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/*
* Copyright 2018 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.CompletableFuture;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.Executor;
import java.util.function.BiFunction;
import java.util.function.Function;
import org.checkerframework.checker.nullness.qual.NonNull;
import org.checkerframework.checker.nullness.qual.Nullable;
import com.google.errorprone.annotations.CompatibleWith;
/**
* A semi-persistent mapping from keys to values. Cache entries are manually added using
* {@link #get(Object, Function)} or {@link #put(Object, CompletableFuture)}, and are stored in the
* cache until either evicted or manually invalidated.
*
* Implementations of this interface are expected to be thread-safe, and can be safely accessed by
* multiple concurrent threads.
*
* @author [email protected] (Ben Manes)
* @param the type of keys maintained by this cache
* @param the type of mapped values
*/
public interface AsyncCache {
/**
* Returns the future associated with {@code key} in this cache, or {@code null} if there is no
* cached future for {@code key}.
*
* @param key key whose associated value is to be returned
* @return the current (existing or computed) future value to which the specified key is mapped,
* or {@code null} if this cache contains no mapping for the key
* @throws NullPointerException if the specified key is null
*/
@Nullable
CompletableFuture getIfPresent(@NonNull @CompatibleWith("K") Object key);
/**
* Returns the future associated with {@code key} in this cache, obtaining that value from
* {@code mappingFunction} if necessary. This method provides a simple substitute for the
* conventional "if cached, return; otherwise create, cache and return" pattern.
*
* If the specified key is not already associated with a value, attempts to compute its value
* asynchronously 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. If the asynchronous
* computation fails, the entry will be automatically removed from this cache.
*
* Warning: as with {@link CacheLoader#load}, {@code mappingFunction} must not
* attempt to update any other mappings of this cache.
*
* @param key key with which the specified value is to be associated
* @param mappingFunction the function to asynchronously compute a value
* @return the current (existing or computed) future value associated with the specified key
* @throws NullPointerException if the specified key or mappingFunction is null
*/
@NonNull
CompletableFuture get(@NonNull K key,
@NonNull Function mappingFunction);
/**
* Returns the future associated with {@code key} in this cache, obtaining that value from
* {@code mappingFunction} if necessary. This method provides a simple substitute for the
* conventional "if cached, return; otherwise create, cache and return" pattern.
*
* If the specified key is not already associated with a value, attempts to compute its value
* asynchronously 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. If the asynchronous
* computation fails, the entry will be automatically removed from this cache.
*
* Warning: as with {@link CacheLoader#load}, {@code mappingFunction} must not
* attempt to update any other mappings of this cache.
*
* @param key key with which the specified value is to be associated
* @param mappingFunction the function to asynchronously compute a value
* @return the current (existing or computed) future value associated with the specified key
* @throws NullPointerException if the specified key or mappingFunction is null, or if the
* future returned by the mappingFunction is null
* @throws RuntimeException or Error if the mappingFunction does when constructing the future,
* in which case the mapping is left unestablished
*/
@NonNull
CompletableFuture get(@NonNull K key,
@NonNull BiFunction> mappingFunction);
/**
* Returns the future of a map of the values associated with {@code keys}, creating or retrieving
* those values if necessary. The returned map contains entries that were already cached, combined
* with newly loaded entries; it will never contain null keys or values. If the any of the
* asynchronous computations fail, those entries will be automatically removed from this cache.
*
* A single request to the {@code mappingFunction} is performed for all keys which are not already
* present in the cache. If another call to {@link #get} tries to load the value for a key in
* {@code keys}, that thread retrieves a future that is completed by this bulk computation. Any
* loaded values for keys that were not specifically requested will not be returned, but will be
* stored in the cache. Note that multiple threads can concurrently load values for distinct keys.
*
* 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
* @param mappingFunction the function to asynchronously compute the values
* @return the future containing an unmodifiable mapping of keys to values for the specified keys
* in this cache
* @throws NullPointerException if the specified collection is null or contains a null element, or
* if the future returned by the mappingFunction is null
* @throws RuntimeException or Error if the mappingFunction does so, in which case the mapping is
* left unestablished
*/
@NonNull
default CompletableFuture> getAll(@NonNull Iterable keys,
@NonNull Function, @NonNull Map> mappingFunction) {
// This method was added & implemented in version 2.8.0
throw new UnsupportedOperationException();
}
/**
* Returns the future of a map of the values associated with {@code keys}, creating or retrieving
* those values if necessary. The returned map contains entries that were already cached, combined
* with newly loaded entries; it will never contain null keys or values. If the any of the
* asynchronous computations fail, those entries will be automatically removed from this cache.
*
* A single request to the {@code mappingFunction} is performed for all keys which are not already
* present in the cache. If another call to {@link #get} tries to load the value for a key in
* {@code keys}, that thread retrieves a future that is completed by this bulk computation. Any
* loaded values for keys that were not specifically requested will not be returned, but will be
* stored in the cache. Note that multiple threads can concurrently load values for distinct keys.
*
* 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
* @param mappingFunction the function to asynchronously compute the values
* @return the future containing an unmodifiable mapping of keys to values for the specified keys
* in this cache
* @throws NullPointerException if the specified collection is null or contains a null element, or
* if the future returned by the mappingFunction is null
* @throws RuntimeException or Error if the mappingFunction does so, in which case the mapping is
* left unestablished
*/
@NonNull
default CompletableFuture> getAll(@NonNull Iterable keys,
@NonNull BiFunction, Executor, CompletableFuture>> mappingFunction) {
// This method was added & implemented in version 2.8.0
throw new UnsupportedOperationException();
}
/**
* Associates {@code value} with {@code key} in this cache. If the cache previously contained a
* value associated with {@code key}, the old value is replaced by {@code value}. If the
* asynchronous computation fails, the entry will be automatically removed.
*
* Prefer {@link #get(Object, Function)} when using the conventional "if cached, return; otherwise
* create, cache and return" pattern.
*
* @param key key with which the specified value is to be associated
* @param valueFuture value to be associated with the specified key
* @throws NullPointerException if the specified key or value is null
*/
void put(@NonNull K key, @NonNull CompletableFuture valueFuture);
/**
* Returns a view of the entries stored in this cache as a thread-safe map. Modifications made to
* the map directly affect the cache.
*
* A computation operation, such as {@link ConcurrentMap#compute}, performs the entire method
* invocation atomically, so the function is applied at most once per key. Some attempted update
* operations by other threads may be blocked while computation is in progress. The computation
* must not attempt to update any other mappings of this cache.
*
* Iterators from the returned map are at least weakly consistent: 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<@NonNull K, @NonNull CompletableFuture> asMap();
/**
* Returns a view of the entries stored in this cache as a synchronous {@link Cache}. A mapping is
* not present if the value is currently being loaded. Modifications made to the synchronous cache
* directly affect the asynchronous cache. If a modification is made to a mapping that is
* currently loading, the operation blocks until the computation completes.
*
* @return a thread-safe synchronous view of this cache
*/
@NonNull
Cache synchronous();
}