Programming considerations

The following are processing considerations for Exit 7:

Use the PCEID field to determine which processor is reading or writing the JCT; this avoids unnecessary processing.
You can determine if Exit 7 is being invoked for a transaction program or a batch job by either:
- Determining if a $DSCT is contained in the $IOT.
- Determining if byte JCTFLAG3 is set to JCT3TPI to indicate the job is a transaction program.
Bit X007CBIN in the parameter list indicates that the control block contains either an incorrect eyecatcher or job key. When this bit is on, the exit should not rely on the contents of the control block. After the exit returns, JES2 will issue a disastrous error.
Extending the JCT Control Block
If field X007CBID contains the 4-character string 'JCT ' (note the trailing blank), you can add, expand, locate, and remove extensions to the job control table ($JCT) control block from this exit using the $JCTX macro extension service for all control block WRITEs.

For control block READs you should neither add nor expand extensions, because JES2 might not write any modifications from control block READs to spool. For more information about using the $JCTX macro extension service, see z/OS JES2 Macros.