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: > > ŠThe initiator (in general terms) is what reads the Šparsed JCL and >> creates >> the SWA control blocks which represent the job. This code then knows the >> DSNs in the job and issues a single ENQ for _all_ of them before starting >> the first step. As each step ends, the initiator does a DEQ on the DSNs >> which are not going to be used in subsequent steps. At the end of the job, >> it DEQs whatever DSNs are left. >> > > > 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. 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 . -- If you sent twitter messages while exploring, are you on a textpedition? He's about as useful as a wax frying pan. 10 to the 12th power microphones = 1 Megaphone Maranatha! <>< John McKown ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
