On Wed, 11 Jan 2017 10:12:30 -0700, Paul Gilmartin (0000000433f07816-dmarc-requ...@listserv.ua.edu) wrote about "Re: "task level" TIOT & XTIOT? A crazy thought?" (in <e858c541-1247-484b-a475-6ef8b5f65...@aim.com>):
> On 2017-01-10, at 17:46, David W Noon wrote: >> >>> And how would you preserve one of the aboriginal design objectives of >>> OS/360: >>> the ability to ENQ all needed resources before job initiation to avoid >>> deadlocks. >> >> That went out the window with the arrival of MVS/370, which introduced >> SVC 99. >> > I believe ENQs with job scope remain in "the bread and butter of > commercial data processing." You mean "job duration". That bread would be a bit stale these days. There has never been a guarantee of no deadlocks. The pre-emptive ENQs issued by the initiators have only been a best effort at preventing deadlocks. For the last 37 years or so, dynamic allocation has been able to generate deadlocks whenever the design of the allocation strategy has not take deadlocks into account. >> Well, MVT was a single address space system. All regions were in >> separate extents of the same physical address space. >> > I see some suggestion in this thread that the same DDNAME can not > refer to different data sets within a single address space. But > didn't MVT work that way? No, it did not. Under MVT, OS/VS1 and OS/VS2 the TIOT was associated with a region (or partition under OS/VS1), not an address space. The dataset associated with a DDNAME was specific to a region/partition, but could vary across regions/partitions. > Each job (up to 15, limited by storage > keys?) could use common DDNAMEs, such as SYSIN, SYSPRINT, SYSUT1, ... > referring to different data sets. How have we lost that facility? No, we have not. That's because from MVS/370 onwards, each region is its own address space. So SYSIN, SYSPRINT, etc., in different address spaces can refer to different datasets, SYSOUT classes, etc., but within an address space a DDNAME remains tied to a specific dataset (or whatever). -- Regards, Dave [RLU #314465] *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* david.w.n...@googlemail.com (David W Noon) *-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-* ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
