An address space without a JSAB is one that is started under a subsystem that 
does not build one (typically "MSTR").

An address space started under JES control will have a JSAB and any address 
space that invokes the "request JOBID" SSI call to JES will get a JSAB (I 
believe this is how *MASTER* gets a JSAB - it waits for ENF 40 and then issues 
SSI-20).

As you have noted, JSABs can be stacked and invalidated during the address 
space lifetime and this is normally down to requirements for ASCHINT, BPXAS and 
INIT style processing.

IAZXJSAB is your friend for most things, however there are always fringe cases 
that you have to be aware of - eg "*MASTER*" and "SYSLOG".


-----Original Message-----
From: IBM Mainframe Discussion List <[email protected]> On Behalf Of 
Charles Mills
Sent: Friday, October 12, 2018 3:15 PM
To: [email protected]
Subject: Reasons for address space with no JSAB/other sources of job name

I've got code -- and it works without problems -- that chains
ASCBASSB->ASSBJSAB and then loops through JSABs until it finds one with
JSABNVAL not set. I don't recall where I originally came up with the logic.
I note two things about the code: it allows for the possibility that ASSBJSAB 
is zero, and for the possibility that it gets to the end of the JSAB chain 
without finding a "valid" JSAB (which the application can tolerate).

As I said, the code works. I am just trying to understand the situation a 
little better. My questions are these:

- What are the reasons that an address space would not have a JSAB?
*MASTER*? Address spaces started under *MASTER* rather than by JESx?
- Is there a better source of job name and any userid than the JSAB? I see that 
SDSF has a jobname for every A/S. I note the existence of ASCBJBNI/S but don't 
know much about them.

Charles

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