At 10:49 -0500 on 04/21/2015, Paul Gilmartin wrote about Re: ENQ for
the life of the job:
On Tue, 21 Apr 2015 11:20:24 -0400, Robert A. Rosenberg wrote:
>
... a IMO major design flaw in the ENQ process
the Initiator can be forced to hold an ENQ for subsequent steps where
it is no longer needed. The case I am talking about is there is no
way to convert an EXC ENQ into a SHR one.
What z/OS release are you thinking of?
I was thinking of all the releases up until 2.1. I was unaware that
this long standing Design Flaw was going to be addressed in that
release as mentioned below.
At 11:05 -0500 on 04/21/2015, John McKown wrote about Re: ENQ for the
life of the job:
On Tue, Apr 21, 2015 at 10:20 AM, Robert A. Rosenberg <[email protected]>
wrote:
> At 06:50 -0500 on 04/21/2015, John McKown wrote about Re: ENQ for the life
> of the job:
>> The initiator (in general terms) is what reads the parsed JCL and creates
>> the SWA control blocks which represent the job.
{snip]
> While this description of ENQ and DEQ handling is correct it leaves out
the fact that due to a IMO major design flaw in the ENQ process the
Initiator can be forced to hold an ENQ for subsequent steps where it is no
longer needed. The case I am talking about is there is no way to convert an
EXC ENQ into a SHR one. The Initiator is forced to keep an EXC ENQ active
for steps where only SHR is what is enough/desired. This design flaw in ENQ
mains that if a DSN is DISP=OLD/MOD in step 1 and DISP=SHR in all the
following steps the DISP=OLD/MOD ENQ is unnecessarily held until the last
DISP=SHR step (or the JOB) is over. This prevents other jobs that should be
allowed to run from being allowed to run due to the no longer needed EXC
> ENQ being held during DISP=SHR steps.
> In theory allowing the EXC->SHR ENQ change would be simple since all that
is needed is to alter the ENQ entry in the queue from EXC to SHR and then
drive the part of the DEQ routine that runs the queue to release pending
SHR entries that are waiting for the DEQ of the EXC ENQ at the head of the
> chain.
ÐThe ability to atomically downgrade an ENQ from EXC to SHR is now/soon to
be available in z/OS. I don't remember if it is a PTF or release 2.1.1 .
Thank you for this information. Note that I am aware that my code
change above would be easy to do so long as we are dealing with a
single system. All that would be needed in addition to the above
coding change would be the assigning of a flag in the ENQ parm list
to request the EXC to be changed to SHR. The complications would
involve GRS and the need for Tolerance PTFs.
Maranatha! <><
John McKown
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