If you truly need a triple compare and swap then PLO will not help you. But if
you need a disjoint double compare and swap, you use the compare-and-swap
field as a counter and then you con do a compare swap and double store.
Example:
Fetch counter
A PLO compare-and-fetch value1
CC>0, go to A
PLO compare-and-fetch value 2
CC>0, go to A
calculate new value1 and 2
Add one to fetched counter
PLO CSDST fetched-counter new-fetched-counter, new value1, new-value2
CC>0, go to A
This requires that all processes that update value1 or value2 use PLO with the
same lock word.
On Sun, 3 Nov 2013 19:58:12 -0800 Jon Perryman <[email protected]> wrote:
:>I sure missed that one with the locks.
:>
:>PLO CDS does exactly what is wanted. It does 2 CS's within the locked
instruction.
:>
:>PLO CSDST on the other hand only does a single CS followed by 2 ST's. Since 3
separate load instructions (not under PLO control) are required when not in
contiguous storage, there is not any method that will guarantee the 3 values
are consistent with the others. A counter as suggested by Peter Relson won't
help either for this same reason.
:>
:>
:>I can't think of a situation where PLO CSDST is useful. Can anyone describe a
situation where it is useful?
:>
:>Jon Perryman.
:>
:>
:>
:>>________________________________
:>> From: Rob Scott <[email protected]>
:>>
:>>
:>>
:>>I think the OP stated that his code could hold locks - in which case the
latch services cannot be used.
:>>
:>
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--
Binyamin Dissen <[email protected]>
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