gtpa2m3o | Application Programming |
TPF allows all active entries to share the programs that are currently in main storage. Whenever an external function is called, TPF first determines if its program segment is already in main storage or previously requested by another entry, in which case a new retrieval is not required. It is this feature that makes it essential that all programs be reentrant. Any number of entries may be using the same program segment, but each at a different point in the logic flow.
Program sharing is a key of TPF's high performance. However, you must assume the potential for a file retrieval every time a program is entered. Processing for every message type should be designed to minimize the requirement.