3745. std::atomic_wait and its friends lack noexcept

Section: 32.5.2 [atomics.syn] Status: C++23 Submitter: Jiang An Opened: 2022-07-25 Last modified: 2023-11-22

Priority: Not Prioritized

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Discussion:

Currently function templates std::atomic_wait, std::atomic_wait_explicit, std::atomic_notify_one, and std::atomic_notify_all are not noexcept in the Working Draft, but the equivalent member functions are all noexcept. I think these function templates should be specified as noexcept, in order to be consistent with the std::atomic_flag_* free functions, the corresponding member functions, and other std::atomic_* function templates.

Mainstream implementations (libc++, libstdc++, and MSVC STL) have already added noexcept to them.

[2022-07-30; Daniel provides wording]

[2022-08-23; Reflector poll]

Set status to Tentatively Ready after six votes in favour during reflector poll.

"Technically there's a difference between these and the member functions - the pointer can be null - but we don't seem to have let that stop us from adding noexcept to the rest of these functions."

[2022-11-12 Approved at November 2022 meeting in Kona. Status changed: Voting → WP.]

Proposed resolution:

This wording is relative to N4910.

1. Modify 32.5.2 [atomics.syn], header <atomic> synopsis, as indicated:

   […]
   template<class T>
     void atomic_wait(const volatile atomic<T>*, typename atomic<T>::value_type) noexcept;
   template<class T>
     void atomic_wait(const atomic<T>*, typename atomic<T>::value_type) noexcept;
   template<class T>
     void atomic_wait_explicit(const volatile atomic<T>*, typename atomic<T>::value_type,
                               memory_order) noexcept;
   template<class T>
     void atomic_wait_explicit(const atomic<T>*, typename atomic<T>::value_type,
                               memory_order) noexcept;
   template<class T>
     void atomic_notify_one(volatile atomic<T>*) noexcept;
   template<class T>
     void atomic_notify_one(atomic<T>*) noexcept;
   template<class T>
     void atomic_notify_all(volatile atomic<T>*) noexcept;
   template<class T>
     void atomic_notify_all(atomic<T>*) noexcept;
   […]