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1475. weak compare-and-exchange confusion II

Section: 32.5.8.2 [atomics.types.operations] Status: Dup Submitter: Switzerland Opened: 2010-08-25 Last modified: 2016-01-28

Priority: Not Prioritized

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Duplicate of: 1474

Discussion:

Addresses CH-23

32.5.8.2 [atomics.types.operations] p. 23: The first sentence has non-English syntax.

[ Resolution proposed in ballot comment: ]

Change to "The weak compare-and-exchange operations may fail spuriously, that is, return false while leaving the contents of memory pointed to by expected unchanged."

[ Daniel translates NB comment in a proposed resolution ]

Change 32.5.8.2 [atomics.types.operations] p. 23 as indicated:

23 Remark: The weak compare-and-exchange operations may fail spuriously, that is, return false while leaving the contents of memory pointed to by expected before the operation is the same that same as that of the object and the same as that of expected after the operationThe weak compare-and-exchange operations may fail spuriously, that is, return false while leaving the contents of memory pointed to by expected unchanged.. [ Note: This spurious failure enables implementation of compare-and-exchange on a broader class of machines, e.g., loadlocked store-conditional machines. A consequence of spurious failure is that nearly all uses of weak compare-and-exchange will be in a loop.

When a compare-and-exchange is in a loop, the weak version will yield better performance on some platforms. When a weak compare-and-exchange would require a loop and a strong one would not, the strong one is preferable. — end note ]

[ See 1474⁽ⁱ⁾ for the proposed resolution ]

Proposed resolution: