epics-libcom-rs 0.25.1

//! Selects the `runtime::task` spawn/sleep/interval backend at compile time.
//!
//! The task seam (`src/runtime/task.rs`) has two mutually exclusive backends,
//! chosen here so the ~two dozen seam sites gate on one uniform condition
//! rather than repeating the target/feature predicate at each:
//!
//! * `exec_backend` — the std-thread background executor (callback pool +
//!   delayed timer + scanOnce worker, `runtime::background`). This is the
//!   only option on `epics_embedded_target` (RTEMS or VxWorks — no tokio
//!   reactor on either), and — via the `rtems-exec-model` cargo feature — the
//!   **host-selectable RTEMS execution model**: a real product mechanism for a
//!   Linux (e.g. PREEMPT_RT) blocking-front-end deployment that wants the same
//!   runtime-free spawn/timer backend the embedded build uses, driving async
//!   record-processing completion on dedicated OS threads instead of a tokio
//!   runtime.
//! * `tokio_backend` — the tokio runtime. The hosted default (feature off,
//!   non-embedded target).
//!
//! Exactly one of the two is set for any build.

fn main() {
    println!("cargo::rustc-check-cfg=cfg(exec_backend)");
    println!("cargo::rustc-check-cfg=cfg(tokio_backend)");
    println!("cargo::rustc-check-cfg=cfg(epics_embedded_target)");

    let target_os = std::env::var("CARGO_CFG_TARGET_OS").unwrap_or_default();
    // The reactor-free targets: no tokio reactor exists on either, so both the
    // exec-model selection below and every dependency/socket-portability seam
    // above `epics-libcom-rs` gate on this one capability cfg instead of
    // repeating `any(target_os = "rtems", target_os = "vxworks")`.
    let embedded_target = matches!(target_os.as_str(), "rtems" | "vxworks");
    if embedded_target {
        println!("cargo::rustc-cfg=epics_embedded_target");
    }

    // Cargo exports `CARGO_FEATURE_<NAME>` (uppercased, `-` → `_`) for every
    // enabled feature of this crate.
    let host_exec_model = std::env::var_os("CARGO_FEATURE_RTEMS_EXEC_MODEL").is_some();

    if embedded_target || host_exec_model {
        println!("cargo::rustc-cfg=exec_backend");
    } else {
        println!("cargo::rustc-cfg=tokio_backend");
    }
}