return to the database-wrapping-storage setup

Author: nikomatsakis

components/salsa-macros/src/db.rs

@@ -32,6 +32,13 @@ struct DbMacro {
 impl DbMacro {
     fn try_db(self, input: syn::Item) -> syn::Result<TokenStream> {
         match input {
+            syn::Item::Struct(input) => {
+                let has_storage_impl = self.has_storage_impl(&input)?;
+                Ok(quote! {
+                    #has_storage_impl
+                    #input
+                })
+            }
             syn::Item::Trait(mut input) => {
                 self.add_salsa_view_method(&mut input)?;
                 Ok(quote! {
@@ -46,11 +53,54 @@ impl DbMacro {
             }
             _ => Err(syn::Error::new_spanned(
                 input,
-                "`db` must be applied to a trait or impl",
+                "`db` must be applied to a struct, trait, or impl",
             )),
         }
     }
 
+    fn find_storage_field(&self, input: &syn::ItemStruct) -> syn::Result<syn::Ident> {
+        let storage = "storage";
+        for field in input.fields.iter() {
+            if let Some(i) = &field.ident {
+                if i == storage {
+                    return Ok(i.clone());
+                }
+            } else {
+                return Err(syn::Error::new_spanned(
+                    field,
+                    "database struct must be a braced struct (`{}`) with a field named `storage`",
+                ));
+            }
+        }
+
+        Err(syn::Error::new_spanned(
+            &input.ident,
+            "database struct must be a braced struct (`{}`) with a field named `storage`",
+        ))
+    }
+
+    fn has_storage_impl(&self, input: &syn::ItemStruct) -> syn::Result<TokenStream> {
+        let storage = self.find_storage_field(input)?;
+        let db = &input.ident;
+        let zalsa = self.hygiene.ident("zalsa");
+
+        Ok(quote! {
+            const _: () = {
+                use salsa::plumbing as #zalsa;
+
+                unsafe impl #zalsa::HasStorage for #db {
+                    fn storage(&self) -> &#zalsa::Storage<Self> {
+                        &self.#storage
+                    }
+
+                    fn storage_mut(&mut self) -> &mut #zalsa::Storage<Self> {
+                        &mut self.#storage
+                    }
+                }
+            };
+        })
+    }
+
     fn add_salsa_view_method(&self, input: &mut syn::ItemTrait) -> syn::Result<()> {
         input.items.push(parse_quote! {
             #[doc(hidden)]

examples/calc/db.rs

@@ -1,18 +1,17 @@
 use std::sync::{Arc, Mutex};
 
-use salsa::UserData;
-
-pub type CalcDatabaseImpl = salsa::DatabaseImpl<Calc>;
-
 // ANCHOR: db_struct
+#[salsa::db]
 #[derive(Default)]
-pub struct Calc {
+pub struct CalcDatabaseImpl {
+    storage: salsa::Storage<Self>,
+
     // The logs are only used for testing and demonstrating reuse:
     logs: Arc<Mutex<Option<Vec<String>>>>,
 }
 // ANCHOR_END: db_struct
 
-impl Calc {
+impl CalcDatabaseImpl {
     /// Enable logging of each salsa event.
     #[cfg(test)]
     pub fn enable_logging(&self) {
@@ -34,12 +33,13 @@ impl Calc {
 }
 
 // ANCHOR: db_impl
-impl UserData for Calc {
-    fn salsa_event(db: &CalcDatabaseImpl, event: &dyn Fn() -> salsa::Event) {
+#[salsa::db]
+impl salsa::Database for CalcDatabaseImpl {
+    fn salsa_event(&self, event: &dyn Fn() -> salsa::Event) {
         let event = event();
         eprintln!("Event: {event:?}");
         // Log interesting events, if logging is enabled
-        if let Some(logs) = &mut *db.logs.lock().unwrap() {
+        if let Some(logs) = &mut *self.logs.lock().unwrap() {
             // only log interesting events
             if let salsa::EventKind::WillExecute { .. } = event.kind {
                 logs.push(format!("Event: {event:?}"));

examples/lazy-input/main.rs

@@ -8,13 +8,13 @@ use notify_debouncer_mini::{
     notify::{RecommendedWatcher, RecursiveMode},
     DebounceEventResult, Debouncer,
 };
-use salsa::{Accumulator, DatabaseImpl, Setter, UserData};
+use salsa::{Accumulator, Setter, Storage};
 
 // ANCHOR: main
 fn main() -> Result<()> {
     // Create the channel to receive file change events.
     let (tx, rx) = unbounded();
-    let mut db = DatabaseImpl::with(LazyInput::new(tx));
+    let mut db = LazyInputDatabase::new(tx);
 
     let initial_file_path = std::env::args_os()
         .nth(1)
@@ -74,34 +74,38 @@ trait Db: salsa::Database {
     fn input(&self, path: PathBuf) -> Result<File>;
 }
 
-struct LazyInput {
+#[salsa::db]
+struct LazyInputDatabase {
+    storage: Storage<Self>,
     logs: Mutex<Vec<String>>,
     files: DashMap<PathBuf, File>,
     file_watcher: Mutex<Debouncer<RecommendedWatcher>>,
 }
 
-impl LazyInput {
+impl LazyInputDatabase {
     fn new(tx: Sender<DebounceEventResult>) -> Self {
         Self {
+            storage: Default::default(),
             logs: Default::default(),
             files: DashMap::new(),
             file_watcher: Mutex::new(new_debouncer(Duration::from_secs(1), tx).unwrap()),
         }
     }
 }
 
-impl UserData for LazyInput {
-    fn salsa_event(db: &DatabaseImpl<Self>, event: &dyn Fn() -> salsa::Event) {
+#[salsa::db]
+impl salsa::Database for LazyInputDatabase {
+    fn salsa_event(&self, event: &dyn Fn() -> salsa::Event) {
         // don't log boring events
         let event = event();
         if let salsa::EventKind::WillExecute { .. } = event.kind {
-            db.logs.lock().unwrap().push(format!("{:?}", event));
+            self.logs.lock().unwrap().push(format!("{:?}", event));
         }
     }
 }
 
 #[salsa::db]
-impl Db for DatabaseImpl<LazyInput> {
+impl Db for LazyInputDatabase {
     fn input(&self, path: PathBuf) -> Result<File> {
         let path = path
             .canonicalize()

src/database.rs

@@ -1,24 +1,11 @@
-use std::{any::Any, marker::PhantomData, panic::RefUnwindSafe, sync::Arc};
+use std::any::Any;
 
-use parking_lot::{Condvar, Mutex};
-
-use crate::{
-    self as salsa,
-    zalsa::Zalsa,
-    zalsa_local::{self, ZalsaLocal},
-    Durability, Event, EventKind, Revision,
-};
+use crate::{zalsa::ZalsaDatabase, Durability, Event, Revision};
 
 /// The trait implemented by all Salsa databases.
-/// You can create your own subtraits of this trait using the `#[salsa::db]` procedural macro.
-///
-/// # Safety
-///
-/// This trait can only safely be implemented by Salsa's [`DatabaseImpl`][] type.
-///
-/// FIXME: Document better the unsafety conditions we require.
-#[salsa_macros::db]
-pub unsafe trait Database: Send + AsDynDatabase + Any {
+/// You can create your own subtraits of this trait using the `#[salsa::db]`(`crate::db`) procedural macro.
+#[crate::db]
+pub trait Database: Send + AsDynDatabase + Any + ZalsaDatabase {
     /// This function is invoked by the salsa runtime at various points during execution.
     /// You can customize what happens by implementing the [`UserData`][] trait.
     /// By default, the event is logged at level debug using tracing facade.
@@ -58,21 +45,6 @@ pub unsafe trait Database: Send + AsDynDatabase + Any {
     {
         crate::attach::attach(self, || op(self))
     }
-
-    /// Plumbing method: Access the internal salsa methods.
-    #[doc(hidden)]
-    fn zalsa(&self) -> &Zalsa;
-
-    /// Plumbing method: Access the internal salsa methods for mutating the database.
-    ///
-    /// **WARNING:** Triggers a new revision, canceling other database handles.
-    /// This can lead to deadlock!
-    #[doc(hidden)]
-    fn zalsa_mut(&mut self) -> &mut Zalsa;
-
-    /// Access the thread-local state associated with this database
-    #[doc(hidden)]
-    fn zalsa_local(&self) -> &ZalsaLocal;
 }
 
 /// Upcast to a `dyn Database`.
@@ -108,174 +80,3 @@ impl dyn Database {
         self.zalsa().views().try_view_as(self).unwrap()
     }
 }
-
-/// Concrete implementation of the [`Database`][] trait.
-/// Takes an optional type parameter `U` that allows you to thread your own data.
-pub struct DatabaseImpl<U: UserData = ()> {
-    /// Reference to the database. This is always `Some` except during destruction.
-    zalsa_impl: Option<Arc<Zalsa>>,
-
-    /// Coordination data for cancellation of other handles when `zalsa_mut` is called.
-    /// This could be stored in Zalsa but it makes things marginally cleaner to keep it separate.
-    coordinate: Arc<Coordinate>,
-
-    /// Per-thread state
-    zalsa_local: zalsa_local::ZalsaLocal,
-
-    /// The `U` is stored as a `dyn Any` in `zalsa_impl`
-    phantom: PhantomData<U>,
-}
-
-impl<U: UserData + Default> Default for DatabaseImpl<U> {
-    fn default() -> Self {
-        Self::with(U::default())
-    }
-}
-
-impl DatabaseImpl<()> {
-    /// Create a new database with the given user data.
-    ///
-    /// You can also use the [`Default`][] trait if your userdata implements it.
-    pub fn new() -> Self {
-        Self::with(())
-    }
-}
-
-impl<U: UserData> DatabaseImpl<U> {
-    /// Create a new database with the given user data.
-    ///
-    /// You can also use the [`Default`][] trait if your userdata implements it.
-    pub fn with(u: U) -> Self {
-        Self {
-            zalsa_impl: Some(Arc::new(Zalsa::with(u))),
-            coordinate: Arc::new(Coordinate {
-                clones: Mutex::new(1),
-                cvar: Default::default(),
-            }),
-            zalsa_local: ZalsaLocal::new(),
-            phantom: PhantomData::<U>,
-        }
-    }
-
-    /// Access the `Arc<Zalsa>`. This should always be
-    /// possible as `zalsa_impl` only becomes
-    /// `None` once we are in the `Drop` impl.
-    fn zalsa_impl(&self) -> &Arc<Zalsa> {
-        self.zalsa_impl.as_ref().unwrap()
-    }
-
-    // ANCHOR: cancel_other_workers
-    /// Sets cancellation flag and blocks until all other workers with access
-    /// to this storage have completed.
-    ///
-    /// This could deadlock if there is a single worker with two handles to the
-    /// same database!
-    fn cancel_others(&mut self) {
-        let zalsa = self.zalsa_impl();
-        zalsa.set_cancellation_flag();
-
-        self.salsa_event(&|| Event {
-            thread_id: std::thread::current().id(),
-
-            kind: EventKind::DidSetCancellationFlag,
-        });
-
-        let mut clones = self.coordinate.clones.lock();
-        while *clones != 1 {
-            self.coordinate.cvar.wait(&mut clones);
-        }
-    }
-    // ANCHOR_END: cancel_other_workers
-}
-
-impl<U: UserData> std::ops::Deref for DatabaseImpl<U> {
-    type Target = U;
-
-    fn deref(&self) -> &U {
-        self.zalsa_impl().user_data().downcast_ref::<U>().unwrap()
-    }
-}
-
-impl<U: UserData> std::ops::DerefMut for DatabaseImpl<U> {
-    fn deref_mut(&mut self) -> &mut U {
-        self.zalsa_mut()
-            .user_data_mut()
-            .downcast_mut::<U>()
-            .unwrap()
-    }
-}
-
-impl<U: UserData + RefUnwindSafe> RefUnwindSafe for DatabaseImpl<U> {}
-
-#[salsa_macros::db]
-unsafe impl<U: UserData> Database for DatabaseImpl<U> {
-    fn zalsa(&self) -> &Zalsa {
-        &**self.zalsa_impl()
-    }
-
-    fn zalsa_mut(&mut self) -> &mut Zalsa {
-        self.cancel_others();
-
-        // The ref count on the `Arc` should now be 1
-        let arc_zalsa_mut = self.zalsa_impl.as_mut().unwrap();
-        let zalsa_mut = Arc::get_mut(arc_zalsa_mut).unwrap();
-        zalsa_mut.new_revision();
-        zalsa_mut
-    }
-
-    fn zalsa_local(&self) -> &ZalsaLocal {
-        &self.zalsa_local
-    }
-
-    // Report a salsa event.
-    fn salsa_event(&self, event: &dyn Fn() -> Event) {
-        U::salsa_event(self, event)
-    }
-}
-
-impl<U: UserData> Clone for DatabaseImpl<U> {
-    fn clone(&self) -> Self {
-        *self.coordinate.clones.lock() += 1;
-
-        Self {
-            zalsa_impl: self.zalsa_impl.clone(),
-            coordinate: Arc::clone(&self.coordinate),
-            zalsa_local: ZalsaLocal::new(),
-            phantom: PhantomData::<U>,
-        }
-    }
-}
-
-impl<U: UserData> Drop for DatabaseImpl<U> {
-    fn drop(&mut self) {
-        // Drop the database handle *first*
-        self.zalsa_impl.take();
-
-        // *Now* decrement the number of clones and notify once we have completed
-        *self.coordinate.clones.lock() -= 1;
-        self.coordinate.cvar.notify_all();
-    }
-}
-
-pub trait UserData: Any + Sized + Send + Sync {
-    /// Callback invoked by the [`Database`][] at key points during salsa execution.
-    /// By overriding this method, you can inject logging or other custom behavior.
-    ///
-    /// By default, the event is logged at level debug using the `tracing` crate.
-    ///
-    /// # Parameters
-    ///
-    /// * `event` a fn that, if called, will return the event that occurred
-    fn salsa_event(_db: &DatabaseImpl<Self>, event: &dyn Fn() -> Event) {
-        tracing::debug!("salsa_event: {:?}", event())
-    }
-}
-
-impl UserData for () {}
-
-struct Coordinate {
-    /// Counter of the number of clones of actor. Begins at 1.
-    /// Incremented when cloned, decremented when dropped.
-    clones: Mutex<usize>,
-    cvar: Condvar,
-}