeNano + kPredictedLinuxKernelTimeNano) * 3;

    //static const AuUInt64 kPredictedNTOSSwitchTimeMS        = 10;
    //static const AuUInt64 kPredictedNTOSSwitchTimeYDMS      = kPredictedNTOSSwitchTimeMS  / 4;
    //static const AuUInt64 kPredictedNTOSSwitchTimeRTMS      = kPredictedNTOSSwitchTimeMS + kPredictedNTOSSwitchTimeMS;
    static const AuUInt64 kPredictedNTOSSwitchTimeRTNS = 1000000;// kPredictedNTOSSwitchTimeRTMS* 1000000;
    //static const AuUInt64 kPredictedNTOSSwitchTimeNS        = 3* 1000000;
    static const AuUInt64 kPredictedNTOSSwitchTimeYDNS = 1000000 / 4;// kPredictedNTOSSwitchTimeNS  / 4;

    static const AuMach kYieldFlagsNone = 0;
    static const AuMach kYieldFlagsRemoved = 1;
    static const AuMach kYieldFlagsContextSwitchASAP = 2;
    static const AuMach kYieldFlagsContextSwitchForever = 4;
    static const AuMach kYieldFlagsRegular = kYieldFlagsContextSwitchASAP | kYieldFlagsContextSwitchForever;

    template<AuMach yieldFaster>
    void FastSnooze(long &count, AuUInt64 &startTime, AuUInt64 maxStallMS);


    bool YieldPoll(bool permitMultipleContextSwitches, AuUInt64 timeoutMs, Threading::PollCallback_cb cb);

    void YieldToOtherThread();
}