Struct DashMap

pub struct DashMap<K, V, S = RandomState> { /* private fields */ }

DashMap is an implementation of a concurrent associative array/hashmap in Rust.

DashMap tries to implement an easy to use API similar to std::collections::HashMap with some slight changes to handle concurrency.

DashMap tries to be very simple to use and to be a direct replacement for RwLock<HashMap<K, V>>. To accomplish this, all methods take &self instead of modifying methods taking &mut self. This allows you to put a DashMap in an Arc<T> and share it between threads while being able to modify it.

Documentation mentioning locking behaviour acts in the reference frame of the calling thread. This means that it is safe to ignore it across multiple threads.

Implementations

impl<K, V, S> DashMap<K, V, S>

where K: Send + Sync + Eq + Hash, V: Send + Sync,

pub fn par_iter_mut(&self) -> IterMut<'_, K, V>

impl<'a, K: 'a + Eq + Hash, V: 'a> DashMap<K, V, RandomState>

pub fn new() -> Self

Creates a new DashMap with a capacity of 0.

Examples

use dashmap::DashMap;

let reviews = DashMap::new();
reviews.insert("Veloren", "What a fantastic game!");

pub fn with_capacity(capacity: usize) -> Self

Creates a new DashMap with a specified starting capacity.

Examples

use dashmap::DashMap;

let mappings = DashMap::with_capacity(2);
mappings.insert(2, 4);
mappings.insert(8, 16);

pub fn with_shard_amount(shard_amount: usize) -> Self

Creates a new DashMap with a specified shard amount

shard_amount should greater than 0 and be a power of two. If a shard_amount which is not a power of two is provided, the function will panic.

Examples

use dashmap::DashMap;

let mappings = DashMap::with_shard_amount(32);
mappings.insert(2, 4);
mappings.insert(8, 16);

pub fn with_capacity_and_shard_amount( capacity: usize, shard_amount: usize, ) -> Self

Creates a new DashMap with a specified capacity and shard amount.

shard_amount should greater than 0 and be a power of two. If a shard_amount which is not a power of two is provided, the function will panic.

Examples

use dashmap::DashMap;

let mappings = DashMap::with_capacity_and_shard_amount(32, 32);
mappings.insert(2, 4);
mappings.insert(8, 16);

impl<'a, K: 'a + Eq + Hash, V: 'a, S: BuildHasher + Clone> DashMap<K, V, S>

pub fn into_read_only(self) -> ReadOnlyView<K, V, S>

Wraps this DashMap into a read-only view. This view allows to obtain raw references to the stored values.

pub fn with_hasher(hasher: S) -> Self

Creates a new DashMap with a capacity of 0 and the provided hasher.

Examples

use dashmap::DashMap;
use std::collections::hash_map::RandomState;

let s = RandomState::new();
let reviews = DashMap::with_hasher(s);
reviews.insert("Veloren", "What a fantastic game!");

pub fn with_capacity_and_hasher(capacity: usize, hasher: S) -> Self

Creates a new DashMap with a specified starting capacity and hasher.

Examples

use dashmap::DashMap;
use std::collections::hash_map::RandomState;

let s = RandomState::new();
let mappings = DashMap::with_capacity_and_hasher(2, s);
mappings.insert(2, 4);
mappings.insert(8, 16);

pub fn with_hasher_and_shard_amount(hasher: S, shard_amount: usize) -> Self

Creates a new DashMap with a specified hasher and shard amount

shard_amount should be greater than 0 and a power of two. If a shard_amount which is not a power of two is provided, the function will panic.

Examples

use dashmap::DashMap;
use std::collections::hash_map::RandomState;

let s = RandomState::new();
let mappings = DashMap::with_hasher_and_shard_amount(s, 32);
mappings.insert(2, 4);
mappings.insert(8, 16);

pub fn with_capacity_and_hasher_and_shard_amount( capacity: usize, hasher: S, shard_amount: usize, ) -> Self

Creates a new DashMap with a specified starting capacity, hasher and shard_amount.

shard_amount should greater than 0 and be a power of two. If a shard_amount which is not a power of two is provided, the function will panic.

Examples

use dashmap::DashMap;
use std::collections::hash_map::RandomState;

let s = RandomState::new();
let mappings = DashMap::with_capacity_and_hasher_and_shard_amount(2, s, 32);
mappings.insert(2, 4);
mappings.insert(8, 16);

pub fn hash_usize<T: Hash>(&self, item: &T) -> usize

Hash a given item to produce a usize. Uses the provided or default HashBuilder.

pub fn hasher(&self) -> &S

Returns a reference to the map’s BuildHasher.

Examples

use dashmap::DashMap;
use std::collections::hash_map::RandomState;

let hasher = RandomState::new();
let map: DashMap<i32, i32> = DashMap::new();
let hasher: &RandomState = map.hasher();

pub fn insert(&self, key: K, value: V) -> Option<V>

Inserts a key and a value into the map. Returns the old value associated with the key if there was one.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let map = DashMap::new();
map.insert("I am the key!", "And I am the value!");

pub fn remove<Q>(&self, key: &Q) -> Option<(K, V)>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Removes an entry from the map, returning the key and value if they existed in the map.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let soccer_team = DashMap::new();
soccer_team.insert("Jack", "Goalie");
assert_eq!(soccer_team.remove("Jack").unwrap().1, "Goalie");

pub fn remove_if<Q>( &self, key: &Q, f: impl FnOnce(&K, &V) -> bool, ) -> Option<(K, V)>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Removes an entry from the map, returning the key and value if the entry existed and the provided conditional function returned true.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

use dashmap::DashMap;

let soccer_team = DashMap::new();
soccer_team.insert("Sam", "Forward");
soccer_team.remove_if("Sam", |_, position| position == &"Goalie");
assert!(soccer_team.contains_key("Sam"));

use dashmap::DashMap;

let soccer_team = DashMap::new();
soccer_team.insert("Sam", "Forward");
soccer_team.remove_if("Sam", |_, position| position == &"Forward");
assert!(!soccer_team.contains_key("Sam"));

pub fn remove_if_mut<Q>( &self, key: &Q, f: impl FnOnce(&K, &mut V) -> bool, ) -> Option<(K, V)>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

pub fn iter(&'a self) -> Iter<'a, K, V, S, DashMap<K, V, S>>

Creates an iterator over a DashMap yielding immutable references.

Locking behaviour: May deadlock if called when holding a mutable reference into the map.

Examples

use dashmap::DashMap;

let words = DashMap::new();
words.insert("hello", "world");
assert_eq!(words.iter().count(), 1);

pub fn iter_mut(&'a self) -> IterMut<'a, K, V, S, DashMap<K, V, S>>

Iterator over a DashMap yielding mutable references.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let map = DashMap::new();
map.insert("Johnny", 21);
map.iter_mut().for_each(|mut r| *r += 1);
assert_eq!(*map.get("Johnny").unwrap(), 22);

pub fn get<Q>(&'a self, key: &Q) -> Option<Ref<'a, K, V>>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Get an immutable reference to an entry in the map

Locking behaviour: May deadlock if called when holding a mutable reference into the map.

Examples

use dashmap::DashMap;

let youtubers = DashMap::new();
youtubers.insert("Bosnian Bill", 457000);
assert_eq!(*youtubers.get("Bosnian Bill").unwrap(), 457000);

pub fn get_mut<Q>(&'a self, key: &Q) -> Option<RefMut<'a, K, V>>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Get a mutable reference to an entry in the map

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let class = DashMap::new();
class.insert("Albin", 15);
*class.get_mut("Albin").unwrap() -= 1;
assert_eq!(*class.get("Albin").unwrap(), 14);

pub fn try_get<Q>(&'a self, key: &Q) -> TryResult<Ref<'a, K, V>>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Get an immutable reference to an entry in the map, if the shard is not locked. If the shard is locked, the function will return TryResult::Locked.

Examples

use dashmap::DashMap;
use dashmap::try_result::TryResult;

let map = DashMap::new();
map.insert("Johnny", 21);

assert_eq!(*map.try_get("Johnny").unwrap(), 21);

let _result1_locking = map.get_mut("Johnny");

let result2 = map.try_get("Johnny");
assert!(result2.is_locked());

pub fn try_get_mut<Q>(&'a self, key: &Q) -> TryResult<RefMut<'a, K, V>>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Get a mutable reference to an entry in the map, if the shard is not locked. If the shard is locked, the function will return TryResult::Locked.

Examples

use dashmap::DashMap;
use dashmap::try_result::TryResult;

let map = DashMap::new();
map.insert("Johnny", 21);

*map.try_get_mut("Johnny").unwrap() += 1;
assert_eq!(*map.get("Johnny").unwrap(), 22);

let _result1_locking = map.get("Johnny");

let result2 = map.try_get_mut("Johnny");
assert!(result2.is_locked());

pub fn shrink_to_fit(&self)

Remove excess capacity to reduce memory usage.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;
use dashmap::try_result::TryResult;

let map = DashMap::new();
map.insert("Johnny", 21);
assert!(map.capacity() > 0);
map.remove("Johnny");
map.shrink_to_fit();
assert_eq!(map.capacity(), 0);

pub fn retain(&self, f: impl FnMut(&K, &mut V) -> bool)

Retain elements that whose predicates return true and discard elements whose predicates return false.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let people = DashMap::new();
people.insert("Albin", 15);
people.insert("Jones", 22);
people.insert("Charlie", 27);
people.retain(|_, v| *v > 20);
assert_eq!(people.len(), 2);

pub fn len(&self) -> usize

Fetches the total number of key-value pairs stored in the map.

Locking behaviour: May deadlock if called when holding a mutable reference into the map.

Examples

use dashmap::DashMap;

let people = DashMap::new();
people.insert("Albin", 15);
people.insert("Jones", 22);
people.insert("Charlie", 27);
assert_eq!(people.len(), 3);

pub fn is_empty(&self) -> bool

Checks if the map is empty or not.

Locking behaviour: May deadlock if called when holding a mutable reference into the map.

Examples

use dashmap::DashMap;

let map = DashMap::<(), ()>::new();
assert!(map.is_empty());

pub fn clear(&self)

Removes all key-value pairs in the map.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let stats = DashMap::new();
stats.insert("Goals", 4);
assert!(!stats.is_empty());
stats.clear();
assert!(stats.is_empty());

pub fn capacity(&self) -> usize

Returns how many key-value pairs the map can store without reallocating.

Locking behaviour: May deadlock if called when holding a mutable reference into the map.

pub fn alter<Q>(&self, key: &Q, f: impl FnOnce(&K, V) -> V)

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Modify a specific value according to a function.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let stats = DashMap::new();
stats.insert("Goals", 4);
stats.alter("Goals", |_, v| v * 2);
assert_eq!(*stats.get("Goals").unwrap(), 8);

Panics

If the given closure panics, then alter will abort the process

pub fn alter_all(&self, f: impl FnMut(&K, V) -> V)

Modify every value in the map according to a function.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let stats = DashMap::new();
stats.insert("Wins", 4);
stats.insert("Losses", 2);
stats.alter_all(|_, v| v + 1);
assert_eq!(*stats.get("Wins").unwrap(), 5);
assert_eq!(*stats.get("Losses").unwrap(), 3);

Panics

If the given closure panics, then alter_all will abort the process

pub fn view<Q, R>(&self, key: &Q, f: impl FnOnce(&K, &V) -> R) -> Option<R>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Scoped access into an item of the map according to a function.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

Examples

use dashmap::DashMap;

let warehouse = DashMap::new();
warehouse.insert(4267, ("Banana", 100));
warehouse.insert(2359, ("Pear", 120));
let fruit = warehouse.view(&4267, |_k, v| *v);
assert_eq!(fruit, Some(("Banana", 100)));

Panics

If the given closure panics, then view will abort the process

pub fn contains_key<Q>(&self, key: &Q) -> bool

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

Checks if the map contains a specific key.

Locking behaviour: May deadlock if called when holding a mutable reference into the map.

Examples

use dashmap::DashMap;

let team_sizes = DashMap::new();
team_sizes.insert("Dakota Cherries", 23);
assert!(team_sizes.contains_key("Dakota Cherries"));

pub fn entry(&'a self, key: K) -> Entry<'a, K, V>

Advanced entry API that tries to mimic std::collections::HashMap. See the documentation on dashmap::mapref::entry for more details.

Locking behaviour: May deadlock if called when holding any sort of reference into the map.

pub fn try_entry(&'a self, key: K) -> Option<Entry<'a, K, V>>

Advanced entry API that tries to mimic std::collections::HashMap. See the documentation on dashmap::mapref::entry for more details.

Returns None if the shard is currently locked.

pub fn try_reserve(&mut self, additional: usize) -> Result<(), TryReserveError>

Advanced entry API that tries to mimic std::collections::HashMap::try_reserve. Tries to reserve capacity for at least shard * additional and may reserve more space to avoid frequent reallocations.

Errors

If the capacity overflows, or the allocator reports a failure, then an error is returned.

Trait Implementations

impl<'a, K, V: 'a, S: BuildHasher + Clone, Q> BitAnd<&Q> for &'a DashMap<K, V, S>

where K: Borrow<Q> + 'a + Eq + Hash, Q: Hash + Eq + ?Sized,

type Output = bool

The resulting type after applying the & operator.

fn bitand(self, key: &Q) -> Self::Output

Performs the & operation.

impl<'a, K, V: 'a, S: BuildHasher + Clone, Q> BitOr<&Q> for &'a DashMap<K, V, S>

where K: Borrow<Q> + 'a + Eq + Hash, Q: Hash + Eq + ?Sized,

type Output = RefMut<'a, K, V>

The resulting type after applying the | operator.

fn bitor(self, key: &Q) -> Self::Output

Performs the | operation.

impl<K: Eq + Hash + Clone, V: Clone, S: Clone> Clone for DashMap<K, V, S>

fn clone(&self) -> Self

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<K: Eq + Hash + Debug, V: Debug, S: BuildHasher + Clone> Debug for DashMap<K, V, S>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<K, V, S> Default for DashMap<K, V, S>

where K: Eq + Hash, S: Default + BuildHasher + Clone,

fn default() -> Self

Returns the “default value” for a type.

impl<K: Eq + Hash, V, S: BuildHasher + Clone> Extend<(K, V)> for DashMap<K, V, S>

fn extend<I: IntoIterator<Item = (K, V)>>(&mut self, intoiter: I)

Extends a collection with the contents of an iterator.

fn extend_one(&mut self, item: A)

🔬This is a nightly-only experimental API. (extend_one)

Extends a collection with exactly one element.

fn extend_reserve(&mut self, additional: usize)

🔬This is a nightly-only experimental API. (extend_one)

Reserves capacity in a collection for the given number of additional elements.

impl<K: Eq + Hash, V, S: BuildHasher + Clone + Default> FromIterator<(K, V)> for DashMap<K, V, S>

fn from_iter<I: IntoIterator<Item = (K, V)>>(intoiter: I) -> Self

Creates a value from an iterator.

impl<K, V, S> FromParallelIterator<(K, V)> for DashMap<K, V, S>

where K: Send + Sync + Eq + Hash, V: Send + Sync, S: Send + Sync + Clone + Default + BuildHasher,

fn from_par_iter<I>(par_iter: I) -> Self

where I: IntoParallelIterator<Item = (K, V)>,

Creates an instance of the collection from the parallel iterator par_iter.

impl<'a, K: Eq + Hash, V, S: BuildHasher + Clone> IntoIterator for &'a DashMap<K, V, S>

type Item = RefMulti<'a, K, V>

The type of the elements being iterated over.

type IntoIter = Iter<'a, K, V, S>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<K: Eq + Hash, V, S: BuildHasher + Clone> IntoIterator for DashMap<K, V, S>

type Item = (K, V)

The type of the elements being iterated over.

type IntoIter = OwningIter<K, V, S>

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<'a, K, V, S> IntoParallelIterator for &'a DashMap<K, V, S>

where K: Send + Sync + Eq + Hash, V: Send + Sync, S: Send + Sync + Clone + BuildHasher,

type Iter = Iter<'a, K, V>

The parallel iterator type that will be created.

type Item = RefMulti<'a, K, V>

The type of item that the parallel iterator will produce.

fn into_par_iter(self) -> Self::Iter

Converts self into a parallel iterator.

impl<'a, K, V> IntoParallelIterator for &'a mut DashMap<K, V>

where K: Send + Sync + Eq + Hash, V: Send + Sync,

type Iter = IterMut<'a, K, V>

The parallel iterator type that will be created.

type Item = RefMutMulti<'a, K, V>

The type of item that the parallel iterator will produce.

fn into_par_iter(self) -> Self::Iter

Converts self into a parallel iterator.

impl<K, V, S> IntoParallelIterator for DashMap<K, V, S>

where K: Send + Eq + Hash, V: Send, S: Send + Clone + BuildHasher,

type Iter = OwningIter<K, V>

The parallel iterator type that will be created.

type Item = (K, V)

The type of item that the parallel iterator will produce.

fn into_par_iter(self) -> Self::Iter

Converts self into a parallel iterator.

impl<'a, K: 'a + Eq + Hash, V: 'a, S: 'a + BuildHasher + Clone> Map<'a, K, V, S> for DashMap<K, V, S>

fn _shard_count(&self) -> usize

unsafe fn _get_read_shard( &'a self, i: usize, ) -> &'a RawTable<(K, SharedValue<V>)>

Safety

unsafe fn _yield_read_shard( &'a self, i: usize, ) -> RwLockReadGuard<'a, RawRwLock, RawTable<(K, SharedValue<V>)>>

Safety

unsafe fn _yield_write_shard( &'a self, i: usize, ) -> RwLockWriteGuard<'a, RawRwLock, RawTable<(K, SharedValue<V>)>>

Safety

unsafe fn _try_yield_read_shard( &'a self, i: usize, ) -> Option<RwLockReadGuard<'a, RawRwLock, RawTable<(K, SharedValue<V>)>>>

Safety

unsafe fn _try_yield_write_shard( &'a self, i: usize, ) -> Option<RwLockWriteGuard<'a, RawRwLock, RawTable<(K, SharedValue<V>)>>>

Safety

fn _insert(&self, key: K, value: V) -> Option<V>

fn _remove<Q>(&self, key: &Q) -> Option<(K, V)>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

fn _remove_if<Q>( &self, key: &Q, f: impl FnOnce(&K, &V) -> bool, ) -> Option<(K, V)>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

fn _remove_if_mut<Q>( &self, key: &Q, f: impl FnOnce(&K, &mut V) -> bool, ) -> Option<(K, V)>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

fn _iter(&'a self) -> Iter<'a, K, V, S, DashMap<K, V, S>>

fn _iter_mut(&'a self) -> IterMut<'a, K, V, S, DashMap<K, V, S>>

fn _get<Q>(&'a self, key: &Q) -> Option<Ref<'a, K, V>>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

fn _get_mut<Q>(&'a self, key: &Q) -> Option<RefMut<'a, K, V>>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

fn _try_get<Q>(&'a self, key: &Q) -> TryResult<Ref<'a, K, V>>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

fn _try_get_mut<Q>(&'a self, key: &Q) -> TryResult<RefMut<'a, K, V>>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

fn _shrink_to_fit(&self)

fn _retain(&self, f: impl FnMut(&K, &mut V) -> bool)

fn _len(&self) -> usize

fn _capacity(&self) -> usize

fn _alter<Q>(&self, key: &Q, f: impl FnOnce(&K, V) -> V)

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

fn _alter_all(&self, f: impl FnMut(&K, V) -> V)

fn _view<Q, R>(&self, key: &Q, f: impl FnOnce(&K, &V) -> R) -> Option<R>

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

fn _entry(&'a self, key: K) -> Entry<'a, K, V>

fn _try_entry(&'a self, key: K) -> Option<Entry<'a, K, V>>

fn _hasher(&self) -> S

fn _clear(&self)

fn _contains_key<Q>(&'a self, key: &Q) -> bool

where K: Borrow<Q>, Q: Hash + Eq + ?Sized,

fn _is_empty(&self) -> bool

impl<K, V, S> ParallelExtend<(K, V)> for &DashMap<K, V, S>

where K: Send + Sync + Eq + Hash, V: Send + Sync, S: Send + Sync + Clone + BuildHasher,

fn par_extend<I>(&mut self, par_iter: I)

where I: IntoParallelIterator<Item = (K, V)>,

Extends an instance of the collection with the elements drawn from the parallel iterator par_iter.

impl<K, V, S> ParallelExtend<(K, V)> for DashMap<K, V, S>

where K: Send + Sync + Eq + Hash, V: Send + Sync, S: Send + Sync + Clone + BuildHasher,

fn par_extend<I>(&mut self, par_iter: I)

where I: IntoParallelIterator<Item = (K, V)>,

Extends an instance of the collection with the elements drawn from the parallel iterator par_iter.

impl<'a, K: 'a + Eq + Hash, V: 'a, S: BuildHasher + Clone> Shl<(K, V)> for &'a DashMap<K, V, S>

type Output = Option<V>

The resulting type after applying the << operator.

fn shl(self, pair: (K, V)) -> Self::Output

Performs the << operation.

impl<'a, K, V: 'a, S: BuildHasher + Clone, Q> Shr<&Q> for &'a DashMap<K, V, S>

where K: Borrow<Q> + 'a + Eq + Hash, Q: Hash + Eq + ?Sized,

type Output = Ref<'a, K, V>

The resulting type after applying the >> operator.

fn shr(self, key: &Q) -> Self::Output

Performs the >> operation.

impl<'a, K, V: 'a, S: BuildHasher + Clone, Q> Sub<&Q> for &'a DashMap<K, V, S>

where K: Borrow<Q> + 'a + Eq + Hash, Q: Hash + Eq + ?Sized,

type Output = Option<(K, V)>

The resulting type after applying the - operator.

fn sub(self, key: &Q) -> Self::Output

Performs the - operation.