inability to connect to DBus.Properties resolved

Plugins/ZShell/lidwatcher.cpp

@@ -3,7 +3,9 @@
 #include <QtDBus/QDBusConnection>
 #include <QtDBus/QDBusMessage>
 #include <QtDBus/QDBusReply>
+#include <QtDBus/QDBusServiceWatcher>
 #include <QLoggingCategory>
+#include <QTimer>
 
 Q_LOGGING_CATEGORY(lcLidWatcher, "ZShell.lidwatcher", QtInfoMsg)
 
@@ -15,32 +17,32 @@ static constexpr auto kLogin1Interface = "org.freedesktop.login1.Manager";
 static constexpr auto kDBusPropertiesInterface =
 	"org.freedesktop.DBus.Properties";
 
-LidWatcher::LidWatcher(QObject* parent) : QObject(parent), m_available(false) {
+LidWatcher::LidWatcher(QObject* parent)
+	: QObject(parent)
+	, m_watcher(nullptr)
+	, m_pollTimer(nullptr)
+	, m_available(false)
+{
 	QDBusConnection bus = QDBusConnection::systemBus();
-	m_available = bus.isConnected();
-
-	if (!m_available) {
+	if (!bus.isConnected()) {
 		qCWarning(lcLidWatcher) << "system bus unavailable";
 		emit availableChanged();
 		return;
 	}
 
-	const auto ok = bus.connect(
+	m_pollTimer = new QTimer(this);
+	m_pollTimer->setInterval(5000);
+	connect(m_pollTimer, &QTimer::timeout, this, &LidWatcher::queryLidState);
+
+	m_watcher = new QDBusServiceWatcher(
 		kLogin1Service,
-		kLogin1Path,
-		kDBusPropertiesInterface,
-		"PropertiesChanged",
-		this,
-		SLOT(onPropertiesChanged(QString, QVariantMap, QStringList)));
+		bus,
+		QDBusServiceWatcher::WatchForRegistration,
+		this);
+	connect(m_watcher, &QDBusServiceWatcher::serviceRegistered,
+			this, &LidWatcher::tryConnect);
 
-	m_available = ok;
-	emit availableChanged();
-	if (!m_available) {
-		qCWarning(lcLidWatcher) << "login1 properties signal unavailable";
-		return;
-	}
-
-	queryInitialState();
+	tryConnect();
 }
 
 bool LidWatcher::available() const {
@@ -51,7 +53,37 @@ LidWatcher::LidState LidWatcher::state() const {
 	return m_state;
 }
 
-void LidWatcher::queryInitialState() {
+void LidWatcher::tryConnect() {
+	QDBusConnection bus = QDBusConnection::systemBus();
+
+	const auto connected = bus.connect(
+		kLogin1Service,
+		kLogin1Path,
+		kDBusPropertiesInterface,
+		"PropertiesChanged",
+		this,
+		SLOT(onPropertiesChanged(QString, QVariantMap, QStringList)));
+
+	queryLidState();
+
+	if (connected) {
+		m_pollTimer->stop();
+		qCInfo(lcLidWatcher) << "login1 PropertiesChanged connected";
+	} else {
+		qCWarning(lcLidWatcher)
+			<< "login1 PropertiesChanged unavailable, polling";
+		if (!m_pollTimer->isActive()) {
+			m_pollTimer->start();
+}
+	}
+
+	if (!m_available) {
+		m_available = true;
+		emit availableChanged();
+	}
+}
+
+void LidWatcher::queryLidState() {
 	auto msg = QDBusMessage::createMethodCall(kLogin1Service,
 											  kLogin1Path,
 											  kDBusPropertiesInterface,
@@ -63,8 +95,11 @@ void LidWatcher::queryInitialState() {
 			<< "cannot query LidClosed:" << reply.error().message();
 		return;
 	}
-	m_state = reply.value().toBool() ? Closed : Opened;
-	emit stateChanged();
+	const auto newState = reply.value().toBool() ? Closed : Opened;
+	if (m_state != newState) {
+		m_state = newState;
+		emit stateChanged();
+	}
 }
 
 void LidWatcher::onPropertiesChanged(const QString& interface,
@@ -76,8 +111,11 @@ void LidWatcher::onPropertiesChanged(const QString& interface,
 	if (!changed.contains("LidClosed")) {
 		return;
 	}
-	m_state = changed.value("LidClosed").toBool() ? Closed : Opened;
-	emit stateChanged();
+	const auto newState = changed.value("LidClosed").toBool() ? Closed : Opened;
+	if (m_state != newState) {
+		m_state = newState;
+		emit stateChanged();
+	}
 }
 
 } // namespace ZShell