// Copyright Epic Games, Inc. All Rights Reserved.

#include "Zenaphore.h"
#include "HAL/Event.h"
#include "HAL/PlatformProcess.h"
#include "Misc/ScopeLock.h"

FZenaphore::FZenaphore()
{
    Event = FPlatformProcess::GetSynchEventFromPool(true);
}

FZenaphore::~FZenaphore()
{
    FPlatformProcess::ReturnSynchEventToPool(Event);
}

void FZenaphore::NotifyInternal(FZenaphoreWaiterNode* Waiter)
{
    TRACE_CPUPROFILER_EVENT_SCOPE(ZenaphoreTrigger);
    check(Waiter);
    FScopeLock Lock(&Mutex);
    Waiter->bTriggered = true;
    Event->Trigger();
}

void FZenaphore::NotifyOne()
{
    for (;;)
    {
        FZenaphoreWaiterNode* Waiter = HeadWaiter.Load();
        if (!Waiter)
        {
            return;
        }
        if (HeadWaiter.CompareExchange(Waiter, Waiter->Next))
        {
            NotifyInternal(Waiter);
            return;
        }
    }
}

void FZenaphore::NotifyAll()
{
    for (;;)
    {
        FZenaphoreWaiterNode* Waiter = HeadWaiter.Load();
        if (!Waiter)
        {
            return;
        }
        if (HeadWaiter.CompareExchange(Waiter, Waiter->Next))
        {
            NotifyInternal(Waiter);
        }
    }
}

FZenaphoreWaiter::~FZenaphoreWaiter()
{
    if (SpinCount)
    {
        WaitInternal();
    }
}

void FZenaphoreWaiter::WaitInternal()
{
    for (;;)
    {
        Outer.Event->Wait(INT32_MAX, true);
        FScopeLock Lock(&Outer.Mutex);
        if (WaiterNode.bTriggered)
        {
            Outer.Event->Reset();
            return;
        }
    }
}

void FZenaphoreWaiter::Wait()
{
    if (SpinCount == 0)
    {
        FZenaphoreWaiterNode* OldHeadWaiter = nullptr;
        WaiterNode.bTriggered               = false;
        WaiterNode.Next                     = nullptr;
        while (!Outer.HeadWaiter.CompareExchange(OldHeadWaiter, &WaiterNode))
        {
            WaiterNode.Next = OldHeadWaiter;
        }
        ++SpinCount;
    }
    else
    {
        WaitInternal();
        SpinCount = 0;
    }
}