/*
* 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.airlift.concurrent;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.function.Function;
import static com.google.common.base.Preconditions.checkArgument;
import static java.util.Objects.requireNonNull;
/**
* Provides a ThreadLocal cache with a maximum cache size per thread.
* Values must not be null.
*
* @param <K> cache key type
* @param <V> cache value type
*/
public final class ThreadLocalCache<K, V>
{
@SuppressWarnings("ThreadLocalNotStaticFinal")
private final ThreadLocal<Map<K, V>> cache;
private final Function<K, V> loader;
public ThreadLocalCache(int maxSizePerThread, Function<K, V> loader)
{
checkArgument(maxSizePerThread > 0, "max size must be greater than zero");
this.cache = ThreadLocal.withInitial(() -> new BoundedMap<K, V>(maxSizePerThread));
this.loader = requireNonNull(loader, "loader is null");
}
public V get(K key)
{
V value = cache.get().computeIfAbsent(key, loader);
return requireNonNull(value, "loader returned null value");
}
@SuppressWarnings("CloneableClassWithoutClone")
private static class BoundedMap<K, V>
extends LinkedHashMap<K, V>
{
private final int maxSize;
public BoundedMap(int maxSize)
{
this.maxSize = maxSize;
}
@Override
protected boolean removeEldestEntry(Map.Entry<K, V> eldest)
{
return size() > maxSize;
}
}
}