atomic-polyfill

This crate polyfills atomics on targets where they're not available, using critical sections. It is intended to be a drop-in replacement for core::sync::atomic.

There is three "levels" of polyfilling: - Native: No polyfilling is performed, the native core::sync::atomic::AtomicXX is reexported. - CAS: Only compare-and-set operations are polyfilled, while loads and stores are native. - Full: Both load/store and compare-and-set operations are polyfilled.

Target support

The right polyfill level is automatically picked based on the target and the atomic width:

| Target | Level | Level for u64/i64 | |--------------------|------------------|-------------------| | thumbv6m | CAS | Full | | thumbv7, thumbv8 | Native | Full | | riscv32imc | Full¹ | Full | | riscv32imac | Native | Full | | Other² | Native | Native |

¹: The hardware is capable of supporting atomic load/stores up to 32 bits, so this could be "CAS" instead of "Full". However, support for this is missing in Rust. See discussion here.

²: atomic-polyfill assumes unknown targets have full native support. This may not be true, in which case the build may fail. PRs for polyfilling more targets are welcome :)

Note: polyfill is based on critical sections using the critical-section crate. The default implementation is based on disabling all interrupts, so it's unsound on multi-core targets. It is possible to supply a custom critical section implementation, check the critical-section docs for details.

License

This work is licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

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.