Implement synchronous outlet for zero-copy writes.

examples/ReceiveDataInChunks.cpp

@@ -8,14 +8,18 @@
 int main(int argc, char **argv) {
 	std::cout << "ReceiveDataInChunks" << std::endl;
 	std::cout << "ReceiveDataInChunks StreamName max_buflen flush" << std::endl;
+	std::cout << "- max_buffered -- duration in msec to buffer" << std::endl;
+	std::cout << "- flush -- set non-zero to flush data instead of pulling; useful for testing throughput" << std::endl;
 
 	try {
 
 		std::string name{argc > 1 ? argv[1] : "MyAudioStream"};
-		int32_t max_buflen = argc > 2 ? std::stol(argv[2]) : 360;
+		double max_buflen = argc > 2 ? std::stod(argv[2]) : 360.;
 		bool flush = argc > 3;
 		// resolve the stream of interest & make an inlet
-		lsl::stream_inlet inlet(lsl::resolve_stream("name", name).at(0), max_buflen);
+		int32_t buf_samples = (int32_t)(max_buflen * 1000);
+		lsl::stream_inlet inlet(lsl::resolve_stream("name", name).at(0), max_buflen,
+			transp_bufsize_thousandths);
 
 		// Use set_postprocessing to get the timestamps in a common base clock.
 		// Do not use if this application will record timestamps to disk -- it is better to 

examples/SendDataInChunks.cpp

@@ -44,9 +44,11 @@ struct fake_device {
 		pattern.reserve(pattern_samples * n_channels);
 		for (auto sample_ix = 0; sample_ix < pattern_samples; ++sample_ix) {
 			for (auto chan_ix = 0; chan_ix < n_channels; ++chan_ix) {
+				// sin(2*pi*f*t), where f cycles from 1 Hz to Nyquist: srate / 2
+				double f = (chan_ix + 1) % (int)(srate / 2);
 				pattern.emplace_back(
 					offset_0 + chan_ix * offset_step +
-					magnitude * static_cast<int16_t>(sin(M_PI * chan_ix * sample_ix / n_channels)));
+					magnitude * static_cast<int16_t>(sin(2 * M_PI * f * sample_ix / srate)));
 			}
 		}
 		last_time = std::chrono::steady_clock::now();
@@ -64,15 +66,15 @@ struct fake_device {
 		return output;
 	}
 
-	std::size_t get_data(std::vector<int16_t> &buffer) {
+	std::size_t get_data(std::vector<int16_t> &buffer, bool nodata = false) {
 		auto now = std::chrono::steady_clock::now();
 		auto elapsed_nano =
 			std::chrono::duration_cast<std::chrono::nanoseconds>(now - last_time).count();
 		int64_t elapsed_samples = std::size_t(elapsed_nano * srate * 1e-9); // truncate OK.
 		elapsed_samples = std::min(elapsed_samples, (int64_t)(buffer.size() / n_channels));
-		if (false) {
+		if (nodata) {
 			// The fastest but no patterns.
-			memset(&buffer[0], 23, buffer.size() * sizeof buffer[0]);
+			// memset(&buffer[0], 23, buffer.size() * sizeof buffer[0]);
 		} else {
 			std::size_t end_sample = head + elapsed_samples;
 			std::size_t nowrap_samples = std::min(pattern_samples - head, elapsed_samples);
@@ -89,22 +91,26 @@ struct fake_device {
 
 int main(int argc, char **argv) {
 	std::cout << "SendDataInChunks" << std::endl;
-	std::cout << "SendDataInChunks StreamName StreamType samplerate n_channels max_buffered chunk_rate" << std::endl;
+	std::cout << "SendDataInChunks StreamName StreamType samplerate n_channels max_buffered chunk_rate nodata use_sync" << std::endl;
 	std::cout << "- max_buffered -- duration in sec (or x100 samples if samplerate is 0) to buffer for each outlet" << std::endl;
 	std::cout << "- chunk_rate -- number of chunks pushed per second. For this example, make it a common factor of samplingrate and 1000." << std::endl;
-
+	std::cout << "- nodata -- Set non-zero to cause the fake device to not copy pattern data into the buffer." << std::endl;
+	std::cout << "- use_sync -- Set to non-zero to use blocking send." << std::endl;
+
 	std::string name{argc > 1 ? argv[1] : "MyAudioStream"}, type{argc > 2 ? argv[2] : "Audio"};
 	int samplingrate = argc > 3 ? std::stol(argv[3]) : 44100;  // Here we specify srate, but typically this would come from the device.
 	int n_channels = argc > 4 ? std::stol(argv[4]) : 2;        // Here we specify n_chans, but typically this would come from theh device.
-	int32_t max_buffered = argc > 5 ? std::stol(argv[5]) : 360;
+	double max_buffered = argc > 5 ? std::stod(argv[5]) : 360.;
 	int32_t chunk_rate = argc > 6 ? std::stol(argv[6]) : 10;  // Chunks per second.
+	bool nodata = argc > 7;
+	bool do_sync = argc > 8 ? (bool)std::stol(argv[8]) : true;
+
 	int32_t chunk_samples = samplingrate > 0 ? std::max((samplingrate / chunk_rate), 1) : 100;  // Samples per chunk.
 	int32_t chunk_duration = 1000 / chunk_rate;  // Milliseconds per chunk
 
 	try {
 		// Prepare the LSL stream.
-		lsl::stream_info info(name, type, n_channels, samplingrate, lsl::cf_int16);
-		lsl::stream_outlet outlet(info, 0, max_buffered);
+		lsl::stream_info info(name, type, n_channels, samplingrate, lsl::cf_int16, "example-SendDataInChunks");
 		lsl::xml_element desc = info.desc();
 		desc.append_child_value("manufacturer", "LSL");
 		lsl::xml_element chns = desc.append_child("channels");
@@ -114,13 +120,19 @@ int main(int argc, char **argv) {
 			chn.append_child_value("unit", "microvolts");
 			chn.append_child_value("type", "EEG");
 		}
+		int32_t buf_samples = max_buffered * samplingrate;
+		lsl::stream_outlet outlet(info, chunk_samples, buf_samples,
+			transp_bufsize_samples | (do_sync ? transp_sync_blocking: transp_default));
+		info = outlet.info();  // Refresh info with whatever the outlet captured.
+		std::cout << "Stream UID: " << info.uid() << std::endl;
 
 		// Create a connection to our device.
 		fake_device my_device(n_channels, (float)samplingrate);
 
 		// Prepare buffer to get data from 'device'.
 		//  The buffer should be larger than you think you need. Here we make it 4x as large.
 		std::vector<int16_t> chunk_buffer(4 * chunk_samples * n_channels);
+		std::fill(chunk_buffer.begin(), chunk_buffer.end(), 0);
 
 		std::cout << "Now sending data..." << std::endl;
 
@@ -133,11 +145,12 @@ int main(int argc, char **argv) {
 			std::this_thread::sleep_until(next_chunk_time);
 
 			// Get data from device
-			std::size_t returned_samples = my_device.get_data(chunk_buffer);
+			std::size_t returned_samples = my_device.get_data(chunk_buffer, nodata);
 
 			// send it to the outlet. push_chunk_multiplexed is one of the more complicated approaches.
 			//  other push_chunk methods are easier but slightly slower.
-			outlet.push_chunk_multiplexed(chunk_buffer.data(), returned_samples * n_channels, 0.0, true);
+			double ts = lsl::local_clock();
+			outlet.push_chunk_multiplexed(chunk_buffer.data(), returned_samples * n_channels, ts, true);
 		}
 
 	} catch (std::exception &e) { std::cerr << "Got an exception: " << e.what() << std::endl; }

include/lsl/common.h

@@ -161,6 +161,9 @@ typedef enum {
 	/// The supplied max_buf should be scaled by 0.001.
 	transp_bufsize_thousandths = 2,
 
+	/// The outlet will use synchronous (blocking) calls to asio to push data
+	transp_sync_blocking = 4,
+
 	// prevent compilers from assuming an instance fits in a single byte
 	_lsl_transport_options_maxval = 0x7f000000
 } lsl_transport_options_t;

src/stream_outlet_impl.cpp

@@ -12,15 +12,22 @@
 namespace lsl {
 
 stream_outlet_impl::stream_outlet_impl(
-	const stream_info_impl &info, int32_t chunk_size, int32_t max_capacity)
+	const stream_info_impl &info, int32_t chunk_size, int32_t max_capacity, uint32_t flags)
 	: sample_factory_(std::make_shared<factory>(info.channel_format(), info.channel_count(),
 		  static_cast<uint32_t>(
 			  info.nominal_srate()
 				  ? info.nominal_srate() * api_config::get_instance()->outlet_buffer_reserve_ms() /
 						1000
 				  : api_config::get_instance()->outlet_buffer_reserve_samples()))),
 	  chunk_size_(chunk_size), info_(std::make_shared<stream_info_impl>(info)),
-	  send_buffer_(std::make_shared<send_buffer>(max_capacity)) {
+	  send_buffer_(std::make_shared<send_buffer>(max_capacity)),
+	  do_sync_(flags & transp_sync_blocking) {
+
+	if ((info.channel_format() == cft_string) && (flags & transp_sync_blocking)) {
+		LOG_F(WARNING, "sync push not supported for string-formatted streams. Reverting to async.");
+		do_sync_ = false;
+	}
+
 	ensure_lsl_initialized();
 	const api_config *cfg = api_config::get_instance();
 
@@ -143,8 +150,24 @@ void stream_outlet_impl::push_numeric_raw(const void *data, double timestamp, bo
 	if (lsl::api_config::get_instance()->force_default_timestamps()) timestamp = 0.0;
 	sample_p smp(
 		sample_factory_->new_sample(timestamp == 0.0 ? lsl_clock() : timestamp, pushthrough));
-	smp->assign_untyped(data);
-	send_buffer_->push_sample(smp);
+	if (!do_sync_) {
+		smp->assign_untyped(data);  // Note: Makes a copy!
+		send_buffer_->push_sample(smp);
+	} else {
+		if (timestamp == DEDUCED_TIMESTAMP) {
+			sync_buffs_.push_back(asio::buffer(&TAG_DEDUCED_TIMESTAMP, 1));
+		} else {
+			sync_buffs_.push_back(asio::buffer(&TAG_TRANSMITTED_TIMESTAMP, 1));
+			sync_buffs_.push_back(asio::buffer(&timestamp, sizeof(timestamp)));
+		}
+		sync_buffs_.push_back(asio::buffer(data, smp->datasize()));
+		if (pushthrough) {
+			for (auto &tcp_server : tcp_servers_)
+				tcp_server->write_all_blocking(sync_buffs_);
+			sync_buffs_.clear();
+		}
+	}
+
 }
 
 bool stream_outlet_impl::have_consumers() { return send_buffer_->have_consumers(); }
@@ -158,8 +181,23 @@ void stream_outlet_impl::enqueue(const T *data, double timestamp, bool pushthrou
 	if (lsl::api_config::get_instance()->force_default_timestamps()) timestamp = 0.0;
 	sample_p smp(
 		sample_factory_->new_sample(timestamp == 0.0 ? lsl_clock() : timestamp, pushthrough));
-	smp->assign_typed(data);
-	send_buffer_->push_sample(smp);
+	if (!do_sync_) {
+		smp->assign_typed(data);
+		send_buffer_->push_sample(smp);
+	} else {
+		if (timestamp == DEDUCED_TIMESTAMP) {
+			sync_buffs_.push_back(asio::buffer(&TAG_DEDUCED_TIMESTAMP, 1));
+		} else {
+			sync_buffs_.push_back(asio::buffer(&TAG_TRANSMITTED_TIMESTAMP, 1));
+			sync_buffs_.push_back(asio::buffer(&timestamp, sizeof(timestamp)));
+		}
+		sync_buffs_.push_back(asio::buffer(data, smp->datasize()));
+		if (pushthrough) {
+			for (auto &tcp_server : tcp_servers_)
+				tcp_server->write_all_blocking(sync_buffs_);
+			sync_buffs_.clear();
+		}
+	}
 }
 
 template void stream_outlet_impl::enqueue<char>(const char *data, double, bool);

src/stream_outlet_impl.h

@@ -10,6 +10,7 @@
 #include <string>
 #include <thread>
 #include <vector>
+#include <asio/buffer.hpp>
 
 using asio::ip::tcp;
 using asio::ip::udp;
@@ -35,9 +36,11 @@ class stream_outlet_impl {
 	 * @param max_capacity The maximum number of samples buffered for unresponsive receivers. If
 	 * more samples get pushed, the oldest will be dropped. The default is sufficient to hold a bit
 	 * more than 15 minutes of data at 512Hz, while consuming not more than ca. 512MB of RAM.
+	 * @param flags Bitwise-OR'd flags from lsl_transport_options_t
 	 */
 	stream_outlet_impl(
-		const stream_info_impl &info, int32_t chunk_size = 0, int32_t max_capacity = 512000);
+		const stream_info_impl &info, int32_t chunk_size = 0, int32_t max_capacity = 512000,
+		uint32_t flags = transp_default);
 
 	/**
 	 * Destructor.
@@ -317,6 +320,8 @@ class stream_outlet_impl {
 	stream_info_impl_p info_;
 	/// the single-producer, multiple-receiver send buffer
 	send_buffer_p send_buffer_;
+	/// Flag to indicate that push_* operations should be blocking synchronous. false by default.
+	bool do_sync_;
 	/// the IO service objects (two per stack: one for UDP and one for TCP)
 	std::vector<io_context_p> ios_;
 
@@ -329,6 +334,8 @@ class stream_outlet_impl {
 	std::vector<udp_server_p> responders_;
 	/// threads that handle the I/O operations (two per stack: one for UDP and one for TCP)
 	std::vector<thread_p> io_threads_;
+	/// buffers used in synchronous call to gather-write data directly to the socket.
+	std::vector<asio::const_buffer> sync_buffs_;
 };
 
 } // namespace lsl

src/tcp_server.cpp

@@ -222,36 +222,68 @@ void tcp_server::handle_accept_outcome(std::shared_ptr<client_session> newsessio
 	accept_next_connection();
 }
 
+// === synchronous transfer
+
+void tcp_server::write_all_blocking(std::vector<asio::const_buffer> buffs) {
+	std::lock_guard<std::recursive_mutex> lock(inflight_mut_);
+	std::size_t bytes_sent;
+	asio::error_code ec;
+	for (const auto &x : inflight_ready_) {
+		if (x.second && x.first->is_open()) {
+			bytes_sent = x.first->send(buffs, 0, ec);
+			if (ec) {
+				switch(ec.value()) {
+				case asio::error::broken_pipe:
+				case asio::error::connection_reset:
+					LOG_F(WARNING, "Broken Pipe / Connection Reset detected. Closing socket.");
+					inflight_ready_[x.first] = false;
+					post(*io_, [x]() {
+						close_inflight_socket(x);
+					});
+					// We leave it up to the client_session destructor to remove the socket.
+					break;
+				default:
+					LOG_F(WARNING, "Unhandled write_all_blocking error: %s.", ec.message().c_str());
+				}
+			}
+		}
+	}
+}
+
 // === graceful cancellation of in-flight sockets ===
 
 void tcp_server::register_inflight_socket(const tcp_socket_p &sock) {
 	std::lock_guard<std::recursive_mutex> lock(inflight_mut_);
-	inflight_.insert(sock);
+	inflight_ready_.insert({sock, false});
 }
 
 void tcp_server::unregister_inflight_socket(const tcp_socket_p &sock) {
 	std::lock_guard<std::recursive_mutex> lock(inflight_mut_);
-	inflight_.erase(sock);
+	inflight_ready_[sock] = false;
+	inflight_ready_.erase(sock);
 }
 
-void tcp_server::close_inflight_sockets() {
-	std::lock_guard<std::recursive_mutex> lock(inflight_mut_);
-	for (const auto &sock : inflight_)
-		post(*io_, [sock]() {
+void tcp_server::close_inflight_socket(std::pair<tcp_socket_p, bool> x) {
+	try {
+		if (x.first->is_open()) {
 			try {
-				if (sock->is_open()) {
-					try {
-						// (in some cases shutdown may fail)
-						sock->shutdown(sock->shutdown_both);
-					} catch (...) {}
-					sock->close();
-				}
-			} catch (std::exception &e) {
-				LOG_F(WARNING, "Error during shutdown_and_close: %s", e.what());
-			}
-		});
+				// (in some cases shutdown may fail)
+				x.first->shutdown(x.first->shutdown_both);
+			} catch (...) {}
+			x.first->close();
+		}
+	} catch (std::exception &e) {
+		LOG_F(WARNING, "Error during shutdown_and_close: %s", e.what());
+	}
 }
 
+void tcp_server::close_inflight_sockets() {
+	std::lock_guard<std::recursive_mutex> lock(inflight_mut_);
+	for (const auto &x : inflight_ready_) {
+		inflight_ready_[x.first] = false;
+		post(*io_, [x]() { close_inflight_socket(x); });
+	}
+}
 
 // === implementation of the client_session class ===
 
@@ -511,7 +543,11 @@ void client_session::handle_send_feedheader_outcome(err_t err, std::size_t n) {
 		feedbuf_.consume(n);
 		// register outstanding work at the server (will be unregistered at session destruction)
 		work_ = std::make_shared<work_p::element_type>(serv_->io_->get_executor());
-		// spawn a sample transfer thread
+		serv_->inflight_ready_[sock_] = true;
+		if (serv_->transfer_is_sync_)
+			LOG_F(WARNING, "Using synchronous blocking transfers for new client session.");
+		// spawn a sample transfer thread.
+		// TODO: only spawn thread in async, but then we need `this` to belong to something else.
 		std::thread(&client_session::transfer_samples_thread, this, shared_from_this()).detach();
 	} catch (std::exception &e) {
 		LOG_F(WARNING, "Unexpected error while handling the feedheader send outcome: %s", e.what());