GUI2/Network Transmission: delegate connection polling to a worker thread

src/gui/dialogs/network_transmission.cpp

@@ -27,36 +27,69 @@
 #include "serialization/string_utils.hpp"
 #include "wesnothd_connection.hpp"
 
+#include <chrono>
+
 namespace gui2
 {
 namespace dialogs
 {
+using namespace std::chrono_literals;
 
 REGISTER_DIALOG(network_transmission)
 
+network_transmission::pump_monitor::pump_monitor(connection_data*& connection)
+	: connection_(connection)
+	, window_()
+	, completed_(0)
+	, total_(0)
+	, poller_(std::async(std::launch::async, [this]() {
+		while(true) {
+			// connection_ will be null if we reset the ptr in the main thread before canceling the dialog
+			if(!connection_) {
+				return false;
+			}
+
+			// Check for updates
+			connection_->poll();
+
+			if(connection_->finished()) {
+				return true;
+			}
+
+			completed_ = connection_->current();
+			total_ = connection_->total();
+
+			std::this_thread::sleep_for(10ms);
+		}
+	}))
+{
+}
+
 void network_transmission::pump_monitor::process(events::pump_info&)
 {
-	if(!window_)
+	if(!window_) {
 		return;
-	connection_->poll();
-	if(connection_->finished()) {
+	}
+
+	// Check if the thread is complete. If it is, loading is done.
+	if(poller_.wait_for(0ms) == std::future_status::ready && poller_.get()) {
 		window_.get().set_retval(retval::OK);
-	} else {
-		std::size_t completed, total;
-			completed = connection_->current();
-			total = connection_->total();
-		if(total) {
-			find_widget<progress_bar>(&(window_.get()), "progress", false)
-					.set_percentage((completed * 100.) / total);
+		return;
+	}
 
-			std::stringstream ss;
-			ss << utils::si_string(completed, true, _("unit_byte^B")) << "/"
-			   << utils::si_string(total, true, _("unit_byte^B"));
+	if(total_) {
+		find_widget<progress_bar>(&(window_.get()), "progress", false)
+			.set_percentage((completed_ * 100.) / total_);
 
-			find_widget<label>(&(window_.get()), "numeric_progress", false)
-					.set_label(ss.str());
-			window_->invalidate_layout();
-		}
+		std::ostringstream ss;
+		ss
+			<< utils::si_string(completed_, true, _("unit_byte^B")) << "/"
+			<< utils::si_string(total_, true, _("unit_byte^B"));
+
+		find_widget<label>(&(window_.get()), "numeric_progress", false)
+			.set_label(ss.str());
+
+		window_->invalidate_layout();
 	}
 }
 
@@ -76,8 +109,8 @@ void network_transmission::pre_show(window& window)
 {
 	// ***** ***** ***** ***** Set up the widgets ***** ***** ***** *****
 	if(!subtitle_.empty()) {
-		label& subtitle_label
-				= find_widget<label>(&window, "subtitle", false);
+		label& subtitle_label = find_widget<label>(&window, "subtitle", false);
+
 		subtitle_label.set_label(subtitle_);
 		subtitle_label.set_use_markup(true);
 	}
@@ -90,7 +123,18 @@ void network_transmission::post_show(window& /*window*/)
 	pump_monitor_.window_.reset();
 
 	if(get_retval() == retval::CANCEL) {
-		connection_->cancel();
+		// The worker thread holds a reference to connection_ and checks whether it's null before polling.
+		// The actual object to which connection_ is pointing will be destroyed by cancel(), so we're
+		// setting connection_ to null here before that so the worker thread will exit next run.
+		connection_data* const connection_ptr_copy = connection_;
+		connection_ = nullptr;
+
+		// Wait for the current polling loop to conclude before exiting so we don't invalidate the pointer
+		// mid-loop. The thread should return false if connection_ is null.
+		pump_monitor_.poller_.wait();
+		assert(pump_monitor_.poller_.get() == false);
+
+		connection_ptr_copy->cancel();
 	}
 }
 

src/gui/dialogs/network_transmission.hpp

@@ -21,6 +21,9 @@
 
 #include <boost/optional.hpp>
 
+#include <atomic>
+#include <future>
+
 namespace gui2
 {
 namespace dialogs
@@ -53,15 +56,17 @@ private:
 	class pump_monitor : public events::pump_monitor
 	{
 	public:
-		connection_data*& connection_;
-		virtual void process(events::pump_info&);
+		virtual void process(events::pump_info&) override;
 
-		pump_monitor(connection_data*& connection)
-			: connection_(connection), window_()
-		{
-		}
+		pump_monitor(connection_data*& connection);
+
+		connection_data*& connection_;
 
 		boost::optional<window&> window_;
+
+		std::atomic_size_t completed_, total_;
+
+		std::future<bool> poller_;
 	} pump_monitor_;
 
 public: