Add a test for a cycle with changing cycle heads

Author: MichaReiser

tests/parallel/cycle_nested_deep_conditional.rs

@@ -0,0 +1,110 @@
+//! Test a deeply nested-cycle scenario where cycles have changing query dependencies.
+//!
+//! The trick is that different threads call into the same cycle from different entry queries and
+//! the cycle heads change over different iterations
+//!
+//! * Thread 1: `a` -> b -> c
+//! * Thread 2: `b`
+//! * Thread 3: `d` -> `c`
+//! * Thread 4: `e` -> `c`
+//!
+//! `c` calls:
+//! * `d` and `a` in the first few iterations
+//! * `d`, `b` and `e` in the last iterations
+use crate::sync::thread;
+use crate::{Knobs, KnobsDatabase};
+
+use salsa::CycleRecoveryAction;
+
+#[derive(Debug, PartialEq, Eq, PartialOrd, Ord, Hash, Clone, Copy, salsa::Update)]
+struct CycleValue(u32);
+
+const MIN: CycleValue = CycleValue(0);
+const MAX: CycleValue = CycleValue(3);
+
+#[salsa::tracked(cycle_fn=cycle_fn, cycle_initial=initial)]
+fn query_a(db: &dyn KnobsDatabase) -> CycleValue {
+    query_b(db)
+}
+
+#[salsa::tracked(cycle_fn=cycle_fn, cycle_initial=initial)]
+fn query_b(db: &dyn KnobsDatabase) -> CycleValue {
+    let c_value = query_c(db);
+    CycleValue(c_value.0 + 1).min(MAX)
+}
+
+#[salsa::tracked(cycle_fn=cycle_fn, cycle_initial=initial)]
+fn query_c(db: &dyn KnobsDatabase) -> CycleValue {
+    let d_value = query_d(db);
+
+    if d_value > CycleValue(0) {
+        let e_value = query_e(db);
+        let b_value = query_b(db);
+        CycleValue(d_value.0.max(e_value.0).max(b_value.0))
+    } else {
+        let a_value = query_a(db);
+        CycleValue(d_value.0.max(a_value.0))
+    }
+}
+
+#[salsa::tracked(cycle_fn=cycle_fn, cycle_initial=initial)]
+fn query_d(db: &dyn KnobsDatabase) -> CycleValue {
+    query_c(db)
+}
+
+#[salsa::tracked(cycle_fn=cycle_fn, cycle_initial=initial)]
+fn query_e(db: &dyn KnobsDatabase) -> CycleValue {
+    query_c(db)
+}
+
+fn cycle_fn(
+    _db: &dyn KnobsDatabase,
+    _value: &CycleValue,
+    _count: u32,
+) -> CycleRecoveryAction<CycleValue> {
+    CycleRecoveryAction::Iterate
+}
+
+fn initial(_db: &dyn KnobsDatabase) -> CycleValue {
+    MIN
+}
+
+#[test_log::test]
+fn the_test() {
+    crate::sync::check(|| {
+        tracing::debug!("New run");
+        let db_t1 = Knobs::default();
+        let db_t2 = db_t1.clone();
+        let db_t3 = db_t1.clone();
+        let db_t4 = db_t1.clone();
+
+        let t1 = thread::spawn(move || {
+            let _span = tracing::debug_span!("t1", thread_id = ?thread::current().id()).entered();
+            let result = query_a(&db_t1);
+            db_t1.signal(1);
+            result
+        });
+        let t2 = thread::spawn(move || {
+            let _span = tracing::debug_span!("t4", thread_id = ?thread::current().id()).entered();
+            db_t4.wait_for(1);
+            query_b(&db_t4)
+        });
+        let t3 = thread::spawn(move || {
+            let _span = tracing::debug_span!("t2", thread_id = ?thread::current().id()).entered();
+            db_t2.wait_for(1);
+            query_d(&db_t2)
+        });
+        let t4 = thread::spawn(move || {
+            let _span = tracing::debug_span!("t3", thread_id = ?thread::current().id()).entered();
+            db_t3.wait_for(1);
+            query_e(&db_t3)
+        });
+
+        let r_t1 = t1.join().unwrap();
+        let r_t2 = t2.join().unwrap();
+        let r_t3 = t3.join().unwrap();
+        let r_t4 = t4.join().unwrap();
+
+        assert_eq!((r_t1, r_t2, r_t3, r_t4), (MAX, MAX, MAX, MAX));
+    });
+}