InputCommon: Fix callback dispatch deadlock

Make sure m_is_populating_devices is true when a WM_INPUT_DEVICE_CHANGE
event is received directly on the ciface thread, so that callbacks do
not occur while removing devices. This breaks a hold-and-wait deadlock
between the ciface thread and the CPU thread when using emulated
Wiimotes.

Co-authored-by: brainleq <brainleq@users.noreply.github.com>
Co-authored-by: oldmud0 <oldmud0@users.noreply.github.com>

Source/Core/InputCommon/ControllerInterface/ControllerInterface.cpp

@@ -140,6 +140,19 @@ void ControllerInterface::RefreshDevices()
   InvokeDevicesChangedCallbacks();
 }
 
+void ControllerInterface::PlatformPopulateDevices(std::function<void()> callback)
+{
+  if (!m_is_init)
+    return;
+
+  m_is_populating_devices = true;
+
+  callback();
+
+  m_is_populating_devices = false;
+  InvokeDevicesChangedCallbacks();
+}
+
 // Remove all devices and call library cleanup functions
 void ControllerInterface::Shutdown()
 {

Source/Core/InputCommon/ControllerInterface/ControllerInterface.h

@@ -50,6 +50,7 @@ public:
   void Shutdown();
   void AddDevice(std::shared_ptr<ciface::Core::Device> device);
   void RemoveDevice(std::function<bool(const ciface::Core::Device*)> callback);
+  void PlatformPopulateDevices(std::function<void()> callback);
   bool IsInit() const { return m_is_init; }
   void UpdateInput();
 

Source/Core/InputCommon/ControllerInterface/Win32/Win32.cpp

@@ -28,8 +28,10 @@ static LRESULT CALLBACK WindowProc(HWND hwnd, UINT message, WPARAM wparam, LPARA
 {
   if (message == WM_INPUT_DEVICE_CHANGE)
   {
-    ciface::DInput::PopulateDevices(s_hwnd);
-    ciface::XInput::PopulateDevices();
+    g_controller_interface.PlatformPopulateDevices([] {
+      ciface::DInput::PopulateDevices(s_hwnd);
+      ciface::XInput::PopulateDevices();
+    });
     s_done_populating.Set();
   }