salsa 0.26.1

A generic framework for on-demand, incrementalized computation (experimental)
Documentation 
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//! Test a nested-cycle scenario across three threads:
//!
//! ```text
//! Thread T1          Thread T2         Thread T3
//! ---------          ---------         ---------
//!    |                  |                  |
//!    v                  |                  |
//! query_a()             |                  |
//!  ^  |                 v                  |
//!  |  +------------> query_b()             |
//!  |                  ^   |                v
//!  |                  |   +------------> query_c()
//!  |                  |                    |
//!  +------------------+--------------------+
//!
//! ```
use crate::sync::thread;
use crate::{Knobs, KnobsDatabase};

#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy, salsa::Update)]
struct CycleValue(u32);

const MIN: CycleValue = CycleValue(0);
const MAX: CycleValue = CycleValue(3);

// Signal 1: T1 has entered `query_a`
// Signal 2: T2 has entered `query_b`
// Signal 3: T3 has entered `query_c`

#[salsa::tracked(cycle_initial=initial)]
fn query_a(db: &dyn KnobsDatabase) -> CycleValue {
    db.signal(1);
    db.wait_for(3);

    query_b(db)
}

#[salsa::tracked(cycle_initial=initial)]
fn query_b(db: &dyn KnobsDatabase) -> CycleValue {
    db.wait_for(1);
    db.signal(2);
    db.wait_for(3);

    let c_value = query_c(db);
    CycleValue(c_value.0 + 1).min(MAX)
}

#[salsa::tracked(cycle_initial=initial)]
fn query_c(db: &dyn KnobsDatabase) -> CycleValue {
    db.wait_for(2);
    db.signal(3);

    let a_value = query_a(db);
    let b_value = query_b(db);
    CycleValue(a_value.0.max(b_value.0))
}

fn initial(_db: &dyn KnobsDatabase, _id: salsa::Id) -> CycleValue {
    MIN
}

#[test_log::test]
fn the_test() {
    crate::sync::check(|| {
        let db_t1 = Knobs::default();
        let db_t2 = db_t1.clone();
        let db_t3 = db_t1.clone();

        let t1 = thread::spawn(move || {
            let _span = tracing::info_span!("t1", thread_id = ?thread::current().id()).entered();
            query_a(&db_t1)
        });
        let t2 = thread::spawn(move || {
            let _span = tracing::info_span!("t2", thread_id = ?thread::current().id()).entered();
            query_b(&db_t2)
        });
        let t3 = thread::spawn(move || {
            let _span = tracing::info_span!("t3", thread_id = ?thread::current().id()).entered();
            query_c(&db_t3)
        });

        let r_t1 = t1.join().unwrap();
        let r_t2 = t2.join().unwrap();
        let r_t3 = t3.join().unwrap();

        assert_eq!((r_t1, r_t2, r_t3), (MAX, MAX, MAX));
    });
}