ubq 4.0.0

Lock-free unbounded MPMC queue backed by a linked ring of fixed-size blocks.
Documentation 
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use std::fmt::Write as FmtWrite;
use std::path::PathBuf;

// (preset, pool_values)
const PRESET_INFO: &[(&str, &[u8])] = &[
    // pool=0 gives no-pool behaviour; non-zero values enable block recycling.
    ("balanced", &[0, 1, 2, 4, 8, 16, 32, 64]),
];

const BLOCK_ALIGN: &[(u16, &str)] = &[
    (31, "align::A64"),
    (63, "align::A128"),
    (127, "align::A256"),
    (255, "align::A512"),
    (511, "align::A1024"),
    (1023, "align::A2048"),
    (2047, "align::A4096"),
    (4095, "align::A8192"),
];

const BACKOFF_INFO: &[(&str, &str)] = &[
    ("crossbeam", "backoff::Crossbeam"),
    ("yield", "backoff::Yield"),
];

fn main() {
    println!("cargo:rerun-if-changed=build.rs");

    let out_dir = std::env::var("OUT_DIR").expect("OUT_DIR not set");
    let path = PathBuf::from(&out_dir).join("bench_registry.rs");

    let feature_enabled = std::env::var("CARGO_FEATURE_BENCH_REGISTRY").is_ok();
    if !feature_enabled {
        // Write a stub so the include! always succeeds.
        std::fs::write(
            path,
            "// bench_registry feature not enabled — stub only.\n\
             fn lookup_ubq_job_factory(\n\
             \x20\x20\x20\x20_label: &str,\n\
             \x20\x20\x20\x20_scenario: ScenarioConfig,\n\
             \x20\x20\x20\x20_repeat_index: usize,\n\
             \x20\x20\x20\x20_mode: Mode,\n\
             \x20\x20\x20\x20_items_per_producer: u64,\n\
             ) -> Option<JobFactory> { None }\n",
        )
        .expect("failed to write bench_registry.rs stub");
        return;
    }

    let mut code = String::with_capacity(256 * 1024);
    writeln!(code, "// Auto-generated by build.rs — do not edit.").unwrap();
    writeln!(code, "fn lookup_ubq_job_factory(").unwrap();
    writeln!(code, "    label: &str,").unwrap();
    writeln!(code, "    scenario: ScenarioConfig,").unwrap();
    writeln!(code, "    repeat_index: usize,").unwrap();
    writeln!(code, "    mode: Mode,").unwrap();
    writeln!(code, "    items_per_producer: u64,").unwrap();
    writeln!(code, ") -> Option<JobFactory> {{").unwrap();
    writeln!(code, "    match label {{").unwrap();

    for &(preset, pool_values) in PRESET_INFO {
        for &pool in pool_values {
            for &(block, align_ty) in BLOCK_ALIGN {
                for &(backoff_name, backoff_ty) in BACKOFF_INFO {
                    let label_str = format!("{},{},{},{}", preset, pool, block, backoff_name);
                    let type_expr =
                        format!("ConfiguredUBQ<u64, {backoff_ty}, {pool}, {block}, {align_ty}>");
                    writeln!(
                        code,
                        "        {:?} => Some(make_ubq_job_factory::<{type_expr}>(label, scenario, repeat_index, mode, items_per_producer)),",
                        label_str,
                    )
                    .unwrap();
                }
            }
        }
    }

    writeln!(code, "        _ => None,").unwrap();
    writeln!(code, "    }}").unwrap();
    writeln!(code, "}}").unwrap();

    std::fs::write(path, code).expect("failed to write bench_registry.rs");
}