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Merge pull request #36 from matklad/weak-memoized

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Merge Memoized and Dependency storages
This commit is contained in:
Niko Matsakis 2018-10-09 08:53:57 -04:00 committed by GitHub
commit 121821117d
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3 changed files with 148 additions and 295 deletions
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245
src/dependencies.rs
View file

@ -1,245 +0,0 @@
use crate::runtime::QueryDescriptorSet;
use crate::runtime::Revision;
use crate::runtime::StampedValue;
use crate::CycleDetected;
use crate::Database;
use crate::QueryDescriptor;
use crate::QueryFunction;
use crate::QueryStorageOps;
use crate::QueryTable;
use log::debug;
use parking_lot::{RwLock, RwLockUpgradableReadGuard};
use rustc_hash::FxHashMap;
use std::any::Any;
use std::cell::RefCell;
use std::collections::hash_map::Entry;
use std::fmt::Debug;
use std::fmt::Display;
use std::fmt::Write;
use std::hash::Hash;
/// "Dependency" queries just track their dependencies and not the
/// actual value (which they produce on demand). This lessens the
/// storage requirements.
pub struct DependencyStorage<DB, Q>
where
Q: QueryFunction<DB>,
DB: Database,
{
map: RwLock<FxHashMap<Q::Key, QueryState<DB>>>,
}
/// Defines the "current state" of query's memoized results.
enum QueryState<DB>
where
DB: Database,
{
/// We are currently computing the result of this query; if we see
/// this value in the table, it indeeds a cycle.
InProgress,
/// We have computed the query already, and here is the result.
Memoized(Memo<DB>),
}
struct Memo<DB>
where
DB: Database,
{
inputs: QueryDescriptorSet<DB>,
/// Last time that we checked our inputs to see if they have
/// changed. If this is equal to the current revision, then the
/// value is up to date. If not, we need to check our inputs and
/// see if any of them have changed since our last check -- if so,
/// we'll need to re-execute.
verified_at: Revision,
/// Last time that our value changed.
changed_at: Revision,
}
impl<DB, Q> Default for DependencyStorage<DB, Q>
where
Q: QueryFunction<DB>,
DB: Database,
{
fn default() -> Self {
DependencyStorage {
map: RwLock::new(FxHashMap::default()),
}
}
}
impl<DB, Q> DependencyStorage<DB, Q>
where
Q: QueryFunction<DB>,
DB: Database,
{
fn read(
&self,
db: &DB,
key: &Q::Key,
descriptor: &DB::QueryDescriptor,
) -> Result<StampedValue<Q::Value>, CycleDetected> {
let revision_now = db.salsa_runtime().current_revision();
debug!(
"{:?}({:?}): invoked at {:?}",
Q::default(),
key,
revision_now,
);
{
let map_read = self.map.upgradable_read();
if let Some(value) = map_read.get(key) {
match value {
QueryState::InProgress => return Err(CycleDetected),
QueryState::Memoized(_) => {}
}
}
let mut map_write = RwLockUpgradableReadGuard::upgrade(map_read);
map_write.insert(key.clone(), QueryState::InProgress);
}
// Note that, unlike with a memoized query, we must always
// re-execute.
let (stamped_value, inputs) = db
.salsa_runtime()
.execute_query_implementation::<Q>(db, descriptor, key);
// 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!(
db.salsa_runtime().current_revision(),
revision_now,
"revision altered during query execution",
);
{
let mut map_write = self.map.write();
let old_value = map_write.insert(
key.clone(),
QueryState::Memoized(Memo {
inputs,
verified_at: revision_now,
changed_at: stamped_value.changed_at,
}),
);
assert!(
match old_value {
Some(QueryState::InProgress) => true,
_ => false,
},
"expected in-progress state",
);
}
Ok(stamped_value)
}
fn overwrite_placeholder(
&self,
map_write: &mut FxHashMap<Q::Key, QueryState<DB>>,
key: &Q::Key,
value: Option<QueryState<DB>>,
) {
let old_value = if let Some(v) = value {
map_write.insert(key.clone(), v)
} else {
map_write.remove(key)
};
assert!(
match old_value {
Some(QueryState::InProgress) => true,
_ => false,
},
"expected in-progress state",
);
}
}
impl<DB, Q> QueryStorageOps<DB, Q> for DependencyStorage<DB, Q>
where
Q: QueryFunction<DB>,
DB: Database,
{
fn try_fetch<'q>(
&self,
db: &'q DB,
key: &Q::Key,
descriptor: &DB::QueryDescriptor,
) -> Result<Q::Value, CycleDetected> {
let StampedValue { value, changed_at } = self.read(db, key, &descriptor)?;
db.salsa_runtime().report_query_read(descriptor, changed_at);
Ok(value)
}
fn maybe_changed_since(
&self,
db: &'q DB,
revision: Revision,
key: &Q::Key,
_descriptor: &DB::QueryDescriptor,
) -> bool {
let revision_now = db.salsa_runtime().current_revision();
debug!(
"{:?}({:?})::maybe_changed_since(revision={:?}, revision_now={:?})",
Q::default(),
key,
revision,
revision_now,
);
let value = {
let map_read = self.map.upgradable_read();
match map_read.get(key) {
None | Some(QueryState::InProgress) => return true,
Some(QueryState::Memoized(memo)) => {
// If our memo is still up to date, then check if we've
// changed since the revision.
if memo.verified_at == revision_now {
return memo.changed_at > revision;
}
}
}
let mut map_write = RwLockUpgradableReadGuard::upgrade(map_read);
map_write.insert(key.clone(), QueryState::InProgress)
};
// Otherwise, walk the inputs we had and check them. Note that
// we don't want to hold the lock while we do this.
let mut memo = match value {
Some(QueryState::Memoized(memo)) => memo,
_ => unreachable!(),
};
if memo
.inputs
.iter()
.all(|old_input| !old_input.maybe_changed_since(db, memo.verified_at))
{
memo.verified_at = revision_now;
self.overwrite_placeholder(
&mut self.map.write(),
key,
Some(QueryState::Memoized(memo)),
);
return false;
}
// Just remove the existing entry. It's out of date.
self.overwrite_placeholder(&mut self.map.write(), key, None);
true
}
}

3
src/lib.rs
View file

@ -16,7 +16,6 @@ use std::fmt::Display;
use std::fmt::Write;
use std::hash::Hash;
pub mod dependencies;
pub mod input;
pub mod memoized;
pub mod runtime;
@ -415,7 +414,7 @@ macro_rules! query_group {
(
@storage_ty[$DB:ident, $Self:ident, dependencies]
) => {
$crate::dependencies::DependencyStorage<$DB, $Self>
$crate::memoized::DependencyStorage<$DB, $Self>
};
(

195
src/memoized.rs
View file

@ -18,16 +18,56 @@ use std::fmt::Debug;
use std::fmt::Display;
use std::fmt::Write;
use std::hash::Hash;
use std::marker::PhantomData;
/// Memoized queries store the result plus a list of the other queries
/// that they invoked. This means we can avoid recomputing them when
/// none of those inputs have changed.
pub struct MemoizedStorage<DB, Q>
pub type MemoizedStorage<DB, Q> = WeakMemoizedStorage<DB, Q, AlwaysMemoizeValue>;
/// "Dependency" queries just track their dependencies and not the
/// actual value (which they produce on demand). This lessens the
/// storage requirements.
pub type DependencyStorage<DB, Q> = WeakMemoizedStorage<DB, Q, NeverMemoizeValue>;
pub struct WeakMemoizedStorage<DB, Q, MP>
where
Q: QueryFunction<DB>,
DB: Database,
MP: MemoizationPolicy<DB, Q>,
{
map: RwLock<FxHashMap<Q::Key, QueryState<DB, Q>>>,
policy: PhantomData<MP>,
}
pub trait MemoizationPolicy<DB, Q>
where
Q: QueryFunction<DB>,
DB: Database,
{
map: RwLock<FxHashMap<Q::Key, QueryState<DB, Q>>>,
fn should_memoize_value(key: &Q::Key) -> bool;
}
pub enum AlwaysMemoizeValue {}
impl<DB, Q> MemoizationPolicy<DB, Q> for AlwaysMemoizeValue
where
Q: QueryFunction<DB>,
DB: Database,
{
fn should_memoize_value(_key: &Q::Key) -> bool {
true
}
}
pub enum NeverMemoizeValue {}
impl<DB, Q> MemoizationPolicy<DB, Q> for NeverMemoizeValue
where
Q: QueryFunction<DB>,
DB: Database,
{
fn should_memoize_value(_key: &Q::Key) -> bool {
false
}
}
/// Defines the "current state" of query's memoized results.
@ -49,7 +89,12 @@ where
Q: QueryFunction<DB>,
DB: Database,
{
stamped_value: StampedValue<Q::Value>,
/// Last time the value has actually changed.
/// changed_at can be less than verified_at.
changed_at: Revision,
/// The result of the query, if we decide to memoize it.
value: Option<Q::Value>,
inputs: QueryDescriptorSet<DB>,
@ -61,22 +106,25 @@ where
verified_at: Revision,
}
impl<DB, Q> Default for MemoizedStorage<DB, Q>
impl<DB, Q, MP> Default for WeakMemoizedStorage<DB, Q, MP>
where
Q: QueryFunction<DB>,
DB: Database,
MP: MemoizationPolicy<DB, Q>,
{
fn default() -> Self {
MemoizedStorage {
WeakMemoizedStorage {
map: RwLock::new(FxHashMap::default()),
policy: PhantomData,
}
}
}
impl<DB, Q> MemoizedStorage<DB, Q>
impl<DB, Q, MP> WeakMemoizedStorage<DB, Q, MP>
where
Q: QueryFunction<DB>,
DB: Database,
MP: MemoizationPolicy<DB, Q>,
{
fn read(
&self,
@ -106,15 +154,22 @@ where
m.verified_at,
);
// We've found that the query is definitely up-to-date.
// If the value is also memoized, return it.
// Otherwise fallback to recomputing the value.
if m.verified_at == revision_now {
debug!(
"{:?}({:?}): returning memoized value (changed_at={:?})",
Q::default(),
key,
m.stamped_value.changed_at,
);
return Ok(m.stamped_value.clone());
if let Some(value) = &m.value {
debug!(
"{:?}({:?}): returning memoized value (changed_at={:?})",
Q::default(),
key,
m.changed_at,
);
return Ok(StampedValue {
value: value.clone(),
changed_at: m.changed_at,
});
};
}
}
}
@ -129,25 +184,29 @@ where
// first things first, let's walk over each of our previous
// inputs and check whether they are out of date.
if let Some(QueryState::Memoized(old_memo)) = &mut old_value {
if old_memo.inputs.iter().all(|old_input| {
!old_input.maybe_changed_since(db, old_memo.stamped_value.changed_at)
}) {
debug!("{:?}({:?}): inputs still valid", Q::default(), key);
if old_memo.value.is_some() {
if old_memo
.inputs
.iter()
.all(|old_input| !old_input.maybe_changed_since(db, old_memo.changed_at))
{
debug!("{:?}({:?}): inputs still valid", Q::default(), key);
// If none of out inputs have changed since the last time we refreshed
// our value, then our value must still be good. We'll just patch
// the verified-at date and re-use it.
old_memo.verified_at = revision_now;
let value = old_memo.value.clone().unwrap();
let changed_at = old_memo.changed_at;
// If none of out inputs have changed since the last time we refreshed
// our value, then our value must still be good. We'll just patch
// the verified-at date and re-use it.
old_memo.verified_at = revision_now;
let stamped_value = old_memo.stamped_value.clone();
let mut map_write = self.map.write();
self.overwrite_placeholder(&mut map_write, key, old_value.unwrap());
return Ok(stamped_value);
let mut map_write = self.map.write();
self.overwrite_placeholder(&mut map_write, key, old_value.unwrap());
return Ok(StampedValue { value, changed_at });
}
}
}
// Query was not previously executed or value is potentially
// stale. Let's execute!
// Query was not previously executed, or value is potentially
// stale, or value is absent. Let's execute!
let (mut stamped_value, inputs) = db
.salsa_runtime()
.execute_query_implementation::<Q>(db, descriptor, key);
@ -166,19 +225,25 @@ where
// "backdate" its `changed_at` revision to be the same as the
// old value.
if let Some(QueryState::Memoized(old_memo)) = &old_value {
if old_memo.stamped_value.value == stamped_value.value {
assert!(old_memo.stamped_value.changed_at <= stamped_value.changed_at);
stamped_value.changed_at = old_memo.stamped_value.changed_at;
if old_memo.value.as_ref() == Some(&stamped_value.value) {
assert!(old_memo.changed_at <= stamped_value.changed_at);
stamped_value.changed_at = old_memo.changed_at;
}
}
{
let value = if self.should_memoize_value(key) {
Some(stamped_value.value.clone())
} else {
None
};
let mut map_write = self.map.write();
self.overwrite_placeholder(
&mut map_write,
key,
QueryState::Memoized(Memo {
stamped_value: stamped_value.clone(),
changed_at: stamped_value.changed_at,
value,
inputs,
verified_at: revision_now,
}),
@ -203,12 +268,17 @@ where
"expected in-progress state",
);
}
fn should_memoize_value(&self, key: &Q::Key) -> bool {
MP::should_memoize_value(key)
}
}
impl<DB, Q> QueryStorageOps<DB, Q> for MemoizedStorage<DB, Q>
impl<DB, Q, MP> QueryStorageOps<DB, Q> for WeakMemoizedStorage<DB, Q, MP>
where
Q: QueryFunction<DB>,
DB: Database,
MP: MemoizationPolicy<DB, Q>,
{
fn try_fetch<'q>(
&self,
@ -240,32 +310,60 @@ where
revision_now,
);
// Check for the case where we have no cache entry, or our cache
// entry is up to date (common case):
{
let map_read = self.map.read();
let value = {
let map_read = self.map.upgradable_read();
match map_read.get(key) {
None | Some(QueryState::InProgress) => return true,
Some(QueryState::Memoized(memo)) => {
if memo.verified_at >= revision_now {
return memo.stamped_value.changed_at > revision;
// If our memo is still up to date, then check if we've
// changed since the revision.
if memo.verified_at == revision_now {
return memo.changed_at > revision;
}
if memo.value.is_some() {
// Otherwise, if we cache values, fall back to the full read to compute the result.
drop(memo);
drop(map_read);
return match self.read(db, key, descriptor) {
Ok(v) => v.changed_at > revision,
Err(CycleDetected) => true,
};
}
}
}
};
// If, however, we don't cache values, then optimistically
// try to advance `verified_at` by walking the inputs.
let mut map_write = RwLockUpgradableReadGuard::upgrade(map_read);
map_write.insert(key.clone(), QueryState::InProgress)
};
let mut memo = match value {
Some(QueryState::Memoized(memo)) => memo,
_ => unreachable!(),
};
if memo
.inputs
.iter()
.all(|old_input| !old_input.maybe_changed_since(db, memo.verified_at))
{
memo.verified_at = revision_now;
self.overwrite_placeholder(&mut self.map.write(), key, QueryState::Memoized(memo));
return false;
}
// Otherwise fall back to the full read to compute the result.
match self.read(db, key, descriptor) {
Ok(v) => v.changed_at > revision,
Err(CycleDetected) => true,
}
// Just remove the existing entry. It's out of date.
self.map.write().remove(key);
true
}
}
impl<DB, Q> UncheckedMutQueryStorageOps<DB, Q> for MemoizedStorage<DB, Q>
impl<DB, Q, MP> UncheckedMutQueryStorageOps<DB, Q> for WeakMemoizedStorage<DB, Q, MP>
where
Q: QueryFunction<DB>,
DB: Database,
MP: MemoizationPolicy<DB, Q>,
{
fn set_unchecked(&self, db: &DB, key: &Q::Key, value: Q::Value) {
let key = key.clone();
@ -277,7 +375,8 @@ where
map_write.insert(
key,
QueryState::Memoized(Memo {
stamped_value: StampedValue { value, changed_at },
value: Some(value),
changed_at,
inputs: QueryDescriptorSet::new(),
verified_at: changed_at,
}),