Add overload of QSqlDatabase::cloneDatabase to allow cloning cross threads

Since QSqlDatabase::database() cannot be used to access another database
from another thread, then the overload is provided to make it possible
to clone with just the connection name. This will handle the cloning
internally safely then.

Fixes: QTBUG-72545
Change-Id: I861cc5aa2c38c1e3797f6f086594a1228f05bada
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>

src/sql/kernel/qsqldatabase.cpp

@@ -1379,6 +1379,40 @@ QSqlDatabase QSqlDatabase::cloneDatabase(const QSqlDatabase &other, const QStrin
     return db;
 }
 
+/*!
+    \since 5.13
+    \overload
+
+    Clones the database connection \a other and stores it as \a
+    connectionName. All the settings from the original database, e.g.
+    databaseName(), hostName(), etc., are copied across. Does nothing
+    if \a other is an invalid database. Returns the newly created
+    database connection.
+
+    \note The new connection has not been opened. Before using the new
+    connection, you must call open().
+
+    This overload is useful when cloning the database in another thread to the
+    one that is used by the database represented by \a other.
+*/
+
+QSqlDatabase QSqlDatabase::cloneDatabase(const QString &other, const QString &connectionName)
+{
+    const QConnectionDict *dict = dbDict();
+    Q_ASSERT(dict);
+
+    dict->lock.lockForRead();
+    QSqlDatabase otherDb = dict->value(other);
+    dict->lock.unlock();
+    if (!otherDb.isValid())
+        return QSqlDatabase();
+
+    QSqlDatabase db(otherDb.driverName());
+    db.d->copy(otherDb.d);
+    QSqlDatabasePrivate::addDatabase(db, connectionName);
+    return db;
+}
+
 /*!
     \since 4.4
 

src/sql/kernel/qsqldatabase.h

@@ -118,6 +118,7 @@ public:
     static QSqlDatabase addDatabase(QSqlDriver* driver,
                                  const QString& connectionName = QLatin1String(defaultConnection));
     static QSqlDatabase cloneDatabase(const QSqlDatabase &other, const QString& connectionName);
+    static QSqlDatabase cloneDatabase(const QString &other, const QString& connectionName);
     static QSqlDatabase database(const QString& connectionName = QLatin1String(defaultConnection),
                                  bool open = true);
     static void removeDatabase(const QString& connectionName);

tests/auto/sql/kernel/qsqldatabase/tst_qsqldatabase.cpp

@@ -2422,6 +2422,16 @@ public slots:
 
         QSqlDatabase invalidDb = QSqlDatabase::database("invalid");
         QVERIFY(!invalidDb.isValid());
+
+        {
+            QSqlDatabase clonedDatabase = QSqlDatabase::cloneDatabase(dbName, "CloneDB");
+            QVERIFY(!clonedDatabase.isOpen());
+            QVERIFY(clonedDatabase.isValid());
+            QVERIFY(clonedDatabase.open());
+            QVERIFY(clonedDatabase.isOpen());
+            clonedDatabase.close();
+        }
+
         QThread::currentThread()->exit();
     }
 private: