The LANSA OPEN command can be used to keep file(s) open until a specific CLOSE command is issued against them.
For instance, imagine a small order processing system that could be visualized like this:
ORDWRK
|
----------|----------
| | |
ORD001 ORD002 ORD003
When a user enters this system and begins jumping from ORD001 to ORD002 to ORD003, and so on, a fair amount of computer resource can be wasted opening and closing files used by all the functions.
For instance, all 3 functions might use files TABLES (system tables), ORDHDR (order header details) and ORDLIN (order line details).
Thus when the user exits from ORD001 all 3 files are closed. When the user invokes ORD002, all 3 files are opened again. This continual opening and closing is a waste of computer resource and degrades response times.
To fix this problem we might code a "file opener" called ORD004 that looked like this:
OPEN FILE(TABLES) USE_OPTION(*KEEPOPEN) OPEN FILE(ORDHDR) USE_OPTION(*KEEPOPEN) OPEN FILE(ORDLIN) USE_OPTION(*KEEPOPEN) CALL PROCESS(ORDWRK)
which would fit into the existing system like this:
ORD004 | | ORDWRK | ------|------ | | | ORD001 ORD002 ORD003
In this situation, the implicit OPEN and CLOSE requests issued by ORD001, ORD002 and ORD003 are ignored, which results in much faster processing.