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Showing content from https://cplusplus.github.io/LWG/issue3417 below:

Issue 3417: Missing volatile atomic deprecations

This page is a snapshot from the LWG issues list, see the Library Active Issues List for more information and the meaning of SG1 status.

3417. Missing volatile atomic deprecations

Section: 32.5.8.2 [atomics.types.operations] Status: SG1 Submitter: Alisdair Meredith Opened: 2020-03-19 Last modified: 2020-09-06

Priority: 3

View all other issues in [atomics.types.operations].

View all issues with SG1 status.

Discussion:

Paper P1831R1 aimed to deprecate all the atomic overloads for volatile qualified member function of std::atomic unless is_always_lock_free is true. There are a few omissions in the wording.

First, operator++ and operator-- are correctly constrained, but the deprecated overloads are not restored in Annex D, unlike the other member functions. I confirmed with the paper author this is an accidental oversight, and not an intended change of behavior for C++20. Secondly, the wait/notify APIs were added after the initial wording For this paper was drafted, and the paper did not catch up. Again, I confirmed with the paper author that these functions should be similarly constrained and deprecated.

[2020-04-04 Issue Prioritization]

Priority to 3 after reflector discussion. The suggested wording was generally accepted, but there were considerable doubts that it is necessary to add deprecated functions of the new wait/notify functions instead of declaring only the non-volatile overloads. The wish was expressed that both SG1 and LEWG should express their opinion here.

Proposed resolution:

This wording is relative to N4861.

Modify 32.5.8.2 [atomics.types.operations] as indicated:
```
void wait(T old, memory_order order = memory_order::seq_cst) const volatile noexcept;
void wait(T old, memory_order order = memory_order::seq_cst) const noexcept;
```
Constraints: For the volatile overload of this function, is_always_lock_free is true.
-29- Preconditions: […] […]
```
void notify_one() volatile noexcept;
void notify_one() noexcept;
```
Constraints: For the volatile overload of this function, is_always_lock_free is true.
-32- Effects: […] […]
```
void notify_all() volatile noexcept;
void notify_all() noexcept;
```
Constraints: For the volatile overload of this function, is_always_lock_free is true.
-34- Effects: […] […]

Modify D.23.2 [depr.atomics.volatile], annex D, as indicated:

If an atomic specialization has one of the following overloads, then that overload participates in overload resolution even if atomic<T>::is_always_lock_free is false:

void store(T desired, memory_order order = memory_order::seq_cst) volatile noexcept;
[…]
T* fetch_key(ptrdiff_t operand, memory_order order = memory_order::seq_cst) volatile noexcept;
value_type operator++(int) volatile noexcept;
value_type operator--(int) volatile noexcept;
value_type operator++() volatile noexcept;
value_type operator--() volatile noexcept;
void wait(T old, memory_order order = memory_order::seq_cst) const volatile noexcept;
void notify_one() volatile noexcept;
void notify_all() volatile noexcept;

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