Crate deep_causality_par 

Shared parallelism primitives for the DeepCausality workspace.

Two items live here:

• MaybeParallel, the feature-conditional thread-safety marker that the parallel features of deep_causality_topology, deep_causality_fft, and their consumers share. Hosting it in one Tier-0 crate guarantees a single definition; Cargo feature unification on deep_causality_par/parallel keeps every crate in a build agreeing on whether the bound means Send + Sync or nothing.
• scoped_map, the minimal in-house fork-join surface for few, long, data-independent tasks such as counterfactual branch fan-outs: an order-preserving parallel map over a slice on std::thread::scope threads under the parallel feature, a plain inline map without it. No thread pool, no external dependency.

Feature levels

default = ["std"], std = ["alloc"], alloc = [], and no-std = ["alloc"] follow the workspace three-level convention. The crate’s own needs are small: core for the marker trait, alloc for the Vec that scoped_map returns. There is no external dependency to forward a level to, so std and no-std differ only in whether the crate declares no_std. Bare-metal builds use --no-default-features --features no-std and get the serial inline map.

Why parallel = ["std"] stays

The parallel arm of scoped_map calls std::thread::scope and std::thread::available_parallelism, and neither exists in core or alloc. parallel therefore declares a dependency on std, and that declaration earns its place: it is what makes a bare --features parallel resolve to a working configuration, and what lets a downstream crate forward deep_causality_par/parallel on its own (deep_causality_algorithms, deep_causality_topology, deep_causality_cfd, and deep_causality_physics all do) without also having to remember deep_causality_par/std. Dropping it would turn every one of those into a build error on the host, which is the common case. deep_causality_fft states the same requirement the same way.

What the declaration does not do is make no-std plus parallel unrepresentable. Cargo features are additive and cannot express mutual exclusion: --features no-std,parallel does not disable parallel, it re-enables std underneath the no-std request. On a host that is harmless, because the resulting std build is a valid one and only the no-std request is dropped; --all-features relies on exactly that. On a target that has no std to re-enable, it used to surface as can't find crate for std`` plus a cascade of prelude errors that name neither the feature that caused them nor the way out. The compile_error! below states both instead.

Re-exports

pub use crate::traits::maybe_parallel::MaybeParallel;

Modules

traits

Functions

scoped_map

Map f over items, preserving input order in the returned Vec.