Execute scene slices on worker threads

src/swrenderer/r_renderthread.h

@@ -23,6 +23,7 @@
 #pragma once
 
 #include <memory>
+#include <thread>
 
 class DrawerCommandQueue;
 typedef std::shared_ptr<DrawerCommandQueue> DrawerCommandQueuePtr;
@@ -67,6 +68,8 @@ namespace swrenderer
 		std::unique_ptr<RenderClipSegment> ClipSegments;
 		DrawerCommandQueuePtr DrawQueue;
 
+		std::thread thread;
+
 		// VisibleSprite working buffers
 		short clipbot[MAXWIDTH];
 		short cliptop[MAXWIDTH];

src/swrenderer/scene/r_scene.cpp

@@ -63,6 +63,11 @@ namespace swrenderer
 		Threads.push_back(std::make_unique<RenderThread>(this));
 	}
 
+	RenderScene::~RenderScene()
+	{
+		StopThreads();
+	}
+
 	void RenderScene::SetClearColor(int color)
 	{
 		clearcolor = color;
@@ -161,26 +166,38 @@ namespace swrenderer
 	void RenderScene::RenderThreadSlices()
 	{
 		int numThreads = r_scene_multithreaded ? 8 : 1;
-
+		if (numThreads != Threads.size())
-		while (Threads.size() > (size_t)numThreads)
 		{
-			Threads.pop_back();
+			StopThreads();
-		}
+			StartThreads(numThreads);
-
-		while (Threads.size() < (size_t)numThreads)
-		{
-			Threads.push_back(std::make_unique<RenderThread>(this));
 		}
 
+		// Setup threads:
+		std::unique_lock<std::mutex> start_lock(start_mutex);
 		for (int i = 0; i < numThreads; i++)
 		{
 			Threads[i]->X1 = viewwidth * i / numThreads;
 			Threads[i]->X2 = viewwidth * (i + 1) / numThreads;
 		}
+		run_id++;
+		start_lock.unlock();
 
-		for (int i = 0; i < numThreads; i++)
+		// Notify threads to run
+		if (Threads.size() > 1)
 		{
-			RenderThreadSlice(Threads[i].get());
+			start_condition.notify_all();
+		}
+
+		// Do the main thread ourselves:
+		RenderThreadSlice(MainThread());
+
+		// Wait for everyone to finish:
+		if (Threads.size() > 1)
+		{
+			std::unique_lock<std::mutex> end_lock(end_mutex);
+			finished_threads++;
+			end_condition.wait(end_lock, [&]() { return finished_threads == Threads.size(); });
+			finished_threads = 0;
 		}
 	}
 
@@ -246,6 +263,54 @@ namespace swrenderer
 		}
 	}
 
+	void RenderScene::StartThreads(size_t numThreads)
+	{
+		while (Threads.size() < (size_t)numThreads)
+		{
+			auto thread = std::make_unique<RenderThread>(this);
+			auto renderthread = thread.get();
+			int start_run_id = run_id;
+			thread->thread = std::thread([=]()
+			{
+				int last_run_id = start_run_id;
+				while (true)
+				{
+					// Wait until we are signalled to run:
+					std::unique_lock<std::mutex> start_lock(start_mutex);
+					start_condition.wait(start_lock, [&]() { return run_id != last_run_id || shutdown_flag; });
+					if (shutdown_flag)
+						break;
+					last_run_id = run_id;
+					start_lock.unlock();
+
+					RenderThreadSlice(renderthread);
+
+					// Notify main thread that we finished:
+					std::unique_lock<std::mutex> end_lock(end_mutex);
+					finished_threads++;
+					end_lock.unlock();
+					end_condition.notify_all();
+				}
+			});
+			Threads.push_back(std::move(thread));
+		}
+	}
+
+	void RenderScene::StopThreads()
+	{
+		std::unique_lock<std::mutex> lock(start_mutex);
+		shutdown_flag = true;
+		lock.unlock();
+		start_condition.notify_all();
+		while (Threads.size() > 1)
+		{
+			Threads.back()->thread.join();
+			Threads.pop_back();
+		}
+		lock.lock();
+		shutdown_flag = false;
+	}
+
 	void RenderScene::RenderViewToCanvas(AActor *actor, DCanvas *canvas, int x, int y, int width, int height, bool dontmaplines)
 	{
 		auto viewport = RenderViewport::Instance();

src/swrenderer/scene/r_scene.h

@@ -14,7 +14,11 @@
 #pragma once
 
 #include <stddef.h>
+#include <vector>
 #include <memory>
+#include <thread>
+#include <mutex>
+#include <condition_variable>
 #include "r_defs.h"
 #include "d_player.h"
 
@@ -30,6 +34,7 @@ namespace swrenderer
 	{
 	public:
 		RenderScene();
+		~RenderScene();
 
 		void Init();
 		void ScreenResized();
@@ -50,9 +55,19 @@ namespace swrenderer
 		void RenderThreadSlices();
 		void RenderThreadSlice(RenderThread *thread);
 
+		void StartThreads(size_t numThreads);
+		void StopThreads();
+		
 		bool dontmaplines = false;
 		int clearcolor = 0;
 
 		std::vector<std::unique_ptr<RenderThread>> Threads;
+		std::mutex start_mutex;
+		std::condition_variable start_condition;
+		bool shutdown_flag = false;
+		int run_id = 0;
+		std::mutex end_mutex;
+		std::condition_variable end_condition;
+		size_t finished_threads = 0;
 	};
 }