VideoCommon: add resource manager and new asset loader; the resource manager uses a least recently used cache to determine which assets get priority for loading. Additionally, if the system is low on memory, assets will be purged with the less requested assets being the first to go. The loader is multithreaded now and loads assets as quickly as possible as long as memory is available

Co-authored-by: Jordan Woyak <jordan.woyak@gmail.com>

Source/Core/VideoCommon/Assets/CustomResourceManager.h

@@ -0,0 +1,215 @@
+// Copyright 2025 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <list>
+#include <map>
+#include <memory>
+#include <set>
+#include <vector>
+
+#include "Common/CommonTypes.h"
+#include "Common/HookableEvent.h"
+
+#include "VideoCommon/Assets/CustomAsset.h"
+#include "VideoCommon/Assets/CustomAssetLibrary.h"
+#include "VideoCommon/Assets/CustomAssetLoader.h"
+#include "VideoCommon/Assets/CustomTextureData.h"
+
+namespace VideoCommon
+{
+class TextureAsset;
+
+// The resource manager manages custom resources (textures, shaders, meshes)
+// called assets.  These assets are loaded using a priority system,
+// where assets requested more often gets loaded first.  This system
+// also tracks memory usage and if memory usage goes over a calculated limit,
+// then assets will be purged with older assets being targeted first.
+class CustomResourceManager
+{
+public:
+  void Initialize();
+  void Shutdown();
+
+  void Reset();
+
+  // Request that an asset be reloaded
+  void MarkAssetDirty(const CustomAssetLibrary::AssetID& asset_id);
+
+  void XFBTriggered();
+
+  using TextureTimePair = std::pair<std::shared_ptr<CustomTextureData>, CustomAsset::TimeType>;
+
+  // Returns a pair with the custom texture data and the time it was last loaded
+  // Callees are not expected to hold onto the shared_ptr as that will prevent
+  // the resource manager from being able to properly release data
+  TextureTimePair GetTextureDataFromAsset(const CustomAssetLibrary::AssetID& asset_id,
+                                          std::shared_ptr<VideoCommon::CustomAssetLibrary> library);
+
+private:
+  // A generic interface to describe an assets' type
+  // and load state
+  struct AssetData
+  {
+    std::unique_ptr<CustomAsset> asset;
+    CustomAsset::TimeType load_request_time = {};
+    bool has_load_error = false;
+
+    enum class AssetType
+    {
+      TextureData
+    };
+    AssetType type;
+
+    enum class LoadStatus
+    {
+      PendingReload,
+      LoadFinished,
+      ResourceDataAvailable,
+      Unloaded,
+    };
+    LoadStatus load_status = LoadStatus::PendingReload;
+  };
+
+  // A structure to represent some raw texture data
+  // (this data hasn't hit the GPU yet, used for custom textures)
+  struct InternalTextureDataResource
+  {
+    AssetData* asset_data = nullptr;
+    VideoCommon::TextureAsset* asset = nullptr;
+    std::shared_ptr<CustomTextureData> texture_data;
+  };
+
+  void LoadTextureDataAsset(const CustomAssetLibrary::AssetID& asset_id,
+                            std::shared_ptr<VideoCommon::CustomAssetLibrary> library,
+                            InternalTextureDataResource* resource);
+
+  void ProcessDirtyAssets();
+  void ProcessLoadedAssets();
+  void RemoveAssetsUntilBelowMemoryLimit();
+
+  template <typename T>
+  T* CreateAsset(const CustomAssetLibrary::AssetID& asset_id, AssetData::AssetType asset_type,
+                 std::shared_ptr<VideoCommon::CustomAssetLibrary> library)
+  {
+    const auto [it, added] =
+        m_asset_id_to_handle.try_emplace(asset_id, m_asset_handle_to_data.size());
+
+    if (added)
+    {
+      AssetData asset_data;
+      asset_data.asset = std::make_unique<T>(library, asset_id, it->second);
+      asset_data.type = asset_type;
+      asset_data.load_request_time = {};
+      asset_data.has_load_error = false;
+
+      m_asset_handle_to_data.insert_or_assign(it->second, std::move(asset_data));
+    }
+    auto& asset_data_from_handle = m_asset_handle_to_data[it->second];
+    asset_data_from_handle.load_status = AssetData::LoadStatus::PendingReload;
+
+    return static_cast<T*>(asset_data_from_handle.asset.get());
+  }
+
+  // Maintains a priority-sorted list of assets.
+  // Used to figure out which assets to load or unload first.
+  // Most recently used assets get marked with highest priority.
+  class AssetPriorityQueue
+  {
+  public:
+    const auto& Elements() const { return m_assets; }
+
+    // Inserts or moves the asset to the top of the queue.
+    void MakeAssetHighestPriority(u64 asset_handle, CustomAsset* asset)
+    {
+      RemoveAsset(asset_handle);
+      m_assets.push_front(asset);
+
+      // See CreateAsset for how a handle gets defined
+      if (asset_handle >= m_iterator_lookup.size())
+        m_iterator_lookup.resize(asset_handle + 1, m_assets.end());
+
+      m_iterator_lookup[asset_handle] = m_assets.begin();
+    }
+
+    // Inserts an asset at lowest priority or
+    //  does nothing if asset is already in the queue.
+    void InsertAsset(u64 asset_handle, CustomAsset* asset)
+    {
+      if (asset_handle >= m_iterator_lookup.size())
+        m_iterator_lookup.resize(asset_handle + 1, m_assets.end());
+
+      if (m_iterator_lookup[asset_handle] == m_assets.end())
+      {
+        m_assets.push_back(asset);
+        m_iterator_lookup[asset_handle] = std::prev(m_assets.end());
+      }
+    }
+
+    CustomAsset* RemoveLowestPriorityAsset()
+    {
+      if (m_assets.empty()) [[unlikely]]
+        return nullptr;
+      auto* const ret = m_assets.back();
+      if (ret != nullptr)
+      {
+        m_iterator_lookup[ret->GetHandle()] = m_assets.end();
+      }
+      m_assets.pop_back();
+      return ret;
+    }
+
+    void RemoveAsset(u64 asset_handle)
+    {
+      if (asset_handle >= m_iterator_lookup.size())
+        return;
+
+      const auto iter = m_iterator_lookup[asset_handle];
+      if (iter != m_assets.end())
+      {
+        m_assets.erase(iter);
+        m_iterator_lookup[asset_handle] = m_assets.end();
+      }
+    }
+
+    bool IsEmpty() const { return m_assets.empty(); }
+
+    std::size_t Size() const { return m_assets.size(); }
+
+  private:
+    std::list<CustomAsset*> m_assets;
+
+    // Handle-to-iterator lookup for fast access.
+    // Grows as needed on insert.
+    std::vector<decltype(m_assets)::iterator> m_iterator_lookup;
+  };
+
+  // Assets that are currently active in memory, in order of most recently used by the game.
+  AssetPriorityQueue m_active_assets;
+
+  // Assets that need to be loaded.
+  // e.g. Because the game tried to use them or because they changed on disk.
+  // Ordered by most recently used.
+  AssetPriorityQueue m_pending_assets;
+
+  std::map<std::size_t, AssetData> m_asset_handle_to_data;
+  std::map<CustomAssetLibrary::AssetID, std::size_t> m_asset_id_to_handle;
+
+  // Memory used by currently "loaded" assets.
+  u64 m_ram_used = 0;
+
+  // A calculated amount of memory to avoid exceeding.
+  u64 m_max_ram_available = 0;
+
+  std::map<CustomAssetLibrary::AssetID, InternalTextureDataResource> m_texture_data_asset_cache;
+
+  std::mutex m_dirty_mutex;
+  std::set<CustomAssetLibrary::AssetID> m_dirty_assets;
+
+  CustomAssetLoader m_asset_loader;
+
+  Common::EventHook m_xfb_event;
+};
+
+}  // namespace VideoCommon