HP 3000 Manuals HP 3000 Manuals
File Sharing Your system supports a multi-user environment in which several users can share the same files. While a program is updating data records in a file it can deny other users access to those records or to the entire file. In a multi-user environment, your files are either active or inactive. An active file is open to a program while an inactive file is not. Furthermore, active files can be in either of two modes: exclusive and sharable. Active Files in Exclusive Mode Exclusive mode files are only open to one program at a time. Any other program that attempts to access the file receives a "file locked" error (file status 9/065) and is denied access. When a file is in exclusive mode, a file lock is held by the one program that is able to access the file. The exclusive mode file lock is released when the program closes the file. Active Files in Shareable Mode A sharable mode file is available to one or more programs. A program can protect data in a record or records while using the file by locking those records. Locking records in a file prevents other programs from accessing those particular records as long as they are locked; it does not prevent other programs accessing other records in the file. Each program accessing the file can lock either a single record or multiple records. A program cannot select both single record locking and multiple record locking for the same file. To make a file sharable you specify LOCK MODE IS MANUAL or LOCK MODE IS AUTOMATIC in its SELECT statement. Even with no such clause the file is sharable provided users open it in INPUT mode; that is, when you have it open for reading, other users can open it for reading too but they cannot update it. This restriction means the file handler can buffer records, with no risk of a record being updated after being copied to the buffer. Buffering gives significantly better performance than would otherwise be possible.