portable-atomic

Portable atomic types.

• Provide all atomic integer types (Atomic{I,U}{8,16,32,64}) for all targets that can use atomic CAS. (i.e., all targets that can use std, and most no-std targets)
• Provide atomic load/store for targets where atomic is not available at all in the standard library. (riscv without A-extension, msp430, avr)
• (optional) Provide Atomic{I,U}128.
• (optional) Provide AtomicF{32,64}.
• (optional, single-core only) Provide atomic CAS for targets where atomic CAS is not available in the standard library. (thumbv6m, riscv without A-extension, msp430, avr)

Optional features

• fallback (enabled by default)
  Enable fallback implementations.

• i128
  Provide Atomic{I,U}128.

  Note:

  • This implicitly enables the fallback feature.
  • Atomic operations are only available for Rust 1.59+ on x86_64 and nightly on aarch64, otherwise the fallback implementation is used.
  • On x86_64, when cmpxchg16b target feature is not enabled at compile time, this uses the fallback implementation. cmpxchg16b is enabled by default only on macOS.

  The above status is likely to change in the future:

  • When Atomic{I,U}128 is stabilized in the standard library.
  • When 128-bit atomic operations are supported in other architectures. (riscv)

  If you need support for dynamic CPU feature detection, use the i128-dynamic feature.

• i128-dynamic
  Similar to the i128 feature, but tries to use cmpxchg16b in more cases based on dynamic CPU feature detection.

  Note:

  • Dynamic detection is only enabled in nightly, otherwise it works the same as the i128 feature.
  • When cmpxchg16b target feature is enabled at compile time, this works exactly the same as the i128 feature.
  • If both i128 and i128-dynamic features are used in the dependency graph, i128-dynamic takes precedence.
  • This is compatible with no-std (as with all features except std and parking_lot).

• float
  Provide AtomicF{32,64}. Note that most of fetch_* operations of atomic floats are implemented using CAS loops, which can be slower than equivalent operations of atomic integers.

• std
  Use std.

• serde
  Implement serde::{Serialize,Deserialize} for atomic types.

  Note:

  • The MSRV when this feature enables depends on the MSRV of [serde].

• parking_lot
  Use [parking_lot] in global locks of fallback implementation.

  Note:

  • This is not compatible with no-std.
  • The MSRV when this feature enables depends on the MSRV of [parking_lot].

Optional cfg

• --cfg portable_atomic_unsafe_assume_single_core
  Assume that the target is single-core. When this cfg is enabled, this crate provides atomic CAS for targets where atomic CAS is not available in the standard library.

  Note: This cfg is unsafe, and enabling this cfg for multi-core systems is unsound.

  This is intentionally not an optional feature. If this is an optional feature, dependencies can implicitly enable the feature, resulting in the use of unsound code without the end-user being aware of it.

License

Licensed under either of Apache License, Version 2.0 or MIT license at your option.

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.