Perform autosaves on a background thread rather than blocking the UI

src/subs_controller.cpp

@@ -32,6 +32,7 @@
 #include "subtitle_format.h"
 #include "text_selection_controller.h"
 
+#include <libaegisub/dispatch.h>
 #include <libaegisub/format_path.h>
 #include <libaegisub/fs.h>
 #include <libaegisub/path.h>
@@ -146,27 +147,18 @@ SubsController::SubsController(agi::Context *context)
 : context(context)
 , undo_connection(context->ass->AddUndoManager(&SubsController::OnCommit, this))
 , text_selection_connection(context->textSelectionController->AddSelectionListener(&SubsController::OnTextSelectionChanged, this))
+, autosave_queue(agi::dispatch::Create())
 {
 	autosave_timer_changed(&autosave_timer);
 	OPT_SUB("App/Auto/Save", [=] { autosave_timer_changed(&autosave_timer); });
 	OPT_SUB("App/Auto/Save Every Seconds", [=] { autosave_timer_changed(&autosave_timer); });
-
-	autosave_timer.Bind(wxEVT_TIMER, [=](wxTimerEvent&) {
-		try {
-			auto fn = AutoSave();
-			if (!fn.empty())
-				context->frame->StatusTimeout(fmt_tl("File backup saved as \"%s\".", fn));
-		}
-		catch (const agi::Exception& err) {
-			context->frame->StatusTimeout(to_wx("Exception when attempting to autosave file: " + err.GetMessage()));
-		}
-		catch (...) {
-			context->frame->StatusTimeout("Unhandled exception when attempting to autosave file.");
-		}
-	});
+	autosave_timer.Bind(wxEVT_TIMER, [=](wxTimerEvent&) { AutoSave(); });
 }
 
-SubsController::~SubsController() { }
+SubsController::~SubsController() {
+	// Make sure there are no autosaves in progress
+	autosave_queue->Sync([]{ });
+}
 
 void SubsController::SetSelectionController(SelectionController *selection_controller) {
 	active_line_connection = context->selectionController->AddActiveLineListener(&SubsController::OnActiveLineChanged, this);
@@ -260,26 +252,43 @@ int SubsController::TryToClose(bool allow_cancel) const {
 	return result;
 }
 
-agi::fs::path SubsController::AutoSave() {
+void SubsController::AutoSave() {
 	if (commit_id == autosaved_commit_id)
-		return "";
+		return;
 
-	auto path = config::path->Decode(OPT_GET("Path/Auto/Save")->GetString());
-	if (path.empty())
-		path = filename.parent_path();
-
-	agi::fs::CreateDirectory(path);
+	auto directory = config::path->Decode(OPT_GET("Path/Auto/Save")->GetString());
+	if (directory.empty())
+		directory = filename.parent_path();
 
 	auto name = filename.filename();
 	if (name.empty())
 		name = "Untitled";
 
-	path /= agi::format("%s.%s.AUTOSAVE.ass", name.string(), agi::util::strftime("%Y-%m-%d-%H-%M-%S"));
-
-	SubtitleFormat::GetWriter(path)->WriteFile(context->ass.get(), path, 0);
 	autosaved_commit_id = commit_id;
+	auto frame = context->frame;
+	auto subs_copy = new AssFile(*context->ass);
+	autosave_queue->Async([subs_copy, name, directory, frame] {
+		wxString msg;
+		std::unique_ptr<AssFile> subs(subs_copy);
 
-	return path;
+		try {
+			agi::fs::CreateDirectory(directory);
+			auto path = directory /  agi::format("%s.%s.AUTOSAVE.ass", name.string(),
+			                                     agi::util::strftime("%Y-%m-%d-%H-%M-%S"));
+			SubtitleFormat::GetWriter(path)->WriteFile(subs.get(), path, 0);
+			msg = fmt_tl("File backup saved as \"%s\".", path);
+		}
+		catch (const agi::Exception& err) {
+			msg = to_wx("Exception when attempting to autosave file: " + err.GetMessage());
+		}
+		catch (...) {
+			msg = "Unhandled exception when attempting to autosave file.";
+		}
+
+		agi::dispatch::Main().Async([frame, msg] {
+			frame->StatusTimeout(msg);
+		});
+	});
 }
 
 bool SubsController::CanSave() const {

src/subs_controller.h

@@ -22,7 +22,12 @@
 #include <wx/timer.h>
 
 class SelectionController;
-namespace agi { struct Context; }
+namespace agi {
+	namespace dispatch {
+		class Queue;
+	}
+	struct Context;
+}
 struct AssFileCommit;
 struct ProjectProperties;
 
@@ -47,6 +52,9 @@ class SubsController {
 	/// Timer for triggering autosaves
 	wxTimer autosave_timer;
 
+	/// Queue which autosaves are performed on
+	std::unique_ptr<agi::dispatch::Queue> autosave_queue;
+
 	/// A new file has been opened (filename)
 	agi::signal::Signal<agi::fs::path> FileOpen;
 	/// The file has been saved
@@ -58,6 +66,9 @@ class SubsController {
 	/// Set the filename, updating things like the MRU and last used path
 	void SetFileName(agi::fs::path const& file);
 
+	/// Autosave the file if there have been any chances since the last autosave
+	void AutoSave();
+
 	void OnCommit(AssFileCommit c);
 	void OnActiveLineChanged();
 	void OnSelectionChanged();
@@ -97,10 +108,6 @@ public:
 	/// @return wxYES, wxNO or wxCANCEL (note: all three are true in a boolean context)
 	int TryToClose(bool allow_cancel = true) const;
 
-	/// @brief Autosave the file if there have been any chances since the last autosave
-	/// @return File name used or empty if no save was performed
-	agi::fs::path AutoSave();
-
 	/// Can the file be saved in its current format?
 	bool CanSave() const;