Serious users of VTAM exits (e.g. session managers) run authorized and set
their LUs fastpath.  VTAM responds by using SRB intead of IRB.

Old memory, but no protection was in place to handle same exit running
multiple times.  May have had something to do that sends and receives were
executed on multiple tasks.

There is a field passed to VTAM which she returns (correlator field?) used
to handle parallelism.  Woe betide the programmer who does not have all
code rent.  I remember a case where one of our exits was non-rent.  The
fix was labeled "any abend anywhere any time any symptom".

It was necessary to have each correlator value be assigned to run on only
one task.

IBM Mainframe Assembler List <[email protected]> wrote on
06/01/2011 08:49:04 AM:

> From: Chris Mason <[email protected]>

> >> no asynchronous exit routine can interrupt another asynchronous exit
> >> routine

> > Perhaps VTAM does something special, but in general this is not true.

>
http://publibz.boulder.ibm.com/cgi-bin/bookmgr_OS390/BOOKS/f1a1d930/2.5.4

> Unless VTAM development is lying through its collective teeth, there's
no
> "perhaps" about it.

> Chris Mason


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