In a recent note, Edward Jaffe said: > Date: Mon, 31 Jul 2006 23:48:57 -0700 > > Robert A. Rosenberg wrote: > > My error. I remembered that the ENQ had the ability to change the ENQ > > type but forgot that it was from SHARED to EXCLUSIVE (which is not as > > useful as from EXCLUSIVE to SHARED - if there is some purpose in > > allowing S->E, it should be in addition to not in lieu of E->S). In > > fact, I can not think of any situation where you'd want to be able to > > gain EXCLUSIVE access after having SHARED Access ... > > Huh? You have this completely reveresed in your mind. Upgrading your ENQ > from shared to exclusive is the common case and is a *required* function > in order to maintain the integrity of the data. Going the other way > would be far less common ... so uncommon, in fact, that OS/MVT/MVS never > bothered to create a service for it! There's just no need. If you want > You're misperceiving familiarity as utility or even necessity; I agree with Robert.
View this from the perspective of the initiator: RET=CHNG is available, yet the initiator never exploits it -- it can't by design objective. In the obvious case when an earlier job step specifies DISP=SHR and a later step specifies DISP=OLD, the initiator doesn't initially do a SHR ENQ, and prior to the later step RET=CHNG. To do so would introduce the high likelihood of a deadlock, if the initiator specified WAIT, or an ABEND/JCL error, if the initiator eschewed WAIT. Contrariwise, if RET=DOWNGRADE to change EXCL to SHR were available, the initiator could readily (SMOP) exploit it so that a data set created with DISP=NEW in an early step could be accessed both by the creating job in a later step, and concurrently by other jobs. > to downgrade from exclusive to shared, you simply DEQ and re-ENQ with > shared scope. > Likewise, if RET=CHNG were not available, you could equally well simply DEQ and re-ENQ with EXCL scope. -- gil -- StorageTek INFORMATION made POWERFUL ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
