I have some question at test my assignment: 1) i start the server, then start two client. i use one client to lock an record, and the other client lock the same record and wait,then i close the first client. Why the server-side not call the unreferenced method? (In the unreferenced method,i have print clause and some operation.) 2)In server-side, do i need to set an share lock? i consider when the client to read the record that is being modifyed by the other client, the message that is received by the first client is dirty data. i planning to design an buffer area that mapping the database and the client to read it, not to directly read data in the db.db file. when each written-operation complete, it write back to the buffer-area. is right?? or not do it?