smarm/tests/spawn_opts.rs

//! RFC 019 commit 2 — the `SpawnOpts` surface.
//!
//! Covers: per-spawn stack shape overrides on every spawn surface, the
//! `None ⇒ Config default` resolution, the pool rule from the outside
//! (obligation 4: a custom-shaped stack never enters the pool), and that a
//! big reserve behaviorally takes effect (deep recursion completes).

use smarm::runtime::{Config, DEFAULT_STACK_GUARD, DEFAULT_STACK_RESERVE};
use smarm::{
    self_pid, spawn, spawn_under_with, spawn_with, GenServerBuilder, SpawnOpts,
};
use std::sync::atomic::{AtomicBool, Ordering};
use std::sync::Arc;

fn rt1() -> smarm::runtime::Runtime {
    smarm::runtime::init(Config::exact(1))
}

#[test]
fn default_spawn_has_default_shape() {
    rt1().run(|| {
        let h = spawn(|| {
            let shape = smarm::introspect::stack_shape(self_pid()).unwrap();
            assert_eq!(shape, (DEFAULT_STACK_RESERVE, DEFAULT_STACK_GUARD));
        });
        h.join().unwrap();
    });
}

#[test]
fn spawn_with_overrides_reserve_and_guard() {
    rt1().run(|| {
        let opts = SpawnOpts {
            stack_reserve: Some(1024 * 1024),
            guard_size: Some(256 * 1024),
        };
        let h = spawn_with(opts, || {
            let shape = smarm::introspect::stack_shape(self_pid()).unwrap();
            assert_eq!(shape, (1024 * 1024, 256 * 1024));
        });
        h.join().unwrap();
    });
}

#[test]
fn spawn_with_partial_override_keeps_config_default_for_the_rest() {
    rt1().run(|| {
        let opts = SpawnOpts { stack_reserve: Some(1024 * 1024), ..SpawnOpts::default() };
        let h = spawn_with(opts, || {
            let shape = smarm::introspect::stack_shape(self_pid()).unwrap();
            assert_eq!(shape, (1024 * 1024, DEFAULT_STACK_GUARD));
        });
        h.join().unwrap();
    });
}

#[test]
fn spawn_with_rounds_to_pages() {
    rt1().run(|| {
        let opts = SpawnOpts { stack_reserve: Some(64 * 1024 + 1), guard_size: Some(4097) };
        let h = spawn_with(opts, || {
            let (reserve, guard) = smarm::introspect::stack_shape(self_pid()).unwrap();
            assert_eq!(reserve % 4096, 0);
            assert_eq!(guard % 4096, 0);
            assert!(reserve >= 64 * 1024 + 1);
            assert!(guard >= 4097);
        });
        h.join().unwrap();
    });
}

#[test]
fn spawn_under_with_takes_opts() {
    rt1().run(|| {
        let me = self_pid();
        let opts = SpawnOpts { stack_reserve: Some(128 * 1024), ..SpawnOpts::default() };
        let h = spawn_under_with(me, opts, || {
            let (reserve, _) = smarm::introspect::stack_shape(self_pid()).unwrap();
            assert_eq!(reserve, 128 * 1024);
        });
        h.join().unwrap();
    });
}

/// Obligation 4, from the outside: a dead custom stack must not be handed to
/// the next default spawn. The pool is LIFO, so if the custom stack had been
/// (wrongly) pushed at death, the very next default-shaped spawn on this
/// single-threaded runtime would pop it and report a custom shape.
#[test]
fn custom_stack_never_enters_the_pool() {
    rt1().run(|| {
        spawn_with(
            SpawnOpts { stack_reserve: Some(512 * 1024), guard_size: Some(128 * 1024) },
            || {},
        )
        .join()
        .unwrap();
        let h = spawn(|| {
            let shape = smarm::introspect::stack_shape(self_pid()).unwrap();
            assert_eq!(shape, (DEFAULT_STACK_RESERVE, DEFAULT_STACK_GUARD));
        });
        h.join().unwrap();
    });
}

/// The reverse direction of the pool rule: a default-shaped stack IS pooled
/// and reused (cap = threads × 4 ≥ 1 here, pool empty at start).
#[test]
fn default_stack_is_recycled() {
    rt1().run(|| {
        spawn(|| {}).join().unwrap();
        let h = spawn(|| {
            let shape = smarm::introspect::stack_shape(self_pid()).unwrap();
            assert_eq!(shape, (DEFAULT_STACK_RESERVE, DEFAULT_STACK_GUARD));
        });
        h.join().unwrap();
    });
}

/// Burn ~`frames` × 4 KiB of stack (see tests/runtime.rs twin).
#[inline(never)]
fn burn_stack(frames: usize) -> u64 {
    let mut local = [0u8; 4096];
    local[0] = frames as u8;
    let below = if frames == 0 { 0 } else { burn_stack(frames - 1) };
    std::hint::black_box(&mut local);
    below.wrapping_add(local[0] as u64)
}

#[test]
fn big_reserve_behaviorally_takes_effect() {
    // ~1 MiB deep on an 8 MiB per-spawn reserve, runtime default untouched.
    rt1().run(|| {
        let done = Arc::new(AtomicBool::new(false));
        let done2 = done.clone();
        spawn_with(
            SpawnOpts { stack_reserve: Some(8 * 1024 * 1024), ..SpawnOpts::default() },
            move || {
                std::hint::black_box(burn_stack(256));
                done2.store(true, Ordering::SeqCst);
            },
        )
        .join()
        .unwrap();
        assert!(done.load(Ordering::SeqCst));
    });
}

// ---------------------------------------------------------------------------
// Builder surfaces
// ---------------------------------------------------------------------------

struct Echo;
impl smarm::GenServer for Echo {
    type Call = ();
    type Reply = (usize, usize);
    type Cast = ();
    type Info = ();
    type Timer = ();
    fn handle_call(&mut self, _c: ()) -> (usize, usize) {
        smarm::introspect::stack_shape(self_pid()).unwrap()
    }
    fn handle_cast(&mut self, _c: ()) {}
}

#[test]
fn gen_server_builder_stack_opts() {
    rt1().run(|| {
        let server = GenServerBuilder::new(Echo)
            .stack_opts(SpawnOpts { stack_reserve: Some(256 * 1024), ..SpawnOpts::default() })
            .start();
        let (reserve, guard) = server.call(()).unwrap();
        assert_eq!(reserve, 256 * 1024);
        assert_eq!(guard, DEFAULT_STACK_GUARD);
        server.shutdown();
    });
}

struct Probe;
impl smarm::Machine for Probe {
    type Ev = smarm::channel::Sender<(usize, usize)>;
    fn state_timeout_ev() -> Self::Ev {
        unreachable!("no timers in this test")
    }
    fn timeout_ev(_name: &'static str) -> Self::Ev {
        unreachable!("no timers in this test")
    }
    fn on_start(&mut self, _cx: &mut smarm::Cx<Self::Ev>) {}
    fn handle(
        &mut self,
        ev: Self::Ev,
        _cx: &mut smarm::Cx<Self::Ev>,
    ) -> smarm::gen_statem::Step<Self::Ev> {
        let _ = ev.send(smarm::introspect::stack_shape(self_pid()).unwrap());
        smarm::gen_statem::Step::Stayed
    }
}

#[test]
fn gen_statem_spawn_with_stack_opts() {
    rt1().run(|| {
        let m = smarm::gen_statem::spawn_with(
            SpawnOpts { stack_reserve: Some(256 * 1024), ..SpawnOpts::default() },
            Probe,
        );
        let (tx, rx) = smarm::channel::channel();
        m.send(tx).unwrap();
        let (reserve, guard) = rx.recv().unwrap();
        assert_eq!(reserve, 256 * 1024);
        assert_eq!(guard, DEFAULT_STACK_GUARD);
    });
}