Merge pull request #13 from matklad/volatile-cycles

Detect volatile cycles

src/lib.rs

@@ -368,7 +368,7 @@ macro_rules! query_definition {
     (
         @storage_ty[$QC:ident, $Self:ident, volatile]
     ) => {
-        $crate::volatile::VolatileStorage
+        $crate::volatile::VolatileStorage<$QC, $Self>
     };
 
     // Accept a "field-like" query definition (input)

src/volatile.rs

@@ -5,8 +5,8 @@ use crate::QueryContext;
 use crate::QueryStorageOps;
 use crate::QueryTable;
 use log::debug;
-use parking_lot::{RwLock, RwLockUpgradableReadGuard};
-use rustc_hash::FxHashMap;
+use parking_lot::Mutex;
+use rustc_hash::FxHashSet;
 use std::any::Any;
 use std::cell::RefCell;
 use std::collections::hash_map::Entry;
@@ -17,10 +17,29 @@ use std::hash::Hash;
 
 /// Volatile Storage is just **always** considered dirty. Any time you
 /// ask for the result of such a query, it is recomputed.
-#[derive(Default)]
-pub struct VolatileStorage;
+pub struct VolatileStorage<QC, Q>
+where
+    Q: Query<QC>,
+    QC: QueryContext,
+{
+    /// We don't store the results of volatile queries,
+    /// but we track in-progress set to detect cycles.
+    in_progress: Mutex<FxHashSet<Q::Key>>,
+}
 
-impl<QC, Q> QueryStorageOps<QC, Q> for VolatileStorage
+impl<QC, Q> Default for VolatileStorage<QC, Q>
+where
+    Q: Query<QC>,
+    QC: QueryContext,
+{
+    fn default() -> Self {
+        VolatileStorage {
+            in_progress: Mutex::new(FxHashSet::default()),
+        }
+    }
+}
+
+impl<QC, Q> QueryStorageOps<QC, Q> for VolatileStorage<QC, Q>
 where
     Q: Query<QC>,
     QC: QueryContext,
@@ -31,12 +50,18 @@ where
         key: &Q::Key,
         descriptor: &QC::QueryDescriptor,
     ) -> Result<Q::Value, CycleDetected> {
+        if !self.in_progress.lock().insert(key.clone()) {
+            return Err(CycleDetected);
+        }
+
         // FIXME: Should we even call `execute_query_implementation`
         // here? Or should we just call `Q::execute`, and maybe
         // separate out the `push`/`pop` operations.
         let (value, _inputs) = query
             .salsa_runtime()
             .execute_query_implementation::<Q>(query, descriptor, key);
+        let was_in_progress = self.in_progress.lock().remove(key);
+        assert!(was_in_progress);
 
         query.salsa_runtime().report_query_read(descriptor);
 

tests/cycles.rs

@@ -0,0 +1,73 @@
+#![feature(crate_visibility_modifier)]
+
+#[derive(Default)]
+pub struct QueryContextImpl {
+    runtime: salsa::runtime::Runtime<QueryContextImpl>,
+}
+
+impl salsa::QueryContext for QueryContextImpl {
+    fn salsa_runtime(&self) -> &salsa::runtime::Runtime<QueryContextImpl> {
+        &self.runtime
+    }
+}
+
+salsa::query_context_storage! {
+    pub struct QueryContextImplStorage for QueryContextImpl {
+        impl QueryContext {
+            fn memoized_a() for MemoizedA;
+            fn memoized_b() for MemoizedB;
+            fn volatile_a() for VolatileA;
+            fn volatile_b() for VolatileB;
+        }
+    }
+}
+
+trait QueryContext: salsa::QueryContext {
+    salsa::query_prototype! {
+        // `a` and `b` depend on each other and form a cycle
+        fn memoized_a() for MemoizedA;
+        fn memoized_b() for MemoizedB;
+        fn volatile_a() for VolatileA;
+        fn volatile_b() for VolatileB;
+    }
+}
+
+salsa::query_definition! {
+    crate MemoizedA(query: &impl QueryContext, (): ()) -> () {
+        query.memoized_b().get(())
+    }
+}
+
+salsa::query_definition! {
+    crate MemoizedB(query: &impl QueryContext, (): ()) -> () {
+        query.memoized_a().get(())
+    }
+}
+
+salsa::query_definition! {
+    #[storage(volatile)]
+    crate VolatileA(query: &impl QueryContext, (): ()) -> () {
+        query.volatile_b().get(())
+    }
+}
+
+salsa::query_definition! {
+    #[storage(volatile)]
+    crate VolatileB(query: &impl QueryContext, (): ()) -> () {
+        query.volatile_a().get(())
+    }
+}
+
+#[test]
+#[should_panic(expected = "cycle detected")]
+fn cycle_memoized() {
+    let query = QueryContextImpl::default();
+    query.memoized_a().get(());
+}
+
+#[test]
+#[should_panic(expected = "cycle detected")]
+fn cycle_volatile() {
+    let query = QueryContextImpl::default();
+    query.volatile_a().get(());
+}