ra_salsa/lib.rs
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#![allow(clippy::type_complexity)]
#![allow(clippy::question_mark)]
#![allow(missing_docs)]
#![warn(rust_2018_idioms)]
//! The salsa crate is a crate for incremental recomputation. It
//! permits you to define a "database" of queries with both inputs and
//! values derived from those inputs; as you set the inputs, you can
//! re-execute the derived queries and it will try to re-use results
//! from previous invocations as appropriate.
mod derived;
mod derived_lru;
mod durability;
mod hash;
mod input;
mod intern_id;
mod interned;
mod lru;
mod revision;
mod runtime;
mod storage;
pub mod debug;
/// Items in this module are public for implementation reasons,
/// and are exempt from the SemVer guarantees.
#[doc(hidden)]
pub mod plumbing;
use crate::plumbing::CycleRecoveryStrategy;
use crate::plumbing::DerivedQueryStorageOps;
use crate::plumbing::InputQueryStorageOps;
use crate::plumbing::LruQueryStorageOps;
use crate::plumbing::QueryStorageMassOps;
use crate::plumbing::QueryStorageOps;
pub use crate::revision::Revision;
use std::fmt::{self, Debug};
use std::hash::Hash;
use std::panic::AssertUnwindSafe;
use std::panic::{self, UnwindSafe};
pub use crate::durability::Durability;
pub use crate::intern_id::InternId;
pub use crate::interned::{InternKey, InternValue, InternValueTrivial};
pub use crate::runtime::Runtime;
pub use crate::runtime::RuntimeId;
pub use crate::storage::Storage;
/// The base trait which your "query context" must implement. Gives
/// access to the salsa runtime, which you must embed into your query
/// context (along with whatever other state you may require).
pub trait Database: plumbing::DatabaseOps {
/// This function is invoked at key points in the salsa
/// runtime. It permits the database to be customized and to
/// inject logging or other custom behavior.
fn salsa_event(&self, event_fn: Event) {
_ = event_fn;
}
/// Starts unwinding the stack if the current revision is cancelled.
///
/// This method can be called by query implementations that perform
/// potentially expensive computations, in order to speed up propagation of
/// cancellation.
///
/// Cancellation will automatically be triggered by salsa on any query
/// invocation.
///
/// This method should not be overridden by `Database` implementors. A
/// `salsa_event` is emitted when this method is called, so that should be
/// used instead.
#[inline]
fn unwind_if_cancelled(&self) {
let runtime = self.salsa_runtime();
self.salsa_event(Event {
runtime_id: runtime.id(),
kind: EventKind::WillCheckCancellation,
});
let current_revision = runtime.current_revision();
let pending_revision = runtime.pending_revision();
tracing::debug!(
"unwind_if_cancelled: current_revision={:?}, pending_revision={:?}",
current_revision,
pending_revision
);
if pending_revision > current_revision {
runtime.unwind_cancelled();
}
}
/// Gives access to the underlying salsa runtime.
///
/// This method should not be overridden by `Database` implementors.
fn salsa_runtime(&self) -> &Runtime {
self.ops_salsa_runtime()
}
/// A "synthetic write" causes the system to act *as though* some
/// input of durability `durability` has changed. This is mostly
/// useful for profiling scenarios.
///
/// **WARNING:** Just like an ordinary write, this method triggers
/// cancellation. If you invoke it while a snapshot exists, it
/// will block until that snapshot is dropped -- if that snapshot
/// is owned by the current thread, this could trigger deadlock.
fn synthetic_write(&mut self, durability: Durability) {
plumbing::DatabaseOps::synthetic_write(self, durability)
}
}
/// The `Event` struct identifies various notable things that can
/// occur during salsa execution. Instances of this struct are given
/// to `salsa_event`.
pub struct Event {
/// The id of the snapshot that triggered the event. Usually
/// 1-to-1 with a thread, as well.
pub runtime_id: RuntimeId,
/// What sort of event was it.
pub kind: EventKind,
}
impl Event {
/// Returns a type that gives a user-readable debug output.
/// Use like `println!("{:?}", index.debug(db))`.
pub fn debug<'me, D>(&'me self, db: &'me D) -> impl std::fmt::Debug + 'me
where
D: ?Sized + plumbing::DatabaseOps,
{
EventDebug { event: self, db }
}
}
impl fmt::Debug for Event {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("Event")
.field("runtime_id", &self.runtime_id)
.field("kind", &self.kind)
.finish()
}
}
struct EventDebug<'me, D: ?Sized>
where
D: plumbing::DatabaseOps,
{
event: &'me Event,
db: &'me D,
}
impl<D: ?Sized> fmt::Debug for EventDebug<'_, D>
where
D: plumbing::DatabaseOps,
{
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
fmt.debug_struct("Event")
.field("runtime_id", &self.event.runtime_id)
.field("kind", &self.event.kind.debug(self.db))
.finish()
}
}
/// An enum identifying the various kinds of events that can occur.
pub enum EventKind {
/// Occurs when we found that all inputs to a memoized value are
/// up-to-date and hence the value can be re-used without
/// executing the closure.
///
/// Executes before the "re-used" value is returned.
DidValidateMemoizedValue {
/// The database-key for the affected value. Implements `Debug`.
database_key: DatabaseKeyIndex,
},
/// Indicates that another thread (with id `other_runtime_id`) is processing the
/// given query (`database_key`), so we will block until they
/// finish.
///
/// Executes after we have registered with the other thread but
/// before they have answered us.
///
/// (NB: you can find the `id` of the current thread via the
/// `salsa_runtime`)
WillBlockOn {
/// The id of the runtime we will block on.
other_runtime_id: RuntimeId,
/// The database-key for the affected value. Implements `Debug`.
database_key: DatabaseKeyIndex,
},
/// Indicates that the function for this query will be executed.
/// This is either because it has never executed before or because
/// its inputs may be out of date.
WillExecute {
/// The database-key for the affected value. Implements `Debug`.
database_key: DatabaseKeyIndex,
},
/// Indicates that `unwind_if_cancelled` was called and salsa will check if
/// the current revision has been cancelled.
WillCheckCancellation,
}
impl EventKind {
/// Returns a type that gives a user-readable debug output.
/// Use like `println!("{:?}", index.debug(db))`.
pub fn debug<'me, D>(&'me self, db: &'me D) -> impl std::fmt::Debug + 'me
where
D: ?Sized + plumbing::DatabaseOps,
{
EventKindDebug { kind: self, db }
}
}
impl fmt::Debug for EventKind {
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
EventKind::DidValidateMemoizedValue { database_key } => fmt
.debug_struct("DidValidateMemoizedValue")
.field("database_key", database_key)
.finish(),
EventKind::WillBlockOn { other_runtime_id, database_key } => fmt
.debug_struct("WillBlockOn")
.field("other_runtime_id", other_runtime_id)
.field("database_key", database_key)
.finish(),
EventKind::WillExecute { database_key } => {
fmt.debug_struct("WillExecute").field("database_key", database_key).finish()
}
EventKind::WillCheckCancellation => fmt.debug_struct("WillCheckCancellation").finish(),
}
}
}
struct EventKindDebug<'me, D: ?Sized>
where
D: plumbing::DatabaseOps,
{
kind: &'me EventKind,
db: &'me D,
}
impl<D: ?Sized> fmt::Debug for EventKindDebug<'_, D>
where
D: plumbing::DatabaseOps,
{
fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result {
match self.kind {
EventKind::DidValidateMemoizedValue { database_key } => fmt
.debug_struct("DidValidateMemoizedValue")
.field("database_key", &database_key.debug(self.db))
.finish(),
EventKind::WillBlockOn { other_runtime_id, database_key } => fmt
.debug_struct("WillBlockOn")
.field("other_runtime_id", &other_runtime_id)
.field("database_key", &database_key.debug(self.db))
.finish(),
EventKind::WillExecute { database_key } => fmt
.debug_struct("WillExecute")
.field("database_key", &database_key.debug(self.db))
.finish(),
EventKind::WillCheckCancellation => fmt.debug_struct("WillCheckCancellation").finish(),
}
}
}
/// Indicates a database that also supports parallel query
/// evaluation. All of Salsa's base query support is capable of
/// parallel execution, but for it to work, your query key/value types
/// must also be `Send`, as must any additional data in your database.
pub trait ParallelDatabase: Database + Send {
/// Creates a second handle to the database that holds the
/// database fixed at a particular revision. So long as this
/// "frozen" handle exists, any attempt to [`set`] an input will
/// block.
///
/// [`set`]: struct.QueryTable.html#method.set
///
/// This is the method you are meant to use most of the time in a
/// parallel setting where modifications may arise asynchronously
/// (e.g., a language server). In this context, it is common to
/// wish to "fork off" a snapshot of the database performing some
/// series of queries in parallel and arranging the results. Using
/// this method for that purpose ensures that those queries will
/// see a consistent view of the database (it is also advisable
/// for those queries to use the [`Database::unwind_if_cancelled`]
/// method to check for cancellation).
///
/// # Panics
///
/// It is not permitted to create a snapshot from inside of a
/// query. Attempting to do so will panic.
///
/// # Deadlock warning
///
/// The intended pattern for snapshots is that, once created, they
/// are sent to another thread and used from there. As such, the
/// `snapshot` acquires a "read lock" on the database --
/// therefore, so long as the `snapshot` is not dropped, any
/// attempt to `set` a value in the database will block. If the
/// `snapshot` is owned by the same thread that is attempting to
/// `set`, this will cause a problem.
///
/// # How to implement this
///
/// Typically, this method will create a second copy of your
/// database type (`MyDatabaseType`, in the example below),
/// cloning over each of the fields from `self` into this new
/// copy. For the field that stores the salsa runtime, you should
/// use [the `Runtime::snapshot` method][rfm] to create a snapshot of the
/// runtime. Finally, package up the result using `Snapshot::new`,
/// which is a simple wrapper type that only gives `&self` access
/// to the database within (thus preventing the use of methods
/// that may mutate the inputs):
///
/// [rfm]: struct.Runtime.html#method.snapshot
///
/// ```rust,ignore
/// impl ParallelDatabase for MyDatabaseType {
/// fn snapshot(&self) -> Snapshot<Self> {
/// Snapshot::new(
/// MyDatabaseType {
/// runtime: self.runtime.snapshot(self),
/// other_field: self.other_field.clone(),
/// }
/// )
/// }
/// }
/// ```
fn snapshot(&self) -> Snapshot<Self>;
}
/// Simple wrapper struct that takes ownership of a database `DB` and
/// only gives `&self` access to it. See [the `snapshot` method][fm]
/// for more details.
///
/// [fm]: trait.ParallelDatabase.html#method.snapshot
#[derive(Debug)]
pub struct Snapshot<DB: ?Sized>
where
DB: ParallelDatabase,
{
db: DB,
}
impl<DB> Snapshot<DB>
where
DB: ParallelDatabase,
{
/// Creates a `Snapshot` that wraps the given database handle
/// `db`. From this point forward, only shared references to `db`
/// will be possible.
pub fn new(db: DB) -> Self {
Snapshot { db }
}
}
impl<DB> std::ops::Deref for Snapshot<DB>
where
DB: ParallelDatabase,
{
type Target = DB;
fn deref(&self) -> &DB {
&self.db
}
}
/// An integer that uniquely identifies a particular query instance within the
/// database. Used to track dependencies between queries. Fully ordered and
/// equatable but those orderings are arbitrary, and meant to be used only for
/// inserting into maps and the like.
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
pub struct DatabaseKeyIndex {
group_index: u16,
query_index: u16,
key_index: u32,
}
impl DatabaseKeyIndex {
/// Returns the index of the query group containing this key.
#[inline]
pub fn group_index(self) -> u16 {
self.group_index
}
/// Returns the index of the query within its query group.
#[inline]
pub fn query_index(self) -> u16 {
self.query_index
}
/// Returns the index of this particular query key within the query.
#[inline]
pub fn key_index(self) -> u32 {
self.key_index
}
/// Returns a type that gives a user-readable debug output.
/// Use like `println!("{:?}", index.debug(db))`.
pub fn debug<D>(self, db: &D) -> impl std::fmt::Debug + '_
where
D: ?Sized + plumbing::DatabaseOps,
{
DatabaseKeyIndexDebug { index: self, db }
}
}
/// Helper type for `DatabaseKeyIndex::debug`
struct DatabaseKeyIndexDebug<'me, D: ?Sized>
where
D: plumbing::DatabaseOps,
{
index: DatabaseKeyIndex,
db: &'me D,
}
impl<D: ?Sized> std::fmt::Debug for DatabaseKeyIndexDebug<'_, D>
where
D: plumbing::DatabaseOps,
{
fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
self.db.fmt_index(self.index, fmt)
}
}
/// Trait implements by all of the "special types" associated with
/// each of your queries.
///
/// Base trait of `Query` that has a lifetime parameter to allow the `DynDb` to be non-'static.
pub trait QueryDb<'d>: Sized {
/// Dyn version of the associated trait for this query group.
type DynDb: ?Sized + Database + HasQueryGroup<Self::Group> + 'd;
/// Associate query group struct.
type Group: plumbing::QueryGroup<GroupStorage = Self::GroupStorage>;
/// Generated struct that contains storage for all queries in a group.
type GroupStorage;
}
/// Trait implements by all of the "special types" associated with
/// each of your queries.
pub trait Query: Debug + Default + Sized + for<'d> QueryDb<'d> {
/// Type that you give as a parameter -- for queries with zero
/// or more than one input, this will be a tuple.
type Key: Clone + Debug + Hash + Eq;
/// What value does the query return?
type Value: Clone + Debug;
/// Internal struct storing the values for the query.
// type Storage: plumbing::QueryStorageOps<Self>;
type Storage;
/// A unique index identifying this query within the group.
const QUERY_INDEX: u16;
/// Name of the query method (e.g., `foo`)
const QUERY_NAME: &'static str;
/// Extract storage for this query from the storage for its group.
fn query_storage<'a>(
group_storage: &'a <Self as QueryDb<'_>>::GroupStorage,
) -> &'a std::sync::Arc<Self::Storage>;
/// Extract storage for this query from the storage for its group.
fn query_storage_mut<'a>(
group_storage: &'a <Self as QueryDb<'_>>::GroupStorage,
) -> &'a std::sync::Arc<Self::Storage>;
}
/// Return value from [the `query` method] on `Database`.
/// Gives access to various less common operations on queries.
///
/// [the `query` method]: trait.Database.html#method.query
pub struct QueryTable<'me, Q>
where
Q: Query,
{
db: &'me <Q as QueryDb<'me>>::DynDb,
storage: &'me Q::Storage,
}
impl<'me, Q> QueryTable<'me, Q>
where
Q: Query,
Q::Storage: QueryStorageOps<Q>,
{
/// Constructs a new `QueryTable`.
pub fn new(db: &'me <Q as QueryDb<'me>>::DynDb, storage: &'me Q::Storage) -> Self {
Self { db, storage }
}
/// Execute the query on a given input. Usually it's easier to
/// invoke the trait method directly. Note that for variadic
/// queries (those with no inputs, or those with more than one
/// input) the key will be a tuple.
pub fn get(&self, key: Q::Key) -> Q::Value {
self.storage.fetch(self.db, &key)
}
/// Completely clears the storage for this query.
///
/// This method breaks internal invariants of salsa, so any further queries
/// might return nonsense results. It is useful only in very specific
/// circumstances -- for example, when one wants to observe which values
/// dropped together with the table
pub fn purge(&self)
where
Q::Storage: plumbing::QueryStorageMassOps,
{
self.storage.purge();
}
pub fn storage(&self) -> &<Q as Query>::Storage {
self.storage
}
}
/// Return value from [the `query_mut` method] on `Database`.
/// Gives access to the `set` method, notably, that is used to
/// set the value of an input query.
///
/// [the `query_mut` method]: trait.Database.html#method.query_mut
pub struct QueryTableMut<'me, Q>
where
Q: Query + 'me,
{
runtime: &'me mut Runtime,
storage: &'me Q::Storage,
}
impl<'me, Q> QueryTableMut<'me, Q>
where
Q: Query,
{
/// Constructs a new `QueryTableMut`.
pub fn new(runtime: &'me mut Runtime, storage: &'me Q::Storage) -> Self {
Self { runtime, storage }
}
/// Assign a value to an "input query". Must be used outside of
/// an active query computation.
///
/// If you are using `snapshot`, see the notes on blocking
/// and cancellation on [the `query_mut` method].
///
/// [the `query_mut` method]: trait.Database.html#method.query_mut
pub fn set(&mut self, key: Q::Key, value: Q::Value)
where
Q::Storage: plumbing::InputQueryStorageOps<Q>,
{
self.set_with_durability(key, value, Durability::LOW);
}
/// Assign a value to an "input query", with the additional
/// promise that this value will **never change**. Must be used
/// outside of an active query computation.
///
/// If you are using `snapshot`, see the notes on blocking
/// and cancellation on [the `query_mut` method].
///
/// [the `query_mut` method]: trait.Database.html#method.query_mut
pub fn set_with_durability(&mut self, key: Q::Key, value: Q::Value, durability: Durability)
where
Q::Storage: plumbing::InputQueryStorageOps<Q>,
{
self.storage.set(self.runtime, &key, value, durability);
}
/// Sets the size of LRU cache of values for this query table.
///
/// That is, at most `cap` values will be preset in the table at the same
/// time. This helps with keeping maximum memory usage under control, at the
/// cost of potential extra recalculations of evicted values.
///
/// If `cap` is zero, all values are preserved, this is the default.
pub fn set_lru_capacity(&self, cap: u16)
where
Q::Storage: plumbing::LruQueryStorageOps,
{
self.storage.set_lru_capacity(cap);
}
/// Marks the computed value as outdated.
///
/// This causes salsa to re-execute the query function on the next access to
/// the query, even if all dependencies are up to date.
///
/// This is most commonly used as part of the [on-demand input
/// pattern](https://salsa-rs.github.io/salsa/common_patterns/on_demand_inputs.html).
pub fn invalidate(&mut self, key: &Q::Key)
where
Q::Storage: plumbing::DerivedQueryStorageOps<Q>,
{
self.storage.invalidate(self.runtime, key)
}
}
/// A panic payload indicating that execution of a salsa query was cancelled.
///
/// This can occur for a few reasons:
/// *
/// *
/// *
#[derive(Debug)]
#[non_exhaustive]
pub enum Cancelled {
/// The query was operating on revision R, but there is a pending write to move to revision R+1.
#[non_exhaustive]
PendingWrite,
/// The query was blocked on another thread, and that thread panicked.
#[non_exhaustive]
PropagatedPanic,
}
impl Cancelled {
fn throw(self) -> ! {
// We use resume and not panic here to avoid running the panic
// hook (that is, to avoid collecting and printing backtrace).
std::panic::resume_unwind(Box::new(self));
}
/// Runs `f`, and catches any salsa cancellation.
pub fn catch<F, T>(f: F) -> Result<T, Cancelled>
where
F: FnOnce() -> T + UnwindSafe,
{
match panic::catch_unwind(f) {
Ok(t) => Ok(t),
Err(payload) => match payload.downcast() {
Ok(cancelled) => Err(*cancelled),
Err(payload) => panic::resume_unwind(payload),
},
}
}
}
impl std::fmt::Display for Cancelled {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
let why = match self {
Cancelled::PendingWrite => "pending write",
Cancelled::PropagatedPanic => "propagated panic",
};
f.write_str("cancelled because of ")?;
f.write_str(why)
}
}
impl std::error::Error for Cancelled {}
/// Captures the participants of a cycle that occurred when executing a query.
///
/// This type is meant to be used to help give meaningful error messages to the
/// user or to help salsa developers figure out why their program is resulting
/// in a computation cycle.
///
/// It is used in a few ways:
///
/// * During [cycle recovery](https://https://salsa-rs.github.io/salsa/cycles/fallback.html),
/// where it is given to the fallback function.
/// * As the panic value when an unexpected cycle (i.e., a cycle where one or more participants
/// lacks cycle recovery information) occurs.
///
/// You can read more about cycle handling in
/// the [salsa book](https://https://salsa-rs.github.io/salsa/cycles.html).
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub struct Cycle {
participants: plumbing::CycleParticipants,
}
impl Cycle {
pub(crate) fn new(participants: plumbing::CycleParticipants) -> Self {
Self { participants }
}
/// True if two `Cycle` values represent the same cycle.
pub(crate) fn is(&self, cycle: &Cycle) -> bool {
triomphe::Arc::ptr_eq(&self.participants, &cycle.participants)
}
pub(crate) fn throw(self) -> ! {
tracing::debug!("throwing cycle {:?}", self);
std::panic::resume_unwind(Box::new(self))
}
pub(crate) fn catch<T>(execute: impl FnOnce() -> T) -> Result<T, Cycle> {
match std::panic::catch_unwind(AssertUnwindSafe(execute)) {
Ok(v) => Ok(v),
Err(err) => match err.downcast::<Cycle>() {
Ok(cycle) => Err(*cycle),
Err(other) => std::panic::resume_unwind(other),
},
}
}
/// Iterate over the [`DatabaseKeyIndex`] for each query participating
/// in the cycle. The start point of this iteration within the cycle
/// is arbitrary but deterministic, but the ordering is otherwise determined
/// by the execution.
pub fn participant_keys(&self) -> impl Iterator<Item = DatabaseKeyIndex> + '_ {
self.participants.iter().copied()
}
/// Returns a vector with the debug information for
/// all the participants in the cycle.
pub fn all_participants<DB: ?Sized + Database>(&self, db: &DB) -> Vec<String> {
self.participant_keys().map(|d| format!("{:?}", d.debug(db))).collect()
}
/// Returns a vector with the debug information for
/// those participants in the cycle that lacked recovery
/// information.
pub fn unexpected_participants<DB: ?Sized + Database>(&self, db: &DB) -> Vec<String> {
self.participant_keys()
.filter(|&d| db.cycle_recovery_strategy(d) == CycleRecoveryStrategy::Panic)
.map(|d| format!("{:?}", d.debug(db)))
.collect()
}
/// Returns a "debug" view onto this strict that can be used to print out information.
pub fn debug<'me, DB: ?Sized + Database>(&'me self, db: &'me DB) -> impl std::fmt::Debug + 'me {
struct UnexpectedCycleDebug<'me> {
c: &'me Cycle,
db: &'me dyn Database,
}
impl std::fmt::Debug for UnexpectedCycleDebug<'_> {
fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
fmt.debug_struct("UnexpectedCycle")
.field("all_participants", &self.c.all_participants(self.db))
.field("unexpected_participants", &self.c.unexpected_participants(self.db))
.finish()
}
}
UnexpectedCycleDebug { c: self, db: db.ops_database() }
}
}
// Re-export the procedural macros.
#[allow(unused_imports)]
#[macro_use]
extern crate ra_salsa_macros;
use plumbing::HasQueryGroup;
pub use ra_salsa_macros::*;