AuroraRuntime/Source/Async/ThreadPool.cpp

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

    File: ThreadPool.cpp
    Date: 2021-10-30
    Author: Reece
***/
#include <Source/RuntimeInternal.hpp>
#include "Async.hpp"
#include "ThreadPool.hpp"
#include "AsyncApp.hpp"
#include "WorkItem.hpp"
#include "Schedular.hpp"
#include "ThreadWorkerQueueShim.hpp"

namespace Aurora::Async
{
    //STATIC_TLS(WorkerId_t, tlsWorkerId);
    static thread_local AuWPtr<ThreadPool> gCurrentPool;
    static const auto kMagicResortThreshold = 15;

    static thread_local int tlsCallStack;
    inline auto GetWorkerInternal(const AuSPtr<IThreadPool> &pool)
    {
        if (pool.get() == AuStaticCast<IAsyncApp>(gAsyncApp))
        {
            return AuUnsafeRaiiToShared(AuStaticCast<ThreadPool>(gAsyncApp));
        }

        return AuStaticPointerCast<ThreadPool>(pool);
    }

    AUKN_SYM WorkerPId_t GetCurrentWorkerPId()
    {
        auto lkPool = gCurrentPool.lock();
        if (!lkPool) return {};
        auto cpy = *lkPool->tlsWorkerId;
        auto lkPool2 = cpy.pool.lock();
        return WorkerPId_t(lkPool, cpy);
    }
    
    //

    ThreadPool::ThreadPool()
    {
        this->rwlock_ = AuThreadPrimitives::RWLockUnique();
        SysAssert(static_cast<bool>(this->rwlock_), "Couldn't initialize ThreadPool. Unable to allocate an RWLock");
    }

    // internal pool interface

    bool ThreadPool::WaitFor(WorkerId_t unlocker, const AuSPtr<Threading::IWaitable> &primitive, AuUInt32 timeoutMs)
    {
        auto curThread = GetThreadState();

        if (!curThread)
        {
            return Threading::WaitFor(primitive.get(), timeoutMs);
        }

        bool workerIdMatches     =  (unlocker.second == curThread->id.second) || ((unlocker.second == Async::kThreadIdAny) && (GetThreadWorkersCount(unlocker.first) == 1));

        if ((unlocker.first == curThread->id.first) &&  // work group matches
            (workerIdMatches)) // well, crap
        {

            bool queryAsync = false;
            while (!(queryAsync ? primitive->TryLock() : Threading::WaitFor(primitive.get(), 2)))
            {
                queryAsync = CtxYield();
            }

            return true;
        }
        else
        {
            return Threading::WaitFor(primitive.get(), timeoutMs);
        }
    }

    void ThreadPool::Run(WorkerId_t target, AuSPtr<IAsyncRunnable> runnable)
    {
        auto state = GetGroup(target.first);
        SysAssert(static_cast<bool>(state), "couldn't dispatch a task to an offline group");

        IncrementTasksRunning();

        {
            AU_LOCK_GUARD(state->cvWorkMutex);

        #if defined(STAGING) || defined(DEBUG)
            AU_LOCK_GUARD(rwlock_->AsReadable());

            if (target.second != Async::kThreadIdAny)
            {
                auto itr = state->workers.find(target.second);
                if ((itr == state->workers.end()) || (itr->second->rejecting))
                {
                    SysPushErrorGen("worker: {}:{} is offline", target.first, target.second);
                    DecrementTasksRunning();
                #if 0
                    throw "Requested job worker is offline";
                #else
                    runnable->CancelAsync();
                    return;
                #endif
                }
            }
            else
            {
                auto workers = state->workers;
                bool found = false;

                for (const auto &worker : state->workers)
                {
                    if (!worker.second->rejecting)
                    {
                        found = true;
                        break;
                    }
                }

                if (!found)
                {
                    DecrementTasksRunning();
                #if 0
                    throw "No workers available";
                #else
                    runnable->CancelAsync();
                    return;
                #endif
                }
            }
        #endif

            if (!AuTryInsert(state->workQueue, AuMakePair(target.second, runnable)))
            {
                DecrementTasksRunning();
                runnable->CancelAsync();
                return;
            }

            state->dirty++;
            if (state->dirty > kMagicResortThreshold)
            {
                state->dirty = 0;
                state->sorted = false;
            }
            state->eventLs->Set();
        }
        if (target.second == Async::kThreadIdAny)
        {
            state->cvVariable->Signal();
        }
        else
        {
            // sad :(
            // TODO: when we have wait any, add support (^ the trigger) for it here
            state->cvVariable->Broadcast();
        }
    }

    IThreadPool *ThreadPool::ToThreadPool()
    {
        return this;
    }
    
    void ThreadPool::IncrementTasksRunning()
    {
        this->tasksRunning_++;
    }
    
    void ThreadPool::DecrementTasksRunning()
    {
        if ((--this->tasksRunning_) == 0)
        {
            if (InRunnerMode())
            {
                Shutdown();
            }
        }
    }

    // ithreadpool

    size_t ThreadPool::GetThreadWorkersCount(ThreadGroup_t group)
    {
        AU_LOCK_GUARD(this->rwlock_->AsReadable());
        return GetGroup(group)->workers.size();
    }

    void ThreadPool::SetRunningMode(bool eventRunning)
    {
        this->runnersRunning_ = eventRunning;
    }
    
    bool ThreadPool::Spawn(WorkerId_t workerId)
    {
        return Spawn(workerId, false);
    }
    
    bool ThreadPool::Create(WorkerId_t workerId)
    {
        return Spawn(workerId, true);
    }
    
    bool ThreadPool::InRunnerMode()
    {
        return this->runnersRunning_;
    }
    
    bool ThreadPool::Poll()
    {
        return InternalRunOne(false);
    }
    
    bool ThreadPool::RunOnce()
    {
        return InternalRunOne(true);
    }
    
    bool ThreadPool::Run()
    {
        bool ranOnce {};
       
        auto auThread = AuThreads::GetThread();
        auto job      = GetThreadState();

        if (!job)
        {
            SysPushErrorUninitialized("Not an async thread");
        }

        while ((!auThread->Exiting()) && (!job->shuttingdown))
        {
            // Do work (blocking)
            InternalRunOne(true);
            ranOnce = true;
        }

        return ranOnce;
    }
    
    bool ThreadPool::InternalRunOne(bool block)
    {
        auto state = GetThreadState();
        if (!state)
        {
            SysPushErrorUninitialized("Not an async thread");
        }

        bool success {};
        auto runMode = GetCurrentThreadRunMode();

        //do
        {
            auto asyncLoop = state->asyncLoop;

            asyncLoop->OnFrame();

            if (asyncLoop->GetSourceCount() > 1)
            {
                bool bShouldTrySleepForKernel {};

                if (runMode == ERunMode::eLowLatencyFreqKernel)
                {
                    if (state->rateLimiter.CheckExchangePass())
                    {
                    #if defined(AURORA_PLATFORM_WIN32)
                        bShouldTrySleepForKernel = asyncLoop->PumpNonblocking();
                    #else
                        bShouldTrySleepForKernel = asyncLoop->IsSignaledPeek();
                    #endif
                    }
                    else
                    {
                        if (!PollInternal(false))
                        {
                            AuThreading::ContextYield();
                        }
                        else
                        {
                            success = true;
                        }
                    }
                }
                else if (runMode == ERunMode::eLowLatencyYield)
                {
                    AuThreading::ContextYield();
                    block = false;
                    #if defined(AURORA_PLATFORM_WIN32)
                        bShouldTrySleepForKernel = asyncLoop->PumpNonblocking();
                    #else
                        bShouldTrySleepForKernel = asyncLoop->IsSignaledPeek();
                    #endif
                }
                else if (runMode == ERunMode::eEfficient)
                {
                    bShouldTrySleepForKernel = block;
                    if (!block)
                    {
                        bShouldTrySleepForKernel = asyncLoop->IsSignaledPeek();
                    }
                }

                if (bShouldTrySleepForKernel
                    // epoll and such like can be checked without read success. kevent works on availablity, not scheduling read like iosubmit
                    // allow windows to atomically pump instead of wasting time buffering the primitives state
                    && ((AuBuild::kIsNtDerived && runMode == ERunMode::eEfficient) ||
                        (!AuBuild::kIsNtDerived))

                    && (asyncLoop->WaitAny(0))
                    )
                {
                    PollInternal(false);
                    success = true;
                }
                else
                {
                    success |= PollInternal(block);
                }
            }
            else
            {
                success = PollInternal(block);
            }
        } //while (success);

        return success;
    }

    bool ThreadPool::PollInternal(bool block)
    {
        auto state = GetThreadState();
        if (!state)
        {
            SysPushErrorUninitialized("Not an async thread");
        }

        auto group = state->parent.lock();

        //state->pendingWorkItems.clear();

        auto magic = CtxPollPush();

        {
            AU_LOCK_GUARD(group->cvWorkMutex);

            // TODO: reimplement this 
            // this is stupid and gross
            if (group->workQueue.size() > group->workers.size()*3)
            {
                if (!group->sorted)
                {
                    auto cpy = group->workQueue;

                    std::sort(group->workQueue.begin(), group->workQueue.end(), [&](const WorkEntry_t &a, const WorkEntry_t &b)
                    {
                        if (a.second->GetPrio() != b.second->GetPrio())
                            return a.second->GetPrio() > b.second->GetPrio();

                        AuUInt32 ia {}, ib {};
                        for (; ia < cpy.size(); ia++)
                            if (cpy[ia].second == a.second)
                                break;

                        for (; ib < cpy.size(); ib++)
                            if (cpy[ib].second == b.second)
                                break;

                        return ia < ib;
                    });

                    group->sorted = true;
                    group->dirty = 0;
                }
            }
        
            do
            {
                // Deque tasks the current thread runner could dipatch
                // Noting that `multipopCount` determines how aggressive threads are in dequeuing work
                // It's probable `multipopCount` will equal 1 for your use case
                //
                // Only increment when you know tasks within a group queue will not depend on one another
                //  *and* tasks require a small amount of execution time 
                //
                // This could be potentially useful for an event dispatcher whereby you're dispatching 
                //  hundreds of items per second, across a thread or two, knowing dequeuing one instead of all
                //  is a waste of CPU cycles. 
                //
                // Remember, incrementing `multipopCount` is potentially dangerous the second you have local
                //  thread group waits 
                for (auto itr = group->workQueue.begin(); 
                     ((itr != group->workQueue.end()) && 
                      (state->pendingWorkItems.size() < state->multipopCount));
                     )
                {
                    // TODO: catch low memory condition
                    if (itr->first == Async::kThreadIdAny)
                    {
                        state->pendingWorkItems.push_back(*itr);
                        itr = group->workQueue.erase(itr);
                        continue;
                    }

                    if ((itr->first != Async::kThreadIdAny) && (itr->first == state->id.second))
                    {
                        state->pendingWorkItems.push_back(*itr);
                        itr = group->workQueue.erase(itr);
                        continue;
                    }

                    itr++;
                }

                // Consider blocking for more work
                if (!block)
                {
                    break;
                }

                // pre-wakeup thread terminating check
                if (state->threadObject->Exiting() || state->shuttingdown)
                {
                    break;
                }

                // Block if no work items are present
                if (state->pendingWorkItems.empty())
                {
                    group->cvVariable->WaitForSignal();
                }

                // Post-wakeup thread terminating check
                if (state->threadObject->Exiting() || state->shuttingdown)
                {
                    break;
                }

                if (state->pendingWorkItems.empty() && (
                    (this->GetThreadState()->asyncLoop->GetSourceCount() > 1) ||
                    this->GetThreadState()->asyncLoop->CommitPending()))                    //(this->ToKernelWorkQueue()->IsSignaledPeek()))
                {
                    return false;
                }

            } while (state->pendingWorkItems.empty());

            if (group->workQueue.empty())
            {
                group->eventLs->Reset();
            }
        }

        if (state->pendingWorkItems.empty())
        {
            CtxPollReturn(state, magic, false);
            return false;
        }

        int runningTasks {};

        auto oldTlsHandle = AuExchange(gCurrentPool, AuSharedFromThis());

        bool lowPrioCont {};
        bool lowPrioContCached {};

        state->cookie++;

        int start = state->cookie;

        // Account for 
        //            while (AuAsync.GetCurrentPool()->runForever());
        // in the first task (or deeper)
        if (InRunnerMode() && tlsCallStack) // are we one call deep?
        {
            auto queue = ToKernelWorkQueue();

            if ((this->tasksRunning_ == tlsCallStack) &&
                (!queue || queue->GetSourceCount() <= 1))
            {
                return false;
            }
        }

        //

        for (auto itr = state->pendingWorkItems.begin(); itr != state->pendingWorkItems.end(); )
        {
            if (state->threadObject->Exiting() || state->shuttingdown)
            {
                break;
            }

            // Set the last frame time for a watchdog later down the line 
            state->lastFrameTime = Time::CurrentClockMS();
            
            if (itr->second->GetPrio() < 0.25)
            {
                group->sorted = false;

                if (lowPrioCont)
                {
                    itr++;
                    continue;
                }
                
                if (!lowPrioContCached)
                {
                    AU_LOCK_GUARD(group->cvWorkMutex);
                    {
                        for (const auto &[pendingWorkA, pendingWorkB] : group->workQueue)
                        {
                            if (pendingWorkB->GetPrio() > .5)
                            {
                                lowPrioCont = true;
                                break;
                            }
                        }
                    }
                 
                    lowPrioContCached = true;
                    if (lowPrioCont)
                    {
                        itr++;
                        continue;
                    }
                }
            }

            // Dispatch
            auto oops = itr->second;

            // Remove from our local job queue
            itr = state->pendingWorkItems.erase(itr);

            tlsCallStack++;

            // Dispatch
            oops->RunAsync();

            // Atomically decrement global task counter
            runningTasks = this->tasksRunning_.fetch_sub(1) - 1;

            tlsCallStack--;

            if (start != state->cookie)
            {
                start = state->cookie;
                itr = state->pendingWorkItems.begin();
            }
        }

        gCurrentPool = oldTlsHandle;
        
        // Return popped work back to the groups work pool when our -pump loops were preempted 
        if (state->pendingWorkItems.size())
        {
            AU_LOCK_GUARD(group->cvWorkMutex);
            // TODO: low memory condition slow path
            group->workQueue.insert(group->workQueue.end(), state->pendingWorkItems.begin(), state->pendingWorkItems.end());
            group->eventLs->Set();
            state->pendingWorkItems.clear();
        }

        CtxPollReturn(state, magic, true);


        // Account for 
        //            while (AuAsync.GetCurrentPool()->runForever());
        // in the top most task
        if (InRunnerMode())
        {
            auto queue = ToKernelWorkQueue();

            if ((runningTasks == 0) &&
                (this->tasksRunning_ == 0 ) &&
                (!queue || queue->GetSourceCount() <= 1))
            {
                Shutdown();
            }
        }
        
        return true;
    }

    void ThreadPool::Shutdown()
    {
        // Nested shutdowns can happen; prevent a write lock
        {
            AU_LOCK_GUARD(this->rwlock_->AsReadable());
            if (this->shuttingdown_)
            {
                return;
            }
        }

        // Set shutdown flag
        {
            AU_LOCK_GUARD(this->rwlock_->AsWritable());
            if (AuExchange(this->shuttingdown_, true))
            {
                return;
            }
        }
        
        // Noting 
        // 1) that StopSched may lockup under a writable lock
        //   -> we will terminate a thread that may be dispatching a sys pump event
        // 2) that barrier doesn't need to be under a write lock
        // 
        // Perform the following shutdown of the schedular and other available threads under a read lock
        {
            AU_LOCK_GUARD(this->rwlock_->AsReadable());
            
            StopSched();

            for (auto &[groupId, group] : this->threads_)
            {
                for (auto &[id, worker] : group->workers)
                {
                    Barrier(worker->id, 0, false, true);
                }
            }
        }

        // Finally set the shutdown flag on all of our thread contexts
        // then release them from the runners/workers list
        // then release all group contexts
        AuList<AuThreads::ThreadShared_t> threads;
        {
            AU_LOCK_GUARD(this->rwlock_->AsWritable());

            for (auto &[groupId, group] : this->threads_)
            {
                for (auto &[id, worker] : group->workers)
                {
                    if (group->cvWorkMutex && group->cvVariable)
                    {
                        AU_LOCK_GUARD(group->cvWorkMutex);
                        worker->shuttingdown = true;
                        group->cvVariable->Broadcast();
                    }
                    else
                    {
                        worker->shuttingdown = true;
                    }

                    if (!group->IsSysThread())
                    {
                        worker->threadObject->SendExitSignal();
                        threads.push_back(worker->threadObject);
                    }

                    auto &event = worker->running;
                    if (event)
                    {
                        event->Set();
                    }
                }
            }
        }

        // Sync to shutdown threads to prevent a race condition whereby the async subsystem shuts down before the threads
        for (const auto &thread : threads)
        {
            thread->Exit();
        }
    }
    
    bool ThreadPool::Exiting()
    {
        return this->shuttingdown_ || GetThreadState()->exiting;
    }
    
    AuSPtr<IWorkItem> ThreadPool::NewWorkItem(const WorkerId_t &worker, const AuSPtr<IWorkItemHandler> &task, bool supportsBlocking)
    {
        if (!task)
        {
            return {};
        }
        return AuMakeShared<WorkItem>(this, worker, task, supportsBlocking);
    }
    
    AuSPtr<IWorkItem> ThreadPool::NewFence()
    {
        return AuMakeShared<WorkItem>(this, WorkerId_t{}, AuSPtr<IWorkItemHandler>{}, true);
    }

    AuThreads::ThreadShared_t ThreadPool::ResolveHandle(WorkerId_t id)
    {
        return GetThreadHandle(id)->threadObject;
    }
    
    AuBST<ThreadGroup_t, AuList<ThreadId_t>> ThreadPool::GetThreads()
    {
        AU_LOCK_GUARD(rwlock_->AsReadable());

        AuBST<ThreadGroup_t, AuList<ThreadId_t>> ret;

        for (const auto &group : this->threads_)
        {
            AuList<ThreadId_t> workers;
            
            for (const auto &thread : group.second->workers)
            {
                workers.push_back(thread.second->id.second);
            }

            ret[group.first] = workers;
        }

        return ret;
    }
    
    WorkerId_t ThreadPool::GetCurrentThread()
    {
        return tlsWorkerId;
    }
    
    bool ThreadPool::Sync(WorkerId_t workerId, AuUInt32 timeoutMs, bool requireSignal)
    {
        AU_LOCK_GUARD(this->rwlock_->AsReadable());
        
        auto group = GetGroup(workerId.first);
        auto currentWorkerId = GetCurrentThread().second;

        if (workerId.second == Async::kThreadIdAny)
        {
            for (auto &jobWorker : group->workers)
            {
                if (!Barrier(jobWorker.second->id, timeoutMs, requireSignal && jobWorker.second->id.second != currentWorkerId, false)) // BAD!, should subtract time elapsed, clamp to, i dunno, 5ms min?
                {
                    return false;
                }
            }
        }
        else
        {
            return Barrier(workerId, timeoutMs, requireSignal && workerId.second != currentWorkerId, false);
        }

        return true;
    }
    
    void ThreadPool::Signal(WorkerId_t workerId)
    {
        AU_LOCK_GUARD(this->rwlock_->AsReadable());

        auto group = GetGroup(workerId.first);
        if (workerId.second == Async::kThreadIdAny)
        {
            for (auto &jobWorker : group->workers)
            {
                jobWorker.second->running->Set();
            }
        }
        else
        {
            GetThreadHandle(workerId)->running->Set();
        }
    }

    AuSPtr<AuLoop::ILoopSource> ThreadPool::WorkerToLoopSource(WorkerId_t workerId)
    {
        AU_LOCK_GUARD(this->rwlock_->AsReadable());

        auto a = GetThreadHandle(workerId);
        if (!a)
        {
            return {};
        }

        return a->parent.lock()->asyncLoopSourceShared;
    }
    
    void ThreadPool::SyncAllSafe()
    {
        AU_LOCK_GUARD(this->rwlock_->AsReadable());

        for (const auto &re : this->threads_)
        {
            for (auto &jobWorker : re.second->workers)
            {
                SysAssert(Barrier(jobWorker.second->id, 0, false, false));
            }
        }
    }
    
    void ThreadPool::AddFeature(WorkerId_t id, AuSPtr<AuThreads::IThreadFeature> feature, bool async)
    {
        auto work = AuMakeShared<BasicWorkStdFunc>(([=]()
        {
            GetThreadState()->features.push_back(feature);
            feature->Init();
        }));
        

        auto workItem = this->NewWorkItem(id, work, !async)->Dispatch();
        SysAssert(workItem);

        if (!async)
        {
            workItem->BlockUntilComplete();
        }
    }
    
    void ThreadPool::AssertInThreadGroup(ThreadGroup_t group)
    {
        SysAssert(static_cast<WorkerId_t>(tlsWorkerId).first == group);
    }

    void ThreadPool::AssertWorker(WorkerId_t id)
    {
        SysAssert(static_cast<WorkerId_t>(tlsWorkerId) == id);
    }
    
    AuSPtr<AuLoop::ILoopQueue> ThreadPool::ToKernelWorkQueue()
    {
        return this->GetThreadState()->asyncLoop;
    }

    AuSPtr<AuLoop::ILoopQueue> ThreadPool::ToKernelWorkQueue(WorkerId_t workerId)
    {
        auto worker = this->GetThreadHandle(workerId);
        if (!worker)
        {
            SysPushErrorGen("Couldn't find requested worker");
            return {};
        }
        return worker->asyncLoop;
    }

    void ThreadPool::UpdateWorkMode(WorkerId_t workerId, RunMode mode)
    {
        auto states = this->GetThreadHandles(workerId);
        if (!states.size())
        {
            SysPushErrorGen("Couldn't find requested worker");
            return;
        }

        for (const auto &state : states)
        {
            state->runMode = mode.mode;
            if (mode.freqMsTick)
            {
                state->rateLimiter.SetNextStep(mode.freqMsTick * 1'000'000);
            }
        }
    }

    ERunMode ThreadPool::GetCurrentThreadRunMode()
    {
        auto state = this->GetThreadState();
        if (!state)
        {
            return ERunMode::eEfficient;
        }
        return state->runMode;
    }

    ERunMode ThreadPool::GetThreadRunMode(WorkerId_t workerId)
    {
        auto worker = this->GetThreadHandle(workerId);
        if (!worker)
        {
            SysPushErrorGen("Couldn't find requested worker");
            return {};
        }
        return worker->runMode;
    }

    // Unimplemented fiber hooks, 'twas used for science
    
    int ThreadPool::CtxPollPush()
    {
        // TOOD (Reece): implement a context switching library  
        // Refer to the old implementation of this on pastebin
        return 0;
    }

    void ThreadPool::CtxPollReturn(const AuSPtr<ThreadState> &state, int status, bool hitTask)
    {
    }

    bool ThreadPool::CtxYield()
    {
        bool ranAtLeastOne = false;

        while (this->InternalRunOne(false))
        {
            ranAtLeastOne = true;
        }

        return ranAtLeastOne;
    }


    // internal api
    
    bool ThreadPool::Spawn(WorkerId_t workerId, bool create)
    {
        AU_LOCK_GUARD(rwlock_->AsWritable());

        if (GetCurrentWorkerPId().pool && create)
        {
            SysPushErrorGeneric("TODO (reece): add support for multiple runners per thread");
            return {};
        }

        AuSPtr<GroupState> group;

        // Try fetch or allocate group
        {
            AuSPtr<GroupState>* groupPtr;
            if (!AuTryFind(this->threads_, workerId.first, groupPtr))
            {
                group = AuMakeShared<GroupState>();
                
                if (!group->Init())
                {
                    SysPushErrorMem("Not enough memory to intiialize a new group state");
                    return false;
                }

                if (!AuTryInsert(this->threads_, AuMakePair(workerId.first, group)))
                {
                    return false;
                }
            }
            else
            {
                group = *groupPtr;
            }
        }

        // Assert worker does not already exist
        {
            AuSPtr<ThreadState>* ret;

            if (AuTryFind(group->workers, workerId.second, ret))
            {
                SysPushErrorGen("Thread ID already exists");
                return false;
            }
        }

        auto threadState = AuMakeShared<ThreadState>();
        if (!threadState)
        {
            SysPushErrorMem();
            return {};
        }

        threadState->parent = group;
        threadState->running = AuThreadPrimitives::EventUnique(true, false, true);
        threadState->syncSema = AuThreadPrimitives::SemaphoreUnique(0);
        threadState->id = workerId;
        threadState->asyncLoop = AuMakeShared<AsyncLoop>();
        threadState->asyncLoop->pParent = threadState.get();
        threadState->rateLimiter.SetNextStep(1'000'000); // 1MS in nanoseconds
        threadState->runMode = ERunMode::eEfficient;

        if (!threadState->asyncLoop)
        {
            SysPushErrorMem();
            return {};
        }

        if (!threadState->syncSema)
        {
            SysPushErrorMem();
            return {};
        }

        if (!threadState->syncSema)
        {
            SysPushErrorMem();
            return {};
        }

        threadState->asyncLoop->SourceAdd(group->eventLs);

        if (!create)
        {
            threadState->threadObject = AuThreads::ThreadShared(AuThreads::ThreadInfo(
                AuMakeShared<AuThreads::IThreadVectorsFunctional>(AuThreads::IThreadVectorsFunctional::OnEntry_t(std::bind(&ThreadPool::Entrypoint, this, threadState->id)),
                                                                  AuThreads::IThreadVectorsFunctional::OnExit_t{}),
                gRuntimeConfig.async.threadPoolDefaultStackSize
            ));
            if (!threadState->threadObject)
            {
                return {};
            }
            threadState->threadObject->Run();
        }
        else
        {
            threadState->threadObject = AuSPtr<AuThreads::IAuroraThread>(AuThreads::GetThread(), [](AuThreads::IAuroraThread *){});
            
            // TODO: this is just a hack
            // we should implement this properly
            threadState->threadObject->AddLastHopeTlsHook(AuMakeShared<AuThreads::IThreadFeatureFunctional>([]() -> void
            {

            }, []() -> void
            {
                auto pid = GetCurrentWorkerPId();
                if (pid.pool)
                {
                    GetWorkerInternal(pid.pool)->ThisExiting();
                }
            }));

            //
            gCurrentPool = AuWeakFromThis();
            tlsWorkerId = WorkerPId_t(AuSharedFromThis(), workerId);
        }
        
        group->workers.insert(AuMakePair(workerId.second, threadState));
        return true;
    }

    // private api

    bool ThreadPool::Barrier(WorkerId_t workerId, AuUInt32 ms, bool requireSignal, bool drop)
    {
        auto self = GetThreadState();
        if (!self)
        {
            return {};
        }

        auto &semaphore = self->syncSema;
        auto unsafeSemaphore = semaphore.get();
        bool failed {};

        auto work = AuMakeShared<AsyncFuncRunnable>(
            [=]()
            {
                auto state = GetThreadState();

                if (drop)
                {
                    state->rejecting = true;
                }

                if (requireSignal)
                {
                    state->running->Reset();
                }

                unsafeSemaphore->Unlock(1);

                if (requireSignal)
                {
                    state->running->Lock();
                }
            },
            [&]()
            {
                unsafeSemaphore->Unlock(1);
                failed = true;
            }
        );

        if (!work)
        {
            return false;
        }

        Run(workerId, work);

        return WaitFor(workerId, AuUnsafeRaiiToShared(semaphore), ms) && !failed;
    }

    void ThreadPool::Entrypoint(WorkerId_t id)
    {
        gCurrentPool  = AuWeakFromThis();
        tlsWorkerId   = WorkerPId_t(AuSharedFromThis(), id);

        auto job      = GetThreadState();

        Run();

        if (id != WorkerId_t {0, 0})
        {
            AU_LOCK_GUARD(this->rwlock_->AsReadable());

            if (!this->shuttingdown_ && !job->rejecting)
            {
                // Pump and barrier + reject all after atomically
                Barrier(id, 0, false, true);
            }
        }

        ThisExiting();
        
        if (id == WorkerId_t {0, 0})
        {
            CleanWorkerPoolReservedZeroFree();
        }
    }
    
    void ThreadPool::ThisExiting()
    {
        auto id    = GetCurrentThread();
        auto state = GetGroup(id.first);

        {
            AU_LOCK_GUARD(this->rwlock_->AsWritable());

            auto itr = state->workers.find(id.second);
            auto &jobWorker = itr->second;

            CleanUpWorker(id);

            // Abort scheduled tasks
            TerminateSceduledTasks(this, id);

            // Clean up thread features 
            //  -> transferable TLS handles
            //  -> thread specific vms
            //  -> anything your brain wishes to imagination
            for (const auto &thread : jobWorker->features)
            {
                try
                {
                    thread->Cleanup();
                }
                catch (...)
                {
                    AuLogWarn("Couldn't clean up thread feature!");
                    Debug::PrintError();
                }
            }

            jobWorker->features.clear();
            
            state->workers.erase(itr);
        }
    }

    AuSPtr<GroupState>  ThreadPool::GetGroup(ThreadGroup_t type)
    {
        AU_LOCK_GUARD(this->rwlock_->AsReadable());
        AuSPtr<GroupState>* ret;
        if (!AuTryFind(this->threads_, type, ret))
        {
            return {};
        }
        return *ret;
    }

    AuSPtr<ThreadState> ThreadPool::GetThreadState()
    {
        AU_LOCK_GUARD(this->rwlock_->AsReadable());
        
        auto thread = gCurrentPool.lock();
        if (!thread)
        {
            return {};
        }

    #if defined(AU_CFG_ID_INTERNAL) || defined(AU_CFG_ID_DEBUG)
        if (thread.get() != this)
        {
            SysPushErrorGeneric("wrong thread");
            return {};
        }
    #endif 

        auto worker = *tlsWorkerId;
        
        auto state = GetGroup(worker.first);
        if (!state)
        {
            return {};
        }

        return state->workers[worker.second];
    }

    AuSPtr<ThreadState> ThreadPool::GetThreadHandle(WorkerId_t id)
    {
        AU_LOCK_GUARD(this->rwlock_->AsReadable());

        auto group = GetGroup(id.first);
        if (!group)
        {
            return {};
        }
        
        AuSPtr<ThreadState> *ret;
        if (!AuTryFind(group->workers, id.second, ret))
        {
            return {};
        }

        return *ret;
    }

    AuList<AuSPtr<ThreadState>> ThreadPool::GetThreadHandles(WorkerId_t id)
    {
        AU_LOCK_GUARD(this->rwlock_->AsReadable());

        auto group = GetGroup(id.first);
        if (!group)
        {
            return {};
        }
       
        AuList<AuSPtr<ThreadState>> ret;
        if (id.second != Async::kThreadIdAny)
        {
            AuSPtr<ThreadState> *ptr;
            if (!AuTryFind(group->workers, id.second, ptr))
            {
                return {};
            }
            ret.push_back(*ptr);
        }
        else
        {
            for (const auto &[key, value] : group->workers)
            {
                ret.push_back(value);
            }
        }
    

        return ret;
    }

    AUKN_SYM AuSPtr<IThreadPool> NewThreadPool()
    {
        // apps that don't require async shouldn't be burdened with the overhead of this litl spiner
        StartSched();
        return AuMakeShared<ThreadPool>();
    }
}