⚡ Event-driven change detection

refs #35

Author: fredemmott

src/APILayerStore.hpp

@@ -2,6 +2,8 @@
 // SPDX-License-Identifier: ISC
 
 #pragma once
+#include <boost/signals2.hpp>
+
 #include <span>
 #include <vector>
 
@@ -21,16 +23,27 @@ class APILayerStore {
   // e.g. if we're a 64-bit build, we won't see 32-bit layers
   virtual bool IsForCurrentArchitecture() const noexcept = 0;
 
-  virtual bool Poll() const noexcept = 0;
+  virtual boost::signals2::scoped_connection OnChange(
+    std::function<void()> callback) noexcept {
+    return mOnChangeSignal.connect(std::move(callback));
+  }
+
+  static std::span<APILayerStore*> Get() noexcept;
+
+ protected:
+  void NotifyChange() {
+    mOnChangeSignal();
+  }
 
-  static std::span<const APILayerStore*> Get() noexcept;
+ private:
+  boost::signals2::signal<void()> mOnChangeSignal;
 };
 
 class ReadWriteAPILayerStore : public virtual APILayerStore {
  public:
   virtual bool SetAPILayers(const std::vector<APILayer>&) const noexcept = 0;
 
-  static std::span<const ReadWriteAPILayerStore*> Get() noexcept;
+  static std::span<ReadWriteAPILayerStore*> Get() noexcept;
 };
 
 }// namespace FredEmmott::OpenXRLayers

src/GUI.cpp

@@ -59,8 +59,10 @@ void GUI::DrawFrame() {
 }
 
 GUI::GUI() {
+  const auto stores = ReadWriteAPILayerStore::Get();
+  mLayerSets.reserve(stores.size());
   for (auto&& store: ReadWriteAPILayerStore::Get()) {
-    mLayerSets.push_back({store});
+    mLayerSets.emplace_back(store);
   }
 }
 
@@ -69,6 +71,13 @@ void GUI::Run() {
   platform.GUIMain(std::bind_front(&GUI::DrawFrame, this));
 }
 
+GUI::LayerSet::~LayerSet() = default;
+
+GUI::LayerSet::LayerSet(ReadWriteAPILayerStore* store) : mStore(store) {
+  mOnChangeConnection
+    = store->OnChange([this] { this->mLayerDataIsStale = true; });
+}
+
 void GUI::LayerSet::GUILayersList() {
   auto viewport = ImGui::GetMainViewport();
   const auto dpiScale = Platform::Get().GetDPIScaling();
@@ -632,9 +641,6 @@ void GUI::LayerSet::DragDropReorder(
 }
 
 void GUI::LayerSet::Draw() {
-  if (mStore->Poll()) {
-    mLayerDataIsStale = true;
-  }
   if (mLayerDataIsStale) {
     this->ReloadLayerDataNow();
   }

src/GUI.hpp

@@ -3,6 +3,8 @@
 
 #pragma once
 
+#include <boost/signals2/connection.hpp>
+
 #include <vector>
 
 #include "APILayer.hpp"
@@ -20,8 +22,17 @@ class GUI final {
  private:
   using LintErrors = std::vector<std::shared_ptr<LintError>>;
 
-  class LayerSet {
+  class LayerSet final {
    public:
+    LayerSet() = delete;
+    ~LayerSet();
+    explicit LayerSet(ReadWriteAPILayerStore* store);
+
+    LayerSet(const LayerSet&) = delete;
+    LayerSet& operator=(const LayerSet&) = delete;
+    LayerSet(LayerSet&&) = default;
+    LayerSet& operator=(LayerSet&&) = default;
+
     std::type_identity_t<const ReadWriteAPILayerStore>* mStore {nullptr};
 
     std::vector<APILayer> mLayers;
@@ -51,6 +62,9 @@ class GUI final {
 
     void AddLayersClicked();
     void DragDropReorder(const APILayer& source, const APILayer& target);
+
+   private:
+    boost::signals2::scoped_connection mOnChangeConnection;
   };
 
   std::vector<LayerSet> mLayerSets;

src/windows/WindowsAPILayerStore.cpp

@@ -62,8 +62,11 @@ WindowsAPILayerStore::WindowsAPILayerStore(
     mKey = {};
     return;
   }
-  mEvent.reset(CreateEvent(nullptr, false, false, nullptr));
-  this->WindowsAPILayerStore::Poll();
+
+  mWatcher = wil::make_registry_watcher(
+    mKey.get(), /* no subkey. nullptr not allowed */ L"", true, [this](auto) {
+      this->NotifyChange();
+    });
 }
 
 WindowsAPILayerStore::~WindowsAPILayerStore() = default;
@@ -136,13 +139,6 @@ std::vector<APILayer> WindowsAPILayerStore::GetAPILayers() const noexcept {
   return layers;
 }
 
-bool WindowsAPILayerStore::Poll() const noexcept {
-  const auto result = WaitForSingleObject(mEvent.get(), 0);
-  RegNotifyChangeKeyValue(
-    mKey.get(), false, REG_NOTIFY_CHANGE_LAST_SET, mEvent.get(), true);
-  return (result == WAIT_OBJECT_0);
-}
-
 class ReadOnlyWindowsAPILayerStore final : public WindowsAPILayerStore {
  public:
   ReadOnlyWindowsAPILayerStore(
@@ -229,26 +225,26 @@ class ReadWriteWindowsAPILayerStore final : public WindowsAPILayerStore,
 };
 
 template <class TInterface, class TConcrete>
-std::span<const TInterface*> GetStaticStores() noexcept {
+std::span<TInterface*> GetStaticStores() noexcept {
   using RB = WindowsAPILayerStore::RegistryBitness;
   using enum APILayer::Kind;
-  static const TConcrete sHKLM64 {
+  static TConcrete sHKLM64 {
     "Win64-HKLM", Implicit, RB::Wow64_64, HKEY_LOCAL_MACHINE};
-  static const TConcrete sHKCU64 {
+  static TConcrete sHKCU64 {
     "Win64-HKCU", Implicit, RB::Wow64_64, HKEY_CURRENT_USER};
-  static const TConcrete sHKLM32 {
+  static TConcrete sHKLM32 {
     "Win32-HKLM", Implicit, RB::Wow64_32, HKEY_LOCAL_MACHINE};
-  static const TConcrete sHKCU32 {
+  static TConcrete sHKCU32 {
     "Win32-HKCU", Implicit, RB::Wow64_32, HKEY_CURRENT_USER};
-  static const TConcrete sExplicitHKLM64 {
+  static TConcrete sExplicitHKLM64 {
     "Explicit Win64-HKLM", Explicit, RB::Wow64_64, HKEY_LOCAL_MACHINE};
-  static const TConcrete sExplicitHKCU64 {
+  static TConcrete sExplicitHKCU64 {
     "Explicit Win64-HKCU", Explicit, RB::Wow64_64, HKEY_CURRENT_USER};
-  static const TConcrete sExplicitHKLM32 {
+  static TConcrete sExplicitHKLM32 {
     "Explicit Win32-HKLM", Explicit, RB::Wow64_32, HKEY_LOCAL_MACHINE};
-  static const TConcrete sExplicitHKCU32 {
+  static TConcrete sExplicitHKCU32 {
     "Explicit Win32-HKCU", Explicit, RB::Wow64_32, HKEY_CURRENT_USER};
-  static const TInterface* sStores[] {
+  static TInterface* sStores[] {
     &sHKLM64,
     &sHKCU64,
     &sHKLM32,
@@ -261,12 +257,11 @@ std::span<const TInterface*> GetStaticStores() noexcept {
   return sStores;
 }
 
-std::span<const APILayerStore*> APILayerStore::Get() noexcept {
+std::span<APILayerStore*> APILayerStore::Get() noexcept {
   return GetStaticStores<APILayerStore, ReadOnlyWindowsAPILayerStore>();
 };
 
-std::span<const ReadWriteAPILayerStore*>
-ReadWriteAPILayerStore::Get() noexcept {
+std::span<ReadWriteAPILayerStore*> ReadWriteAPILayerStore::Get() noexcept {
   return GetStaticStores<
     ReadWriteAPILayerStore,
     ReadWriteWindowsAPILayerStore>();

src/windows/WindowsAPILayerStore.hpp

@@ -27,8 +27,6 @@ class WindowsAPILayerStore : public virtual APILayerStore {
 
   std::vector<APILayer> GetAPILayers() const noexcept override;
 
-  bool Poll() const noexcept override;
-
   bool IsForCurrentArchitecture() const noexcept override {
     return std::to_underlying(mRegistryBitness) == sizeof(void*);
   }
@@ -50,13 +48,13 @@ class WindowsAPILayerStore : public virtual APILayerStore {
     REGSAM desiredAccess);
 
   wil::unique_hkey mKey {};
-  wil::unique_event mEvent {};
 
  private:
   const std::string mDisplayName;
   const APILayer::Kind mLayerKind;
   const RegistryBitness mRegistryBitness;
   const HKEY mRootKey;
+  wil::unique_registry_watcher mWatcher;
 };
 
 }// namespace FredEmmott::OpenXRLayers

vcpkg.json

@@ -14,6 +14,7 @@
         "win32-binding"
       ]
     },
+    "boost-signals2",
     "nlohmann-json",
     "fmt",
     "openxr-loader"