Struct moka::sync::SegmentedCache

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

Available on crate feature sync only.

A thread-safe concurrent in-memory cache, with multiple internal segments.

SegmentedCache has multiple internal Cache instances for increased concurrent update performance. However, it has little overheads on retrievals and updates for managing these segments.

For usage examples, see the document of the Cache.

Implementations

impl<K, V> SegmentedCache<K, V, RandomState>

where K: Hash + Eq + Send + Sync + 'static, V: Clone + Send + Sync + 'static,

pub fn new(max_capacity: u64, num_segments: usize) -> Self

Constructs a new SegmentedCache<K, V> that has multiple internal segments and will store up to the max_capacity.

To adjust various configuration knobs such as initial_capacity or time_to_live, use the CacheBuilder.

Panics

Panics if num_segments is 0.

pub fn builder( num_segments: usize ) -> CacheBuilder<K, V, SegmentedCache<K, V, RandomState>>

Returns a CacheBuilder, which can builds a SegmentedCache with various configuration knobs.

impl<K, V, S> SegmentedCache<K, V, S>

pub fn name(&self) -> Option<&str>

Returns cache’s name.

pub fn policy(&self) -> Policy

Returns a read-only cache policy of this cache.

At this time, cache policy cannot be modified after cache creation. A future version may support to modify it.

pub fn entry_count(&self) -> u64

Returns an approximate number of entries in this cache.

The value returned is an estimate; the actual count may differ if there are concurrent insertions or removals, or if some entries are pending removal due to expiration. This inaccuracy can be mitigated by performing a sync() first.

Example

use moka::sync::SegmentedCache;

let cache = SegmentedCache::new(10, 4);
cache.insert('n', "Netherland Dwarf");
cache.insert('l', "Lop Eared");
cache.insert('d', "Dutch");

// Ensure an entry exists.
assert!(cache.contains_key(&'n'));

// However, followings may print stale number zeros instead of threes.
println!("{}", cache.entry_count());   // -> 0
println!("{}", cache.weighted_size()); // -> 0

// To mitigate the inaccuracy, call `run_pending_tasks` method to run
// pending internal tasks.
cache.run_pending_tasks();

// Followings will print the actual numbers.
println!("{}", cache.entry_count());   // -> 3
println!("{}", cache.weighted_size()); // -> 3

pub fn weighted_size(&self) -> u64

Returns an approximate total weighted size of entries in this cache.

The value returned is an estimate; the actual size may differ if there are concurrent insertions or removals, or if some entries are pending removal due to expiration. This inaccuracy can be mitigated by performing a sync() first. See entry_count for a sample code.

impl<K, V, S> SegmentedCache<K, V, S>

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

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

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

Returns true if the cache contains a value for the key.

Unlike the get method, this method is not considered a cache read operation, so it does not update the historic popularity estimator or reset the idle timer for the key.

The key may be any borrowed form of the cache’s key type, but Hash and Eq on the borrowed form must match those for the key type.

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

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

Returns a clone of the value corresponding to the key.

If you want to store values that will be expensive to clone, wrap them by std::sync::Arc before storing in a cache. Arc is a thread-safe reference-counted pointer and its clone() method is cheap.

The key may be any borrowed form of the cache’s key type, but Hash and Eq on the borrowed form must match those for the key type.

pub fn entry(&self, key: K) -> OwnedKeyEntrySelector<'_, K, V, S>

where K: Hash + Eq,

pub fn entry_by_ref<'a, Q>( &'a self, key: &'a Q ) -> RefKeyEntrySelector<'a, K, Q, V, S>

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

pub fn get_or_insert_with(&self, key: K, init: impl FnOnce() -> V) -> V

👎Deprecated since 0.8.0: Replaced with get_with

TODO: Remove this in v0.13.0. Deprecated, replaced with get_with

pub fn get_or_try_insert_with<F, E>(&self, key: K, init: F) -> Result<V, Arc<E>>

where F: FnOnce() -> Result<V, E>, E: Send + Sync + 'static,

👎Deprecated since 0.8.0: Replaced with try_get_with

TODO: Remove this in v0.13.0. Deprecated, replaced with try_get_with

pub fn get_with(&self, key: K, init: impl FnOnce() -> V) -> V

Returns a clone of the value corresponding to the key. If the value does not exist, evaluates the init closure and inserts the output.

Concurrent calls on the same key

This method guarantees that concurrent calls on the same not-existing key are coalesced into one evaluation of the init closure. Only one of the calls evaluates its closure, and other calls wait for that closure to complete. See Cache::get_with for more details.

pub fn get_with_by_ref<Q>(&self, key: &Q, init: impl FnOnce() -> V) -> V

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

Similar to get_with, but instead of passing an owned key, you can pass a reference to the key. If the key does not exist in the cache, the key will be cloned to create new entry in the cache.

pub fn get_with_if( &self, key: K, init: impl FnOnce() -> V, replace_if: impl FnMut(&V) -> bool ) -> V

Works like get_with, but takes an additional replace_if closure.

This method will evaluate the init closure and insert the output to the cache when:

• The key does not exist.
• Or, replace_if closure returns true.

pub fn optionally_get_with<F>(&self, key: K, init: F) -> Option<V>

where F: FnOnce() -> Option<V>,

Returns a clone of the value corresponding to the key. If the value does not exist, evaluates the init closure, and inserts the value if Some(value) was returned. If None was returned from the closure, this method does not insert a value and returns None.

Concurrent calls on the same key

This method guarantees that concurrent calls on the same not-existing key are coalesced into one evaluation of the init closure. Only one of the calls evaluates its closure, and other calls wait for that closure to complete. See Cache::optionally_get_with for more details.

pub fn optionally_get_with_by_ref<F, Q>(&self, key: &Q, init: F) -> Option<V>

where F: FnOnce() -> Option<V>, K: Borrow<Q>, Q: ToOwned<Owned = K> + Hash + Eq + ?Sized,

Similar to optionally_get_with, but instead of passing an owned key, you can pass a reference to the key. If the key does not exist in the cache, the key will be cloned to create new entry in the cache.

pub fn try_get_with<F, E>(&self, key: K, init: F) -> Result<V, Arc<E>>

where F: FnOnce() -> Result<V, E>, E: Send + Sync + 'static,

Returns a clone of the value corresponding to the key. If the value does not exist, evaluates the init closure, and inserts the value if Ok(value) was returned. If Err(_) was returned from the closure, this method does not insert a value and returns the Err wrapped by std::sync::Arc.

Concurrent calls on the same key

This method guarantees that concurrent calls on the same not-existing key are coalesced into one evaluation of the init closure (as long as these closures return the same error type). Only one of the calls evaluates its closure, and other calls wait for that closure to complete. See Cache::try_get_with for more details.

pub fn try_get_with_by_ref<F, E, Q>( &self, key: &Q, init: F ) -> Result<V, Arc<E>>

where F: FnOnce() -> Result<V, E>, E: Send + Sync + 'static, K: Borrow<Q>, Q: ToOwned<Owned = K> + Hash + Eq + ?Sized,

Similar to try_get_with, but instead of passing an owned key, you can pass a reference to the key. If the key does not exist in the cache, the key will be cloned to create new entry in the cache.

pub fn insert(&self, key: K, value: V)

Inserts a key-value pair into the cache.

If the cache has this key present, the value is updated.

pub fn invalidate<Q>(&self, key: &Q)

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

Discards any cached value for the key.

If you need to get a the value that has been discarded, use the remove method instead.

The key may be any borrowed form of the cache’s key type, but Hash and Eq on the borrowed form must match those for the key type.

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

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

Discards any cached value for the key and returns a clone of the value.

If you do not need to get the value that has been discarded, use the invalidate method instead.

The key may be any borrowed form of the cache’s key type, but Hash and Eq on the borrowed form must match those for the key type.

pub fn invalidate_all(&self)

Discards all cached values.

This method returns immediately and a background thread will evict all the cached values inserted before the time when this method was called. It is guaranteed that the get method must not return these invalidated values even if they have not been evicted.

Like the invalidate method, this method does not clear the historic popularity estimator of keys so that it retains the client activities of trying to retrieve an item.

pub fn invalidate_entries_if<F>( &self, predicate: F ) -> Result<(), PredicateError>

where F: Fn(&K, &V) -> bool + Send + Sync + 'static,

Discards cached values that satisfy a predicate.

invalidate_entries_if takes a closure that returns true or false. This method returns immediately and a background thread will apply the closure to each cached value inserted before the time when invalidate_entries_if was called. If the closure returns true on a value, that value will be evicted from the cache.

Also the get method will apply the closure to a value to determine if it should have been invalidated. Therefore, it is guaranteed that the get method must not return invalidated values.

Note that you must call CacheBuilder::support_invalidation_closures at the cache creation time as the cache needs to maintain additional internal data structures to support this method. Otherwise, calling this method will fail with a PredicateError::InvalidationClosuresDisabled.

Like the invalidate method, this method does not clear the historic popularity estimator of keys so that it retains the client activities of trying to retrieve an item.

pub fn iter(&self) -> Iter<'_, K, V>

Creates an iterator visiting all key-value pairs in arbitrary order. The iterator element type is (Arc<K>, V), where V is a clone of a stored value.

Iterators do not block concurrent reads and writes on the cache. An entry can be inserted to, invalidated or evicted from a cache while iterators are alive on the same cache.

Unlike the get method, visiting entries via an iterator do not update the historic popularity estimator or reset idle timers for keys.

Guarantees

In order to allow concurrent access to the cache, iterator’s next method does not guarantee the following:

• It does not guarantee to return a key-value pair (an entry) if its key has been inserted to the cache after the iterator was created.
  • Such an entry may or may not be returned depending on key’s hash and timing.

and the next method guarantees the followings:

• It guarantees not to return the same entry more than once.
• It guarantees not to return an entry if it has been removed from the cache after the iterator was created.
  • Note: An entry can be removed by following reasons:
    • Manually invalidated.
    • Expired (e.g. time-to-live).
    • Evicted as the cache capacity exceeded.

Examples

use moka::sync::SegmentedCache;

let cache = SegmentedCache::new(100, 4);
cache.insert("Julia", 14);

let mut iter = cache.iter();
let (k, v) = iter.next().unwrap(); // (Arc<K>, V)
assert_eq!(*k, "Julia");
assert_eq!(v, 14);

assert!(iter.next().is_none());

pub fn run_pending_tasks(&self)

Performs any pending maintenance operations needed by the cache.

Trait Implementations

impl<K, V, S> Clone for SegmentedCache<K, V, S>

fn clone(&self) -> Self

Makes a clone of this shared cache.

This operation is cheap as it only creates thread-safe reference counted pointers to the shared internal data structures.

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

Performs copy-assignment from source.

impl<K, V, S> Debug for SegmentedCache<K, V, S>

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

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

Formats the value using the given formatter.

impl<'a, K, V, S> IntoIterator for &'a SegmentedCache<K, V, S>

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

type Item = (Arc<K>, V)

The type of the elements being iterated over.

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

Which kind of iterator are we turning this into?

fn into_iter(self) -> Self::IntoIter

Creates an iterator from a value.

impl<K, V, S> Send for SegmentedCache<K, V, S>

where K: Send + Sync, V: Send + Sync, S: Send,

impl<K, V, S> Sync for SegmentedCache<K, V, S>

where K: Send + Sync, V: Send + Sync, S: Sync,