At 15:33 -0600 on 12/02/2009, Paul Gilmartin wrote about Re: IEC143I 213-30:
It's even worse than you've learned so far. If you use static (JCL DD DISP=OLD) allocation, the exclusive ENQ will be obtained at job initiation and persist through the last step that mentions the data set, regardless whether SHR or OLD.
This is because the ENQ support has no way of altering a owned EXCLUSIVE ENQ to a SHARED one (you can only [try to] change from SHARED to EXCLUSIVE). It would be easy to do since all that is needed is to put the share request at the top of the waiting queue and do the DEQ processing. The task now has a SHARED ENQ and all the tasks waiting for the Exclusive ENQ to get released would fire off. With that capability Job Initiation would be able to issue an early DISP=OLD DEQ in lieu of its current need to wait for the last step referencing the dataset.
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