Under MVS you can run a program that dynamically outputs a JCL job stream in the form of a SYSOUT data set, and you can specify that an external writer is to process the job stream. You can use the IBM-supplied external writer, INTRDR, or you can supply your own.
You can request an external writer in any of the following ways:
- In JCL. The name of the external writer is a parameter in the DD statement for the SYSOUT data set
- In a TSO ALLOCATE command
- By issuing the DYNALLOC (SVC 99) service
MSS emulates the IBM-supplied external writer, INTRDR. It does not support user-supplied external writers.
The MSS emulation of INTRDR differs in the following ways from IBM's INTRDR:
- IBM's INTRDR allows a program to submit a job without closing the data set, by writing records that contain control statements such as /*EOF, /*DEL, /*PURGE, and /*SCAN. Each of these statements effectively indicates that all data up to the statement is one or more complete jobs and that the action indicated by the statement should be carried out, for example, /*EOF causes the job to be submitted and is therefore equivalent to closing the data set. However, with the MSS emulation of INTRDR, the program must write an entire jobstream to the SYSOUT data set and then close the data set; the job is then submitted for execution. The program may then reopen the SYSOUT data set, write another complete jobstream and then close the data set for job submission.
- IBM's INTRDR supports multiple jobs in one jobstream, regardless of whether the submission is triggered by a control statement or by the closing of the data set. The MSS emulation of INTRDR does not support multiple jobs in one submission, since MSS itself cannot handle such jobs. Each submission must contain only one job.
- With IBM's INTRDR, the class of the submitted job defaults to the class of the SYSOUT data set. With the MSS emulation of INTRDR, the class of the submitted job is the same as it would be if the job were submitted without a class being specified.
- You cannot request an external writer by issung the DYNALLOC (SVC 99) service
