QtUtils/RunOnObject: Make safe under object destruction

Co-Authored-By: cancel <cancel@cancel.fm>

Source/Core/DolphinQt2/Main.cpp

@@ -34,7 +34,7 @@
 
 static bool QtMsgAlertHandler(const char* caption, const char* text, bool yes_no, MsgType style)
 {
-  return RunOnObject(QApplication::instance(), [&] {
+  std::optional<bool> r = RunOnObject(QApplication::instance(), [&] {
     QMessageBox message_box(QApplication::activeWindow());
     message_box.setWindowTitle(QString::fromUtf8(caption));
     message_box.setText(QString::fromUtf8(text));
@@ -68,6 +68,9 @@ static bool QtMsgAlertHandler(const char* caption, const char* text, bool yes_no
 
     return false;
   });
+  if (r.has_value())
+    return *r;
+  return false;
 }
 
 // N.B. On Windows, this should be called from WinMain. Link against qtmain and specify

Source/Core/DolphinQt2/MainWindow.cpp

@@ -1196,13 +1196,16 @@ void MainWindow::OnImportNANDBackup()
           });
         },
         [this] {
-          return RunOnObject(this, [this] {
+          std::optional<std::string> keys_file = RunOnObject(this, [this] {
             return QFileDialog::getOpenFileName(this, tr("Select the keys file (OTP/SEEPROM dump)"),
                                                 QDir::currentPath(),
                                                 tr("BootMii keys file (*.bin);;"
                                                    "All Files (*)"))
                 .toStdString();
           });
+          if (keys_file)
+            return *keys_file;
+          return std::string("");
         });
     QueueOnObject(dialog, &QProgressDialog::close);
   });

Source/Core/DolphinQt2/NetPlay/NetPlayDialog.cpp

@@ -580,12 +580,15 @@ void NetPlayDialog::OnTraversalError(TraversalClient::FailureReason error)
 
 bool NetPlayDialog::IsRecording()
 {
-  return RunOnObject(m_record_input_box, &QCheckBox::isChecked);
+  std::optional<bool> is_recording = RunOnObject(m_record_input_box, &QCheckBox::isChecked);
+  if (is_recording)
+    return *is_recording;
+  return false;
 }
 
 std::string NetPlayDialog::FindGame(const std::string& game)
 {
-  return RunOnObject(this, [this, game] {
+  std::optional<std::string> path = RunOnObject(this, [this, game] {
     for (int i = 0; i < m_game_list_model->rowCount(QModelIndex()); i++)
     {
       if (m_game_list_model->GetUniqueIdentifier(i).toStdString() == game)
@@ -593,6 +596,9 @@ std::string NetPlayDialog::FindGame(const std::string& game)
     }
     return std::string("");
   });
+  if (path)
+    return *path;
+  return std::string("");
 }
 
 void NetPlayDialog::ShowMD5Dialog(const std::string& file_identifier)

Source/Core/DolphinQt2/QtUtils/RunOnObject.h

@@ -4,7 +4,11 @@
 
 #pragma once
 
+#include <QCoreApplication>
+#include <QEvent>
+#include <QPointer>
 #include <QThread>
+#include <optional>
 #include <type_traits>
 #include <utility>
 
@@ -15,21 +19,53 @@ class QObject;
 
 // QWidget and subclasses are not thread-safe! This helper takes arbitrary code from any thread,
 // safely runs it on the appropriate GUI thread, waits for it to finish, and returns the result.
+//
+// If the target object is destructed before the code gets to run, the QPointer will be nulled and
+// the function will return nullopt.
 
 template <typename F>
 auto RunOnObject(QObject* object, F&& functor)
 {
+  using OptionalResultT = std::optional<std::result_of_t<F()>>;
+
   // If we queue up a functor on the current thread, it won't run until we return to the event loop,
   // which means waiting for it to finish will never complete. Instead, run it immediately.
   if (object->thread() == QThread::currentThread())
-    return functor();
+    return OptionalResultT(functor());
 
-  Common::Event event;
-  std::result_of_t<F()> result;
-  QueueOnObject(object, [&event, &result, functor = std::forward<F>(functor) ] {
-    result = functor();
-    event.Set();
-  });
+  class FnInvokeEvent : public QEvent
+  {
+  public:
+    FnInvokeEvent(F&& functor, QObject* obj, Common::Event& event, OptionalResultT& result)
+        : QEvent(QEvent::None), m_func(std::move(functor)), m_obj(obj), m_event(event),
+          m_result(result)
+    {
+    }
+
+    ~FnInvokeEvent()
+    {
+      if (m_obj)
+      {
+        (*m_result) = m_func();
+      }
+      else
+      {
+        // is already nullopt
+      }
+      m_event.Set();
+    }
+
+  private:
+    F m_func;
+    QPointer<QObject> m_obj;
+    Common::Event& m_event;
+    OptionalResultT& m_result;
+  };
+
+  Common::Event event{};
+  OptionalResultT result = std::nullopt;
+  QCoreApplication::postEvent(object,
+                              new FnInvokeEvent(std::forward<F>(functor), object, event, result));
   event.Wait();
   return result;
 }

Source/Core/DolphinQt2/Updater.cpp

@@ -30,7 +30,7 @@ void Updater::OnUpdateAvailable(const NewVersionInformation& info)
 {
   bool later = false;
 
-  int choice = RunOnObject(m_parent, [&] {
+  std::optional<int> choice = RunOnObject(m_parent, [&] {
     QDialog* dialog = new QDialog(m_parent);
     dialog->setWindowTitle(tr("Update available"));
     dialog->setWindowFlags(dialog->windowFlags() & ~Qt::WindowContextHelpButtonHint);
@@ -79,7 +79,7 @@ void Updater::OnUpdateAvailable(const NewVersionInformation& info)
     return dialog->exec();
   });
 
-  if (choice == QDialog::Accepted)
+  if (choice && *choice == QDialog::Accepted)
   {
     TriggerUpdate(info, later ? AutoUpdateChecker::RestartMode::NO_RESTART_AFTER_UPDATE :
                                 AutoUpdateChecker::RestartMode::RESTART_AFTER_UPDATE);