C++: do not run GC when exiting.

This operation is quite costly if a lot of files are involved, and in
case of exiting Creator, it's also useless.

Change-Id: I97d178d47a3a2f6b214f7ebc45c871edd26b8286
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>

src/plugins/cpptools/cppmodelmanager.cpp

@@ -626,6 +626,7 @@ CppModelManager *CppModelManager::instance()
 
 CppModelManager::CppModelManager(QObject *parent)
     : CppModelManagerInterface(parent)
+    , m_enableGC(true)
     , m_completionAssistProvider(0)
     , m_highlightingFactory(0)
     , m_indexingSupporter(0)
@@ -656,6 +657,9 @@ CppModelManager::CppModelManager(QObject *parent)
     connect(session, SIGNAL(aboutToUnloadSession(QString)),
             this, SLOT(onAboutToUnloadSession()));
 
+    connect(Core::ICore::instance(), SIGNAL(coreAboutToClose()),
+            this, SLOT(onCoreAboutToClose()));
+
     qRegisterMetaType<CPlusPlus::Document::Ptr>("CPlusPlus::Document::Ptr");
 
     // thread connections
@@ -1209,8 +1213,16 @@ void CppModelManager::onAboutToUnloadSession()
     GC();
 }
 
+void CppModelManager::onCoreAboutToClose()
+{
+    m_enableGC = false;
+}
+
 void CppModelManager::GC()
 {
+    if (!m_enableGC)
+        return;
+
     Snapshot currentSnapshot = snapshot();
     QSet<QString> processed;
     QStringList todo = projectFiles();

src/plugins/cpptools/cppmodelmanager.h

@@ -171,6 +171,7 @@ private Q_SLOTS:
     void onExtraDiagnosticsUpdated(const QString &fileName);
     void onAboutToRemoveProject(ProjectExplorer::Project *project);
     void onAboutToUnloadSession();
+    void onCoreAboutToClose();
     void onProjectAdded(ProjectExplorer::Project *project);
     void postEditorUpdate();
     void updateEditorSelections();
@@ -195,6 +196,7 @@ private:
 
 private:
     CPlusPlus::Snapshot m_snapshot;
+    bool m_enableGC;
 
     // cache
     bool m_dirty;