From 7c05b1788e73e5ffa59be70e1af6609f7baa2593 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Mon, 27 Jul 2020 20:25:52 -0400
Subject: [PATCH] Ensures proper thread confinement for `updateStatusBarText`.

---
 OSBindings/Qt/mainwindow.cpp | 11 ++++++-----
 OSBindings/Qt/mainwindow.h   |  6 +++++-
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/OSBindings/Qt/mainwindow.cpp b/OSBindings/Qt/mainwindow.cpp
index 3afe5e70e..8286fe45f 100644
--- a/OSBindings/Qt/mainwindow.cpp
+++ b/OSBindings/Qt/mainwindow.cpp
@@ -1338,24 +1338,25 @@ void MainWindow::addActivityObserver() {
 }
 
 void MainWindow::register_led(const std::string &name) {
+	std::lock_guard guard(ledStatusesLock);
 	ledStatuses[name] = false;
-	updateStatusBarText();
+	QMetaObject::invokeMethod(this, "updateStatusBarText");
 }
 
 void MainWindow::set_led_status(const std::string &name, bool isLit) {
+	std::lock_guard guard(ledStatusesLock);
 	ledStatuses[name] = isLit;
-	updateStatusBarText();	// Assumption here: Qt's attempt at automatic thread confinement will work here.
+	QMetaObject::invokeMethod(this, "updateStatusBarText");
 }
 
 void MainWindow::updateStatusBarText() {
 	QString fullText;
-	bool isFirst = true;
+	std::lock_guard guard(ledStatusesLock);
 	for(const auto &pair: ledStatuses) {
-		if(!isFirst) fullText += " | ";
+		if(!fullText.isEmpty()) fullText += " | ";
 		fullText += QString::fromStdString(pair.first);
 		fullText += " ";
 		fullText += pair.second ? "■" : "□";
-		isFirst = false;
 	}
 	statusBar()->showMessage(fullText);
 }
diff --git a/OSBindings/Qt/mainwindow.h b/OSBindings/Qt/mainwindow.h
index 4bbe4d108..91f3cab2d 100644
--- a/OSBindings/Qt/mainwindow.h
+++ b/OSBindings/Qt/mainwindow.h
@@ -5,6 +5,7 @@
 #include <QMainWindow>
 
 #include <memory>
+#include <mutex>
 #include <optional>
 
 #include "audiobuffer.h"
@@ -80,6 +81,7 @@ class MainWindow : public QMainWindow, public Outputs::Speaker::Speaker::Delegat
 
 	private slots:
 		void startMachine();
+		void updateStatusBarText();
 
 	private:
 		void start_appleII();
@@ -144,9 +146,11 @@ class MainWindow : public QMainWindow, public Outputs::Speaker::Speaker::Delegat
 
 		void register_led(const std::string &) override;
 		void set_led_status(const std::string &, bool) override;
+
+		std::recursive_mutex ledStatusesLock;
 		std::map<std::string, bool> ledStatuses;
+
 		void addActivityObserver();
-		void updateStatusBarText();
 };
 
 #endif // MAINWINDOW_H