AuroraRuntime/Source/IO/Loop/LSLocalMutex.cpp

/***
    Copyright (C) 2023 J Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: LSLocalMutex.cpp
    Date: 2023-10-21
    Author: Reece
***/
#include <RuntimeInternal.hpp>
#include "LSLocalMutex.hpp"
#include <Source/Threading/Primitives/SMTYield.hpp>

namespace Aurora::IO::Loop
{
    static auto const kFutexBitWake	= 256u;

    LSLocalMutex::LSLocalMutex()
    {

    }

    LSLocalMutex::~LSLocalMutex()
    {

    }

    bool LSLocalMutex::TryInit()
    {
        if (!LSSemaphore::TryInit(1))
        {
            return false;
        }

        return true;
    }

    bool LSLocalMutex::OnTrigger(AuUInt handle)
    {
        if (AuAtomicLoad(&this->uAtomicWord) & kFutexBitWake)
        {
            (void)LSSemaphore::OnTrigger(0);
            AuAtomicSub(&this->uAtomicWord, kFutexBitWake);
        }

        return this->TryTakeNoSpin();
    }

    bool LSLocalMutex::Unlock()
    {
        if (!(AuAtomicLoad(&this->uAtomicWord) & 1))
        {
            return false;
        }

        AuAtomicClearU8Lock(&this->uAtomicWord);

        while (true)
        {
            auto uState = AuAtomicLoad(&this->uAtomicWord);
            if (uState & 1)
            {
                return true;
            }

            if (uState & kFutexBitWake)
            {
                if (AuAtomicCompareExchange(&this->uAtomicWord, uState, uState) == uState)
                {
                    return true;
                }
                else
                {
                    continue;
                }
            }

            if (AuAtomicCompareExchange(&this->uAtomicWord, uState + kFutexBitWake, uState) == uState)
            {
                LSSemaphore::AddOne();
                return true;
            }
        }
    }

    bool LSLocalMutex::IsSignaled()
    {
        return this->TryTake();
    }

    bool LSLocalMutex::IsSignaledNoSpinIfUserland()
    {
        return this->TryTakeNoSpin();
    }

    bool LSLocalMutex::WaitOn(AuUInt32 timeout)
    {
        return this->TryTakeWaitMS(timeout);
    }

    ELoopSource LSLocalMutex::GetType()
    {
        return ELoopSource::eSourceFastMutex;
    }

    bool LSLocalMutex::TryTakeNoSpin()
    {
        return AuAtomicTestAndSet(&this->uAtomicWord, 0) == 0;
    }

    bool LSLocalMutex::TryTakeSpin()
    {
        return Threading::Primitives::DoTryIf([&]
        {
            return this->TryTakeNoSpin();
        });
    }

    bool LSLocalMutex::TryTake()
    {
        return this->TryTakeSpin();
    }

    bool LSLocalMutex::TryTakeWaitMS(AuUInt32 timeout)
    {
        auto uEndTime = timeout ?
            AuTime::SteadyClockNS() + AuMSToNS<AuUInt64>(timeout) : 
            0;

        if (this->TryTakeSpin())
        {
            return true;
        }

        while (!this->TryTakeNoSpin())
        {
            if (!timeout)
            {
                if (LSSemaphore::WaitOn(0))
                {
                    return true;
                }
            }
            else
            {
                auto uStartTime = Time::SteadyClockNS();
                if (uStartTime >= uEndTime)
                {
                    return false;
                }

                auto uDeltaMs = AuNSToMS<AuInt64>(uEndTime - uStartTime);
                if (uDeltaMs &&
                    LSSemaphore::WaitOn(uDeltaMs))
                {
                    return true;
                }
                else if (!uDeltaMs)
                {
                    if (this->TryTakeSpin())
                    {
                        return true;
                    }
                }
            }
        }

        return true;
    }

    AUKN_SYM AuSPtr<ILSMutex> NewLSMutex()
    {
        auto pMutex = AuMakeShared<LSLocalMutex>();
        if (!pMutex)
        {
            SysPushErrorGeneric();
            return {};
        }

        if (!pMutex->TryInit())
        {
            SysPushErrorNested();
            return {};
        }

        return pMutex;
    }
}