Handling control blocks and work areas

About this task

The application program handles control blocks and session-related work areas (data areas and status flags) in a number of ways. It can:

Define RPLs, NIBs, or EXLSTs in the application program during assembly or generate them during program execution by using the GENCB macroinstruction or DSECTs
Define RPLs, NIBs, or EXLSTs that reside in 31-bit storage
Assign one RPL or NIB to a specific session during assembly, or assemble or generate RPLs and NIBs that are to be available for any session as the need arises
Retain the RPL used in establishing the session for all further communication on the session
Use one RPL for all session-establishment requests and use another RPL or group of RPLs for all communication requests
Define the RPLs, NIBs, and any other control blocks associated with sessions as a pool so that a limited amount of control block storage is not exceeded.

In application programs that must handle many sessions concurrently, it might be useful to have a control block other than the RPL or NIB associated with a particular session. VTAM® provides a way of associating a storage area with a particular session. See USERFLD field of the NIB for more information on associating specific information with a session.