B Tree files may be created/opened in exclusive or shared mode. Application programs that use shared access should be prepared to handle a busy return from a read or update access to the B Tree file.

An application can gain exclusive access to a B File after it has been opened in shared mode. This is achieved by the btlock function. The btunlock function removes exclusive access.

Several BTree operations are prohibited in shared mode. These are the bnxtky and bprvky functions. In addition, the bupdky, bdelky, btupd, btdel and btrecs functions cannot be used in current context mode (i.e. supplied with a key argument of NULL). These operations are available if the shared index file is locked for exclusive access via the btlock function.