| /* |
| * Licensed to the Apache Software Foundation (ASF) under one |
| * or more contributor license agreements. See the NOTICE file |
| * distributed with this work for additional information |
| * regarding copyright ownership. The ASF licenses this file |
| * to you 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 org.apache.hadoop.hbase.util; |
| |
| import java.lang.ref.Reference; |
| import java.lang.ref.ReferenceQueue; |
| import java.util.Objects; |
| import java.util.concurrent.ConcurrentHashMap; |
| import java.util.concurrent.ConcurrentMap; |
| import java.util.concurrent.locks.Lock; |
| import java.util.concurrent.locks.ReentrantLock; |
| |
| import org.apache.yetus.audience.InterfaceAudience; |
| |
| /** |
| * A thread-safe shared object pool in which object creation is expected to be lightweight, and the |
| * objects may be excessively created and discarded. |
| */ |
| @InterfaceAudience.Private |
| public abstract class ObjectPool<K, V> { |
| /** |
| * An {@code ObjectFactory} object is used to create |
| * new shared objects on demand. |
| */ |
| public interface ObjectFactory<K, V> { |
| /** |
| * Creates a new shared object associated with the given {@code key}, |
| * identified by the {@code equals} method. |
| * This method may be simultaneously called by multiple threads |
| * with the same key, and the excessive objects are just discarded. |
| */ |
| V createObject(K key); |
| } |
| |
| protected final ReferenceQueue<V> staleRefQueue = new ReferenceQueue<>(); |
| |
| private final ObjectFactory<K, V> objectFactory; |
| |
| /** Does not permit null keys. */ |
| protected final ConcurrentMap<K, Reference<V>> referenceCache; |
| |
| /** For preventing parallel purge */ |
| private final Lock purgeLock = new ReentrantLock(); |
| |
| /** |
| * The default initial capacity, |
| * used when not otherwise specified in a constructor. |
| */ |
| public static final int DEFAULT_INITIAL_CAPACITY = 16; |
| |
| /** |
| * The default concurrency level, |
| * used when not otherwise specified in a constructor. |
| */ |
| public static final int DEFAULT_CONCURRENCY_LEVEL = 16; |
| |
| /** |
| * Creates a new pool with the default initial capacity (16) |
| * and the default concurrency level (16). |
| * |
| * @param objectFactory the factory to supply new objects on demand |
| * |
| * @throws NullPointerException if {@code objectFactory} is {@code null} |
| */ |
| public ObjectPool(ObjectFactory<K, V> objectFactory) { |
| this(objectFactory, DEFAULT_INITIAL_CAPACITY, DEFAULT_CONCURRENCY_LEVEL); |
| } |
| |
| /** |
| * Creates a new pool with the given initial capacity |
| * and the default concurrency level (16). |
| * |
| * @param objectFactory the factory to supply new objects on demand |
| * @param initialCapacity the initial capacity to keep objects in the pool |
| * |
| * @throws NullPointerException if {@code objectFactory} is {@code null} |
| * @throws IllegalArgumentException if {@code initialCapacity} is negative |
| */ |
| public ObjectPool(ObjectFactory<K, V> objectFactory, int initialCapacity) { |
| this(objectFactory, initialCapacity, DEFAULT_CONCURRENCY_LEVEL); |
| } |
| |
| /** |
| * Creates a new pool with the given initial capacity |
| * and the given concurrency level. |
| * |
| * @param objectFactory the factory to supply new objects on demand |
| * @param initialCapacity the initial capacity to keep objects in the pool |
| * @param concurrencyLevel the estimated count of concurrently accessing threads |
| * |
| * @throws NullPointerException if {@code objectFactory} is {@code null} |
| * @throws IllegalArgumentException if {@code initialCapacity} is negative or |
| * {@code concurrencyLevel} is non-positive |
| */ |
| public ObjectPool( |
| ObjectFactory<K, V> objectFactory, |
| int initialCapacity, |
| int concurrencyLevel) { |
| |
| this.objectFactory = Objects.requireNonNull(objectFactory, "Object factory cannot be null"); |
| |
| this.referenceCache = |
| new ConcurrentHashMap<K, Reference<V>>(initialCapacity, 0.75f, concurrencyLevel); |
| } |
| |
| /** |
| * Removes stale references of shared objects from the pool. References newly becoming stale may |
| * still remain. |
| * <p/> |
| * The implementation of this method is expected to be lightweight when there is no stale |
| * reference with the Oracle (Sun) implementation of {@code ReferenceQueue}, because |
| * {@code ReferenceQueue.poll} just checks a volatile instance variable in {@code ReferenceQueue}. |
| */ |
| public void purge() { |
| if (purgeLock.tryLock()) {// no parallel purge |
| try { |
| while (true) { |
| @SuppressWarnings("unchecked") |
| Reference<V> ref = (Reference<V>) staleRefQueue.poll(); |
| if (ref == null) { |
| break; |
| } |
| referenceCache.remove(getReferenceKey(ref), ref); |
| } |
| } finally { |
| purgeLock.unlock(); |
| } |
| } |
| } |
| |
| /** |
| * Create a reference associated with the given object |
| * @param key the key to store in the reference |
| * @param obj the object to associate with |
| * @return the reference instance |
| */ |
| public abstract Reference<V> createReference(K key, V obj); |
| |
| /** |
| * Get key of the given reference |
| * @param ref The reference |
| * @return key of the reference |
| */ |
| public abstract K getReferenceKey(Reference<V> ref); |
| |
| /** |
| * Returns a shared object associated with the given {@code key}, |
| * which is identified by the {@code equals} method. |
| * @throws NullPointerException if {@code key} is {@code null} |
| */ |
| public V get(K key) { |
| Reference<V> ref = referenceCache.get(Objects.requireNonNull(key)); |
| if (ref != null) { |
| V obj = ref.get(); |
| if (obj != null) { |
| return obj; |
| } |
| referenceCache.remove(key, ref); |
| } |
| |
| V newObj = objectFactory.createObject(key); |
| Reference<V> newRef = createReference(key, newObj); |
| while (true) { |
| Reference<V> existingRef = referenceCache.putIfAbsent(key, newRef); |
| if (existingRef == null) { |
| return newObj; |
| } |
| |
| V existingObject = existingRef.get(); |
| if (existingObject != null) { |
| return existingObject; |
| } |
| referenceCache.remove(key, existingRef); |
| } |
| } |
| |
| /** |
| * Returns an estimated count of objects kept in the pool. |
| * This also counts stale references, |
| * and you might want to call {@link #purge()} beforehand. |
| */ |
| public int size() { |
| return referenceCache.size(); |
| } |
| } |