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.cpp

@@ -0,0 +1,157 @@
+// Copyright 2025 Dolphin Emulator Project
+// SPDX-License-Identifier: GPL-2.0-or-later
+
+#include "VideoCommon/Assets/CustomAssetLoader.h"
+
+#include <fmt/format.h>
+
+#include "Common/Logging/Log.h"
+#include "Common/Thread.h"
+
+#include "UICommon/UICommon.h"
+
+namespace VideoCommon
+{
+void CustomAssetLoader::Initialize()
+{
+  ResizeWorkerThreads(2);
+}
+
+void CustomAssetLoader::Shutdown()
+{
+  Reset(false);
+}
+
+bool CustomAssetLoader::StartWorkerThreads(u32 num_worker_threads)
+{
+  for (u32 i = 0; i < num_worker_threads; i++)
+  {
+    m_worker_threads.emplace_back(&CustomAssetLoader::WorkerThreadRun, this, i);
+  }
+
+  return HasWorkerThreads();
+}
+
+bool CustomAssetLoader::ResizeWorkerThreads(u32 num_worker_threads)
+{
+  if (m_worker_threads.size() == num_worker_threads)
+    return true;
+
+  StopWorkerThreads();
+  return StartWorkerThreads(num_worker_threads);
+}
+
+bool CustomAssetLoader::HasWorkerThreads() const
+{
+  return !m_worker_threads.empty();
+}
+
+void CustomAssetLoader::StopWorkerThreads()
+{
+  if (!HasWorkerThreads())
+    return;
+
+  // Signal worker threads to stop, and wake all of them.
+  {
+    std::lock_guard guard(m_assets_to_load_lock);
+    m_exit_flag.Set();
+    m_worker_thread_wake.notify_all();
+  }
+
+  // Wait for worker threads to exit.
+  for (std::thread& thr : m_worker_threads)
+    thr.join();
+  m_worker_threads.clear();
+  m_exit_flag.Clear();
+}
+
+void CustomAssetLoader::WorkerThreadRun(u32 thread_index)
+{
+  Common::SetCurrentThreadName(fmt::format("Asset Loader {}", thread_index).c_str());
+
+  std::unique_lock load_lock(m_assets_to_load_lock);
+  while (true)
+  {
+    m_worker_thread_wake.wait(load_lock,
+                              [&] { return !m_assets_to_load.empty() || m_exit_flag.IsSet(); });
+
+    if (m_exit_flag.IsSet())
+      return;
+
+    // If more memory than allowed has already been loaded, we will load nothing more
+    //  until the next ScheduleAssetsToLoad from Manager.
+    if (m_change_in_memory > m_allowed_memory)
+    {
+      m_assets_to_load.clear();
+      continue;
+    }
+
+    auto* const item = m_assets_to_load.front();
+    m_assets_to_load.pop_front();
+
+    // Make sure another thread isn't loading this handle.
+    if (!m_handles_in_progress.insert(item->GetHandle()).second)
+      continue;
+
+    load_lock.unlock();
+
+    // Unload previously loaded asset.
+    m_change_in_memory -= item->Unload();
+
+    const std::size_t bytes_loaded = item->Load();
+    m_change_in_memory += s64(bytes_loaded);
+
+    load_lock.lock();
+
+    {
+      INFO_LOG_FMT(VIDEO, "CustomAssetLoader thread {} loaded: {} ({})", thread_index,
+                   item->GetAssetId(), UICommon::FormatSize(bytes_loaded));
+
+      std::lock_guard lk{m_assets_loaded_lock};
+      m_asset_handles_loaded.emplace_back(item->GetHandle(), bytes_loaded > 0);
+
+      // Make sure no other threads try to re-process this item.
+      // Manager will take the handles and re-ScheduleAssetsToLoad based on timestamps if needed.
+      std::erase(m_assets_to_load, item);
+    }
+
+    m_handles_in_progress.erase(item->GetHandle());
+  }
+}
+
+auto CustomAssetLoader::TakeLoadResults() -> LoadResults
+{
+  std::lock_guard guard(m_assets_loaded_lock);
+  return {std::move(m_asset_handles_loaded), m_change_in_memory.exchange(0)};
+}
+
+void CustomAssetLoader::ScheduleAssetsToLoad(std::list<CustomAsset*> assets_to_load,
+                                             u64 allowed_memory)
+{
+  if (assets_to_load.empty()) [[unlikely]]
+    return;
+
+  // There's new assets to process, notify worker threads
+  std::lock_guard guard(m_assets_to_load_lock);
+  m_allowed_memory = allowed_memory;
+  m_assets_to_load = std::move(assets_to_load);
+  m_worker_thread_wake.notify_all();
+}
+
+void CustomAssetLoader::Reset(bool restart_worker_threads)
+{
+  const std::size_t worker_thread_count = m_worker_threads.size();
+  StopWorkerThreads();
+
+  m_assets_to_load.clear();
+  m_asset_handles_loaded.clear();
+  m_allowed_memory = 0;
+  m_change_in_memory = 0;
+
+  if (restart_worker_threads)
+  {
+    StartWorkerThreads(static_cast<u32>(worker_thread_count));
+  }
+}
+
+}  // namespace VideoCommon