Radium

Radium provides abstractions and graceful degradation for behavior that must be shared-mutable, but merely may use atomic instructions to do so.

The primary export is the Radium trait. This is implemented on all symbols in the atomic module, and on their Cell<T> equivalents, and presents the atomic inherent API as a trait. Your code can be generic over Radium, use a stable and consistent API, and permit callers to select atomic or Cell behavior as they need.

Additionally, the types Atom<T> and Isotope<T> provide strong and weak guarantees of atomic behavior, respectively, while being generic over the underlying primitive type. Atom<T> will fail to compile when instantiated with a primitive which does not have a corresponding AtomicT type defined for the target, while Isotope<T> always compiles, and falls back to enclosing a Cell<T> when the required atomic support is missing.

Since the type symbols in the atomic module are conditionally defined according to the target architecture’s atomic support, portable code cannot use these names directly without placing them behind a #[cfg(target_has_atomic)] gate. Instead, radium provides RadiumT type aliases which resolve to AtomicT when available and Cell<T> when not.

The Rust compiler stabilized the cfg(target_has_atomic) attribute in version 1.60. This is the MSRV for Radium 1.0. The version-0 series will stay supported for the indeterminate future to allow for pre-1.60 projects to continue to use it. The radium::if_atomic! macro allows projects to simulate #[cfg(target_has_atomic)] in version-0, but is removed in version-1.

This crate is #![no_std]-compatible, as it relies solely on the core::sync::atomic and core::cell modules.

Versioning

radium is by definition attached to the Rust standard library. As the atomic API evolves, radium will follow it. MSRV raising is always at least a minor-version increase.

As of Rust 1.60, support for 128-bit atomics is unstable. Since radium commits to being usable on the stable release series, it does not support 128-bit atomics. As a compromise, Cell<{i,u}128> is integrated with radium to prepare for stabilization in the future.

If 128-bit atomics are removed from the standard library without stabilization, radium will similarly remove support for Cell<{i,u}128> in a major-version increase.

Pre-1.60 Target Discovery

Because the compiler did not easily expose this information to libraries, radium used a build script to detect the target architecture and emit its own directives that mark the presence or absence of an atomic integer. We accomplish this by reading the compiler’s target information records and copying the information directly into the build script.

If radium does not work for your architecture, please update the build script to handle your target string and submit a pull request. We write the build script on an as-needed basis; it is not proactively filled with all of the information listed in the compiler.

NOTE: The build script receives information through two variables: TARGET and CARGO_CFG_TARGET_ARCH. The latter is equivalent to the value in cfg!(target_arch = ""); however, this value does not contain enough information to fully disambiguate the target. The build script attempts to do rudimentary parsing of the env!(TARGET) string; if this does not work for your target, consider using the TARGET_ARCH matcher, or match on the full TARGET string rather than the parse attempt.

Project Origins

@kneecaw - https://twitter.com/kneecaw/status/1132695060812849154

Feelin' lazy: Has someone already written a helper trait abstracting operations over AtomicUsize and Cell<usize> for generic code which may not care about atomicity?

@ManishEarth - https://twitter.com/ManishEarth/status/1132706585300496384

no but call the crate radium

(since people didn't care that it was radioactive and used it in everything)