SQL: Make QSqlDatabase::DriverDict creation thread-safe

Make the QSqlDatabase::DriverDict thread-safe and make sure it's
properly cleaned up on destruction.

Fixes: QTBUG-112961
Change-Id: I1ff70e477579231754ef829fdede944d6042894d
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit 048a68c)

src/sql/kernel/qsqldatabase.cpp

@@ -10,6 +10,7 @@
 #include "qsqldriver.h"
 #include "qsqldriverplugin.h"
 #include "qsqlindex.h"
+#include "QtCore/qapplicationstatic.h"
 #include "private/qfactoryloader_p.h"
 #include "private/qsqlnulldriver_p.h"
 #include "qmutex.h"
@@ -26,8 +27,6 @@ Q_GLOBAL_STATIC_WITH_ARGS(QFactoryLoader, loader,
 
 const char *QSqlDatabase::defaultConnection = const_cast<char *>("qt_sql_default_connection");
 
-typedef QHash<QString, QSqlDriverCreatorBase*> DriverDict;
-
 class QConnectionDict: public QHash<QString, QSqlDatabase>
 {
 public:
@@ -46,6 +45,14 @@ class QConnectionDict: public QHash<QString, QSqlDatabase>
 };
 Q_GLOBAL_STATIC(QConnectionDict, dbDict)
 
+namespace {
+    struct DriverDict : public QHash<QString, QSqlDriverCreatorBase*>
+    {
+        ~DriverDict();
+    };
+}
+Q_APPLICATION_STATIC(DriverDict, qtDriverDict)
+
 class QSqlDatabasePrivate
 {
 public:
@@ -121,23 +128,15 @@ void QSqlDatabasePrivate::cleanConnections()
     dict->clear();
 }
 
-static bool qDriverDictInit = false;
-static void cleanDriverDict()
+DriverDict::~DriverDict()
 {
-    qDeleteAll(QSqlDatabasePrivate::driverDict());
-    QSqlDatabasePrivate::driverDict().clear();
+    qDeleteAll(*this);
     QSqlDatabasePrivate::cleanConnections();
-    qDriverDictInit = false;
 }
 
 DriverDict &QSqlDatabasePrivate::driverDict()
 {
-    static DriverDict dict;
-    if (!qDriverDictInit) {
-        qDriverDictInit = true;
-        qAddPostRoutine(cleanDriverDict);
-    }
-    return dict;
+    return *qtDriverDict();
 }
 
 QSqlDatabasePrivate *QSqlDatabasePrivate::shared_null()
@@ -511,7 +510,8 @@ QStringList QSqlDatabase::drivers()
                 list << it.value();
     }
 
-    DriverDict dict = QSqlDatabasePrivate::driverDict();
+    QReadLocker locker(&dbDict()->lock);
+    const DriverDict &dict = QSqlDatabasePrivate::driverDict();
     for (DriverDict::const_iterator i = dict.constBegin(); i != dict.constEnd(); ++i) {
         if (!list.contains(i.key()))
             list << i.key();
@@ -649,7 +649,8 @@ void QSqlDatabasePrivate::init(const QString &type)
     drvName = type;
 
     if (!driver) {
-        DriverDict dict = QSqlDatabasePrivate::driverDict();
+        QReadLocker locker(&dbDict()->lock);
+        const DriverDict &dict = QSqlDatabasePrivate::driverDict();
         for (DriverDict::const_iterator it = dict.constBegin();
              it != dict.constEnd() && !driver; ++it) {
             if (type == it.key()) {

tests/auto/sql/kernel/qsql/tst_qsql.cpp

@@ -135,6 +135,10 @@ void tst_QSql::open()
 
 void tst_QSql::openInvalid()
 {
+    int argc = 1;
+    char *argv[] = { const_cast<char*>(QTest::currentAppName()) };
+    QCoreApplication app(argc, argv, false);
+
     QSqlDatabase db;
     QVERIFY(!db.open());