Planning for recovery in a subspace environment

As described in Limitations of subspaces, the system abnormally ends programs that specify incorrect parameters on the IARSUBSP macro. While this helps to preserve the integrity of subspaces, the chances that your server program will abnormally end are increased.

You can plan for this by designing recovery routines that intercede when the system abnormally ends your server program. System code X'3C6' in z/OS MVS System Codes describes the IARSUBSP macro errors that cause your program to abnormally end.

To set up a recovery routine for any program, you must understand the topics presented in the recovery section in z/OS MVS Programming: Authorized Assembler Services Guide. To design recovery for programs running in subspaces, you need additional information about the recovery routine's subspace environment. The subspace environment is simply whether the routine is running with full address space addressability or in a subspace, and, if it is running in a subspace, which one? Like a mainline program, a recovery or retry routine can use the BSG instruction to:

Change subspaces, by specifying the ALET of the desired subspace
Run with full address space addressability, by specifying ALET 0
Return to the last subspace to have control, by specifying ALET 1.

(See Using special alets for a more information on using ALETs 0 and 1 with the BSG instruction.) Given that, consider these questions:

In what environment does the recovery routine receive control?
Does a recovery routine that changes its environment need to ensure that the environment is reset if the recovery routine abnormally ends?
In what environment does a retry routine receive control?

These questions are answered in the following topics.