RealtimeEffectState.cpp

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/**********************************************************************
 
  Audacity: A Digital Audio Editor
 
  @file RealtimeEffectState.cpp
 
  Paul Licameli split from RealtimeEffectManager.cpp
 
 *********************************************************************/
 
#include "RealtimeEffectState.h"
 
#include "AudioIOBase.h"
#include "EffectInterface.h"
#include "MessageBuffer.h"
#include "PluginManager.h"
#include "SampleCount.h"
 
#include <chrono>
#include <thread>
#include <condition_variable>
 
class RealtimeEffectState::AccessState : public NonInterferingBase {
public:
   AccessState(const EffectSettingsManager &effect, RealtimeEffectState &state)
      : mEffect{ effect }
      , mState{ state }
   {
      // Clean initial state of the counter
      state.mMainSettings.counter = 0;
      Initialize(state.mMainSettings.settings,
         state.mMessage.get(), state.mMovedOutputs.get());
   }
 
   void Initialize(const EffectSettings &settings,
      const EffectInstance::Message *pMessage,
      const EffectOutputs *pOutputs)
   {
      mLastSettings = { settings, 0 };
      // Initialize each message buffer with two copies
      mChannelToMain.Write(ToMainSlot{ { 0,
         pOutputs ? pOutputs->Clone() : nullptr } });
      mChannelToMain.Write(ToMainSlot{ { 0,
         pOutputs ? pOutputs->Clone() : nullptr } });
      mChannelFromMain.Write(FromMainSlot{ settings, pMessage });
      mChannelFromMain.Write(FromMainSlot{ settings, pMessage });
 
      mMainThreadId = std::this_thread::get_id();
   }
 
   void MainRead() {
      mChannelToMain.Read<ToMainSlot::Reader>(mState.mMovedOutputs.get(),
         mCounter);
   }
   void MainWrite(SettingsAndCounter &&settings,
      std::unique_ptr<EffectInstance::Message> pMessage) {
      // Main thread may simply swap new content into place
      mChannelFromMain.Write(FromMainSlot::Message{
         std::move(settings.settings), settings.counter, std::move(pMessage) });
   }
   void MainWrite(SettingsAndCounter::Counter counter,
      std::unique_ptr<EffectInstance::Message> pMessage) {
      mChannelFromMain.Write(FromMainSlot::ShortMessage{
         counter, std::move(pMessage) });
   }
 
   struct CounterAndOutputs{
      Response::Counter counter;
      EffectOutputs *pOutputs{};
   };
   void WorkerRead() {
      // Worker thread avoids memory allocation.  It copies the contents of any
      mChannelFromMain.Read<FromMainSlot::Reader>(mEffect, mState);
   }
   void WorkerWrite() {
 
      {
         std::unique_lock lk(mLockForCV);
 
         // Worker thread avoids memory allocation.
         mChannelToMain.Write(CounterAndOutputs{
            mState.mWorkerSettings.counter, mState.mOutputs.get() });
      }
      mCV.notify_one();
   }
 
   struct ToMainSlot {
      // For initialization of the channel
      ToMainSlot() = default;
      explicit ToMainSlot(Response response)
         : mResponse{ std::move(response) }
      {}
      ToMainSlot &operator=(ToMainSlot &&) = default;
 
      // Worker thread writes the slot
      ToMainSlot& operator=(CounterAndOutputs &&arg) {
         // This happens during MessageBuffer's busying of the slot
         mResponse.counter = arg.counter;
         if (mResponse.pOutputs && arg.pOutputs)
            mResponse.pOutputs->Assign(std::move(*arg.pOutputs));
         return *this;
      }
 
      struct Reader { Reader(ToMainSlot &&slot, EffectOutputs *pOutputs,
         Response::Counter &counter
      ) {
         // Main thread is not under the performance constraints of the
         // worker, but Assign is still used so that
         // members of underlying vectors or other containers do not
         // relocate
         if (pOutputs && slot.mResponse.pOutputs)
            pOutputs->Assign(std::move(*slot.mResponse.pOutputs));
         counter = slot.mResponse.counter;
      } };
 
      Response mResponse;
   };
 
   struct FromMainSlot {
      struct Message : SettingsAndCounter {
         std::unique_ptr<EffectInstance::Message> pMessage;
      };
      struct ShortMessage {
         SettingsAndCounter::Counter counter;
         std::unique_ptr<EffectInstance::Message> pMessage;
      };
 
      // For initialization of the channel
      FromMainSlot() = default;
      explicit FromMainSlot(const EffectSettings &settings,
         const EffectInstance::Message *pMessage)
         // Copy std::any
         : mMessage{ settings, 0, pMessage ? pMessage->Clone() : nullptr }
      {}
      FromMainSlot &operator=(FromMainSlot &&) = default;
 
      // Main thread writes the slot
      FromMainSlot& operator=(Message &&message) {
         mMessage.SettingsAndCounter::swap(message);
         if (message.pMessage && mMessage.pMessage)
            // Merge the incoming message with any still unconsumed message
            mMessage.pMessage->Merge(std::move(*message.pMessage));
         return *this;
      }
 
      // Main thread writes the slot
      FromMainSlot& operator=(ShortMessage &&message) {
         mMessage.counter = message.counter;
         if (message.pMessage && mMessage.pMessage)
            // Merge the incoming message with any still unconsumed message
            mMessage.pMessage->Merge(std::move(*message.pMessage));
         return *this;
      }
 
      // Worker thread reads the slot
      struct Reader { Reader(FromMainSlot &&slot,
         const EffectSettingsManager &effect, RealtimeEffectState &state) {
         auto &settings = state.mWorkerSettings;
         if(slot.mMessage.counter == settings.counter)
            return;//copy once
         settings.counter = slot.mMessage.counter;
 
         // This happens during MessageBuffer's busying of the slot
         effect.CopySettingsContents(
            slot.mMessage.settings, settings.settings);
         settings.settings.extra = slot.mMessage.settings.extra;
         if (slot.mMessage.pMessage && state.mMovedMessage)
            // Copy the message from the buffer (not a merge)
            state.mMovedMessage->Assign(std::move(*slot.mMessage.pMessage));
      } };
 
      Message mMessage;
   };
 
   const EffectSettingsManager &mEffect;
   RealtimeEffectState &mState;
 
   MessageBuffer<FromMainSlot> mChannelFromMain;
   Response::Counter mCounter;
   SettingsAndCounter mLastSettings;
 
   MessageBuffer<ToMainSlot> mChannelToMain;
 
   std::mutex mLockForCV;
   std::condition_variable mCV;
 
   std::thread::id mMainThreadId;
};
 
struct RealtimeEffectState::Access final : EffectSettingsAccess {
   Access() = default;
   explicit Access(RealtimeEffectState &state)
      : mwState{ state.weak_from_this() }
   {
   }
   ~Access() override = default;
 
 
   const EffectSettings &Get() override {
      if (auto pState = mwState.lock()) {
         if (auto pAccessState = pState->GetAccessState()) {
            if (pAccessState->mState.mInitialized)
            {
               // try once
               assert(pAccessState->mState.mInitialized);
               auto& lastSettings = pAccessState->mLastSettings;
               // Assigns to mCounter
               pAccessState->MainRead();
            }
            else {
               // Not yet waiting on the other thread's progress
               // Not necessarily values yet in the state's Settings objects
            }
            return pAccessState->mLastSettings.settings;
         }
      }
      // Non-modal dialog may have outlived the RealtimeEffectState
      static EffectSettings empty;
      return empty;
   }
   void Set(EffectSettings &&settings, std::unique_ptr<Message> pMessage)
   override {
      if (auto pState = mwState.lock()) {
         if (auto pAccessState = pState->GetAccessState()) {
            if (pMessage && !pAccessState->mState.mInitialized) {
               // Other thread isn't processing.
               // Let the instance consume the message directly.
               if (auto pInstance = pState->mwInstance.lock()) {
                  auto &stateSettings = pState->mMainSettings.settings;
                  stateSettings = std::move(settings);
                  EffectInstance::MessagePackage package{
                     stateSettings, pMessage.get()
                  };
                  pInstance->RealtimeProcessStart(package);
                  pAccessState->mLastSettings.settings = stateSettings;
                  return;
               }
            }
            auto &lastSettings = pAccessState->mLastSettings;
            // move to remember values here
            lastSettings.settings = std::move(settings);
            ++lastSettings.counter;
            // move a copy to there
            pAccessState->MainWrite(
               SettingsAndCounter{ lastSettings }, std::move(pMessage));
         }
      }
   }
   void Set(std::unique_ptr<Message> pMessage)
   override {
      if (auto pState = mwState.lock()) {
         if (auto pAccessState = pState->GetAccessState()) {
            if (pMessage && !pAccessState->mState.mInitialized) {
               // Other thread isn't processing.
               // Let the instance consume the message directly.
               if (auto pInstance = pState->mwInstance.lock()) {
                  auto &stateSettings = pState->mMainSettings.settings;
                  EffectInstance::MessagePackage package{
                     stateSettings, pMessage.get()
                  };
                  pInstance->RealtimeProcessStart(package);
                  // Don't need to update pAccessState->mLastSettings
                  return;
               }
            }
            auto &lastSettings = pAccessState->mLastSettings;
            // Don't update settings, but do count
            ++lastSettings.counter;
            pAccessState->MainWrite(
               lastSettings.counter, std::move(pMessage));
         }
      }
   }
   void Flush() override {
      if (auto pState = mwState.lock()) {
         if (auto pAccessState = pState->GetAccessState()) {
            assert(pAccessState->mMainThreadId == std::this_thread::get_id());
            
            if (pAccessState->mState.mInitialized)
            {
               std::unique_lock lk(pAccessState->mLockForCV);
               pAccessState->mCV.wait(lk,
                  [&] {
                        auto& lastSettings = pAccessState->mLastSettings;
                        pAccessState->MainRead();
                        return pAccessState->mCounter == lastSettings.counter;
                      }
               );
            }
 
            // Update what GetSettings() will return, during play and before
            // Finalize(), but after it is confirmed that any worker thread has
            // seen the values given to the last Set().  These values will also
            // be returned by Get().
            pState->mMainSettings.Set(pAccessState->mLastSettings);
         }
      }
   }
   bool IsSameAs(const EffectSettingsAccess &other) const override {
      if (auto pOther = dynamic_cast<const Access*>(&other)) {
         auto &mine = mwState;
         auto &theirs = pOther->mwState;
         auto less = std::owner_less{};
         return !(less(mine, theirs) || less(theirs, mine));
      }
      return false;
   }
   std::weak_ptr<RealtimeEffectState> mwState;
};
 
RealtimeEffectState::RealtimeEffectState(const PluginID& id)
{
   SetID(id);
   BuildAll();
}
 
RealtimeEffectState::~RealtimeEffectState()
{
 
}
 
void RealtimeEffectState::SetID(const PluginID & id)
{
   bool empty = id.empty();
   if (mID.empty() && !empty) {
      mID = id;
      GetEffect();
   }
   else
      // Set mID to non-empty at most once
      assert(empty);
}
 
const PluginID& RealtimeEffectState::GetID() const noexcept
{
   return mID;
}
 
const EffectInstanceFactory *RealtimeEffectState::GetEffect()
{
   if (!mPlugin) {
      mPlugin = EffectFactory::Call(mID);
      if (mPlugin) {
         // Also make EffectSettings, but preserve activation
         auto wasActive = mMainSettings.settings.extra.GetActive();
         mMainSettings.counter = 0;
         mMainSettings.settings = mPlugin->MakeSettings();
         mMainSettings.settings.extra.SetActive(wasActive);
         mOutputs = mPlugin->MakeOutputs();
         mMovedOutputs = mPlugin->MakeOutputs();
      }
   }
   return mPlugin;
}
 
std::shared_ptr<EffectInstance> RealtimeEffectState::MakeInstance()
{
   mMovedMessage.reset();
   mMessage.reset();
   auto result = mPlugin->MakeInstance();
   if (result) {
      // Allocate presized containers in messages, so later
      // copies of contents might avoid free store operations
      mMessage = result->MakeMessage();
      mMovedMessage = result->MakeMessage();
      if (auto state = GetAccessState())
         state->Initialize(mMainSettings.settings,
            mMessage.get(), mMovedOutputs.get());
   }
   return result;
}
 
std::shared_ptr<EffectInstance>
RealtimeEffectState::EnsureInstance(double sampleRate)
{
   if (!mPlugin)
      return {};
 
   auto pInstance = mwInstance.lock();
   if (!mInitialized) {
      mWorkerSettings = mMainSettings;
      mLastActive = IsActive();
 
      if (!pInstance)
         mwInstance = pInstance = MakeInstance();
      if (!pInstance)
         return {};
 
      // PRL: conserving pre-3.2.0 behavior, but I don't know why this arbitrary
      // number was important
      pInstance->SetBlockSize(512);
 
      if (!pInstance->RealtimeInitialize(mMainSettings.settings, sampleRate))
         return {};
      mInitialized = true;
      return pInstance;
   }
   return pInstance;
}
 
std::shared_ptr<EffectInstance> RealtimeEffectState::GetInstance()
{
   auto pInstance = mwInstance.lock();
   if (!pInstance && mPlugin)
      mwInstance = pInstance = MakeInstance();
   return pInstance;
}
 
std::shared_ptr<EffectInstance>
RealtimeEffectState::Initialize(double sampleRate)
{
   if (!mPlugin)
      return {};
 
   mCurrentProcessor = 0;
   mGroups.clear();
   mLatency = {};
   return EnsureInstance(sampleRate);
}
 
namespace {
// The caller passes the number of channels to process and specifies
// the number of input and output buffers.  There will always be the
// same number of output buffers as there are input buffers.
//
// Effects require a certain number of input and output buffers.
// The number of channels we're currently processing may mismatch
// the effect's requirements.  Allocate some inputs repeatedly to a processor
// that needs more, or allocate multiple processors if they accept too few.
// Continue until the output buffers are all allocated.
template<typename F>
void AllocateChannelsToProcessors(
   unsigned chans, const unsigned numAudioIn, const unsigned numAudioOut,
   const F &f)
{
   unsigned indx = 0;
   for (unsigned ondx = 0; ondx < chans; ondx += numAudioOut) {
      // Pass the function indices into the arrays of buffers
      if (!f(indx, ondx))
         return;
      indx += numAudioIn;
      indx %= chans;
   }
}
}
 
 
std::shared_ptr<EffectInstance>
RealtimeEffectState::AddTrack(Track &track, unsigned chans, float sampleRate)
{
   auto pInstance = EnsureInstance(sampleRate);
   if (!pInstance)
      return {};
   if (!mPlugin)
      return {};
   auto first = mCurrentProcessor;
   const auto numAudioIn = pInstance->GetAudioInCount();
   const auto numAudioOut = pInstance->GetAudioOutCount();
   AllocateChannelsToProcessors(chans, numAudioIn, numAudioOut,
   [&](unsigned, unsigned){
      // Add a NEW processor
      if (pInstance->RealtimeAddProcessor(
         mWorkerSettings.settings, mOutputs.get(), numAudioIn, sampleRate)
      ) {
         mCurrentProcessor++;
         return true;
      }
      else
         return false;
   });
   if (mCurrentProcessor > first) {
      // Remember the sampleRate of the track, so latency can be computed later
      mGroups[&track] = { first, sampleRate };
      return pInstance;
   }
   return {};
}
 
bool RealtimeEffectState::ProcessStart(bool running)
{
   // Get state changes from the main thread
   // Note that it is only here that the answer of IsActive() may be changed,
   // and it is important that for each state the answer is unchanging in one
   // processing scope.
   if (auto pAccessState = TestAccessState())
      pAccessState->WorkerRead();
 
   // Detect transitions of activity state
   auto pInstance = mwInstance.lock();
   bool active = IsActive() && running;
   if (active != mLastActive) {
      if (pInstance) {
         bool success = active
            ? pInstance->RealtimeResume()
            : pInstance->RealtimeSuspend();
         if (!success)
            return false;
      }
      mLastActive = active;
   }
 
   bool result = false;
   if (pInstance) {
      // Consume messages even if not processing
      // (issue #3855: plain UI for VST 2 effects)
 
      // Assuming we are in a processing scope, use the worker settings
      EffectInstance::MessagePackage package{
         mWorkerSettings.settings, mMovedMessage.get()
      };
      result = pInstance->RealtimeProcessStart(package);
   }
 
   if (!pInstance || !active)
      return false;
   else
      return result;
}
 
#define stackAllocate(T, count) static_cast<T*>(alloca(count * sizeof(T)))
 
 
size_t RealtimeEffectState::Process(Track &track, unsigned chans,
   const float *const *inbuf, float *const *outbuf, float *const dummybuf,
   size_t numSamples)
{
   auto pInstance = mwInstance.lock();
   if (!mPlugin || !pInstance || !mLastActive) {
      // Process trivially
      for (size_t ii = 0; ii < chans; ++ii)
         memcpy(outbuf[ii], inbuf[ii], numSamples * sizeof(float));
      return 0;
   }
   const auto numAudioIn = pInstance->GetAudioInCount();
   const auto numAudioOut = pInstance->GetAudioOutCount();
   const auto clientIn = stackAllocate(const float *, numAudioIn);
   const auto clientOut = stackAllocate(float *, numAudioOut);
   size_t len = 0;
   const auto &pair = mGroups[&track];
   auto processor = pair.first;
   // Outer loop over processors
   AllocateChannelsToProcessors(chans, numAudioIn, numAudioOut,
   [&](unsigned indx, unsigned ondx){
      // Point at the correct input buffers
      unsigned copied = std::min(chans - indx, numAudioIn);
      std::copy(inbuf + indx, inbuf + indx + copied, clientIn);
      // If there are too few input channels for what the processor requires,
      // re-use input channels from the beginning
      while (auto need = numAudioIn - copied) {
         auto moreCopied = std::min(chans, need);
         std::copy(inbuf, inbuf + moreCopied, clientIn + copied);
         copied += moreCopied;
      }
 
      // Point at the correct output buffers
      copied = std::min(chans - ondx, numAudioOut);
      std::copy(outbuf + ondx, outbuf + ondx + copied, clientOut);
      if (copied < numAudioOut) {
         // Make determinate pointers
         std::fill(clientOut + copied, clientOut + numAudioOut, dummybuf);
      }
 
      // Inner loop over blocks
      const auto blockSize = pInstance->GetBlockSize();
      for (size_t block = 0; block < numSamples; block += blockSize) {
         auto cnt = std::min(numSamples - block, blockSize);
         // Assuming we are in a processing scope, use the worker settings
         auto processed = pInstance->RealtimeProcess(processor,
            mWorkerSettings.settings, clientIn, clientOut, cnt);
         if (!mLatency)
            // Find latency once only per initialization scope,
            // after processing one block
            mLatency.emplace(
               pInstance->GetLatency(mWorkerSettings.settings, pair.second));
         for (size_t i = 0 ; i < numAudioIn; i++)
            if (clientIn[i])
               clientIn[i] += cnt;
         for (size_t i = 0 ; i < numAudioOut; i++)
            if (clientOut[i])
               clientOut[i] += cnt;
         if (ondx == 0) {
            // For the first processor only
            len += processed;
            auto discard = limitSampleBufferSize(len, *mLatency);
            len -= discard;
            *mLatency -= discard;
         }
      }
      ++processor;
      return true;
   });
   // Report the number discardable during the processing scope
   // We are assuming len as calculated above is the same in case of multiple
   // processors
   return numSamples - len;
}
 
bool RealtimeEffectState::ProcessEnd()
{
   auto pInstance = mwInstance.lock();
   bool result = pInstance && IsActive() && mLastActive &&
      // Assuming we are in a processing scope, use the worker settings
      pInstance->RealtimeProcessEnd(mWorkerSettings.settings);
 
   if (auto pAccessState = TestAccessState())
      // Always done, regardless of activity
      // Some dialogs require communication back from the processor so that
      // they can update their appearance in idle time, and some plug-in
      // libraries (like lv2) require the host program to mediate the
      // communication
      pAccessState->WorkerWrite();
 
   return result;
}
 
bool RealtimeEffectState::IsEnabled() const noexcept
{
   return mMainSettings.settings.extra.GetActive();
}
 
bool RealtimeEffectState::IsActive() const noexcept
{
   return mWorkerSettings.settings.extra.GetActive();
}
 
void RealtimeEffectState::SetActive(bool active)
{
   auto access = GetAccess();
   access->ModifySettings([&](EffectSettings &settings) {
      settings.extra.SetActive(active);
      return nullptr;
   });
   access->Flush();
 
   Publish(active
      ? RealtimeEffectStateChange::EffectOn
      : RealtimeEffectStateChange::EffectOff);
}
 
bool RealtimeEffectState::Finalize() noexcept
{
   // This is the main thread cleaning up a state not now used in processing
   mMainSettings = mWorkerSettings;
 
   mGroups.clear();
   mCurrentProcessor = 0;
 
   auto pInstance = mwInstance.lock();
   if (!pInstance)
      return false;
 
   auto result = pInstance->RealtimeFinalize(mMainSettings.settings);
   mLatency = {};
   mInitialized = false;
   return result;
}
 
const std::string &RealtimeEffectState::XMLTag()
{
   static const std::string result{"effect"};
   return result;
}
 
static const auto idAttribute = "id";
static const auto versionAttribute = "version";
static const auto parametersAttribute = "parameters";
static const auto parameterAttribute = "parameter";
static const auto nameAttribute = "name";
static const auto valueAttribute = "value";
static constexpr auto activeAttribute = "active";
 
bool RealtimeEffectState::HandleXMLTag(
   const std::string_view &tag, const AttributesList &attrs)
{
   if (tag == XMLTag()) {
      mParameters.clear();
      mPlugin = nullptr;
      mID.clear();
      for (auto &[attr, value] : attrs) {
         if (attr == idAttribute) {
            SetID(value.ToWString());
            if (!mPlugin) {
               // TODO - complain!!!!
            }
         }
         else if (attr == versionAttribute) {
         }
         else if (attr == activeAttribute)
            // Updating the EffectSettingsExtra although we haven't yet built
            // the settings
            mMainSettings.settings.extra.SetActive(value.Get<bool>());
      }
      return true;
   }
   else if (tag == parametersAttribute)
      return true;
   else if (tag == parameterAttribute) {
      wxString n;
      wxString v;
      for (auto &[attr, value] : attrs) {
         if (attr == nameAttribute)
            n = value.ToWString();
         else if (attr == valueAttribute)
            v = value.ToWString();
      }
      mParameters += wxString::Format(wxT("\"%s=%s\" "), n, v);
      return true;
   }
   else
      return false;
}
 
void RealtimeEffectState::HandleXMLEndTag(const std::string_view &tag)
{
   if (tag == XMLTag()) {
      if (mPlugin && !mParameters.empty()) {
         CommandParameters parms(mParameters);
         mPlugin->LoadSettings(parms, mMainSettings.settings);
      }
      mParameters.clear();
   }
}
 
XMLTagHandler *RealtimeEffectState::HandleXMLChild(const std::string_view &tag)
{
   // Tag may be for the state, or the list of parameters, or for one parameter.
   // See the writing method below.  All are handled by this
   return this;
}
 
void RealtimeEffectState::WriteXML(XMLWriter &xmlFile)
{
   if (!mPlugin)
      return;
 
   xmlFile.StartTag(XMLTag());
   const auto active = mMainSettings.settings.extra.GetActive();
   xmlFile.WriteAttr(activeAttribute, active);
   xmlFile.WriteAttr(idAttribute, PluginManager::GetID(mPlugin));
   xmlFile.WriteAttr(versionAttribute, mPlugin->GetVersion());
 
   CommandParameters cmdParms;
   if (mPlugin->SaveSettings(mMainSettings.settings, cmdParms)) {
      xmlFile.StartTag(parametersAttribute);
 
      wxString entryName;
      long entryIndex;
      bool entryKeepGoing;
 
      entryKeepGoing = cmdParms.GetFirstEntry(entryName, entryIndex);
      while (entryKeepGoing) {
         wxString entryValue = cmdParms.Read(entryName, "");
 
         xmlFile.StartTag(parameterAttribute);
         xmlFile.WriteAttr(nameAttribute, entryName);
         xmlFile.WriteAttr(valueAttribute, entryValue);
         xmlFile.EndTag(parameterAttribute);
 
         entryKeepGoing = cmdParms.GetNextEntry(entryName, entryIndex);
      }
 
      xmlFile.EndTag(parametersAttribute);
   }
 
   xmlFile.EndTag(XMLTag());
}
 
std::shared_ptr<EffectSettingsAccess> RealtimeEffectState::GetAccess()
{
   if (!GetEffect())
      // Effect not found!
      // Return a dummy
      return std::make_shared<Access>();
 
   // Only the main thread assigns to the atomic pointer, here and
   // once only in the lifetime of the state
   if (!GetAccessState())
   {
      MakeInstance();
      mpAccessState.emplace(*mPlugin, *this);
   }
 
   return std::make_shared<Access>(*this);
}