Struct dashmap::DashMap

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

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, S>>. To accomplish these all methods take &self instead 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.

Implementations

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);

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 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 ahash::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.

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: ?Sized>(&self, key: &Q) -> Option<(K, V)> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

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: ?Sized>(
    &self,
    key: &Q,
    f: impl FnOnce(&K, &V) -> bool
) -> Option<(K, V)> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

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 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: ?Sized>(&'a self, key: &Q) -> Option<Ref<'a, K, V, S>> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

Get a 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: ?Sized>(&'a self, key: &Q) -> Option<RefMut<'a, K, V, S>> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

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 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.

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: ?Sized>(&self, key: &Q, f: impl FnOnce(&K, V) -> V) where
    K: Borrow<Q>,
    Q: Hash + Eq, 

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_all 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 contains_key<Q: ?Sized>(&self, key: &Q) -> bool where
    K: Borrow<Q>,
    Q: Hash + Eq, 

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, S>

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.

Trait Implementations

impl<'a, K: 'a + Eq + Hash, V: 'a, S: BuildHasher + Clone, Q: ?Sized> BitAnd<&'_ Q> for &'a DashMap<K, V, S> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

type Output = bool

The resulting type after applying the & operator.

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

Performs the & operation.

impl<'a, K: 'a + Eq + Hash, V: 'a, S: BuildHasher + Clone, Q: ?Sized> BitOr<&'_ Q> for &'a DashMap<K, V, S> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

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

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.

pub 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.

pub fn extend_one(&mut self, item: A)

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

Extends a collection with exactly one element.

pub 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> FromIterator<(K, V)> for DashMap<K, V, RandomState>

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

Creates a value from an iterator.

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

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

The type of the elements being iterated over.

type IntoIter = Iter<'a, K, V, S, DashMap<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: '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 HashMap<K, SharedValue<V>, S>

Safety

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

Safety

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

Safety

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

fn _remove<Q: ?Sized>(&self, key: &Q) -> Option<(K, V)> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

fn _remove_if<Q: ?Sized>(
    &self,
    key: &Q,
    f: impl FnOnce(&K, &V) -> bool
) -> Option<(K, V)> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

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: ?Sized>(&'a self, key: &Q) -> Option<Ref<'a, K, V, S>> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

fn _get_mut<Q: ?Sized>(&'a self, key: &Q) -> Option<RefMut<'a, K, V, S>> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

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: ?Sized>(&self, key: &Q, f: impl FnOnce(&K, V) -> V) where
    K: Borrow<Q>,
    Q: Hash + Eq, 

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

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

fn _hasher(&self) -> S

fn _clear(&self)

fn _contains_key<Q: ?Sized>(&'a self, key: &Q) -> bool where
    K: Borrow<Q>,
    Q: Hash + Eq, 

fn _is_empty(&self) -> bool

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: 'a + Eq + Hash, V: 'a, S: BuildHasher + Clone, Q: ?Sized> Shr<&'_ Q> for &'a DashMap<K, V, S> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

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

The resulting type after applying the >> operator.

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

Performs the >> operation.

impl<'a, K: 'a + Eq + Hash, V: 'a, S: BuildHasher + Clone, Q: ?Sized> Sub<&'_ Q> for &'a DashMap<K, V, S> where
    K: Borrow<Q>,
    Q: Hash + Eq, 

type Output = Option<(K, V)>

The resulting type after applying the - operator.

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

Performs the - operation.