Use sharded maps for interning #61779
There are no files selected for viewing
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,128 @@ | ||
| use std::hash::{Hasher, Hash}; | ||
| use std::mem; | ||
| use std::borrow::Borrow; | ||
| use std::collections::hash_map::RawEntryMut; | ||
| use crate::fx::{FxHasher, FxHashMap}; | ||
| use crate::sync::{Lock, LockGuard}; | ||
|
|
||
| #[derive(Clone, Default)] | ||
| #[cfg_attr(parallel_compiler, repr(align(64)))] | ||
| struct CacheAligned<T>(T); | ||
|
|
||
| #[cfg(parallel_compiler)] | ||
| // 32 shards is sufficient to reduce contention on an 8-core Ryzen 7 1700, | ||
| // but this should be tested on higher core count CPUs. How the `Sharded` type gets used | ||
| // may also affect the ideal nunber of shards. | ||
| const SHARD_BITS: usize = 5; | ||
|
|
||
| #[cfg(not(parallel_compiler))] | ||
| const SHARD_BITS: usize = 0; | ||
|
|
||
| const SHARDS: usize = 1 << SHARD_BITS; | ||
|
|
||
| /// An array of cache-line aligned inner locked structures with convenience methods. | ||
| #[derive(Clone)] | ||
| pub struct Sharded<T> { | ||
| shards: [CacheAligned<Lock<T>>; SHARDS], | ||
| } | ||
|
|
||
| impl<T: Default> Default for Sharded<T> { | ||
| #[inline] | ||
| fn default() -> Self { | ||
| let mut shards: mem::MaybeUninit<[CacheAligned<Lock<T>>; SHARDS]> = | ||
| mem::MaybeUninit::uninit(); | ||
| let first = shards.as_mut_ptr() as *mut CacheAligned<Lock<T>>; | ||
| unsafe { | ||
| for i in 0..SHARDS { | ||
| first.add(i).write(CacheAligned(Lock::new(T::default()))); | ||
| } | ||
| Sharded { | ||
| shards: shards.assume_init(), | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| impl<T> Sharded<T> { | ||
| #[inline] | ||
| pub fn get_shard_by_value<K: Hash + ?Sized>(&self, val: &K) -> &Lock<T> { | ||
| if SHARDS == 1 { | ||
| &self.shards[0].0 | ||
| } else { | ||
| self.get_shard_by_hash(make_hash(val)) | ||
| } | ||
| } | ||
|
|
||
| #[inline] | ||
| pub fn get_shard_by_hash(&self, hash: u64) -> &Lock<T> { | ||
oli-obk marked this conversation as resolved.
Outdated
Show resolved
Hide resolved
|
||
| let hash_len = mem::size_of::<usize>(); | ||
| // Ignore the top 7 bits as hashbrown uses these and get the next SHARD_BITS highest bits. | ||
| // hashbrown also uses the lowest bits, so we can't use those | ||
| let bits = (hash >> (hash_len * 8 - 7 - SHARD_BITS)) as usize; | ||
| let i = bits % SHARDS; | ||
| &self.shards[i].0 | ||
| } | ||
|
|
||
| pub fn lock_shards(&self) -> Vec<LockGuard<'_, T>> { | ||
| (0..SHARDS).map(|i| self.shards[i].0.lock()).collect() | ||
| } | ||
|
|
||
| pub fn try_lock_shards(&self) -> Option<Vec<LockGuard<'_, T>>> { | ||
| (0..SHARDS).map(|i| self.shards[i].0.try_lock()).collect() | ||
| } | ||
| } | ||
|
|
||
| pub type ShardedHashMap<K, V> = Sharded<FxHashMap<K, V>>; | ||
|
|
||
| impl<K: Eq + Hash, V> ShardedHashMap<K, V> { | ||
| pub fn len(&self) -> usize { | ||
| self.lock_shards().iter().map(|shard| shard.len()).sum() | ||
| } | ||
| } | ||
|
|
||
| impl<K: Eq + Hash + Copy> ShardedHashMap<K, ()> { | ||
|
||
| #[inline] | ||
| pub fn intern_ref<Q: ?Sized>(&self, value: &Q, make: impl FnOnce() -> K) -> K | ||
| where K: Borrow<Q>, | ||
| Q: Hash + Eq | ||
| { | ||
| let hash = make_hash(value); | ||
|
||
| let mut shard = self.get_shard_by_hash(hash).lock(); | ||
| let entry = shard.raw_entry_mut().from_key_hashed_nocheck(hash, value); | ||
|
|
||
| match entry { | ||
| RawEntryMut::Occupied(e) => *e.key(), | ||
| RawEntryMut::Vacant(e) => { | ||
| let v = make(); | ||
|
||
| e.insert_hashed_nocheck(hash, v, ()); | ||
| v | ||
| } | ||
| } | ||
| } | ||
|
|
||
| #[inline] | ||
| pub fn intern<Q>(&self, value: Q, make: impl FnOnce(Q) -> K) -> K | ||
| where K: Borrow<Q>, | ||
| Q: Hash + Eq | ||
| { | ||
| let hash = make_hash(&value); | ||
| let mut shard = self.get_shard_by_hash(hash).lock(); | ||
| let entry = shard.raw_entry_mut().from_key_hashed_nocheck(hash, &value); | ||
|
|
||
| match entry { | ||
| RawEntryMut::Occupied(e) => *e.key(), | ||
| RawEntryMut::Vacant(e) => { | ||
| let v = make(value); | ||
| e.insert_hashed_nocheck(hash, v, ()); | ||
| v | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| #[inline] | ||
| fn make_hash<K: Hash + ?Sized>(val: &K) -> u64 { | ||
| let mut state = FxHasher::default(); | ||
| val.hash(&mut state); | ||
| state.finish() | ||
| } | ||
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Some comment on the magic number would ne nice
There was a problem hiding this comment.
Choose a reason for hiding this comment
The reason will be displayed to describe this comment to others. Learn more.
Added a comment here.