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Move salsa fork in-tree

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Lukas Wirth 2024-02-07 16:29:46 +01:00
parent 1974e7490d
commit 159a03ad7b
69 changed files with 9478 additions and 41 deletions
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277
crates/salsa/src/runtime/dependency_graph.rs Normal file
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use triomphe::Arc;
use crate::{DatabaseKeyIndex, RuntimeId};
use parking_lot::{Condvar, MutexGuard};
use rustc_hash::FxHashMap;
use smallvec::SmallVec;
use super::{ActiveQuery, WaitResult};
type QueryStack = Vec<ActiveQuery>;
#[derive(Debug, Default)]
pub(super) struct DependencyGraph {
/// A `(K -> V)` pair in this map indicates that the the runtime
/// `K` is blocked on some query executing in the runtime `V`.
/// This encodes a graph that must be acyclic (or else deadlock
/// will result).
edges: FxHashMap<RuntimeId, Edge>,
/// Encodes the `RuntimeId` that are blocked waiting for the result
/// of a given query.
query_dependents: FxHashMap<DatabaseKeyIndex, SmallVec<[RuntimeId; 4]>>,
/// When a key K completes which had dependent queries Qs blocked on it,
/// it stores its `WaitResult` here. As they wake up, each query Q in Qs will
/// come here to fetch their results.
wait_results: FxHashMap<RuntimeId, (QueryStack, WaitResult)>,
}
#[derive(Debug)]
struct Edge {
blocked_on_id: RuntimeId,
blocked_on_key: DatabaseKeyIndex,
stack: QueryStack,
/// Signalled whenever a query with dependents completes.
/// Allows those dependents to check if they are ready to unblock.
condvar: Arc<parking_lot::Condvar>,
}
impl DependencyGraph {
/// True if `from_id` depends on `to_id`.
///
/// (i.e., there is a path from `from_id` to `to_id` in the graph.)
pub(super) fn depends_on(&mut self, from_id: RuntimeId, to_id: RuntimeId) -> bool {
let mut p = from_id;
while let Some(q) = self.edges.get(&p).map(|edge| edge.blocked_on_id) {
if q == to_id {
return true;
}
p = q;
}
p == to_id
}
/// Invokes `closure` with a `&mut ActiveQuery` for each query that participates in the cycle.
/// The cycle runs as follows:
///
/// 1. The runtime `from_id`, which has the stack `from_stack`, would like to invoke `database_key`...
/// 2. ...but `database_key` is already being executed by `to_id`...
/// 3. ...and `to_id` is transitively dependent on something which is present on `from_stack`.
pub(super) fn for_each_cycle_participant(
&mut self,
from_id: RuntimeId,
from_stack: &mut QueryStack,
database_key: DatabaseKeyIndex,
to_id: RuntimeId,
mut closure: impl FnMut(&mut [ActiveQuery]),
) {
debug_assert!(self.depends_on(to_id, from_id));
// To understand this algorithm, consider this [drawing](https://is.gd/TGLI9v):
//
// database_key = QB2
// from_id = A
// to_id = B
// from_stack = [QA1, QA2, QA3]
//
// self.edges[B] = { C, QC2, [QB1..QB3] }
// self.edges[C] = { A, QA2, [QC1..QC3] }
//
// The cyclic
// edge we have
// failed to add.
// :
// A : B C
// :
// QA1 v QB1 QC1
// ┌► QA2 ┌──► QB2 ┌─► QC2
// │ QA3 ───┘ QB3 ──┘ QC3 ───┐
// │ │
// └───────────────────────────────┘
//
// Final output: [QB2, QB3, QC2, QC3, QA2, QA3]
let mut id = to_id;
let mut key = database_key;
while id != from_id {
// Looking at the diagram above, the idea is to
// take the edge from `to_id` starting at `key`
// (inclusive) and down to the end. We can then
// load up the next thread (i.e., we start at B/QB2,
// and then load up the dependency on C/QC2).
let edge = self.edges.get_mut(&id).unwrap();
let prefix = edge
.stack
.iter_mut()
.take_while(|p| p.database_key_index != key)
.count();
closure(&mut edge.stack[prefix..]);
id = edge.blocked_on_id;
key = edge.blocked_on_key;
}
// Finally, we copy in the results from `from_stack`.
let prefix = from_stack
.iter_mut()
.take_while(|p| p.database_key_index != key)
.count();
closure(&mut from_stack[prefix..]);
}
/// Unblock each blocked runtime (excluding the current one) if some
/// query executing in that runtime is participating in cycle fallback.
///
/// Returns a boolean (Current, Others) where:
/// * Current is true if the current runtime has cycle participants
/// with fallback;
/// * Others is true if other runtimes were unblocked.
pub(super) fn maybe_unblock_runtimes_in_cycle(
&mut self,
from_id: RuntimeId,
from_stack: &QueryStack,
database_key: DatabaseKeyIndex,
to_id: RuntimeId,
) -> (bool, bool) {
// See diagram in `for_each_cycle_participant`.
let mut id = to_id;
let mut key = database_key;
let mut others_unblocked = false;
while id != from_id {
let edge = self.edges.get(&id).unwrap();
let prefix = edge
.stack
.iter()
.take_while(|p| p.database_key_index != key)
.count();
let next_id = edge.blocked_on_id;
let next_key = edge.blocked_on_key;
if let Some(cycle) = edge.stack[prefix..]
.iter()
.rev()
.find_map(|aq| aq.cycle.clone())
{
// Remove `id` from the list of runtimes blocked on `next_key`:
self.query_dependents
.get_mut(&next_key)
.unwrap()
.retain(|r| *r != id);
// Unblock runtime so that it can resume execution once lock is released:
self.unblock_runtime(id, WaitResult::Cycle(cycle));
others_unblocked = true;
}
id = next_id;
key = next_key;
}
let prefix = from_stack
.iter()
.take_while(|p| p.database_key_index != key)
.count();
let this_unblocked = from_stack[prefix..].iter().any(|aq| aq.cycle.is_some());
(this_unblocked, others_unblocked)
}
/// Modifies the graph so that `from_id` is blocked
/// on `database_key`, which is being computed by
/// `to_id`.
///
/// For this to be reasonable, the lock on the
/// results table for `database_key` must be held.
/// This ensures that computing `database_key` doesn't
/// complete before `block_on` executes.
///
/// Preconditions:
/// * No path from `to_id` to `from_id`
/// (i.e., `me.depends_on(to_id, from_id)` is false)
/// * `held_mutex` is a read lock (or stronger) on `database_key`
pub(super) fn block_on<QueryMutexGuard>(
mut me: MutexGuard<'_, Self>,
from_id: RuntimeId,
database_key: DatabaseKeyIndex,
to_id: RuntimeId,
from_stack: QueryStack,
query_mutex_guard: QueryMutexGuard,
) -> (QueryStack, WaitResult) {
let condvar = me.add_edge(from_id, database_key, to_id, from_stack);
// Release the mutex that prevents `database_key`
// from completing, now that the edge has been added.
drop(query_mutex_guard);
loop {
if let Some(stack_and_result) = me.wait_results.remove(&from_id) {
debug_assert!(!me.edges.contains_key(&from_id));
return stack_and_result;
}
condvar.wait(&mut me);
}
}
/// Helper for `block_on`: performs actual graph modification
/// to add a dependency edge from `from_id` to `to_id`, which is
/// computing `database_key`.
fn add_edge(
&mut self,
from_id: RuntimeId,
database_key: DatabaseKeyIndex,
to_id: RuntimeId,
from_stack: QueryStack,
) -> Arc<parking_lot::Condvar> {
assert_ne!(from_id, to_id);
debug_assert!(!self.edges.contains_key(&from_id));
debug_assert!(!self.depends_on(to_id, from_id));
let condvar = Arc::new(Condvar::new());
self.edges.insert(
from_id,
Edge {
blocked_on_id: to_id,
blocked_on_key: database_key,
stack: from_stack,
condvar: condvar.clone(),
},
);
self.query_dependents
.entry(database_key)
.or_default()
.push(from_id);
condvar
}
/// Invoked when runtime `to_id` completes executing
/// `database_key`.
pub(super) fn unblock_runtimes_blocked_on(
&mut self,
database_key: DatabaseKeyIndex,
wait_result: WaitResult,
) {
let dependents = self
.query_dependents
.remove(&database_key)
.unwrap_or_default();
for from_id in dependents {
self.unblock_runtime(from_id, wait_result.clone());
}
}
/// Unblock the runtime with the given id with the given wait-result.
/// This will cause it resume execution (though it will have to grab
/// the lock on this data structure first, to recover the wait result).
fn unblock_runtime(&mut self, id: RuntimeId, wait_result: WaitResult) {
let edge = self.edges.remove(&id).expect("not blocked");
self.wait_results.insert(id, (edge.stack, wait_result));
// Now that we have inserted the `wait_results`,
// notify the thread.
edge.condvar.notify_one();
}
}

232
crates/salsa/src/runtime/local_state.rs Normal file
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use tracing::debug;
use crate::durability::Durability;
use crate::runtime::ActiveQuery;
use crate::runtime::Revision;
use crate::Cycle;
use crate::DatabaseKeyIndex;
use std::cell::RefCell;
use triomphe::Arc;
/// State that is specific to a single execution thread.
///
/// Internally, this type uses ref-cells.
///
/// **Note also that all mutations to the database handle (and hence
/// to the local-state) must be undone during unwinding.**
pub(super) struct LocalState {
/// Vector of active queries.
///
/// This is normally `Some`, but it is set to `None`
/// while the query is blocked waiting for a result.
///
/// Unwinding note: pushes onto this vector must be popped -- even
/// during unwinding.
query_stack: RefCell<Option<Vec<ActiveQuery>>>,
}
/// Summarizes "all the inputs that a query used"
#[derive(Debug, Clone)]
pub(crate) struct QueryRevisions {
/// The most revision in which some input changed.
pub(crate) changed_at: Revision,
/// Minimum durability of the inputs to this query.
pub(crate) durability: Durability,
/// The inputs that went into our query, if we are tracking them.
pub(crate) inputs: QueryInputs,
}
/// Every input.
#[derive(Debug, Clone)]
pub(crate) enum QueryInputs {
/// Non-empty set of inputs, fully known
Tracked { inputs: Arc<[DatabaseKeyIndex]> },
/// Empty set of inputs, fully known.
NoInputs,
/// Unknown quantity of inputs
Untracked,
}
impl Default for LocalState {
fn default() -> Self {
LocalState {
query_stack: RefCell::new(Some(Vec::new())),
}
}
}
impl LocalState {
#[inline]
pub(super) fn push_query(&self, database_key_index: DatabaseKeyIndex) -> ActiveQueryGuard<'_> {
let mut query_stack = self.query_stack.borrow_mut();
let query_stack = query_stack.as_mut().expect("local stack taken");
query_stack.push(ActiveQuery::new(database_key_index));
ActiveQueryGuard {
local_state: self,
database_key_index,
push_len: query_stack.len(),
}
}
fn with_query_stack<R>(&self, c: impl FnOnce(&mut Vec<ActiveQuery>) -> R) -> R {
c(self
.query_stack
.borrow_mut()
.as_mut()
.expect("query stack taken"))
}
pub(super) fn query_in_progress(&self) -> bool {
self.with_query_stack(|stack| !stack.is_empty())
}
pub(super) fn active_query(&self) -> Option<DatabaseKeyIndex> {
self.with_query_stack(|stack| {
stack
.last()
.map(|active_query| active_query.database_key_index)
})
}
pub(super) fn report_query_read_and_unwind_if_cycle_resulted(
&self,
input: DatabaseKeyIndex,
durability: Durability,
changed_at: Revision,
) {
debug!(
"report_query_read_and_unwind_if_cycle_resulted(input={:?}, durability={:?}, changed_at={:?})",
input, durability, changed_at
);
self.with_query_stack(|stack| {
if let Some(top_query) = stack.last_mut() {
top_query.add_read(input, durability, changed_at);
// We are a cycle participant:
//
// C0 --> ... --> Ci --> Ci+1 -> ... -> Cn --> C0
// ^ ^
// : |
// This edge -----+ |
// |
// |
// N0
//
// In this case, the value we have just read from `Ci+1`
// is actually the cycle fallback value and not especially
// interesting. We unwind now with `CycleParticipant` to avoid
// executing the rest of our query function. This unwinding
// will be caught and our own fallback value will be used.
//
// Note that `Ci+1` may` have *other* callers who are not
// participants in the cycle (e.g., N0 in the graph above).
// They will not have the `cycle` marker set in their
// stack frames, so they will just read the fallback value
// from `Ci+1` and continue on their merry way.
if let Some(cycle) = &top_query.cycle {
cycle.clone().throw()
}
}
})
}
pub(super) fn report_untracked_read(&self, current_revision: Revision) {
self.with_query_stack(|stack| {
if let Some(top_query) = stack.last_mut() {
top_query.add_untracked_read(current_revision);
}
})
}
/// Update the top query on the stack to act as though it read a value
/// of durability `durability` which changed in `revision`.
pub(super) fn report_synthetic_read(&self, durability: Durability, revision: Revision) {
self.with_query_stack(|stack| {
if let Some(top_query) = stack.last_mut() {
top_query.add_synthetic_read(durability, revision);
}
})
}
/// Takes the query stack and returns it. This is used when
/// the current thread is blocking. The stack must be restored
/// with [`Self::restore_query_stack`] when the thread unblocks.
pub(super) fn take_query_stack(&self) -> Vec<ActiveQuery> {
assert!(
self.query_stack.borrow().is_some(),
"query stack already taken"
);
self.query_stack.take().unwrap()
}
/// Restores a query stack taken with [`Self::take_query_stack`] once
/// the thread unblocks.
pub(super) fn restore_query_stack(&self, stack: Vec<ActiveQuery>) {
assert!(self.query_stack.borrow().is_none(), "query stack not taken");
self.query_stack.replace(Some(stack));
}
}
impl std::panic::RefUnwindSafe for LocalState {}
/// When a query is pushed onto the `active_query` stack, this guard
/// is returned to represent its slot. The guard can be used to pop
/// the query from the stack -- in the case of unwinding, the guard's
/// destructor will also remove the query.
pub(crate) struct ActiveQueryGuard<'me> {
local_state: &'me LocalState,
push_len: usize,
database_key_index: DatabaseKeyIndex,
}
impl ActiveQueryGuard<'_> {
fn pop_helper(&self) -> ActiveQuery {
self.local_state.with_query_stack(|stack| {
// Sanity check: pushes and pops should be balanced.
assert_eq!(stack.len(), self.push_len);
debug_assert_eq!(
stack.last().unwrap().database_key_index,
self.database_key_index
);
stack.pop().unwrap()
})
}
/// Invoked when the query has successfully completed execution.
pub(super) fn complete(self) -> ActiveQuery {
let query = self.pop_helper();
std::mem::forget(self);
query
}
/// Pops an active query from the stack. Returns the [`QueryRevisions`]
/// which summarizes the other queries that were accessed during this
/// query's execution.
#[inline]
pub(crate) fn pop(self) -> QueryRevisions {
// Extract accumulated inputs.
let popped_query = self.complete();
// If this frame were a cycle participant, it would have unwound.
assert!(popped_query.cycle.is_none());
popped_query.revisions()
}
/// If the active query is registered as a cycle participant, remove and
/// return that cycle.
pub(crate) fn take_cycle(&self) -> Option<Cycle> {
self.local_state
.with_query_stack(|stack| stack.last_mut()?.cycle.take())
}
}
impl Drop for ActiveQueryGuard<'_> {
fn drop(&mut self) {
self.pop_helper();
}
}