Qt: Fix IOWindow keeping a shared ptr to devices even after them being removed by the ControllerInterface

this prevented some devices from being recreated correctly, as they were exclusive (e.g. DInput Joysticks)

This is achieved by calling Settings::ReleaseDevices(), which releases all the UI devices shared ptrs.
If we are the host (Qt) thread, DevicesChanged() is now called in line, to avoid devices being hanged onto by the UI.
For this, I had to add a method to check whether we are the Host Thread to Qt.

Avoid calling ControllerInterface::RefreshDevices() from the CPU thread if the emulation is running
and we manually refresh devices from Qt, as that is not necessary anymore.

Refactored the way IOWindow lists devices to make it clearer and hold onto disconnected devices.
There were so many issues with the previous code:
-Devices changes would not be reflected until the window was re-opened
-If there was no default device, it would fail to select the device at index 0
-It could have crashed if we had 0 devices
-The default device was not highlighted as such

Source/Core/DolphinQt/Config/Mapping/IOWindow.cpp

@@ -9,8 +9,6 @@
 
 #include <QComboBox>
 #include <QDialogButtonBox>
-#include <QGroupBox>
-#include <QHBoxLayout>
 #include <QHeaderView>
 #include <QItemDelegate>
 #include <QLabel>
@@ -31,6 +29,7 @@
 #include "DolphinQt/Config/Mapping/MappingWindow.h"
 #include "DolphinQt/QtUtils/BlockUserInputFilter.h"
 #include "DolphinQt/QtUtils/ModalMessageBox.h"
+#include "DolphinQt/Settings.h"
 
 #include "InputCommon/ControlReference/ControlReference.h"
 #include "InputCommon/ControlReference/ExpressionParser.h"
@@ -220,6 +219,8 @@ IOWindow::IOWindow(MappingWidget* parent, ControllerEmu::EmulatedController* con
   CreateMainLayout();
 
   connect(parent, &MappingWidget::Update, this, &IOWindow::Update);
+  connect(parent->GetParent(), &MappingWindow::ConfigChanged, this, &IOWindow::ConfigChanged);
+  connect(&Settings::Instance(), &Settings::ConfigChanged, this, &IOWindow::ConfigChanged);
 
   setWindowTitle(type == IOWindow::Type::Input ? tr("Configure Input") : tr("Configure Output"));
   setWindowFlags(windowFlags() & ~Qt::WindowContextHelpButtonHint);
@@ -229,7 +230,7 @@ IOWindow::IOWindow(MappingWidget* parent, ControllerEmu::EmulatedController* con
   ConnectWidgets();
 }
 
-std::shared_ptr<ciface::Core::Device> IOWindow::GetSelectedDevice()
+std::shared_ptr<ciface::Core::Device> IOWindow::GetSelectedDevice() const
 {
   return m_selected_device;
 }
@@ -258,7 +259,7 @@ void IOWindow::CreateMainLayout()
   m_expression_text->setFont(QFontDatabase::systemFont(QFontDatabase::FixedFont));
   new ControlExpressionSyntaxHighlighter(m_expression_text->document());
 
-  m_operators_combo = new QComboBoxWithMouseWheelDisabled();
+  m_operators_combo = new QComboBoxWithMouseWheelDisabled(this);
   m_operators_combo->addItem(tr("Operators"));
   m_operators_combo->insertSeparator(1);
   if (m_type == Type::Input)
@@ -340,6 +341,7 @@ void IOWindow::CreateMainLayout()
     m_option_list->horizontalHeader()->setSectionResizeMode(1, QHeaderView::Fixed);
 
     m_option_list->setItemDelegate(new InputStateDelegate(this, 1, [&](int row) {
+      std::lock_guard lock(m_selected_device_mutex);
       // Clamp off negative values but allow greater than one in the text display.
       return std::max(GetSelectedDevice()->Inputs()[row]->GetState(), 0.0);
     }));
@@ -400,7 +402,7 @@ void IOWindow::CreateMainLayout()
 void IOWindow::ConfigChanged()
 {
   const QSignalBlocker blocker(this);
-  const auto lock = m_controller->GetStateLock();
+  const auto lock = ControllerEmu::EmulatedController::GetStateLock();
 
   // ensure m_parse_text is in the right state
   UpdateExpression(m_reference->GetExpression(), UpdateMode::Force);
@@ -410,10 +412,10 @@ void IOWindow::ConfigChanged()
   m_range_spinbox->setValue(m_reference->range * SLIDER_TICK_COUNT);
   m_range_slider->setValue(m_reference->range * SLIDER_TICK_COUNT);
 
-  m_devq = m_controller->GetDefaultDevice();
+  if (m_devq.ToString().empty())
+    m_devq = m_controller->GetDefaultDevice();
 
   UpdateDeviceList();
-  UpdateOptionList();
 }
 
 void IOWindow::Update()
@@ -425,6 +427,8 @@ void IOWindow::Update()
 void IOWindow::ConnectWidgets()
 {
   connect(m_select_button, &QPushButton::clicked, [this] { AppendSelectedOption(); });
+  connect(&Settings::Instance(), &Settings::ReleaseDevices, this, &IOWindow::ReleaseDevices);
+  connect(&Settings::Instance(), &Settings::DevicesChanged, this, &IOWindow::UpdateDeviceList);
 
   connect(m_detect_button, &QPushButton::clicked, this, &IOWindow::OnDetectButtonPressed);
   connect(m_test_button, &QPushButton::clicked, this, &IOWindow::OnTestButtonPressed);
@@ -479,16 +483,19 @@ void IOWindow::ConnectWidgets()
 
 void IOWindow::AppendSelectedOption()
 {
-  if (m_option_list->currentItem() == nullptr)
+  if (m_option_list->currentRow() < 0)
     return;
 
   m_expression_text->insertPlainText(MappingCommon::GetExpressionForControl(
-      m_option_list->currentItem()->text(), m_devq, m_controller->GetDefaultDevice()));
+      m_option_list->item(m_option_list->currentRow(), 0)->text(), m_devq,
+      m_controller->GetDefaultDevice()));
 }
 
-void IOWindow::OnDeviceChanged(const QString& device)
+void IOWindow::OnDeviceChanged()
 {
-  m_devq.FromString(device.toStdString());
+  const std::string device_name =
+      m_devices_combo->count() > 0 ? m_devices_combo->currentData().toString().toStdString() : "";
+  m_devq.FromString(device_name);
   UpdateOptionList();
 }
 
@@ -500,7 +507,7 @@ void IOWindow::OnDialogButtonPressed(QAbstractButton* button)
     return;
   }
 
-  const auto lock = m_controller->GetStateLock();
+  const auto lock = ControllerEmu::EmulatedController::GetStateLock();
 
   UpdateExpression(m_expression_text->toPlainText().toStdString());
   m_original_expression = m_reference->GetExpression();
@@ -525,6 +532,7 @@ void IOWindow::OnDetectButtonPressed()
 
   const auto list = m_option_list->findItems(expression, Qt::MatchFixedString);
 
+  // Try to select the first. If this fails, the last selected item would still appear as such
   if (!list.empty())
     m_option_list->setCurrentItem(list[0]);
 }
@@ -541,8 +549,15 @@ void IOWindow::OnRangeChanged(int value)
   m_range_slider->setValue(m_reference->range * SLIDER_TICK_COUNT);
 }
 
+void IOWindow::ReleaseDevices()
+{
+  std::lock_guard lock(m_selected_device_mutex);
+  m_selected_device = nullptr;
+}
+
 void IOWindow::UpdateOptionList()
 {
+  std::lock_guard lock(m_selected_device_mutex);
   m_selected_device = g_controller_interface.FindDevice(m_devq);
   m_option_list->setRowCount(0);
 
@@ -575,13 +590,62 @@ void IOWindow::UpdateOptionList()
 
 void IOWindow::UpdateDeviceList()
 {
+  const QSignalBlocker blocker(m_devices_combo);
+
+  const auto previous_device_name = m_devices_combo->currentData().toString().toStdString();
+
   m_devices_combo->clear();
 
+  // Default to the default device or to the first device if there isn't a default.
+  // Try to the keep the previous selected device, mark it as disconnected if it's gone, as it could
+  // reconnect soon after if this is a devices refresh and it would be annoying to lose the value.
+  const auto default_device_name = m_controller->GetDefaultDevice().ToString();
+  int default_device_index = -1;
+  int previous_device_index = -1;
   for (const auto& name : g_controller_interface.GetAllDeviceStrings())
-    m_devices_combo->addItem(QString::fromStdString(name));
+  {
+    QString qname = QString();
+    if (name == default_device_name)
+    {
+      default_device_index = m_devices_combo->count();
+      // Specify "default" even if we only have one device
+      qname.append(QLatin1Char{'['} + tr("default") + QStringLiteral("] "));
+    }
+    if (name == previous_device_name)
+    {
+      previous_device_index = m_devices_combo->count();
+    }
+    qname.append(QString::fromStdString(name));
+    m_devices_combo->addItem(qname, QString::fromStdString(name));
+  }
 
-  m_devices_combo->setCurrentText(
-      QString::fromStdString(m_controller->GetDefaultDevice().ToString()));
+  if (previous_device_index >= 0)
+  {
+    m_devices_combo->setCurrentIndex(previous_device_index);
+  }
+  else if (!previous_device_name.empty())
+  {
+    const QString qname = QString::fromStdString(previous_device_name);
+    QString adjusted_qname;
+    if (previous_device_name == default_device_name)
+    {
+      adjusted_qname.append(QLatin1Char{'['} + tr("default") + QStringLiteral("] "));
+    }
+    adjusted_qname.append(QLatin1Char{'['} + tr("disconnected") + QStringLiteral("] "))
+        .append(qname);
+    m_devices_combo->addItem(adjusted_qname, qname);
+    m_devices_combo->setCurrentIndex(m_devices_combo->count() - 1);
+  }
+  else if (default_device_index >= 0)
+  {
+    m_devices_combo->setCurrentIndex(default_device_index);
+  }
+  else if (m_devices_combo->count() > 0)
+  {
+    m_devices_combo->setCurrentIndex(0);
+  }
+  // The device object might have changed so we need to always refresh it
+  OnDeviceChanged();
 }
 
 void IOWindow::UpdateExpression(std::string new_expression, UpdateMode mode)