Feature gate: #![feature(generic_atomic)]

This is a tracking issue for replacing the distinct Atomic* types with a generic Atomic<T> type. This allows using Atomic with FFI type aliases and helps clean up some API surface. Only types with existing AtomicT are usable in Atomic<T>.

Public API

// core::sync::atomic

pub struct Atomic<T: AtomicPrimitive>(/* private fields*/);

pub type AtomicI32 = Atomic<i32>; // etc

Steps / History

• ACP: ACP: Generic Atomic<T> libs-team#443
• Implement Atomic<T> as an alias to AtomicT: Create Atomic<T> type alias (rebase) #136316
• Flip alias so AtomicT is an alias to Atomic<T>
• Move generic functionality from AtomicT to Atomic<_>
• Pseudo-prerequisite: Stabilize 128-bit atomics: Tracking issue for integer_atomics (AtomicU128/AtomicI128) #99069
• Final comment period (FCP)¹
• Stabilization PR

Unresolved Questions

• Atomic<T> is soft-blocked on 128-bit atomics, because since trait implementations cannot be unstable, gating Atomic<i128> separately from Atomic<i32> isn't possible.
  • If necessary, AtomicI128 could instead name Atomic<Wrapper<i128>> for some unstable name Wrapper until 128-bit atomics are stable, to prevent Atomic<i128> from being usable from stable earlier than intended.