Programming considerations

The following are programming considerations for Exit 11:

If you intend to base your allocation algorithm on values contained in fields of the $JCT, you must consider that the $JCT is sometimes unavailable and write a section of your exit routine to take control in these instances.
Locating JCT Control Block Extensions
You can locate extensions to the job control table ($JCT) control block from this exit using the $JCTXGET macro.
You can determine if a job or transaction program is requesting additional spool space by either:
- Determining if a $DSCT is contained in the $IOT
- Determining if byte JCTFLAG3 is set to JCT3TPI.
Determining whether a job is at its fencing limit or not
- Spool partitioning is active if $MVFENCE is on.
- The field $FNCCNT contains the fencing limit (SPOOLDEF FENCE=VOLUMES=nnnn).
- CCTSPLAF contains the mask of spool volumes with affinity for this member.
- Only count the volumes that have affinity for this member and are in the IOT spools allowed mask when checking to see if the job has reached the fencing limit. To do this, 'and' CCTSPLAF with IOTSAMSK and then use the $CNTBIT macro to obtain the number of volumes to compare with $FNCCNT. The number of bits on in IOTSAMSK may be equal to or exceed $FNCCNT and another volume should still be added if the job obtained some of its spool space on another member which has affinity to different spool volumes.
- CCTVBLOB is the mask of spool volumes with space in the BLOB. Adding a spool volume that is not in CCTVBLOB will do no good since there is no space for it in the BLOB and therefore the job will not be able to allocate space on the volume.