File-definition (FD) storage

On all program invocations, the storage that is associated with a file definition (such as FD records and the record area that is associated with the SAME RECORD AREA clause) is allocated and available in its last-used state.

All threads of execution share this storage. You can depend on automatic serialization for this storage during the execution of the OPEN, CLOSE, READ, WRITE, REWRITE, START, and DELETE statements, but not between uses of these statements.