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Make SelectionCache and EvaluationCache thread-safe #49834

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May 9, 2018
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Make SelectionCache and EvaluationCache thread-safe #49834

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27 changes: 17 additions & 10 deletions src/librustc/traits/select.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -44,9 +44,9 @@ use ty::relate::TypeRelation;
use middle::lang_items;
use mir::interpret::{GlobalId};

use rustc_data_structures::sync::Lock;
use rustc_data_structures::bitvec::BitVector;
use std::iter;
use std::cell::RefCell;
use std::cmp;
use std::fmt;
use std::mem;
Expand Down Expand Up @@ -148,7 +148,7 @@ struct TraitObligationStack<'prev, 'tcx: 'prev> {

#[derive(Clone)]
pub struct SelectionCache<'tcx> {
hashmap: RefCell<FxHashMap<ty::TraitRef<'tcx>,
hashmap: Lock<FxHashMap<ty::TraitRef<'tcx>,
WithDepNode<SelectionResult<'tcx, SelectionCandidate<'tcx>>>>>,
}

Expand Down Expand Up @@ -435,7 +435,7 @@ impl<'tcx> From<OverflowError> for SelectionError<'tcx> {

#[derive(Clone)]
pub struct EvaluationCache<'tcx> {
hashmap: RefCell<FxHashMap<ty::PolyTraitRef<'tcx>, WithDepNode<EvaluationResult>>>
hashmap: Lock<FxHashMap<ty::PolyTraitRef<'tcx>, WithDepNode<EvaluationResult>>>
}

impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
Expand Down Expand Up @@ -1015,14 +1015,19 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
}

if self.can_use_global_caches(param_env) {
let mut cache = self.tcx().evaluation_cache.hashmap.borrow_mut();
if let Some(trait_ref) = self.tcx().lift_to_global(&trait_ref) {
debug!(
"insert_evaluation_cache(trait_ref={:?}, candidate={:?}) global",
trait_ref,
result,
);
cache.insert(trait_ref, WithDepNode::new(dep_node, result));
// This may overwrite the cache with the same value
// FIXME: Due to #50507 this overwrites the different values
// This should be changed to use HashMapExt::insert_same
// when that is fixed
self.tcx().evaluation_cache
.hashmap.borrow_mut()
.insert(trait_ref, WithDepNode::new(dep_node, result));
return;
}
}
Expand Down Expand Up @@ -1368,15 +1373,17 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
let tcx = self.tcx();
let trait_ref = cache_fresh_trait_pred.skip_binder().trait_ref;
if self.can_use_global_caches(param_env) {
let mut cache = tcx.selection_cache.hashmap.borrow_mut();
if let Some(trait_ref) = tcx.lift_to_global(&trait_ref) {
if let Some(candidate) = tcx.lift_to_global(&candidate) {
debug!(
"insert_candidate_cache(trait_ref={:?}, candidate={:?}) global",
trait_ref,
candidate,
);
cache.insert(trait_ref, WithDepNode::new(dep_node, candidate));
// This may overwrite the cache with the same value
tcx.selection_cache
.hashmap.borrow_mut()
.insert(trait_ref, WithDepNode::new(dep_node, candidate));
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Given the comment above, should this also use insert_same()?

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The inserted type doesn't implement Eq.

return;
}
}
Expand Down Expand Up @@ -3404,7 +3411,7 @@ impl<'tcx> TraitObligation<'tcx> {
impl<'tcx> SelectionCache<'tcx> {
pub fn new() -> SelectionCache<'tcx> {
SelectionCache {
hashmap: RefCell::new(FxHashMap())
hashmap: Lock::new(FxHashMap())
}
}

Expand All @@ -3416,7 +3423,7 @@ impl<'tcx> SelectionCache<'tcx> {
impl<'tcx> EvaluationCache<'tcx> {
pub fn new() -> EvaluationCache<'tcx> {
EvaluationCache {
hashmap: RefCell::new(FxHashMap())
hashmap: Lock::new(FxHashMap())
}
}

Expand Down Expand Up @@ -3470,7 +3477,7 @@ impl<'o,'tcx> fmt::Debug for TraitObligationStack<'o,'tcx> {
}
}

#[derive(Clone)]
#[derive(Clone, Eq, PartialEq)]
pub struct WithDepNode<T> {
dep_node: DepNodeIndex,
cached_value: T
Expand Down