Unnamed repository; edit this file 'description' to name the repository.
Diffstat (limited to 'crates/ra-salsa/src/derived/slot.rs')
| -rw-r--r-- | crates/ra-salsa/src/derived/slot.rs | 775 |
1 files changed, 775 insertions, 0 deletions
diff --git a/crates/ra-salsa/src/derived/slot.rs b/crates/ra-salsa/src/derived/slot.rs new file mode 100644 index 0000000000..de7a397607 --- /dev/null +++ b/crates/ra-salsa/src/derived/slot.rs @@ -0,0 +1,775 @@ +use crate::debug::TableEntry; +use crate::durability::Durability; +use crate::plumbing::{DatabaseOps, QueryFunction}; +use crate::revision::Revision; +use crate::runtime::local_state::ActiveQueryGuard; +use crate::runtime::local_state::QueryRevisions; +use crate::runtime::Runtime; +use crate::runtime::RuntimeId; +use crate::runtime::StampedValue; +use crate::runtime::WaitResult; +use crate::Cycle; +use crate::{Database, DatabaseKeyIndex, Event, EventKind, QueryDb}; +use parking_lot::{RawRwLock, RwLock}; +use std::ops::Deref; +use std::sync::atomic::{AtomicBool, Ordering}; +use tracing::{debug, info}; + +pub(super) struct Slot<Q> +where + Q: QueryFunction, +{ + key_index: u32, + // FIXME: Yeet this + group_index: u16, + state: RwLock<QueryState<Q>>, +} + +/// Defines the "current state" of query's memoized results. +enum QueryState<Q> +where + Q: QueryFunction, +{ + NotComputed, + + /// The runtime with the given id is currently computing the + /// result of this query. + InProgress { + id: RuntimeId, + + /// Set to true if any other queries are blocked, + /// waiting for this query to complete. + anyone_waiting: AtomicBool, + }, + + /// We have computed the query already, and here is the result. + Memoized(Memo<Q::Value>), +} + +struct Memo<V> { + /// The result of the query, if we decide to memoize it. + value: V, + + /// Last revision when this memo was verified; this begins + /// as the current revision. + pub(crate) verified_at: Revision, + + /// Revision information + revisions: QueryRevisions, +} + +/// Return value of `probe` helper. +enum ProbeState<V, G> { + /// Another thread was active but has completed. + /// Try again! + Retry, + + /// No entry for this key at all. + NotComputed(G), + + /// There is an entry, but its contents have not been + /// verified in this revision. + Stale(G), + + /// There is an entry which has been verified, + /// and it has the following value-- or, we blocked + /// on another thread, and that resulted in a cycle. + UpToDate(V), +} + +/// Return value of `maybe_changed_after_probe` helper. +enum MaybeChangedSinceProbeState<G> { + /// Another thread was active but has completed. + /// Try again! + Retry, + + /// Value may have changed in the given revision. + ChangedAt(Revision), + + /// There is a stale cache entry that has not been + /// verified in this revision, so we can't say. + Stale(G), +} + +impl<Q> Slot<Q> +where + Q: QueryFunction, + Q::Value: Eq, +{ + pub(super) fn new(database_key_index: DatabaseKeyIndex) -> Self { + Self { + key_index: database_key_index.key_index, + group_index: database_key_index.group_index, + state: RwLock::new(QueryState::NotComputed), + } + } + + pub(super) fn database_key_index(&self) -> DatabaseKeyIndex { + DatabaseKeyIndex { + group_index: self.group_index, + query_index: Q::QUERY_INDEX, + key_index: self.key_index, + } + } + + pub(super) fn read( + &self, + db: &<Q as QueryDb<'_>>::DynDb, + key: &Q::Key, + ) -> StampedValue<Q::Value> { + let runtime = db.salsa_runtime(); + + // NB: We don't need to worry about people modifying the + // revision out from under our feet. Either `db` is a frozen + // database, in which case there is a lock, or the mutator + // thread is the current thread, and it will be prevented from + // doing any `set` invocations while the query function runs. + let revision_now = runtime.current_revision(); + + info!("{:?}: invoked at {:?}", self, revision_now,); + + // First, do a check with a read-lock. + loop { + match self.probe(db, self.state.read(), runtime, revision_now) { + ProbeState::UpToDate(v) => return v, + ProbeState::Stale(..) | ProbeState::NotComputed(..) => break, + ProbeState::Retry => continue, + } + } + + self.read_upgrade(db, key, revision_now) + } + + /// Second phase of a read operation: acquires an upgradable-read + /// and -- if needed -- validates whether inputs have changed, + /// recomputes value, etc. This is invoked after our initial probe + /// shows a potentially out of date value. + fn read_upgrade( + &self, + db: &<Q as QueryDb<'_>>::DynDb, + key: &Q::Key, + revision_now: Revision, + ) -> StampedValue<Q::Value> { + let runtime = db.salsa_runtime(); + + debug!("{:?}: read_upgrade(revision_now={:?})", self, revision_now,); + + // Check with an upgradable read to see if there is a value + // already. (This permits other readers but prevents anyone + // else from running `read_upgrade` at the same time.) + let mut old_memo = loop { + match self.probe(db, self.state.upgradable_read(), runtime, revision_now) { + ProbeState::UpToDate(v) => return v, + ProbeState::Stale(state) | ProbeState::NotComputed(state) => { + type RwLockUpgradableReadGuard<'a, T> = + lock_api::RwLockUpgradableReadGuard<'a, RawRwLock, T>; + + let mut state = RwLockUpgradableReadGuard::upgrade(state); + match std::mem::replace(&mut *state, QueryState::in_progress(runtime.id())) { + QueryState::Memoized(old_memo) => break Some(old_memo), + QueryState::InProgress { .. } => unreachable!(), + QueryState::NotComputed => break None, + } + } + ProbeState::Retry => continue, + } + }; + + let panic_guard = PanicGuard::new(self, runtime); + let active_query = runtime.push_query(self.database_key_index()); + + // If we have an old-value, it *may* now be stale, since there + // has been a new revision since the last time we checked. So, + // first things first, let's walk over each of our previous + // inputs and check whether they are out of date. + if let Some(memo) = &mut old_memo { + if let Some(value) = memo.verify_value(db.ops_database(), revision_now, &active_query) { + info!("{:?}: validated old memoized value", self,); + + db.salsa_event(Event { + runtime_id: runtime.id(), + kind: EventKind::DidValidateMemoizedValue { + database_key: self.database_key_index(), + }, + }); + + panic_guard.proceed(old_memo); + + return value; + } + } + + self.execute(db, runtime, revision_now, active_query, panic_guard, old_memo, key) + } + + fn execute( + &self, + db: &<Q as QueryDb<'_>>::DynDb, + runtime: &Runtime, + revision_now: Revision, + active_query: ActiveQueryGuard<'_>, + panic_guard: PanicGuard<'_, Q>, + old_memo: Option<Memo<Q::Value>>, + key: &Q::Key, + ) -> StampedValue<Q::Value> { + tracing::info!("{:?}: executing query", self.database_key_index().debug(db)); + + db.salsa_event(Event { + runtime_id: db.salsa_runtime().id(), + kind: EventKind::WillExecute { database_key: self.database_key_index() }, + }); + + // Query was not previously executed, or value is potentially + // stale, or value is absent. Let's execute! + let value = match Cycle::catch(|| Q::execute(db, key.clone())) { + Ok(v) => v, + Err(cycle) => { + tracing::debug!( + "{:?}: caught cycle {:?}, have strategy {:?}", + self.database_key_index().debug(db), + cycle, + Q::CYCLE_STRATEGY, + ); + match Q::CYCLE_STRATEGY { + crate::plumbing::CycleRecoveryStrategy::Panic => { + panic_guard.proceed(None); + cycle.throw() + } + crate::plumbing::CycleRecoveryStrategy::Fallback => { + if let Some(c) = active_query.take_cycle() { + assert!(c.is(&cycle)); + Q::cycle_fallback(db, &cycle, key) + } else { + // we are not a participant in this cycle + debug_assert!(!cycle + .participant_keys() + .any(|k| k == self.database_key_index())); + cycle.throw() + } + } + } + } + }; + + let mut revisions = active_query.pop(); + + // We assume that query is side-effect free -- that is, does + // not mutate the "inputs" to the query system. Sanity check + // that assumption here, at least to the best of our ability. + assert_eq!( + runtime.current_revision(), + revision_now, + "revision altered during query execution", + ); + + // If the new value is equal to the old one, then it didn't + // really change, even if some of its inputs have. So we can + // "backdate" its `changed_at` revision to be the same as the + // old value. + if let Some(old_memo) = &old_memo { + // Careful: if the value became less durable than it + // used to be, that is a "breaking change" that our + // consumers must be aware of. Becoming *more* durable + // is not. See the test `constant_to_non_constant`. + if revisions.durability >= old_memo.revisions.durability && old_memo.value == value { + debug!( + "read_upgrade({:?}): value is equal, back-dating to {:?}", + self, old_memo.revisions.changed_at, + ); + + assert!(old_memo.revisions.changed_at <= revisions.changed_at); + revisions.changed_at = old_memo.revisions.changed_at; + } + } + + let new_value = StampedValue { + value, + durability: revisions.durability, + changed_at: revisions.changed_at, + }; + + let memo_value = new_value.value.clone(); + + debug!("read_upgrade({:?}): result.revisions = {:#?}", self, revisions,); + + panic_guard.proceed(Some(Memo { value: memo_value, verified_at: revision_now, revisions })); + + new_value + } + + /// Helper for `read` that does a shallow check (not recursive) if we have an up-to-date value. + /// + /// Invoked with the guard `state` corresponding to the `QueryState` of some `Slot` (the guard + /// can be either read or write). Returns a suitable `ProbeState`: + /// + /// - `ProbeState::UpToDate(r)` if the table has an up-to-date value (or we blocked on another + /// thread that produced such a value). + /// - `ProbeState::StaleOrAbsent(g)` if either (a) there is no memo for this key, (b) the memo + /// has no value; or (c) the memo has not been verified at the current revision. + /// + /// Note that in case `ProbeState::UpToDate`, the lock will have been released. + fn probe<StateGuard>( + &self, + db: &<Q as QueryDb<'_>>::DynDb, + state: StateGuard, + runtime: &Runtime, + revision_now: Revision, + ) -> ProbeState<StampedValue<Q::Value>, StateGuard> + where + StateGuard: Deref<Target = QueryState<Q>>, + { + match &*state { + QueryState::NotComputed => ProbeState::NotComputed(state), + + QueryState::InProgress { id, anyone_waiting } => { + let other_id = *id; + + // NB: `Ordering::Relaxed` is sufficient here, + // as there are no loads that are "gated" on this + // value. Everything that is written is also protected + // by a lock that must be acquired. The role of this + // boolean is to decide *whether* to acquire the lock, + // not to gate future atomic reads. + anyone_waiting.store(true, Ordering::Relaxed); + + self.block_on_or_unwind(db, runtime, other_id, state); + + // Other thread completely normally, so our value may be available now. + ProbeState::Retry + } + + QueryState::Memoized(memo) => { + debug!( + "{:?}: found memoized value, verified_at={:?}, changed_at={:?}", + self, memo.verified_at, memo.revisions.changed_at, + ); + + if memo.verified_at < revision_now { + return ProbeState::Stale(state); + } + + let value = &memo.value; + let value = StampedValue { + durability: memo.revisions.durability, + changed_at: memo.revisions.changed_at, + value: value.clone(), + }; + + info!("{:?}: returning memoized value changed at {:?}", self, value.changed_at); + + ProbeState::UpToDate(value) + } + } + } + + pub(super) fn durability(&self, db: &<Q as QueryDb<'_>>::DynDb) -> Durability { + match &*self.state.read() { + QueryState::NotComputed => Durability::LOW, + QueryState::InProgress { .. } => panic!("query in progress"), + QueryState::Memoized(memo) => { + if memo.check_durability(db.salsa_runtime()) { + memo.revisions.durability + } else { + Durability::LOW + } + } + } + } + + pub(super) fn as_table_entry(&self, key: &Q::Key) -> Option<TableEntry<Q::Key, Q::Value>> { + match &*self.state.read() { + QueryState::NotComputed => None, + QueryState::InProgress { .. } => Some(TableEntry::new(key.clone(), None)), + QueryState::Memoized(memo) => { + Some(TableEntry::new(key.clone(), Some(memo.value.clone()))) + } + } + } + + pub(super) fn invalidate(&self, new_revision: Revision) -> Option<Durability> { + tracing::debug!("Slot::invalidate(new_revision = {:?})", new_revision); + match &mut *self.state.write() { + QueryState::Memoized(memo) => { + memo.revisions.untracked = true; + memo.revisions.inputs = None; + memo.revisions.changed_at = new_revision; + Some(memo.revisions.durability) + } + QueryState::NotComputed => None, + QueryState::InProgress { .. } => unreachable!(), + } + } + + pub(super) fn maybe_changed_after( + &self, + db: &<Q as QueryDb<'_>>::DynDb, + revision: Revision, + key: &Q::Key, + ) -> bool { + let runtime = db.salsa_runtime(); + let revision_now = runtime.current_revision(); + + db.unwind_if_cancelled(); + + debug!( + "maybe_changed_after({:?}) called with revision={:?}, revision_now={:?}", + self, revision, revision_now, + ); + + // Do an initial probe with just the read-lock. + // + // If we find that a cache entry for the value is present + // but hasn't been verified in this revision, we'll have to + // do more. + loop { + match self.maybe_changed_after_probe(db, self.state.read(), runtime, revision_now) { + MaybeChangedSinceProbeState::Retry => continue, + MaybeChangedSinceProbeState::ChangedAt(changed_at) => return changed_at > revision, + MaybeChangedSinceProbeState::Stale(state) => { + drop(state); + return self.maybe_changed_after_upgrade(db, revision, key); + } + } + } + } + + fn maybe_changed_after_probe<StateGuard>( + &self, + db: &<Q as QueryDb<'_>>::DynDb, + state: StateGuard, + runtime: &Runtime, + revision_now: Revision, + ) -> MaybeChangedSinceProbeState<StateGuard> + where + StateGuard: Deref<Target = QueryState<Q>>, + { + match self.probe(db, state, runtime, revision_now) { + ProbeState::Retry => MaybeChangedSinceProbeState::Retry, + + ProbeState::Stale(state) => MaybeChangedSinceProbeState::Stale(state), + + // If we know when value last changed, we can return right away. + // Note that we don't need the actual value to be available. + ProbeState::UpToDate(StampedValue { value: _, durability: _, changed_at }) => { + MaybeChangedSinceProbeState::ChangedAt(changed_at) + } + + // If we have nothing cached, then value may have changed. + ProbeState::NotComputed(_) => MaybeChangedSinceProbeState::ChangedAt(revision_now), + } + } + + fn maybe_changed_after_upgrade( + &self, + db: &<Q as QueryDb<'_>>::DynDb, + revision: Revision, + key: &Q::Key, + ) -> bool { + let runtime = db.salsa_runtime(); + let revision_now = runtime.current_revision(); + + // Get an upgradable read lock, which permits other reads but no writers. + // Probe again. If the value is stale (needs to be verified), then upgrade + // to a write lock and swap it with InProgress while we work. + let mut old_memo = match self.maybe_changed_after_probe( + db, + self.state.upgradable_read(), + runtime, + revision_now, + ) { + MaybeChangedSinceProbeState::ChangedAt(changed_at) => return changed_at > revision, + + // If another thread was active, then the cache line is going to be + // either verified or cleared out. Just recurse to figure out which. + // Note that we don't need an upgradable read. + MaybeChangedSinceProbeState::Retry => { + return self.maybe_changed_after(db, revision, key) + } + + MaybeChangedSinceProbeState::Stale(state) => { + type RwLockUpgradableReadGuard<'a, T> = + lock_api::RwLockUpgradableReadGuard<'a, RawRwLock, T>; + + let mut state = RwLockUpgradableReadGuard::upgrade(state); + match std::mem::replace(&mut *state, QueryState::in_progress(runtime.id())) { + QueryState::Memoized(old_memo) => old_memo, + QueryState::NotComputed | QueryState::InProgress { .. } => unreachable!(), + } + } + }; + + let panic_guard = PanicGuard::new(self, runtime); + let active_query = runtime.push_query(self.database_key_index()); + + if old_memo.verify_revisions(db.ops_database(), revision_now, &active_query) { + let maybe_changed = old_memo.revisions.changed_at > revision; + panic_guard.proceed(Some(old_memo)); + maybe_changed + } else { + // We found that this memoized value may have changed + // but we have an old value. We can re-run the code and + // actually *check* if it has changed. + let StampedValue { changed_at, .. } = self.execute( + db, + runtime, + revision_now, + active_query, + panic_guard, + Some(old_memo), + key, + ); + changed_at > revision + } + } + + /// Helper: see [`Runtime::try_block_on_or_unwind`]. + fn block_on_or_unwind<MutexGuard>( + &self, + db: &<Q as QueryDb<'_>>::DynDb, + runtime: &Runtime, + other_id: RuntimeId, + mutex_guard: MutexGuard, + ) { + runtime.block_on_or_unwind( + db.ops_database(), + self.database_key_index(), + other_id, + mutex_guard, + ) + } +} + +impl<Q> QueryState<Q> +where + Q: QueryFunction, +{ + fn in_progress(id: RuntimeId) -> Self { + QueryState::InProgress { id, anyone_waiting: Default::default() } + } +} + +struct PanicGuard<'me, Q> +where + Q: QueryFunction, + Q::Value: Eq, +{ + slot: &'me Slot<Q>, + runtime: &'me Runtime, +} + +impl<'me, Q> PanicGuard<'me, Q> +where + Q: QueryFunction, + Q::Value: Eq, +{ + fn new(slot: &'me Slot<Q>, runtime: &'me Runtime) -> Self { + Self { slot, runtime } + } + + /// Indicates that we have concluded normally (without panicking). + /// If `opt_memo` is some, then this memo is installed as the new + /// memoized value. If `opt_memo` is `None`, then the slot is cleared + /// and has no value. + fn proceed(mut self, opt_memo: Option<Memo<Q::Value>>) { + self.overwrite_placeholder(WaitResult::Completed, opt_memo); + std::mem::forget(self) + } + + /// Overwrites the `InProgress` placeholder for `key` that we + /// inserted; if others were blocked, waiting for us to finish, + /// then notify them. + fn overwrite_placeholder(&mut self, wait_result: WaitResult, opt_memo: Option<Memo<Q::Value>>) { + let old_value = { + let mut write = self.slot.state.write(); + match opt_memo { + // Replace the `InProgress` marker that we installed with the new + // memo, thus releasing our unique access to this key. + Some(memo) => std::mem::replace(&mut *write, QueryState::Memoized(memo)), + + // We had installed an `InProgress` marker, but we panicked before + // it could be removed. At this point, we therefore "own" unique + // access to our slot, so we can just remove the key. + None => std::mem::replace(&mut *write, QueryState::NotComputed), + } + }; + + match old_value { + QueryState::InProgress { id, anyone_waiting } => { + assert_eq!(id, self.runtime.id()); + + // NB: As noted on the `store`, `Ordering::Relaxed` is + // sufficient here. This boolean signals us on whether to + // acquire a mutex; the mutex will guarantee that all writes + // we are interested in are visible. + if anyone_waiting.load(Ordering::Relaxed) { + self.runtime + .unblock_queries_blocked_on(self.slot.database_key_index(), wait_result); + } + } + _ => panic!( + "\ +Unexpected panic during query evaluation, aborting the process. + +Please report this bug to https://github.com/salsa-rs/salsa/issues." + ), + } + } +} + +impl<'me, Q> Drop for PanicGuard<'me, Q> +where + Q: QueryFunction, + Q::Value: Eq, +{ + fn drop(&mut self) { + if std::thread::panicking() { + // We panicked before we could proceed and need to remove `key`. + self.overwrite_placeholder(WaitResult::Panicked, None) + } else { + // If no panic occurred, then panic guard ought to be + // "forgotten" and so this Drop code should never run. + panic!(".forget() was not called") + } + } +} + +impl<V> Memo<V> +where + V: Clone, +{ + /// Determines whether the value stored in this memo (if any) is still + /// valid in the current revision. If so, returns a stamped value. + /// + /// If needed, this will walk each dependency and + /// recursively invoke `maybe_changed_after`, which may in turn + /// re-execute the dependency. This can cause cycles to occur, + /// so the current query must be pushed onto the + /// stack to permit cycle detection and recovery: therefore, + /// takes the `active_query` argument as evidence. + fn verify_value( + &mut self, + db: &dyn Database, + revision_now: Revision, + active_query: &ActiveQueryGuard<'_>, + ) -> Option<StampedValue<V>> { + if self.verify_revisions(db, revision_now, active_query) { + Some(StampedValue { + durability: self.revisions.durability, + changed_at: self.revisions.changed_at, + value: self.value.clone(), + }) + } else { + None + } + } + + /// Determines whether the value represented by this memo is still + /// valid in the current revision; note that the value itself is + /// not needed for this check. If needed, this will walk each + /// dependency and recursively invoke `maybe_changed_after`, which + /// may in turn re-execute the dependency. This can cause cycles to occur, + /// so the current query must be pushed onto the + /// stack to permit cycle detection and recovery: therefore, + /// takes the `active_query` argument as evidence. + fn verify_revisions( + &mut self, + db: &dyn Database, + revision_now: Revision, + _active_query: &ActiveQueryGuard<'_>, + ) -> bool { + assert!(self.verified_at != revision_now); + let verified_at = self.verified_at; + + debug!( + "verify_revisions: verified_at={:?}, revision_now={:?}, inputs={:#?}", + verified_at, revision_now, self.revisions.inputs + ); + + if self.check_durability(db.salsa_runtime()) { + return self.mark_value_as_verified(revision_now); + } + + match &self.revisions.inputs { + // We can't validate values that had untracked inputs; just have to + // re-execute. + None if self.revisions.untracked => return false, + None => {} + + // Check whether any of our inputs changed since the + // **last point where we were verified** (not since we + // last changed). This is important: if we have + // memoized values, then an input may have changed in + // revision R2, but we found that *our* value was the + // same regardless, so our change date is still + // R1. But our *verification* date will be R2, and we + // are only interested in finding out whether the + // input changed *again*. + Some(inputs) => { + let changed_input = + inputs.slice.iter().find(|&&input| db.maybe_changed_after(input, verified_at)); + if let Some(input) = changed_input { + debug!("validate_memoized_value: `{:?}` may have changed", input); + + return false; + } + } + }; + + self.mark_value_as_verified(revision_now) + } + + /// True if this memo is known not to have changed based on its durability. + fn check_durability(&self, runtime: &Runtime) -> bool { + let last_changed = runtime.last_changed_revision(self.revisions.durability); + debug!( + "check_durability(last_changed={:?} <= verified_at={:?}) = {:?}", + last_changed, + self.verified_at, + last_changed <= self.verified_at, + ); + last_changed <= self.verified_at + } + + fn mark_value_as_verified(&mut self, revision_now: Revision) -> bool { + self.verified_at = revision_now; + true + } +} + +impl<Q> std::fmt::Debug for Slot<Q> +where + Q: QueryFunction, +{ + fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result { + write!(fmt, "{:?}", Q::default()) + } +} + +/// Check that `Slot<Q, >: Send + Sync` as long as +/// `DB::DatabaseData: Send + Sync`, which in turn implies that +/// `Q::Key: Send + Sync`, `Q::Value: Send + Sync`. +#[allow(dead_code)] +fn check_send_sync<Q>() +where + Q: QueryFunction, + + Q::Key: Send + Sync, + Q::Value: Send + Sync, +{ + fn is_send_sync<T: Send + Sync>() {} + is_send_sync::<Slot<Q>>(); +} + +/// Check that `Slot<Q, >: 'static` as long as +/// `DB::DatabaseData: 'static`, which in turn implies that +/// `Q::Key: 'static`, `Q::Value: 'static`. +#[allow(dead_code)] +fn check_static<Q>() +where + Q: QueryFunction + 'static, + Q::Key: 'static, + Q::Value: 'static, +{ + fn is_static<T: 'static>() {} + is_static::<Slot<Q>>(); +} |