| use crate::fx::{FxHashMap, FxHasher}; |
| #[cfg(parallel_compiler)] |
| use crate::sync::{is_dyn_thread_safe, CacheAligned}; |
| use crate::sync::{Lock, LockGuard, Mode}; |
| #[cfg(parallel_compiler)] |
| use either::Either; |
| use std::borrow::Borrow; |
| use std::collections::hash_map::RawEntryMut; |
| use std::hash::{Hash, Hasher}; |
| use std::iter; |
| use std::mem; |
| |
| // 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 number of shards. |
| const SHARD_BITS: usize = 5; |
| |
| #[cfg(parallel_compiler)] |
| const SHARDS: usize = 1 << SHARD_BITS; |
| |
| /// An array of cache-line aligned inner locked structures with convenience methods. |
| /// A single field is used when the compiler uses only one thread. |
| pub enum Sharded<T> { |
| Single(Lock<T>), |
| #[cfg(parallel_compiler)] |
| Shards(Box<[CacheAligned<Lock<T>>; SHARDS]>), |
| } |
| |
| impl<T: Default> Default for Sharded<T> { |
| #[inline] |
| fn default() -> Self { |
| Self::new(T::default) |
| } |
| } |
| |
| impl<T> Sharded<T> { |
| #[inline] |
| pub fn new(mut value: impl FnMut() -> T) -> Self { |
| #[cfg(parallel_compiler)] |
| if is_dyn_thread_safe() { |
| return Sharded::Shards(Box::new( |
| [(); SHARDS].map(|()| CacheAligned(Lock::new(value()))), |
| )); |
| } |
| |
| Sharded::Single(Lock::new(value())) |
| } |
| |
| /// The shard is selected by hashing `val` with `FxHasher`. |
| #[inline] |
| pub fn get_shard_by_value<K: Hash + ?Sized>(&self, _val: &K) -> &Lock<T> { |
| match self { |
| Self::Single(single) => single, |
| #[cfg(parallel_compiler)] |
| Self::Shards(..) => self.get_shard_by_hash(make_hash(_val)), |
| } |
| } |
| |
| #[inline] |
| pub fn get_shard_by_hash(&self, hash: u64) -> &Lock<T> { |
| self.get_shard_by_index(get_shard_hash(hash)) |
| } |
| |
| #[inline] |
| pub fn get_shard_by_index(&self, _i: usize) -> &Lock<T> { |
| match self { |
| Self::Single(single) => single, |
| #[cfg(parallel_compiler)] |
| Self::Shards(shards) => { |
| // SAFETY: The index gets ANDed with the shard mask, ensuring it is always inbounds. |
| unsafe { &shards.get_unchecked(_i & (SHARDS - 1)).0 } |
| } |
| } |
| } |
| |
| /// The shard is selected by hashing `val` with `FxHasher`. |
| #[inline] |
| #[track_caller] |
| pub fn lock_shard_by_value<K: Hash + ?Sized>(&self, _val: &K) -> LockGuard<'_, T> { |
| match self { |
| Self::Single(single) => { |
| // Synchronization is disabled so use the `lock_assume_no_sync` method optimized |
| // for that case. |
| |
| // SAFETY: We know `is_dyn_thread_safe` was false when creating the lock thus |
| // `might_be_dyn_thread_safe` was also false. |
| unsafe { single.lock_assume(Mode::NoSync) } |
| } |
| #[cfg(parallel_compiler)] |
| Self::Shards(..) => self.lock_shard_by_hash(make_hash(_val)), |
| } |
| } |
| |
| #[inline] |
| #[track_caller] |
| pub fn lock_shard_by_hash(&self, hash: u64) -> LockGuard<'_, T> { |
| self.lock_shard_by_index(get_shard_hash(hash)) |
| } |
| |
| #[inline] |
| #[track_caller] |
| pub fn lock_shard_by_index(&self, _i: usize) -> LockGuard<'_, T> { |
| match self { |
| Self::Single(single) => { |
| // Synchronization is disabled so use the `lock_assume_no_sync` method optimized |
| // for that case. |
| |
| // SAFETY: We know `is_dyn_thread_safe` was false when creating the lock thus |
| // `might_be_dyn_thread_safe` was also false. |
| unsafe { single.lock_assume(Mode::NoSync) } |
| } |
| #[cfg(parallel_compiler)] |
| Self::Shards(shards) => { |
| // Synchronization is enabled so use the `lock_assume_sync` method optimized |
| // for that case. |
| |
| // SAFETY (get_unchecked): The index gets ANDed with the shard mask, ensuring it is |
| // always inbounds. |
| // SAFETY (lock_assume_sync): We know `is_dyn_thread_safe` was true when creating |
| // the lock thus `might_be_dyn_thread_safe` was also true. |
| unsafe { shards.get_unchecked(_i & (SHARDS - 1)).0.lock_assume(Mode::Sync) } |
| } |
| } |
| } |
| |
| #[inline] |
| pub fn lock_shards(&self) -> impl Iterator<Item = LockGuard<'_, T>> { |
| match self { |
| #[cfg(not(parallel_compiler))] |
| Self::Single(single) => iter::once(single.lock()), |
| #[cfg(parallel_compiler)] |
| Self::Single(single) => Either::Left(iter::once(single.lock())), |
| #[cfg(parallel_compiler)] |
| Self::Shards(shards) => Either::Right(shards.iter().map(|shard| shard.0.lock())), |
| } |
| } |
| |
| #[inline] |
| pub fn try_lock_shards(&self) -> impl Iterator<Item = Option<LockGuard<'_, T>>> { |
| match self { |
| #[cfg(not(parallel_compiler))] |
| Self::Single(single) => iter::once(single.try_lock()), |
| #[cfg(parallel_compiler)] |
| Self::Single(single) => Either::Left(iter::once(single.try_lock())), |
| #[cfg(parallel_compiler)] |
| Self::Shards(shards) => Either::Right(shards.iter().map(|shard| shard.0.try_lock())), |
| } |
| } |
| } |
| |
| #[inline] |
| pub fn shards() -> usize { |
| #[cfg(parallel_compiler)] |
| if is_dyn_thread_safe() { |
| return SHARDS; |
| } |
| |
| 1 |
| } |
| |
| pub type ShardedHashMap<K, V> = Sharded<FxHashMap<K, V>>; |
| |
| impl<K: Eq, V> ShardedHashMap<K, V> { |
| pub fn len(&self) -> usize { |
| self.lock_shards().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.lock_shard_by_hash(hash); |
| 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.lock_shard_by_hash(hash); |
| 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 |
| } |
| } |
| } |
| } |
| |
| pub trait IntoPointer { |
| /// Returns a pointer which outlives `self`. |
| fn into_pointer(&self) -> *const (); |
| } |
| |
| impl<K: Eq + Hash + Copy + IntoPointer> ShardedHashMap<K, ()> { |
| pub fn contains_pointer_to<T: Hash + IntoPointer>(&self, value: &T) -> bool { |
| let hash = make_hash(&value); |
| let shard = self.lock_shard_by_hash(hash); |
| let value = value.into_pointer(); |
| shard.raw_entry().from_hash(hash, |entry| entry.into_pointer() == value).is_some() |
| } |
| } |
| |
| #[inline] |
| pub fn make_hash<K: Hash + ?Sized>(val: &K) -> u64 { |
| let mut state = FxHasher::default(); |
| val.hash(&mut state); |
| state.finish() |
| } |
| |
| /// Get a shard with a pre-computed hash value. If `get_shard_by_value` is |
| /// ever used in combination with `get_shard_by_hash` on a single `Sharded` |
| /// instance, then `hash` must be computed with `FxHasher`. Otherwise, |
| /// `hash` can be computed with any hasher, so long as that hasher is used |
| /// consistently for each `Sharded` instance. |
| #[inline] |
| fn get_shard_hash(hash: u64) -> usize { |
| 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 |
| (hash >> (hash_len * 8 - 7 - SHARD_BITS)) as usize |
| } |
