RE: Disabling Qinter... (Follow up question)

midrange-l-request@xxxxxxxxxxxx wrote:

>   9. RE: Disabling Qinter... (Follow up question) (jt)
>
>So, the order the subsystems are started is the key, afaik.  Again, that may
>NOT be how it used to work but that's my recollection, and it Certainly may
>not even apply any more as the OS sure Has Changed over the decades.

I've had a slightly different impression over the years that somewhat explains 
the unpredictability of which subsystem gets the device. It isn't exactly which 
subsystem starts first, although that certainly can affect the outcome. I've 
thought it's more accurate that it's which subsystem attempts to allocate the 
device first, regardless of which starts first.

Think of two subsystems started in a CL program one after the other:

 ===> strsbs SBS1
 ===> strsbs SBS2

The first STRSBS command will complete almost immediately, and the second 
command is executed. We then have two subsystems starting up at the (more or 
less) same time. If you watch them perhaps via WRKACTJOB, you'll see them both 
running through devices trying to allocate them.

Now, imagine SBS1 has all workstations listed for allocation while SBS2 is only 
defined to allocate device ZZZZZZZZ, which was created only recently after a 
whole bunch of other devices already existed.

Since SBS2 has only the single device in its table, it almost certainly will be 
able to get it allocated before SBS1 has the time to get around to it. So even 
though SBS2 "started" last, it wins.

I also have thought that device names, or identifiers, aren't necessarily 
stored with the subsystem description in alphabetical order, but instead in 
perhaps a FIFO order tied to the date/time it was first defined to the 
subsystem description. So, if ZZZZZZZZ had been the very first device created 
and assigned, SBS1 might be much more likely to get it before SBS2 can.

Beyond the possible orderings of device identifiers, the handling of errors on 
various devices during allocation can slow the process significantly for one or 
the other subsystem. This would also decrease predictability.

If somebody really knows how it works, it might be instructive to the rest of 
us.

Tom Liotta

-- 
Tom Liotta
The PowerTech Group, Inc.
19426 68th Avenue South
Kent, WA 98032
Phone  253-872-7788 x313
Fax    253-872-7904
http://www.powertech.com


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