On Tue, 21 Apr 2015 11:05:51 -0500, John McKown wrote:
>
>The 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 .
>
In:
z/OS 2.1.0>z/OS MVS>z/OS MVS JCL Reference>JOB statement>DSENQSHR
parameter>Overrides
A similar parameter for the JES JOBCLASS. If the JOBCLASS includes
a DSENQSHR parameter set to DISALLOW, the job specification will
be ignored. A job class with DSENQSHR set to AUTO or ALLOW must be
used to exploit this function.
Note: The DSENQSHR jobclass attribute is JES2-only. When using a
JES3 environment, the DSENQSHR function is never active.
Restriction!
Additionally, when GRS is in RING mode, the DSENQSHR function is disabled.
Restriction, restriction!
Table 1. JOBCLASS attribute for DSENQSHR
LANGUAGE JOBCLASS attribute for DSENQSHR
JCL AUTO ALLOW DISALLOW
ALLOW yes yes no
USEJC yes no no
DISALLOW no no no
When yes is indicated, the system is allowed to change the data
set serialization to shared control and other jobs may share that
data set with this job.
I might expect that when the JCL specifies UseJobClass (the default)
and the JOBCLASS attribute is ALLOW, the matrix entry would be "yes",
not "no".
I suppose there's an underlying parameter to the DEQ macro. I haven't
looked it up. It's probably not sensitive to DSENQSHR.
Something ("Using Data Sets"?) probably describes what happens if the
programmer DYNALLOCs a DSN also appearing in JCL, and one is SHR and
the other is EXC. I haven't looked it up.
-- gil
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