d3d12: Do not detach garbage collection thread

Thanks Neko for the tips.

rpcs3/Emu/RSX/D3D12/D3D12GSRender.cpp

@@ -35,16 +35,11 @@ void SetGetD3DGSFrameCallback(GetGSFrameCb2 value)
 
 GarbageCollectionThread::GarbageCollectionThread()
 {
-	m_isThreadAlive = true;
 	m_askForTermination = false;
 	m_worker = std::thread([this]() {
-		while (m_isThreadAlive)
-		{
 		std::unique_lock<std::mutex> lock(m_mutex);
 		while (!m_askForTermination)
 		{
-				CHECK_EMU_STATUS;
-
 			if (!lock)
 			{
 				lock.lock();
@@ -65,23 +60,26 @@ GarbageCollectionThread::GarbageCollectionThread()
 			}
 			cv.wait(lock);
 		}
-		}
-		m_isThreadAlive = false;
 	});
-	m_worker.detach();
 }
 
 GarbageCollectionThread::~GarbageCollectionThread()
 {
+	{
+		std::unique_lock<std::mutex> lock(m_mutex);
 		m_askForTermination = true;
-	while (m_isThreadAlive);
+		cv.notify_one();
+	}
+	m_worker.join();
 }
 
 void GarbageCollectionThread::pushWork(std::function<void()>&& f)
 {
+	{
 		std::unique_lock<std::mutex> lock(m_mutex);
 		m_queue.push(f);
-	cv.notify_all();
+	}
+	cv.notify_one();
 }
 
 void GarbageCollectionThread::waitForCompletion()

rpcs3/Emu/RSX/D3D12/D3D12GSRender.h

@@ -215,8 +215,7 @@ struct DataHeap
  */
 struct GarbageCollectionThread
 {
-	bool m_isThreadAlive;
-	bool m_askForTermination;
+	std::atomic<bool> m_askForTermination;
 	std::mutex m_mutex;
 	std::condition_variable cv;
 	std::queue<std::function<void()> > m_queue;