001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.pool2;
018
019/**
020 * An interface defining life-cycle methods for
021 * instances to be served by a {@link KeyedObjectPool}.
022 * <p>
023 * By contract, when an {@link KeyedObjectPool}
024 * delegates to a {@link KeyedPooledObjectFactory},
025 * </p>
026 * <ol>
027 *  <li>
028 *   {@link #makeObject} is called whenever a new instance is needed.
029 *  </li>
030 *  <li>
031 *   {@link #activateObject} is invoked on every instance that has been
032 *   {@link #passivateObject passivated} before it is
033 *   {@link KeyedObjectPool#borrowObject borrowed} from the pool.
034 *  </li>
035 *  <li>
036 *   {@link #validateObject} may be invoked on {@link #activateObject activated}
037 *   instances to make sure they can be
038 *   {@link KeyedObjectPool#borrowObject borrowed} from the pool.
039 *   {@code validateObject} may also be used to test an
040 *   instance being {@link KeyedObjectPool#returnObject returned} to the pool
041 *   before it is {@link #passivateObject passivated}. It will only be invoked
042 *   on an activated instance.
043 *  </li>
044 *  <li>
045 *   {@link #passivateObject passivateObject}
046 *   is invoked on every instance when it is returned to the pool.
047 *  </li>
048 *  <li>
049 *   {@link #destroyObject destroyObject}
050 *   is invoked on every instance when it is being "dropped" from the
051 *   pool (whether due to the response from {@code validateObject},
052 *   or for reasons specific to the pool implementation.) There is no
053 *   guarantee that the instance being destroyed will
054 *   be considered active, passive or in a generally consistent state.
055 *  </li>
056 * </ol>
057 * {@link KeyedPooledObjectFactory} must be thread-safe. The only promise
058 * an {@link KeyedObjectPool} makes is that the same instance of an object will
059 * not be passed to more than one method of a
060 * {@code KeyedPooledObjectFactory} at a time.
061 * <p>
062 * While clients of a {@link KeyedObjectPool} borrow and return instances of
063 * the underlying value type V, the factory methods act on instances of
064 * {@link PooledObject PooledObject&lt;V&gt;}.  These are the object wrappers that
065 * pools use to track and maintain state informations about the objects that
066 * they manage.
067 * </p>
068 *
069 * @see KeyedObjectPool
070 * @see BaseKeyedPooledObjectFactory
071 *
072 * @param <K> The type of keys managed by this factory.
073 * @param <V> Type of element managed by this factory.
074 *
075 * @since 2.0
076 */
077public interface KeyedPooledObjectFactory<K, V> {
078
079    /**
080     * Reinitializes an instance to be returned by the pool.
081     *
082     * @param key the key used when selecting the object
083     * @param p a {@code PooledObject} wrapping the instance to be activated
084     *
085     * @throws Exception if there is a problem activating {@code obj},
086     *    this exception may be swallowed by the pool.
087     *
088     * @see #destroyObject
089     */
090    void activateObject(K key, PooledObject<V> p) throws Exception;
091
092    /**
093     * Destroys an instance no longer needed by the pool.
094     * <p>
095     * It is important for implementations of this method to be aware that there
096     * is no guarantee about what state {@code obj} will be in and the
097     * implementation should be prepared to handle unexpected errors.
098     * </p>
099     * <p>
100     * Also, an implementation must take in to consideration that instances lost
101     * to the garbage collector may never be destroyed.
102     * </p>
103     *
104     * @param key the key used when selecting the instance
105     * @param p a {@code PooledObject} wrapping the instance to be destroyed
106     *
107     * @throws Exception should be avoided as it may be swallowed by
108     *    the pool implementation.
109     *
110     * @see #validateObject
111     * @see KeyedObjectPool#invalidateObject
112     */
113    void destroyObject(K key, PooledObject<V> p) throws Exception;
114
115    /**
116     * Destroys an instance no longer needed by the pool, using the provided {@link DestroyMode}.
117     *
118     * @param key the key used when selecting the instance
119     * @param p a {@code PooledObject} wrapping the instance to be destroyed
120     * @param destroyMode DestroyMode providing context to the factory
121     *
122     * @throws Exception should be avoided as it may be swallowed by
123     *    the pool implementation.
124     *
125     * @see #validateObject
126     * @see KeyedObjectPool#invalidateObject
127     * @see #destroyObject(Object, PooledObject)
128     * @see DestroyMode
129     * @since 2.9.0
130     */
131    default void destroyObject(final K key, final PooledObject<V> p, final DestroyMode destroyMode) throws Exception {
132        destroyObject(key, p);
133    }
134
135    /**
136     * Creates an instance that can be served by the pool and
137     * wrap it in a {@link PooledObject} to be managed by the pool.
138     *
139     * @param key the key used when constructing the object
140     *
141     * @return a {@code PooledObject} wrapping an instance that can
142     * be served by the pool.
143     *
144     * @throws Exception if there is a problem creating a new instance,
145     *    this will be propagated to the code requesting an object.
146     */
147    PooledObject<V> makeObject(K key) throws Exception;
148
149    /**
150     * Uninitializes an instance to be returned to the idle object pool.
151     *
152     * @param key the key used when selecting the object
153     * @param p a {@code PooledObject} wrapping the instance to be passivated
154     *
155     * @throws Exception if there is a problem passivating {@code obj},
156     *    this exception may be swallowed by the pool.
157     *
158     * @see #destroyObject
159     */
160    void passivateObject(K key, PooledObject<V> p) throws Exception;
161
162    /**
163     * Ensures that the instance is safe to be returned by the pool.
164     *
165     * @param key the key used when selecting the object
166     * @param p a {@code PooledObject} wrapping the instance to be validated
167     *
168     * @return {@code false} if {@code obj} is not valid and should
169     *         be dropped from the pool, {@code true} otherwise.
170     */
171    boolean validateObject(K key, PooledObject<V> p);
172}
173