/*
* Copyright 2014 Ben Manes. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.github.benmanes.caffeine.cache;
import java.util.Map;
import java.util.concurrent.ConcurrentMap;
import java.util.function.Function;
import javax.annotation.CheckForNull;
import javax.annotation.Nonnegative;
import javax.annotation.Nonnull;
import javax.annotation.concurrent.ThreadSafe;
import com.github.benmanes.caffeine.cache.stats.CacheStats;
/**
* A semi-persistent mapping from keys to values. Cache entries are manually added using
* {@link #get(Object, Function)} or {@link #put(Object, Object)}, and are stored in the cache until
* either evicted or manually invalidated.
* <p>
* Implementations of this interface are expected to be thread-safe, and can be safely accessed by
* multiple concurrent threads.
*
* @author ben.manes@gmail.com (Ben Manes)
* @param <K> the type of keys maintained by this cache
* @param <V> the type of mapped values
*/
@ThreadSafe
public interface Cache<K, V> {
/**
* Returns the value associated with the {@code key} in this cache, or {@code null} if there is no
* cached value for the {@code key}.
*
* @param key the key whose associated value is to be returned
* @return the value to which the specified key is mapped, or {@code null} if this map contains no
* mapping for the key
* @throws NullPointerException if the specified key is null
*/
@CheckForNull
V getIfPresent(@Nonnull Object key);
/**
* Returns the value associated with the {@code key} in this cache, obtaining that value from the
* {@code mappingFunction} if necessary. This method provides a simple substitute for the
* conventional "if cached, return; otherwise create, cache and return" pattern.
* <p>
* If the specified key is not already associated with a value, attempts to compute its value
* using the given mapping function and enters it into this cache unless {@code null}. The entire
* method invocation is performed atomically, so the function is applied at most once per key.
* Some attempted update operations on this cache by other threads may be blocked while the
* computation is in progress, so the computation should be short and simple, and must not attempt
* to update any other mappings of this cache.
* <p>
* <b>Warning:</b> as with {@link CacheLoader#load}, {@code mappingFunction} <b>must not</b>
* attempt to update any other mappings of this cache.
*
* @param key the key with which the specified value is to be associated
* @param mappingFunction the function to compute a value
* @return the current (existing or computed) value associated with the specified key, or null if
* the computed value is null
* @throws NullPointerException if the specified key or mappingFunction is null
* @throws IllegalStateException if the computation detectably attempts a recursive update to this
* cache that would otherwise never complete
* @throws RuntimeException or Error if the mappingFunction does so, in which case the mapping is
* left unestablished
*/
@CheckForNull
V get(@Nonnull K key, @Nonnull Function<? super K, ? extends V> mappingFunction);
/**
* Returns a map of the values associated with the {@code keys} in this cache. The returned map
* will only contain entries which are already present in the cache.
* <p>
* Note that duplicate elements in {@code keys}, as determined by {@link Object#equals}, will be
* ignored.
*
* @param keys the keys whose associated values are to be returned
* @return the unmodifiable mapping of keys to values for the specified keys found in this cache
* @throws NullPointerException if the specified collection is null or contains a null element
*/
@Nonnull
Map<K, V> getAllPresent(@Nonnull Iterable<?> keys);
/**
* Associates the {@code value} with the {@code key} in this cache. If the cache previously
* contained a value associated with the {@code key}, the old value is replaced by the new
* {@code value}.
* <p>
* Prefer {@link #get(Object, Function)} when using the conventional "if cached, return; otherwise
* create, cache and return" pattern.
*
* @param key the key with which the specified value is to be associated
* @param value value to be associated with the specified key
* @throws NullPointerException if the specified key or value is null
*/
void put(@Nonnull K key, @Nonnull V value);
/**
* Copies all of the mappings from the specified map to the cache. The effect of this call is
* equivalent to that of calling {@code put(k, v)} on this map once for each mapping from key
* {@code k} to value {@code v} in the specified map. The behavior of this operation is undefined
* if the specified map is modified while the operation is in progress.
*
* @param map the mappings to be stored in this cache
* @throws NullPointerException if the specified map is null or the specified map contains null
* keys or values
*/
void putAll(@Nonnull Map<? extends K,? extends V> map);
/**
* Discards any cached value for the {@code key}. The behavior of this operation is undefined for
* an entry that is being loaded and is otherwise not present.
*
* @param key the key whose mapping is to be removed from the cache
* @throws NullPointerException if the specified key is null
*/
void invalidate(@Nonnull Object key);
/**
* Discards any cached values for the {@code keys}. The behavior of this operation is undefined
* for an entry that is being loaded and is otherwise not present.
*
* @param keys the keys whose associated values are to be removed
* @throws NullPointerException if the specified collection is null or contains a null element
*/
void invalidateAll(@Nonnull Iterable<?> keys);
/**
* Discards all entries in the cache. The behavior of this operation is undefined for an entry
* that is being loaded and is otherwise not present.
*/
void invalidateAll();
/**
* Returns the 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 or weak/soft reference collection. In the case of stale
* entries this inaccuracy can be mitigated by performing a {@link #cleanUp()} first.
*
* @return the estimated number of mappings
*/
@Nonnegative
long estimatedSize();
/**
* Returns a current snapshot of this cache's cumulative statistics. All statistics are
* initialized to zero, and are monotonically increasing over the lifetime of the cache.
* <p>
* Due to the performance penalty of maintaining statistics, some implementations may not record
* the usage history immediately or at all.
*
* @return the current snapshot of the statistics of this cache
*/
@Nonnull
CacheStats stats();
/**
* Returns a view of the entries stored in this cache as a thread-safe map. Modifications made to
* the map directly affect the cache.
* <p>
* Iterators from the returned map are at least <i>weakly consistent</i>: they are safe for
* concurrent use, but if the cache is modified (including by eviction) after the iterator is
* created, it is undefined which of the changes (if any) will be reflected in that iterator.
*
* @return a thread-safe view of this cache supporting all of the optional {@link Map} operations
*/
@Nonnull
ConcurrentMap<K, V> asMap();
/**
* Performs any pending maintenance operations needed by the cache. Exactly which activities are
* performed -- if any -- is implementation-dependent.
*/
void cleanUp();
/**
* Returns access to inspect and perform low-level operations on this cache based on its runtime
* characteristics. These operations are optional and dependent on how the cache was constructed
* and what abilities the implementation exposes.
*
* @return access to inspect and perform advanced operations based on the cache's characteristics
*/
@Nonnull
Policy<K, V> policy();
}