-----Original Message-----
From: IBM Mainframe Discussion List [mailto:ibm-m...@bama.ua.edu] On
Behalf Of Paul Gilmartin
Sent: Thursday, January 28, 2010 8:58 AM
To: IBM-MAIN@bama.ua.edu
Subject: Re: Re : Extracting STDOUT data from USS
On Thu, 28 Jan 2010 09:02:07 +0100, Hunkeler Peter (KIUP 4) wrote:
>>Gee, you do I/O, you wait ... [snip]
>
>Sure. I don't know if there is a CICS service to do I/O
>to some non-CICS dataset, or if it was simply tolerated.
>Actually, a wait only affects other transactions in the
>same CICS region as the will have to wait, too. I remember
>that in the early releases of OpenEdition / OS/390 UNIX
>CICS and IMS both stated that they do not allow UNIX
>services from within transactions because teh waits that
>could result.
>
My naive understanding of the OS/360 multiprocessing
paradigm is that when one unit of work WAITs, another
is dispatched. How does CICS manage to subvert this?
Why was it ever allowed?
What happens when a CICS transaction must do something
like:
Invalid PIN number; please re-enter
??? Does that spawn a separate transaction?
<SNIP>
CICS required that a transaction NOT cause an "OS" wait. You used a CICS
service (via MACRO or Command level interface) and allowed CICS to
schedule those things that could incur a WAIT.
So when you did this call to CICS, it would recognize you would need to
wait (whether you actually needed to or now, you will now) and then it
would go dispatch another transaction that was ready to run.
In effect, CICS was making virtual TCBs run using one real TCB, with
each virtual TCB being a transaction (pseudo conversational or true
conversational).
Today, CICS has multiple TCBs to handle different things, but still the
MAIN TASK TCB is generally not allowed to incur an "OS" wait because the
whole CICS system may stall as a result.
Since Unix System Services (USS for this posting) may incur a WAIT those
things are not allowed in a transaction that runs in the main task
because of being able to cause the CICS system to stall.
IHTH
Steve Thompson
-- Opinions expressed by this poster may not reflect those held by
poster's employer --
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