From: "Gary Weinhold" <[email protected]>
Sent: Tuesday, August 01, 2017 12:16 AM
I think (TS) Test and Set was/is atomic and AFAIK was the earliest implemented
atomic instruction.
I think that the entire /360 user instruction set would have been of that kind.
AFIK there was no provision to suspend any instrction and to resume it
after an interrupt.
The instruction had to be allowed to complete, and the IAR saved,
so that when control was passed back to the interrupted program,
the next instruction was executed.
I think it addressed the requirement to allow interruptible code to fetch,
test,
and modify a single byte on a single CPU machine with integrity.
An external or I/O interrupt could undermine the integrity of a TM, Bx, OI/NI instruction
sequence in that environment.
Gary Weinhold
Senior Application Architect
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