Revert the singleton PR

It turns out that this isn't working the way it was intended to.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>

core/btdiscovery.cpp

@@ -15,6 +15,7 @@ extern QMap<QString, dc_descriptor_t *> descriptorLookup;
 namespace {
 	QHash<QString, QBluetoothDeviceInfo> btDeviceInfo;
 }
+BTDiscovery *BTDiscovery::m_instance = NULL;
 
 static dc_descriptor_t *getDeviceType(QString btName)
 // central function to convert a BT name to a Subsurface known vendor/model pair
@@ -138,6 +139,11 @@ BTDiscovery::BTDiscovery(QObject*) : m_btValid(false),
 	m_showNonDiveComputers(false),
 	discoveryAgent(nullptr)
 {
+	if (m_instance) {
+		qDebug() << "trying to create an additional BTDiscovery object";
+		return;
+	}
+	m_instance = this;
 #if defined(BT_SUPPORT)
 	QLoggingCategory::setFilterRules(QStringLiteral("qt.bluetooth* = true"));
 	BTDiscoveryReDiscover();
@@ -196,11 +202,19 @@ void BTDiscovery::BTDiscoveryReDiscover()
 
 BTDiscovery::~BTDiscovery()
 {
+	m_instance = NULL;
 #if defined(BT_SUPPORT)
 	delete discoveryAgent;
 #endif
 }
 
+BTDiscovery *BTDiscovery::instance()
+{
+	if (!m_instance)
+		m_instance = new BTDiscovery();
+	return m_instance;
+}
+
 #if defined(BT_SUPPORT)
 extern void addBtUuid(QBluetoothUuid uuid);
 extern QHash<QString, QStringList> productList;

core/btdiscovery.h

@@ -10,7 +10,6 @@
 #include <QBluetoothDeviceDiscoveryAgent>
 #include <QBluetoothUuid>
 #include "core/libdivecomputer.h"
-#include "core/singleton.h"
 
 #if defined(Q_OS_ANDROID)
 #include <QAndroidJniObject>
@@ -24,12 +23,13 @@ QString extractBluetoothAddress(const QString &address);
 QString extractBluetoothNameAddress(const QString &address, QString &name);
 QBluetoothDeviceInfo getBtDeviceInfo(const QString &devaddr);
 
-class BTDiscovery : public QObject, public SillySingleton<BTDiscovery> {
+class BTDiscovery : public QObject {
 	Q_OBJECT
 
 public:
 	BTDiscovery(QObject *parent = NULL);
 	~BTDiscovery();
+	static BTDiscovery *instance();
 
 	struct btPairedDevice {
 		QString address;
@@ -57,6 +57,7 @@ public:
 	void discoverAddress(QString address);
 
 private:
+	static BTDiscovery *m_instance;
 	bool m_btValid;
 	bool m_showNonDiveComputers;
 

core/gpslocation.cpp

@@ -15,12 +15,16 @@
 #include <QApplication>
 #include <QTimer>
 
+GpsLocation *GpsLocation::m_Instance = NULL;
+
 GpsLocation::GpsLocation(void (*showMsgCB)(const char *), QObject *parent) :
 	QObject(parent),
 	m_GpsSource(0),
 	waitingForPosition(false),
 	haveSource(UNKNOWN)
 {
+	Q_ASSERT_X(m_Instance == NULL, "GpsLocation", "GpsLocation recreated");
+	m_Instance = this;
 	showMessageCB = showMsgCB;
 	// create a QSettings object that's separate from the main application settings
 	geoSettings = new QSettings(QSettings::NativeFormat, QSettings::UserScope,
@@ -33,6 +37,23 @@ GpsLocation::GpsLocation(void (*showMsgCB)(const char *), QObject *parent) :
 	connect(qPrefLocationService::instance(), SIGNAL(time_thresholdChanged(int)), this, SLOT(setGpsTimeThreshold(int)));
 }
 
+GpsLocation *GpsLocation::instance()
+{
+	Q_ASSERT(m_Instance != NULL);
+
+	return m_Instance;
+}
+
+bool GpsLocation::hasInstance()
+{
+	return m_Instance != NULL;
+}
+
+GpsLocation::~GpsLocation()
+{
+	m_Instance = NULL;
+}
+
 void GpsLocation::setGpsTimeThreshold(int seconds)
 {
 	if (m_GpsSource) {

core/gpslocation.h

@@ -24,6 +24,9 @@ class GpsLocation : public QObject {
 	Q_OBJECT
 public:
 	GpsLocation(void (*showMsgCB)(const char *msg), QObject *parent);
+	~GpsLocation();
+	static GpsLocation *instance();
+	static bool hasInstance();
 	bool applyLocations();
 	int getGpsNum() const;
 	bool hasLocationsSource();
@@ -40,6 +43,7 @@ private:
 	QNetworkReply *reply;
 	QString userAgent;
 	void (*showMessageCB)(const char *msg);
+	static GpsLocation *m_Instance;
 	bool waitingForPosition;
 	QMap<qint64, gpsTracker> m_trackers;
 	QList<gpsTracker> m_deletedTrackers;

core/singleton.h

@@ -1,74 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * We use singletons in numerous places. In combination with QML this gives
- * us a very fundamental problem, because QML likes to allocate objects by
- * itself. There are known workarounds, but currently we use idiosyncratic
- * singleton classes, which initialize the global instance pointer in the
- * constructor. Things get even more complicated if the same singleton is used
- * on mobile and on desktop. The latter might want to simply use the classical
- * instance() function without having to initialize the singleton first, as
- * that would beat the purpose of the instance() method.
- *
- * The template defined here, SillySingleton, codifies all this. Simply derive
- * a class from this template:
- *	class X : public SillySingleton<X> {
- *		...
- *	};
- * This will generate an instance() method. This will do the right thing for
- * both methods: explicit construction of the singleton via new or implicit
- * by calling the instance() method. It will also generate warnings if a
- * singleton class is generated more than once (i.e. first instance() is called
- * and _then_ new).
- *
- * In the long run we should get rid of all users of this class.
- */
-#ifndef SINGLETON_H
-#define SINGLETON_H
-
-#include <typeinfo>
-#include <QtGlobal>
-
-// 1) Declaration
-template<typename T>
-class SillySingleton {
-	static T *self;
-protected:
-	SillySingleton();
-	~SillySingleton();
-public:
-	static T *instance();
-};
-
-template<typename T>
-T *SillySingleton<T>::self = nullptr;
-
-// 2) Implementation
-
-template<typename T>
-SillySingleton<T>::SillySingleton()
-{
-	if (self)
-		qWarning("Generating second instance of singleton %s", typeid(T).name());
-	self = static_cast<T *>(this);
-	qDebug("Generated singleton %s", typeid(T).name());
-}
-
-template<typename T>
-SillySingleton<T>::~SillySingleton()
-{
-	if (self == this)
-		self = nullptr;
-	else
-		qWarning("Destroying unknown instance of singleton %s", typeid(T).name());
-	qDebug("Destroyed singleton %s", typeid(T).name());
-}
-
-template<typename T>
-T *SillySingleton<T>::instance()
-{
-	if (!self)
-		new T;
-	return self;
-}
-
-#endif