clojure.core.cache.wrapped — org.clojure/core.cache 1.1.234

A higher level way to use clojure.core.cache that assumes the immutable cache is wrapped in an atom.

The API is (almost) the same as clojure.core.cache -- including the factory functions -- but instead of accepting immutable caches, the functions here accept atoms containing those caches. The factory functions return new atoms containing the newly created cache.

In addition, lookup-or-miss provides a safe, atomic way to retrieve a value from a cache or compute it if it is missing, without risking a cache stampede.

basic-cache-factory clj

(basic-cache-factory base)

Returns a pluggable basic cache initialized to base

evict clj

(evict cache-atom e)

Removes an entry from the cache.

Returns the updated cache from the atom.

fifo-cache-factory clj

(fifo-cache-factory base & {threshold :threshold :or {threshold 32}})

Returns a FIFO cache with the cache and FIFO queue initialized to base -- the queue is filled as the values are pulled out of base. If the associative structure can guarantee ordering, then the said ordering will define the eventual eviction order. Otherwise, there are no guarantees for the eventual eviction ordering.

This function takes an optional :threshold argument that defines the maximum number of elements in the cache before the FIFO semantics apply (default is 32).

If the number of elements in base is greater than the limit then some items in base will be dropped from the resulting cache. If the associative structure used as base can guarantee sorting, then the last limit elements will be used as the cache seed values. Otherwise, there are no guarantees about the elements in the resulting cache.

has? clj

(has? cache-atom e)

Checks if the cache contains a value associated with e.

Reads from the current version of the atom.

hit clj

(hit cache-atom e)

Is meant to be called if the cache is determined to contain a value associated with e.

Returns the updated cache from the atom. Provided for completeness.

lirs-cache-factory clj

(lirs-cache-factory base
                    &
                    {:keys [s-history-limit q-history-limit]
                     :or {s-history-limit 32 q-history-limit 32}})

Returns an LIRS cache with the S & R LRU lists set to the indicated limits.

lookup clj

(lookup cache-atom e)

(lookup cache-atom e not-found)

Retrieve the value associated with e if it exists, else nil in the 2-arg case. Retrieve the value associated with e if it exists, else not-found in the 3-arg case.

Reads from the current version of the atom.

lookup-or-miss clj

(lookup-or-miss cache-atom e value-fn)

(lookup-or-miss cache-atom e wrap-fn value-fn)

Retrieve the value associated with e if it exists, else compute the value (using value-fn, and optionally wrap-fn), update the cache for e and then perform the lookup again.

value-fn (and wrap-fn) will only be called (at most) once even in the case of retries, so there is no risk of cache stampede.

Since lookup can cause invalidation in some caches (such as TTL), we trap that case and retry (a maximum of ten times).

lru-cache-factory clj

(lru-cache-factory base & {threshold :threshold :or {threshold 32}})

Returns an LRU cache with the cache and usage-table initialized to base -- each entry is initialized with the same usage value.

This function takes an optional :threshold argument that defines the maximum number of elements in the cache before the LRU semantics apply (default is 32).

lu-cache-factory clj

(lu-cache-factory base & {threshold :threshold :or {threshold 32}})

Returns an LU cache with the cache and usage-table initialized to base.

This function takes an optional :threshold argument that defines the maximum number of elements in the cache before the LU semantics apply (default is 32).

miss clj

(miss cache-atom e ret)

Is meant to be called if the cache is determined to not contain a value associated with e.

Returns the updated cache from the atom. Provided for completeness.

seed clj

(seed cache-atom base)

Is used to signal that the cache should be created with a seed. The contract is that said cache should return an instance of its own type.

Returns the updated cache from the atom. Provided for completeness.

soft-cache-factory clj

(soft-cache-factory base)

Returns a SoftReference cache. Cached values will be referred to with SoftReferences, allowing the values to be garbage collected when there is memory pressure on the JVM.

SoftCache is a mutable cache, since it is always based on a ConcurrentHashMap.

through clj

(through cache-atom item)

(through value-fn cache-atom item)

(through wrap-fn value-fn cache-atom item)

The basic hit/miss logic for the cache system. Expects a wrap function and value function. The wrap function takes the value function and the item in question and is expected to run the value function with the item whenever a cache miss occurs. The intent is to hide any cache-specific cells from leaking into the cache logic itelf.

through-cache clj

(through-cache cache-atom item)

(through-cache cache-atom item value-fn)

(through-cache cache-atom item wrap-fn value-fn)

The basic hit/miss logic for the cache system. Like through but always has the cache argument in the first position.

ttl-cache-factory clj

(ttl-cache-factory base & {ttl :ttl :or {ttl 2000}})

Returns a TTL cache with the cache and expiration-table initialized to base -- each with the same time-to-live.

This function also allows an optional :ttl argument that defines the default time in milliseconds that entries are allowed to reside in the cache.