I love transactional processing.  I still remember the SHARE session where it 
was fully described and thinking that this will make life so much easier in the 
future.  But I may fully retire before we can safely add it to our products 
without dual paths for another technique.  In this case PLO was used for 
maintaining a doubly-linked list.  The alternative, which we use in other 
situations, is a CS or CDS lock, which means code to spin a while, go idle (in 
case of a uni or CICS QR TCB), clean up in case of an abend, timeout, region 
termination, messages to tell us and operators what's happening, and dumps of 
our control blocks.

I requested the PLO info because a programmer came across the instruction while 
debugging a problem and had the PoOp open to the first page of the PLO 
description and I am leaving on vacation.  And, truth be told, I'd have to 
reread the PoOp again to describe just what I was thinking 10-12 years ago when 
I added the instruction after a problem occurred where we'd previously assumed 
the probability of two processes concurrently maintaining a doubly-linked list 
were infinitesimal.  It turns out they were very small but finite.

Perhaps I'll start adding dual path transactional processes just so it's 
documented that there is an alternative.

Gary Weinhold
Senior Application Architect

DATAKINETICS | Data Performance & Optimization

Phone:  +1.613.523.5500 x216<tel:+1.613.523.5500%20x216>
Email:  weinh...@dkl.com<mailto:weinh...@dkl.com>


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On 2017-08-11 09:31, Blaicher, Christopher Y. wrote:

PLO is an expensive instruction.  It can do a little or a lot.  There are about 
10 pages in the POP to describe it.
However, until transactional processing is supported in all environments, 
ISV's, who never know what environment they are running under, need to keep 
using the PLO instruction.  OK, Peter, we could dual path it, but who likes to 
maintain dual paths?

Chris Blaicher
Technical Architect
Mainframe Development
P: 201-930-8234  |  M: 512-627-3803
E: cblaic...@syncsort.com<mailto:cblaic...@syncsort.com>

Syncsort Incorporated
2 Blue Hill Plaza #1563
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-----Original Message-----
From: IBM Mainframe Assembler List [mailto:ASSEMBLER-LIST@LISTSERV.UGA.EDU] On 
Behalf Of John McKown
Sent: Friday, August 11, 2017 9:10 AM
To: MVS List Server 2 
Subject: Re: PLO <subject change: was Just Testing - It got very quiet>

On Fri, Aug 11, 2017 at 6:23 AM, Peter Relson 
<rel...@us.ibm.com><mailto:rel...@us.ibm.com> wrote:

does anyone know of good write-ups/presentations of PLO and its
capabilities and uses for an assembler programmer who knows how to use
CS and CDS.

My hope is that, going forward once you have a machine that supports
it and, for those who care about z/OS under z/VM, once/if it is
supported for z/OS running under z/VM, no one ever uses PLO again but
instead uses transactional execution, particularly TBEGINC for the simpler 

Peter Relson
z/OS Core Technology Design

​Now, that is a very interesting statement. ​

If you look around the poker table & don't see an obvious sucker, it's you.

Maranatha! <><
John McKown

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