frame stream refactor, i like it now

src/content/frame_stream2.hpp

@@ -18,31 +18,38 @@
 //};
 
 template<typename FrameType>
-struct FrameStream2Reader {
+struct FrameStream2 {
 	// get number of available frames
-	virtual int32_t getSize(void) = 0;
+	[[nodiscard]] virtual int32_t size(void) = 0;
 
 	// get next frame
 	// TODO: optional instead?
 	// data sharing? -> no, data is copied for each fsr, if concurency supported
-	virtual std::optional<FrameType>  getNext(void) = 0;
+	[[nodiscard]] virtual std::optional<FrameType> pop(void) = 0;
+
+	// returns true if there are readers (or we dont know)
+	virtual bool push(const FrameType& value) = 0;
 };
 
 // needs count frames queue size
 // having ~1-2sec buffer size is often sufficent
 template<typename FrameType>
-struct QueuedFrameStream2Reader : public FrameStream2Reader<FrameType> {
+struct QueuedFrameStream2 : public FrameStream2<FrameType> {
 	using frame_type = FrameType;
 
 	rigtorp::SPSCQueue<FrameType> _queue;
 
-	explicit QueuedFrameStream2Reader(size_t queue_size) : _queue(queue_size) {}
+	// discard values if queue full
+	// will block if not lossy and full on push
+	const bool _lossy {true};
 
-	[[nodiscard]] int32_t getSize(void) override {
+	explicit QueuedFrameStream2(size_t queue_size, bool lossy = true) : _queue(queue_size), _lossy(lossy) {}
+
+	int32_t size(void) override {
 		return _queue.size();
 	}
 
-	[[nodiscard]] std::optional<FrameType> getNext(void) override {
+	std::optional<FrameType> pop(void) override {
 		auto* ret_ptr = _queue.front();
 		if (ret_ptr == nullptr) {
 			return std::nullopt;
@@ -55,14 +62,21 @@ struct QueuedFrameStream2Reader : public FrameStream2Reader<FrameType> {
 
 		return ret;
 	}
+
+	bool push(const FrameType& value) override {
+		if (_lossy) {
+			[[maybe_unused]] auto _ = _queue.try_emplace(value);
+			// TODO: maybe return ?
+		} else {
+			_queue.push(value);
+		}
+		return true;
+	}
 };
 
 template<typename FrameType>
-struct MultiplexedQueuedFrameStream2Writer {
+struct QueuedFrameStream2Multiplexer : public FrameStream2<FrameType> {
-	using ReaderType = QueuedFrameStream2Reader<FrameType>;
+	using ReaderType = QueuedFrameStream2<FrameType>;
-
-	// TODO: expose
-	const size_t _queue_size {10};
 
 	// pointer stability
 	std::vector<std::unique_ptr<ReaderType>> _readers;
@@ -70,9 +84,9 @@ struct MultiplexedQueuedFrameStream2Writer {
 	// a simple lock here is ok, since this tends to be a rare operation,
 	// except for the push, which is always on the same thread
 
-	ReaderType* aquireReader(void) {
+	ReaderType* aquireReader(size_t queue_size = 10, bool lossy = true) {
 		std::lock_guard lg{_readers_lock};
-		return _readers.emplace_back(std::make_unique<ReaderType>(_queue_size)).get();
+		return _readers.emplace_back(std::make_unique<ReaderType>(queue_size, lossy)).get();
 	}
 
 	void releaseReader(ReaderType* reader) {
@@ -85,13 +99,26 @@ struct MultiplexedQueuedFrameStream2Writer {
 		}
 	}
 
+	// stream interface
+
+	int32_t size(void) override {
+		// TODO: return something sensible?
+		return -1;
+	}
+
+	std::optional<FrameType> pop(void) override {
+		assert(false && "tried to pop from a multiplexer");
+		return std::nullopt;
+	}
+
 	// returns true if there are readers
-	bool pushValue(const FrameType& value) {
+	bool push(const FrameType& value) override {
 		std::lock_guard lg{_readers_lock};
 		bool have_readers{false};
 		for (auto& it : _readers) {
-			[[maybe_unused]] auto _ = it->_queue.try_emplace(value);
+			[[maybe_unused]] auto _ = it->push(value);
 			have_readers = true; // even if queue full, we still continue believing in them
+			// maybe consider push return value?
 		}
 		return have_readers;
 	}

src/content/sdl_video_frame_stream2.cpp

@@ -105,7 +105,7 @@ SDLVideoCameraContent::SDLVideoCameraContent(void) {
 				};
 
 				// creates surface copies
-				someone_listening = pushValue(new_frame_non_owning);
+				someone_listening = push(new_frame_non_owning);
 			}
 			SDL_ReleaseCameraFrame(_camera.get(), sdl_frame_next);
 

src/content/sdl_video_frame_stream2.hpp

@@ -42,10 +42,10 @@ struct SDLVideoFrame {
 	SDLVideoFrame& operator=(const SDLVideoFrame& other) = delete;
 };
 
-using SDLVideoFrameStream2Writer = MultiplexedQueuedFrameStream2Writer<SDLVideoFrame>;
+using SDLVideoFrameStream2Multiplexer = QueuedFrameStream2Multiplexer<SDLVideoFrame>;
-using SDLVideoFrameStream2Reader = SDLVideoFrameStream2Writer::ReaderType;
+using SDLVideoFrameStream2 = SDLVideoFrameStream2Multiplexer::ReaderType;
 
-struct SDLVideoCameraContent : protected SDLVideoFrameStream2Writer {
+struct SDLVideoCameraContent : protected SDLVideoFrameStream2Multiplexer {
 	// meh, empty default
 	std::unique_ptr<SDL_Camera, decltype(&SDL_CloseCamera)> _camera {nullptr, &SDL_CloseCamera};
 	std::atomic<bool> _thread_should_quit {false};
@@ -59,7 +59,7 @@ struct SDLVideoCameraContent : protected SDLVideoFrameStream2Writer {
 	~SDLVideoCameraContent(void);
 
 	// make only some of writer public
-	using SDLVideoFrameStream2Writer::aquireReader;
+	using SDLVideoFrameStream2Multiplexer::aquireReader;
-	using SDLVideoFrameStream2Writer::releaseReader;
+	using SDLVideoFrameStream2Multiplexer::releaseReader;
 };
 

src/main.cpp

@@ -85,7 +85,7 @@ int main(int argc, char** argv) {
 		auto* reader = vcc.aquireReader();
 		for (size_t i = 0; i < 20; i++) {
 			std::this_thread::sleep_for(std::chrono::milliseconds(50));
-			auto new_frame_opt = reader->getNext();
+			auto new_frame_opt = reader->pop();
 			if (new_frame_opt.has_value()) {
 				std::cout << "video frame was " << new_frame_opt.value().surface->w << "x" << new_frame_opt.value().surface->h << " " << new_frame_opt.value().timestampNS << "ns\n";
 			}