AuroraRuntime/Source/Threading/Primitives/AuSemaphore.Linux.cpp

/***
    Copyright (C) 2022 J Reece Wilson (a/k/a "Reece"). All rights reserved.

    File: AuSemaphore.Linux.cpp
    Date: 2022-12-28
    Author: Reece
***/
#include <Source/RuntimeInternal.hpp>
#include "AuSemaphore.Generic.hpp"
#include "SMTYield.hpp"

#if !defined(_AURUNTIME_GENERIC_SEMAPHORE)
#include <Source/Time/Time.hpp>
        
namespace Aurora::Threading::Primitives
{
    SemaphoreImpl::SemaphoreImpl(AuUInt16 uIntialValue) : dwState_(uIntialValue)
    {
    }
    
    SemaphoreImpl::~SemaphoreImpl()
    {
    }

    bool SemaphoreImpl::HasOSHandle(AuMach &mach)
    {
        return false;
    }
    
    bool SemaphoreImpl::HasLockImplementation()
    {
        return true;
    }
    
    bool SemaphoreImpl::TryLockNoSpin()
    {
        auto old = this->dwState_;
        return (old != 0 && AuAtomicCompareExchange(&this->dwState_, old - 1, old) == old);
    }

    bool SemaphoreImpl::TryLock()
    {
        if (gRuntimeConfig.threadingConfig.bPreferLinuxSemaphoreSpinTryLock)
        {
            return TryLockHeavy();
        }
        else
        {
            return TryLockNoSpin();
        }
    }

    bool SemaphoreImpl::TryLockHeavy()
    {
        return DoTryIf([=]()
        {
            return TryLockNoSpin();
        });
    }

    bool SemaphoreImpl::LockMS(AuUInt64 uTimeout)
    {
        return LockNS(AuMSToNS<AuUInt64>(uTimeout));
    }

    bool SemaphoreImpl::LockNS(AuUInt64 uTimeout)
    {
        AuUInt64 uStart {};
        AuUInt64 uEnd {};
        
        if (this->TryLockHeavy())
        {
            return true;
        }

        errno = 0;

        struct timespec tspec;
        if (uTimeout != 0)
        {
            uStart = AuTime::SteadyClockNS();
            uEnd   = uStart + uTimeout;
            
            Time::monoabsns2ts(&tspec, uEnd);
        }

        AuAtomicAdd<AuUInt32>(&this->dwSleeping_, 1u);

        auto old = this->dwState_;
             //!tryLock (with old in a scope we can access)
        while (!((old != 0) &&
                 (AuAtomicCompareExchange(&this->dwState_, old - 1, old) == old)))
        {
            if (uTimeout != 0)
            {
                if (Time::SteadyClockNS() >= uEnd)
                {
                     AuAtomicSub<AuUInt32>(&this->dwSleeping_, 1u);
                    return false;
                }

                int ret {};
                do
                {
                    ret = futex_wait(&this->dwState_, 0, &tspec);
                }
                while (ret == EINTR);
            }
            else
            {
                int ret {};
                bool bStatus {};

                do
                {
                    if ((ret = futex_wait(&this->dwState_, 0)) == 0)
                    {
                        bStatus = true;
                        continue;
                    }

                    if (ret == EAGAIN || errno == EAGAIN)
                    {
                        bStatus = true;
                        continue;
                    }
                    
                }
                while (ret == EINTR);

                RUNTIME_ASSERT_SHUTDOWN_SAFE(bStatus, "semaphore wait failed: {}", ret)
            }

            old = this->dwState_;
        }

        AuAtomicSub<AuUInt32>(&this->dwSleeping_, 1u);
        return true;
    }
    
    void SemaphoreImpl::Lock()
    {
        auto status = LockNS(0);
        SysAssert(status, "Couldn't lock semaphore");
    }
    
    void SemaphoreImpl::Unlock(AuUInt16 count)
    {
        AuAtomicAdd<AuUInt32>(&this->dwState_, count);
        if (this->dwSleeping_)
        {
            futex_wake(&this->dwState_, count);
        }
    }
    
    void SemaphoreImpl::Unlock()
    {
        Unlock(1);
    }
    
    AUKN_SYM ISemaphore *SemaphoreNew(AuUInt16 uInitialCount)
    {
        return _new SemaphoreImpl(uInitialCount);
    }

    AUKN_SYM void SemaphoreRelease(ISemaphore *pSemaphore)
    {
        AuSafeDelete<SemaphoreImpl *>(pSemaphore);
    }

    AUROXTL_INTERFACE_SOO_SRC_EX(AURORA_SYMBOL_EXPORT, Semaphore, SemaphoreImpl)
}
#endif