AuroraRuntime/Source/IO/Loop/LSLocalSemaphore.cpp

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

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

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

    LSLocalSemaphore::LSLocalSemaphore()
    {

    }

    LSLocalSemaphore::~LSLocalSemaphore()
    {

    }

    bool LSLocalSemaphore::TryInit(AuUInt32 initialCount)
    {
        if (!LSSemaphore::TryInit(1))
        {
            return false;
        }

        this->uAtomicSemaphore = initialCount;

        return true;
    }

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

        return this->TryTakeNoSpin();
    }

    bool LSLocalSemaphore::AddOne()
    {
        AuAtomicAdd(&this->uAtomicSemaphore, 1u);

        while (true)
        {
            auto uState = AuAtomicLoad(&this->uAtomicWord);
 
            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 LSLocalSemaphore::IsSignaled()
    {
        return this->TryTake();
    }

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

    ELoopSource LSLocalSemaphore::GetType()
    {
        return ELoopSource::eSourceSemaphore;
    }

    bool LSLocalSemaphore::TryTakeNoSpin()
    {
        AuUInt32 uOld {};

        while ((uOld = this->uAtomicSemaphore))
        {
            if (AuAtomicCompareExchange(&this->uAtomicSemaphore, uOld - 1, uOld) == uOld)
            {
                return true;
            }
        }

        return false;
    }

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

    bool LSLocalSemaphore::TryTake()
    {
        return this->TryTakeNoSpin();
    }

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

        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;
                }
            }
        }

        return true;
    }

    AUKN_SYM AuSPtr<ILSSemaphore> NewLSSemaphore(AuUInt32 initialCount)
    {
        auto pMutex = AuMakeShared<LSLocalSemaphore>();
        if (!pMutex)
        {
            SysPushErrorGeneric();
            return {};
        }

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

        return pMutex;
    }
}