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Hash keys once #194

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merged 2 commits into from
Apr 27, 2022
Merged

Hash keys once #194

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62d9901
Switch underlying hashmap to hashbrown
stepancheg Mar 23, 2022
c20f57f
Hash key only once in map operations
stepancheg Mar 24, 2022
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1 change: 1 addition & 0 deletions Cargo.toml
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Expand Up @@ -20,6 +20,7 @@ send_guard = ["parking_lot/send_guard"]
[dependencies]
num_cpus = "1.13.1"
parking_lot = "0.12.0"
hashbrown = "0.11.2"
serde = { version = "1.0.136", optional = true, features = ["derive"] }
cfg-if = "1.0.0"
rayon = { version = "1.5.1", optional = true }
Expand Down
7 changes: 3 additions & 4 deletions src/iter.rs
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Expand Up @@ -6,7 +6,6 @@ use crate::{DashMap, HashMap};
use core::hash::{BuildHasher, Hash};
use core::mem;
use parking_lot::{RwLockReadGuard, RwLockWriteGuard};
use std::collections::hash_map;
use std::collections::hash_map::RandomState;
use std::sync::Arc;

Expand Down Expand Up @@ -39,7 +38,7 @@ impl<K: Eq + Hash, V, S: BuildHasher + Clone> OwningIter<K, V, S> {
}
}

type GuardOwningIter<K, V> = hash_map::IntoIter<K, SharedValue<V>>;
type GuardOwningIter<K, V> = hashbrown::hash_map::IntoIter<K, SharedValue<V>>;

impl<K: Eq + Hash, V, S: BuildHasher + Clone> Iterator for OwningIter<K, V, S> {
type Item = (K, V);
Expand Down Expand Up @@ -93,12 +92,12 @@ where

type GuardIter<'a, K, V, S> = (
Arc<RwLockReadGuard<'a, HashMap<K, V, S>>>,
hash_map::Iter<'a, K, SharedValue<V>>,
hashbrown::hash_map::Iter<'a, K, SharedValue<V>>,
);

type GuardIterMut<'a, K, V, S> = (
Arc<RwLockWriteGuard<'a, HashMap<K, V, S>>>,
hash_map::IterMut<'a, K, SharedValue<V>>,
hashbrown::hash_map::IterMut<'a, K, SharedValue<V>>,
);

/// Iterator over a DashMap yielding immutable references.
Expand Down
122 changes: 69 additions & 53 deletions src/lib.rs
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Expand Up @@ -43,7 +43,7 @@ cfg_if! {
}
}

pub(crate) type HashMap<K, V, S> = std::collections::HashMap<K, SharedValue<V>, S>;
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@Veykril Veykril Jun 9, 2022 •
edited
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This type alias is exposed by public facing apis and therefor is a semver breakage, this was experienced in using one of the rust-analyzer crates as a dependency rust-lang/rust-analyzer#12344 (comment)

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@xacrimon xacrimon Jun 9, 2022 •
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@Veykril Hey! This is indeed a semver breakage, however this is only visible if you use the raw_api feature which exposes the raw shards. I should probably do a better job at noting this in crate level documentation but this feature is unstable, this means you need to pin the versions if you rely on the types from that API as it may change due to internal needs like this PR and an internal lock change that was also done recently.

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I see, good to know!

pub(crate) type HashMap<K, V, S> = hashbrown::HashMap<K, SharedValue<V>, S>;

fn default_shard_amount() -> usize {
(num_cpus::get() * 4).next_power_of_two()
Expand Down Expand Up @@ -271,14 +271,18 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: BuildHasher + Clone> DashMap<K, V, S> {
}
}

/// Hash a given item to produce a usize.
/// Uses the provided or default HashBuilder.
pub fn hash_usize<T: Hash>(&self, item: &T) -> usize {
fn hash_u64<T: Hash>(&self, item: &T) -> u64 {
let mut hasher = self.hasher.build_hasher();

item.hash(&mut hasher);

hasher.finish() as usize
hasher.finish()
}

/// Hash a given item to produce a usize.
/// Uses the provided or default HashBuilder.
pub fn hash_usize<T: Hash>(&self, item: &T) -> usize {
self.hash_u64(item) as usize
}

cfg_if! {
Expand Down Expand Up @@ -329,8 +333,8 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: BuildHasher + Clone> DashMap<K, V, S> {
K: Borrow<Q>,
Q: Hash + Eq + ?Sized,
{
let hash = self.hash_usize(&key);
self.determine_shard(hash)
let hash = self.hash_u64(&key);
self.determine_shard(hash as usize)
}
}
}
Expand Down Expand Up @@ -837,50 +841,64 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: 'a + BuildHasher + Clone> Map<'a, K, V, S>
}

fn _insert(&self, key: K, value: V) -> Option<V> {
let hash = self.hash_usize(&key);
let hash = self.hash_u64(&key);

let idx = self.determine_shard(hash);
let idx = self.determine_shard(hash as usize);

let mut shard = unsafe { self._yield_write_shard(idx) };

shard
.insert(key, SharedValue::new(value))
.map(|v| v.into_inner())
match shard.raw_entry_mut().from_key_hashed_nocheck(hash, &key) {
hashbrown::hash_map::RawEntryMut::Occupied(mut occupied) => {
Some(occupied.insert(SharedValue::new(value)).into_inner())
}
hashbrown::hash_map::RawEntryMut::Vacant(vacant) => {
vacant.insert(key, SharedValue::new(value));
None
}
}
}

fn _remove<Q>(&self, key: &Q) -> Option<(K, V)>
where
K: Borrow<Q>,
Q: Hash + Eq + ?Sized,
{
let hash = self.hash_usize(&key);
let hash = self.hash_u64(&key);

let idx = self.determine_shard(hash);
let idx = self.determine_shard(hash as usize);

let mut shard = unsafe { self._yield_write_shard(idx) };

shard.remove_entry(key).map(|(k, v)| (k, v.into_inner()))
match shard.raw_entry_mut().from_key_hashed_nocheck(hash, key) {
hashbrown::hash_map::RawEntryMut::Occupied(entry) => {
let (k, v) = entry.remove_entry();
Some((k, v.into_inner()))
}
hashbrown::hash_map::RawEntryMut::Vacant(_) => None,
}
}

fn _remove_if<Q>(&self, key: &Q, f: impl FnOnce(&K, &V) -> bool) -> Option<(K, V)>
where
K: Borrow<Q>,
Q: Hash + Eq + ?Sized,
{
let hash = self.hash_usize(&key);
let hash = self.hash_u64(&key);

let idx = self.determine_shard(hash);
let idx = self.determine_shard(hash as usize);

let mut shard = unsafe { self._yield_write_shard(idx) };

if let Some((k, v)) = shard.get_key_value(key) {
if f(k, v.get()) {
shard.remove_entry(key).map(|(k, v)| (k, v.into_inner()))
} else {
None
match shard.raw_entry_mut().from_key_hashed_nocheck(hash, key) {
hashbrown::hash_map::RawEntryMut::Occupied(occupied) => {
if f(&occupied.key(), &occupied.get().get()) {
let (k, v) = occupied.remove_entry();
Some((k, v.into_inner()))
} else {
None
}
}
} else {
None
hashbrown::hash_map::RawEntryMut::Vacant(_) => None,
}
}

Expand All @@ -889,25 +907,23 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: 'a + BuildHasher + Clone> Map<'a, K, V, S>
K: Borrow<Q>,
Q: Hash + Eq + ?Sized,
{
let hash = self.hash_usize(&key);
let hash = self.hash_u64(&key);

let idx = self.determine_shard(hash);
let idx = self.determine_shard(hash as usize);

let mut shard = unsafe { self._yield_write_shard(idx) };

if let Some((kptr, vptr)) = shard.get_key_value(&key) {
unsafe {
let kptr: *const K = kptr;
let vptr: *mut V = vptr.as_ptr();

if f(&*kptr, &mut *vptr) {
shard.remove_entry(key).map(|(k, v)| (k, v.into_inner()))
match shard.raw_entry_mut().from_key_hashed_nocheck(hash, key) {
hashbrown::hash_map::RawEntryMut::Occupied(mut occupied) => {
let (k, v) = occupied.get_key_value_mut();
if f(k, v.get_mut()) {
let (k, v) = occupied.remove_entry();
Some((k, v.into_inner()))
} else {
None
}
}
} else {
None
hashbrown::hash_map::RawEntryMut::Vacant(_) => None,
}
}

Expand All @@ -924,13 +940,13 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: 'a + BuildHasher + Clone> Map<'a, K, V, S>
K: Borrow<Q>,
Q: Hash + Eq + ?Sized,
{
let hash = self.hash_usize(&key);
let hash = self.hash_u64(&key);

let idx = self.determine_shard(hash);
let idx = self.determine_shard(hash as usize);

let shard = unsafe { self._yield_read_shard(idx) };

if let Some((kptr, vptr)) = shard.get_key_value(key) {
if let Some((kptr, vptr)) = shard.raw_entry().from_key_hashed_nocheck(hash, key) {
unsafe {
let kptr: *const K = kptr;
let vptr: *const V = vptr.get();
Expand All @@ -946,13 +962,13 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: 'a + BuildHasher + Clone> Map<'a, K, V, S>
K: Borrow<Q>,
Q: Hash + Eq + ?Sized,
{
let hash = self.hash_usize(&key);
let hash = self.hash_u64(&key);

let idx = self.determine_shard(hash);
let idx = self.determine_shard(hash as usize);

let shard = unsafe { self._yield_write_shard(idx) };

if let Some((kptr, vptr)) = shard.get_key_value(key) {
if let Some((kptr, vptr)) = shard.raw_entry().from_key_hashed_nocheck(hash, key) {
unsafe {
let kptr: *const K = kptr;
let vptr: *mut V = vptr.as_ptr();
Expand All @@ -968,16 +984,16 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: 'a + BuildHasher + Clone> Map<'a, K, V, S>
K: Borrow<Q>,
Q: Hash + Eq + ?Sized,
{
let hash = self.hash_usize(&key);
let hash = self.hash_u64(&key);

let idx = self.determine_shard(hash);
let idx = self.determine_shard(hash as usize);

let shard = match unsafe { self._try_yield_read_shard(idx) } {
Some(shard) => shard,
None => return TryResult::Locked,
};

if let Some((kptr, vptr)) = shard.get_key_value(key) {
if let Some((kptr, vptr)) = shard.raw_entry().from_key_hashed_nocheck(hash, key) {
unsafe {
let kptr: *const K = kptr;
let vptr: *const V = vptr.get();
Expand All @@ -993,16 +1009,16 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: 'a + BuildHasher + Clone> Map<'a, K, V, S>
K: Borrow<Q>,
Q: Hash + Eq + ?Sized,
{
let hash = self.hash_usize(&key);
let hash = self.hash_u64(&key);

let idx = self.determine_shard(hash);
let idx = self.determine_shard(hash as usize);

let shard = match unsafe { self._try_yield_write_shard(idx) } {
Some(shard) => shard,
None => return TryResult::Locked,
};

if let Some((kptr, vptr)) = shard.get_key_value(key) {
if let Some((kptr, vptr)) = shard.raw_entry().from_key_hashed_nocheck(hash, key) {
unsafe {
let kptr: *const K = kptr;
let vptr: *mut V = vptr.as_ptr();
Expand Down Expand Up @@ -1061,13 +1077,13 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: 'a + BuildHasher + Clone> Map<'a, K, V, S>
}

fn _entry(&'a self, key: K) -> Entry<'a, K, V, S> {
let hash = self.hash_usize(&key);
let hash = self.hash_u64(&key);

let idx = self.determine_shard(hash);
let idx = self.determine_shard(hash as usize);

let shard = unsafe { self._yield_write_shard(idx) };

if let Some((kptr, vptr)) = shard.get_key_value(&key) {
if let Some((kptr, vptr)) = shard.raw_entry().from_key_hashed_nocheck(hash, &key) {
unsafe {
let kptr: *const K = kptr;
let vptr: *mut V = vptr.as_ptr();
Expand All @@ -1079,16 +1095,16 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: 'a + BuildHasher + Clone> Map<'a, K, V, S>
}

fn _try_entry(&'a self, key: K) -> Option<Entry<'a, K, V, S>> {
let hash = self.hash_usize(&key);
let hash = self.hash_u64(&key);

let idx = self.determine_shard(hash);
let idx = self.determine_shard(hash as usize);

let shard = match unsafe { self._try_yield_write_shard(idx) } {
Some(shard) => shard,
None => return None,
};

if let Some((kptr, vptr)) = shard.get_key_value(&key) {
if let Some((kptr, vptr)) = shard.raw_entry().from_key_hashed_nocheck(hash, &key) {
unsafe {
let kptr: *const K = kptr;
let vptr: *mut V = vptr.as_ptr();
Expand Down
27 changes: 18 additions & 9 deletions src/read_only.rs
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Expand Up @@ -59,13 +59,16 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: BuildHasher + Clone> ReadOnlyView<K, V, S>
K: Borrow<Q>,
Q: Hash + Eq + ?Sized,
{
let hash = self.map.hash_usize(&key);
let hash = self.map.hash_u64(&key);

let idx = self.map.determine_shard(hash);
let idx = self.map.determine_shard(hash as usize);

let shard = unsafe { self.map._get_read_shard(idx) };

shard.contains_key(key)
shard
.raw_entry()
.from_key_hashed_nocheck(hash, key)
.is_some()
}

/// Returns a reference to the value corresponding to the key.
Expand All @@ -74,13 +77,16 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: BuildHasher + Clone> ReadOnlyView<K, V, S>
K: Borrow<Q>,
Q: Hash + Eq + ?Sized,
{
let hash = self.map.hash_usize(&key);
let hash = self.map.hash_u64(&key);

let idx = self.map.determine_shard(hash);
let idx = self.map.determine_shard(hash as usize);

let shard = unsafe { self.map._get_read_shard(idx) };

shard.get(key).map(|v| v.get())
shard
.raw_entry()
.from_key_hashed_nocheck(hash, key)
.map(|(_k, v)| v.get())
}

/// Returns the key-value pair corresponding to the supplied key.
Expand All @@ -89,13 +95,16 @@ impl<'a, K: 'a + Eq + Hash, V: 'a, S: BuildHasher + Clone> ReadOnlyView<K, V, S>
K: Borrow<Q>,
Q: Hash + Eq + ?Sized,
{
let hash = self.map.hash_usize(&key);
let hash = self.map.hash_u64(&key);

let idx = self.map.determine_shard(hash);
let idx = self.map.determine_shard(hash as usize);

let shard = unsafe { self.map._get_read_shard(idx) };

shard.get_key_value(key).map(|(k, v)| (k, v.get()))
shard
.raw_entry()
.from_key_hashed_nocheck(hash, key)
.map(|(k, v)| (k, v.get()))
}

fn shard_read_iter(&'a self) -> impl Iterator<Item = &'a HashMap<K, V, S>> + 'a {
Expand Down