[intro.races] CWG 2297, LWG 2506: Unclear specification of atomic operations #1611

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1. jensmaurer

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2. jensmaurer commented on Apr 12, 2017

   

   jensmaurer

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   I'm not seeing where we normatively say "new and delete are defined to be synchronization operations".
3. jensmaurer commented on Apr 12, 2017

   

   jensmaurer

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   It is not sufficiently clear that the only atomic operations are the ones defined in clause 32 [atomics] by the library. The intent is that no accesses are atomic unless the Standard describes them as such.

   This is slightly confused. Since the standard does not define operations other than those in [atomics] to be "atomic operations", and furthermore we usually use "operation on atomic object M" when talking about ordering in [intro.races], there seems to be no leeway for a hostile interpretation.

   The intent is that no accesses are atomic unless the Standard describes them as such.

   A conforming implementation could make all accesses atomic, but a portable user program may only rely on atomic operations specified as such in the standard.

   If there is any doubt what "atomic operations on atomic objects" are, it seems [intro.races] is not the place to fix it, but instead this should be addressed in [atomics].
4. jensmaurer

   added a commit that references this issue on Apr 12, 2017

   [intro.races] Clarify 'synchronization operation'.

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   This issue will close once commit 2a8d97d is merged into the 'master' branch.

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5. timsong-cpp commented on Apr 19, 2017

   

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   I'm not seeing where we normatively say "new and delete are defined to be synchronization operations".

   Maybe it's referring to the last sentence of [new.delete.dataraces]?
6. jensmaurer commented on Apr 19, 2017

   

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   @timsong-cpp: That still doesn't say that new/delete are synchronization operations; those make unrelated memory updates visible to other threads. In contrast, for new/delete we just specify that they are serializable as individual function calls, but we don't say anything about visibility of unrelated memory updates. (I'm not positive [new.delete.dataraces] actually says what it should say; we certainly want to allow thread-optimized allocators that respond to some allocations entirely locally without coordinating with other threads. See LWG 2508 for the opposite viewpoint; to be discussed.)
7. timsong-cpp commented on Apr 19, 2017

   

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   we don't say anything about visibility of unrelated memory updates

   The "happens before" part almost does that (but for consume operations).
8. jensmaurer commented on Apr 19, 2017

   

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   @timsong-cpp: Fine, but I think that direction is misguided to start with. See http://lists.isocpp.org/parallel/2017/04/0856.php for discussion.
9. timsong-cpp commented on Apr 19, 2017

   

   timsong-cpp

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   @jensmaurer I can't see what I can't access :) Was just trying to point out what IMO that portion of the comment probably meant, but I think this is getting a bit off-topic...
10. jensmaurer

    added a commit that references this issue on Jul 21, 2017

    [intro.races] Clarify 'synchronization operation'.

    ...

    This issue will close once commit f279a32 is merged into the 'master' branch.

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11. jensmaurer

    added a commit that references this issue on Jul 30, 2017

    [intro.races] Clarify 'synchronization operation'.

    ...

    This issue will close once commit 23578f8 is merged into the 'master' branch.

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12. jensmaurer

    added a commit that references this issue on Oct 15, 2017

    [intro.races] Clarify 'synchronization operation'.

    ...

    This issue will close once commit ec8aa60 is merged into the 'master' branch.

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13. jensmaurer commented on Apr 13, 2018

    

    jensmaurer

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    This is covered by LWG 2506.
14. jensmaurer

    changed the title [-][intro.races] CWG 2297: Unclear specification of atomic operations[/-] [+][intro.races] CWG 2297, LWG 2506: Unclear specification of atomic operations[/+] on Apr 13, 2018
15. jensmaurer

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    lwgIssue must be reviewed by LWG.Issue must be reviewed by LWG.

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    not-editorialIssue is not deemed editorial; the editorial issue is kept open for tracking.Issue is not deemed editorial; the editorial issue is kept open for tracking.

    on Apr 13, 2018
16. jensmaurer

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17. jensmaurer commented on Apr 13, 2018

    

    jensmaurer

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    SG1 discussion on LWG 2506 asked for a paper to address "atomic object", "atomic operation", "synchronization operation" etc.

    👍React with 👍1Reacted by A. Jiang
18. jensmaurer

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    on Oct 11, 2018