On 2021-03-21, at 07:52:27, Peter Relson wrote: > > The software will not have to do anything in order to get the epoch index > to increase to 1 in September 2042. ... > Thanks. I saw that cleearly in the PoOps.
> The clock comparator remains an 8 byte entity. But the OS will be able to > indicate that the CC is to be treated as signed, so that 00000000_00000000 > will be "later" than (the negative) FFFFFFFF_FFFFFFFF. That exploitation > of the multiple epoch facility does require OS action. And probably > requires a converse action every 70 years or so when the high bit of the > TOD clock changes. > I had envisioned a ±70-year window implemented by continually performing a Subtract Logical TOD - Comparator and testing the sign. The behavior would be more continuous, not requiring "action every 70 years or so". Any implementation is likely to have hazards when: o A programmer sets comparator to 0 to indicate "immediately". o A programmer sets comparator to maximum to indicate "never". o An expiry time is set very near maximum and the CPU is not dispatchable at that time. There is a legend (reported here a few years ago?) of a program that used a value of decimal one billion to indicate "never" and looped when that time occurred. Thanks again, gil ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
