Skip accessibility notifier and all event calculations when we're in PTY mode

src/host/srvinit.cpp

@@ -76,6 +76,15 @@ try
         }
     }
 
+    if (args->InConptyMode())
+    {
+        // If we're in ConPTY mode... set the no-op accessibility notifier
+        // to prevent sending expensive legacy MSAA events when we won't even be
+        // responsible for the terminal user interface.
+        std::unique_ptr<IAccessibilityNotifier> noOpNotifier = std::make_unique<Microsoft::Console::Interactivity::NoOpAccessibilityNotifier>();
+        RETURN_IF_NTSTATUS_FAILED(ServiceLocator::SetAccessibilityNotifier(std::move(noOpNotifier)));
+    }
+
     // Removed allocation of scroll buffer here.
     return S_OK;
 }

src/interactivity/base/ServiceLocator.cpp

@@ -104,6 +104,24 @@ void ServiceLocator::RundownAndExit(const HRESULT hr)
 
 #pragma region Set Methods
 
+[[nodiscard]] NTSTATUS ServiceLocator::SetAccessibilityNotifier(_In_ std::unique_ptr<IAccessibilityNotifier>&& notifier)
+{
+    if (s_accessibilityNotifier)
+    {
+        NT_RETURN_NTSTATUS(STATUS_INVALID_HANDLE);
+    }
+    else if (!notifier)
+    {
+        NT_RETURN_NTSTATUS(STATUS_INVALID_PARAMETER);
+    }
+    else
+    {
+        s_accessibilityNotifier = std::move(notifier);
+    }
+
+    return STATUS_SUCCESS;
+}
+
 [[nodiscard]] NTSTATUS ServiceLocator::SetConsoleControlInstance(_In_ std::unique_ptr<IConsoleControl>&& control)
 {
     if (s_consoleControl)

src/interactivity/inc/IAccessibilityNotifier.hpp

@@ -46,4 +46,19 @@ namespace Microsoft::Console::Interactivity
     };
 
     inline IAccessibilityNotifier::~IAccessibilityNotifier() {}
+
+    class NoOpAccessibilityNotifier final : public IAccessibilityNotifier
+    {
+    public:
+        NoOpAccessibilityNotifier() = default;
+        ~NoOpAccessibilityNotifier() = default;
+        void NotifyConsoleCaretEvent(_In_ RECT /*rectangle*/) override{};
+        void NotifyConsoleCaretEvent(_In_ ConsoleCaretEventFlags /*flags*/, _In_ LONG /*position*/) override{};
+        void NotifyConsoleUpdateScrollEvent(_In_ LONG /*x*/, _In_ LONG /*y*/) override{};
+        void NotifyConsoleUpdateSimpleEvent(_In_ LONG /*start*/, _In_ LONG /*charAndAttribute*/) override{};
+        void NotifyConsoleUpdateRegionEvent(_In_ LONG /*startXY*/, _In_ LONG /*endXY*/) override{};
+        void NotifyConsoleLayoutEvent() override{};
+        void NotifyConsoleStartApplicationEvent(_In_ DWORD /*processId*/) override{};
+        void NotifyConsoleEndApplicationEvent(_In_ DWORD /*processId*/) override{};
+    };
 }

src/interactivity/inc/ServiceLocator.hpp

@@ -37,6 +37,7 @@ namespace Microsoft::Console::Interactivity
         //       In case the on-demand creation fails, the return value
         //       is nullptr and a message is logged.
 
+        [[nodiscard]] static NTSTATUS SetAccessibilityNotifier(_In_ std::unique_ptr<IAccessibilityNotifier>&& notifier);
         static IAccessibilityNotifier* LocateAccessibilityNotifier();
 
         [[nodiscard]] static NTSTATUS SetConsoleControlInstance(_In_ std::unique_ptr<IConsoleControl>&& control);