>What guarantees uniqueness other than STCT(E)? Does the Sysplex Timer/ETR
>guarantee
>uniqueness across the plex?
>
>And monotonicity is a harsher constraint. In the Bad Old Days when each CPU
>had its own
>TOD and uniqueness was achieved by putting the CPU ID in the TOD programmable
>field
>I wondered hereabouts whether a later transaction on a lower CPU could get
>lower
>timestamp than an earlier transaction on a higher CPU.
There is an entire sub-section in the PoOps in the Control chapter
(SA22-7832-13, pp. 4-51 et al., starting most of the way down the second column
of that page) about the monotonicity guarantees for STCK{E/F}, even on multiple
CPU's. I commend it to your reading.
What I would prefer to find in this case is an existing OS-supplied service
subroutine to return a monotonically increasing time value independent of the
language of the calling routine. A service (e.g., named counters, etc.) would,
as you correctly point out, suffer in terms of performance. I can personally
provide a truly efficient assembler subroutine using STCK{E} to guarantee
monotonicity and even return the STCK{E} condition code as an integer return
code, but I am looking for a perhaps slightly (but not enormously) less
efficient solution that has the benefit of avoiding a z/OS shop needing to
maintain a user-land assembler subroutine, no matter how simple and
straight-forward an assembler solution may be.
Alternatively, providing other HLL's with easy, compiler-supported access to
the C/C++ "builtin" instruction functions for STCK{E} (and all the others as
well; after all, a programmer can't have too many tools available) would likely
(but not necessarily) be relatively more efficient than the usual
implementation of HLL- or LE- or Unix-supplied service subroutine functions and
their environmentally-enforced baggage.
Peter
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