/*
* 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 javax.annotation.Nonnull;
import javax.annotation.Nullable;
import javax.annotation.concurrent.ThreadSafe;
/**
* An object that can receive a notification when an entry is removed from a cache. The removal
* resulting in notification could have occurred to an entry being manually removed or replaced, or
* due to eviction resulting from timed expiration, exceeding a maximum size, or garbage collection.
* <p>
* An instance may be called concurrently by multiple threads to process different entries.
* Implementations of this interface should avoid performing blocking calls or synchronizing on
* shared resources.
*
* @author ben.manes@gmail.com (Ben Manes)
* @param <K> the most general type of keys this listener can listen for; for example {@code Object}
* if any key is acceptable
* @param <V> the most general type of values this listener can listen for; for example
* {@code Object} if any value is acceptable
*/
@ThreadSafe
@FunctionalInterface
public interface RemovalListener<K, V> {
/**
* Notifies the listener that a removal occurred at some point in the past.
* <p>
* This does not always signify that the key is now absent from the cache, as it may have already
* been re-added.
*
* @param key the key represented by this entry, or {@code null} if collected
* @param value the value represented by this entry, or {@code null} if collected
* @param cause the reason for which the entry was removed
*/
void onRemoval(@Nullable K key, @Nullable V value, @Nonnull RemovalCause cause);
}