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/CustomAssetLoader.h

@@ -0,0 +1,82 @@
+// Copyright 2025 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#pragma once
+
+#include <atomic>
+#include <condition_variable>
+#include <list>
+#include <mutex>
+#include <set>
+#include <thread>
+#include <vector>
+
+#include "Common/Flag.h"
+#include "VideoCommon/Assets/CustomAsset.h"
+
+namespace VideoCommon
+{
+// This class takes any number of assets
+// and loads them across a configurable
+// thread pool
+class CustomAssetLoader
+{
+public:
+  CustomAssetLoader() = default;
+  ~CustomAssetLoader() = default;
+  CustomAssetLoader(const CustomAssetLoader&) = delete;
+  CustomAssetLoader(CustomAssetLoader&&) = delete;
+  CustomAssetLoader& operator=(const CustomAssetLoader&) = delete;
+  CustomAssetLoader& operator=(CustomAssetLoader&&) = delete;
+
+  void Initialize();
+  void Shutdown();
+
+  using AssetHandle = std::pair<std::size_t, bool>;
+  struct LoadResults
+
+  {
+    std::vector<AssetHandle> asset_handles;
+    s64 change_in_memory;
+  };
+
+  // Returns a vector of loaded asset handle / loaded result pairs
+  //  and the change in memory.
+  LoadResults TakeLoadResults();
+
+  // Schedule assets to load on the worker threads
+  //  and set how much memory is available for loading these additional assets.
+  void ScheduleAssetsToLoad(std::list<CustomAsset*> assets_to_load, u64 allowed_memory);
+
+  void Reset(bool restart_worker_threads = true);
+
+private:
+  bool StartWorkerThreads(u32 num_worker_threads);
+  bool ResizeWorkerThreads(u32 num_worker_threads);
+  bool HasWorkerThreads() const;
+  void StopWorkerThreads();
+
+  void WorkerThreadRun(u32 thread_index);
+
+  Common::Flag m_exit_flag;
+
+  std::vector<std::thread> m_worker_threads;
+
+  std::mutex m_assets_to_load_lock;
+  std::list<CustomAsset*> m_assets_to_load;
+
+  std::condition_variable m_worker_thread_wake;
+
+  std::vector<AssetHandle> m_asset_handles_loaded;
+
+  // Memory available to load new assets.
+  s64 m_allowed_memory = 0;
+
+  // Change in memory from just-loaded/unloaded asset results yet to be taken by the Manager.
+  std::atomic<s64> m_change_in_memory = 0;
+
+  std::mutex m_assets_loaded_lock;
+
+  std::set<std::size_t> m_handles_in_progress;
+};
+}  // namespace VideoCommon