Cloud Service creates unnecessary GlobalContext instances (#4823)

Changes GlobalContext to hide the constructor so this doesn't occur again since it is a singleton.

src/Cloud/CloudService.cpp

@@ -968,8 +968,8 @@ CloudServiceSyncDialog::cancelClicked()
 void
 CloudServiceSyncDialog::refreshClicked()
 {
-    double distanceFactor = GlobalContext().useMetricUnits ? 1.0 : MILES_PER_KM;
-    QString distanceUnits = GlobalContext().useMetricUnits ? tr("km") : tr("mi");
+    double distanceFactor = GlobalContext::context()->useMetricUnits ? 1.0 : MILES_PER_KM;
+    QString distanceUnits = GlobalContext::context()->useMetricUnits ? tr("km") : tr("mi");
 
     progressLabel->setText(tr(""));
     progressBar->setMinimum(0);

src/Core/Context.cpp

@@ -33,8 +33,7 @@
 #include <QMutex>
 #include <QWebEngineProfile>
 
-// singleton
-static GlobalContext *globalContext = NULL;
+
 static QList<Context*> _contexts;
 
 GlobalContext::GlobalContext()
@@ -44,6 +43,14 @@ GlobalContext::GlobalContext()
     readConfig(0); // don't reread user metrics just yet
 }
 
+GlobalContext*
+GlobalContext::context()
+{
+    // Meyer's singleton pattern
+    static GlobalContext globalContext; // Guaranteed thread-safe initialization
+    return &globalContext;
+}
+
 void
 GlobalContext::notifyConfigChanged(qint32 state)
 {
@@ -130,11 +137,6 @@ GlobalContext::userMetricsConfigChanged()
     SpecialFields::getInstance().reloadFields();
 }
 
-GlobalContext *GlobalContext::context()
-{
-    if (globalContext == NULL) globalContext = new GlobalContext();
-    return globalContext;
-}
 
 bool Context::isValid(Context *p) { return p != NULL &&_contexts.contains(p); }
 

src/Core/Context.h

@@ -82,8 +82,8 @@ class GlobalContext : public QObject
 
     public:
 
-        GlobalContext();
         static GlobalContext *context();
+
         void notifyConfigChanged(qint32);
 
         // metadata etc
@@ -100,6 +100,11 @@ class GlobalContext : public QObject
     signals:
         void configChanged(qint32); // for global widgets that aren't athlete specific
 
+    private:
+        // singleton pattern
+        GlobalContext();
+        GlobalContext(const GlobalContext&) = delete;
+        GlobalContext& operator=(const GlobalContext&) = delete;
 };
 
 class RideNavigator;