Issue 2172: Does atomic_compare_exchange_* accept v == nullptr arguments? (original) (raw)

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2172. Does atomic_compare_exchange_* accept v == nullptr arguments?

Section: 99 [depr.util.smartptr.shared.atomic] Status: C++14 Submitter: Howard Hinnant Opened: 2012-07-28 Last modified: 2017-11-29

Priority: Not Prioritized

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Discussion:

Looking at [util.smartptr.shared.atomic]/p31

template bool atomic_compare_exchange_strong_explicit(shared_ptr* p, shared_ptr* v, shared_ptr w, memory_order success, memory_order failure);

-31- Requires: p shall not be null.

What about v? Can it be null? And if so, what happens?

This looks closely related to C++11 issue LWG 1030(i), where we gave every signature in this section a:

Requires: p shall not be null.

It looks like a simple oversight to me that we did not add for the atomic_compare_exchange_*:

Requires: p shall not be null and v shall not be null.

[2012-10 Portland: Move to Ready]

This is clearly the right thing to do, and Lawrence concurs.

[2013-04-20 Bristol]

Proposed resolution:

This wording is relative to N3376.

Change [util.smartptr.shared.atomic] as indicated:

template bool atomic_compare_exchange_weak( shared_ptr* p, shared_ptr* v, shared_ptr w);

-27- Requires: p shall not be null and v shall not be null.

[…]

template bool atomic_compare_exchange_weak_explicit( shared_ptr* p, shared_ptr* v, shared_ptr w, memory_order success, memory_order failure); template bool atomic_compare_exchange_strong_explicit( shared_ptr* p, shared_ptr* v, shared_ptr w, memory_order success, memory_order failure);

-31- Requires: p shall not be null and v shall not be null.

[…]