Qt: Fix emulation thread using 100% CPU when idle

src/duckstation-qt/qthostinterface.cpp

@@ -13,6 +13,7 @@
 #include "qtutils.h"
 #include <QtCore/QCoreApplication>
 #include <QtCore/QDebug>
+#include <QtCore/QEventLoop>
 #include <QtWidgets/QMessageBox>
 #include <memory>
 Log_SetChannel(QtHostInterface);
@@ -374,6 +375,8 @@ void QtHostInterface::pauseSystem(bool paused)
 
   m_paused = paused;
   m_audio_stream->PauseOutput(paused);
+  if (!paused)
+    wakeThread();
   emit emulationPaused(paused);
 }
 
@@ -436,6 +439,7 @@ void QtHostInterface::doBootSystem(QString initial_filename, QString initial_sav
     return;
   }
 
+  wakeThread();
   m_audio_stream->PauseOutput(false);
   emit emulationStarted();
 }
@@ -478,12 +482,13 @@ void QtHostInterface::doStopThread()
 
 void QtHostInterface::threadEntryPoint()
 {
+  m_worker_thread_event_loop = new QEventLoop();
   while (!m_shutdown_flag.load())
   {
-    if (!m_system)
+    if (!m_system || m_paused)
     {
       // wait until we have a system before running
-      QCoreApplication::processEvents(QEventLoop::AllEvents, 1000);
+      m_worker_thread_event_loop->exec();
       continue;
     }
 
@@ -516,15 +521,25 @@ void QtHostInterface::threadEntryPoint()
       UpdatePerformanceCounters();
     }
 
-    QCoreApplication::processEvents(QEventLoop::AllEvents, m_paused ? 16 : 0);
+    m_worker_thread_event_loop->processEvents(QEventLoop::AllEvents);
   }
 
   m_system.reset();
+  delete m_worker_thread_event_loop;
+  m_worker_thread_event_loop = nullptr;
 
   // move back to UI thread
   moveToThread(m_original_thread);
 }
 
+void QtHostInterface::wakeThread()
+{
+  if (isOnWorkerThread())
+    m_worker_thread_event_loop->quit();
+  else
+    QMetaObject::invokeMethod(m_worker_thread_event_loop, "quit", Qt::QueuedConnection);
+}
+
 QtHostInterface::Thread::Thread(QtHostInterface* parent) : QThread(parent), m_parent(parent) {}
 
 QtHostInterface::Thread::~Thread() = default;

src/duckstation-qt/qthostinterface.h

@@ -14,6 +14,7 @@
 
 class ByteStream;
 
+class QEventLoop;
 class QWidget;
 
 class GameList;
@@ -116,6 +117,7 @@ private:
   void createThread();
   void stopThread();
   void threadEntryPoint();
+  void wakeThread();
 
   QSettings m_qsettings;
 
@@ -124,6 +126,7 @@ private:
   QtDisplayWindow* m_display_window = nullptr;
   QThread* m_original_thread = nullptr;
   Thread* m_worker_thread = nullptr;
+  QEventLoop* m_worker_thread_event_loop = nullptr;
 
   std::atomic_bool m_shutdown_flag{false};