Concurrency issues in JDBC driver

Though JDBC specification specifies that "Each Connection object can create multiple Statement objects that may be used concurrently by the program", but that does not work in current Hive JDBC driver. In addition, there also exist race conditions between DatabaseMetaData, Statement and ResultSet as long as they make RPC calls to HS2 using same Thrift transport, which happens within a connection.
So we need a connection level lock to serialize all these RPC calls in a connection.