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/*
* 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.CompletableFuture;
import java.util.concurrent.ConcurrentMap;
import org.checkerframework.checker.nullness.qual.NonNull;
/**
* A semi-persistent mapping from keys to values. Values are automatically loaded by the cache
* asynchronously, 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 AsyncLoadingCache extends AsyncCache {
/**
* Returns the future associated with {@code key} in this cache, obtaining that value from
* {@link AsyncCacheLoader#asyncLoad} if necessary. If the asynchronous computation fails, the
* entry will be automatically removed from this cache.
*
* 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.
*
* @param key key with which the specified value is to be associated
* @return the current (existing or computed) future value associated with the specified key
* @throws NullPointerException if the specified key is null or if the future returned by the
* {@link AsyncCacheLoader} is null
* @throws RuntimeException or Error if the {@link AsyncCacheLoader} does when constructing the
* future, in which case the mapping is left unestablished
*/
@NonNull
CompletableFuture get(@NonNull K key);
/**
* 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.
*
* Caches loaded by a {@link AsyncCacheLoader} supporting bulk loading will issue a single request
* to {@link AsyncCacheLoader#asyncLoadAll} 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. Caches that do not use a
* {@link AsyncCacheLoader} with an optimized bulk load implementation will sequentially load each
* key by making individual {@link AsyncCacheLoader#asyncLoad} calls. 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
* @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 {@link AsyncCacheLoader} is null
* @throws RuntimeException or Error if the {@link AsyncCacheLoader} does so, if
* {@link AsyncCacheLoader#asyncLoadAll} returns {@code null}, or fails when constructing
* the future, in which case the mapping is left unestablished
*/
@NonNull
CompletableFuture> getAll(@NonNull Iterable keys);
/**
* Returns a view of the entries stored in this cache as a thread-safe map. Modifications made to
* the map directly affect the 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
*/
@Override
default @NonNull ConcurrentMap<@NonNull K, @NonNull CompletableFuture> asMap() {
// This method was added & implemented in version 2.7.0
throw new UnsupportedOperationException();
}
/**
* Returns a view of the entries stored in this cache as a synchronous {@link LoadingCache}. 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
@Override
LoadingCache synchronous();
}