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LruCache.java
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/*
* Copyright 2020 The gRPC Authors
*
* 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 io.grpc.rls;
import javax.annotation.CheckReturnValue;
import javax.annotation.Nullable;
/** An LruCache is a cache with least recently used eviction. */
interface LruCache<K, V> {
/**
* Populates a cache entry. If the cache entry for given key already exists, the value will be
* replaced to the new value.
*
* @return the previous value associated with key, otherwise {@code null}
*/
@Nullable
V cache(K key, V value);
/**
* Returns cached value for given key if exists, otherwise {@code null}. This operation doesn't
* return already expired cache entry.
*/
@Nullable
@CheckReturnValue
V read(K key);
/**
* Invalidates an entry for given key if exists. This operation will trigger {@link
* EvictionListener} with {@link EvictionType#EXPLICIT}.
*
* @return the previous value associated with key, otherwise {@code null}
*/
@Nullable
V invalidate(K key);
/**
* Invalidates cache entries for all keys. This operation will trigger {@link EvictionListener}
* with {@link EvictionType#EXPLICIT}.
*/
void invalidateAll();
/** Returns {@code true} if given key is cached. */
@CheckReturnValue
boolean hasCacheEntry(K key);
/**
* Returns the estimated number of entry of the cache. Note that the size can be larger than its
* true size, because there might be already expired cache.
*/
@CheckReturnValue
int estimatedSize();
/** Closes underlying resources. */
void close();
/** A Listener notifies cache eviction events. */
interface EvictionListener<K, V> {
/**
* Notifies the listener when any cache entry is evicted. Implementation can assume that this
* method is called serially. Implementation should be non blocking, for long running task
* consider offloading the task to {@link java.util.concurrent.Executor}.
*/
void onEviction(K key, V value, EvictionType cause);
}
/** Type of cache eviction. */
enum EvictionType {
/** Explicitly removed by user. */
EXPLICIT,
/** Evicted due to size limit. */
SIZE,
/** Evicted due to entry expired. */
EXPIRED,
/** Removed due to error. */
ERROR,
/** Evicted by replacement. */
REPLACED
}
}