    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
    019import java.io.Closeable;
    020import java.util.NoSuchElementException;
    021
    022/**
    023 * A pooling simple interface.
    024 * <p>
    025 * Example of use:
    026 * </p>
    027 * <pre style="border:solid thin; padding: 1ex;"
    028 * > Object obj = <code style="color:#00C">null</code>;
    029 *
    030 * <code style="color:#00C">try</code> {
    031 *     obj = pool.borrowObject();
    032 *     <code style="color:#00C">try</code> {
    033 *         <code style="color:#0C0">//...use the object...</code>
    034 *     } <code style="color:#00C">catch</code> (Exception e) {
    035 *         <code style="color:#0C0">// invalidate the object</code>
    036 *         pool.invalidateObject(obj);
    037 *         <code style="color:#0C0">// do not return the object to the pool twice</code>
    038 *         obj = <code style="color:#00C">null</code>;
    039 *     } <code style="color:#00C">finally</code> {
    040 *         <code style="color:#0C0">// make sure the object is returned to the pool</code>
    041 *         <code style="color:#00C">if</code> (<code style="color:#00C">null</code> != obj) {
    042 *             pool.returnObject(obj);
    043 *        }
    044 *     }
    045 * } <code style="color:#00C">catch</code>(Exception e) {
    046 *       <code style="color:#0C0">// failed to borrow an object</code>
    047 * }</pre>
    048 * <p>
    049 * See {@link BaseObjectPool} for a simple base implementation.
    050 * </p>
    051 *
    052 * @param <T> Type of element pooled in this pool.
    053 *
    054 *
    055 * @see PooledObjectFactory
    056 * @see KeyedObjectPool
    057 * @see BaseObjectPool
    058 *
    059 * @since 2.0
    060 */
    061public interface ObjectPool<T> extends Closeable {
    062
    063    /**
    064     * Creates an object using the {@link PooledObjectFactory factory} or other
    065     * implementation dependent mechanism, passivate it, and then place it in
    066     * the idle object pool. {@code addObject} is useful for "pre-loading"
    067     * a pool with idle objects. (Optional operation).
    068     *
    069     * @throws Exception
    070     *              when {@link PooledObjectFactory#makeObject} fails.
    071     * @throws IllegalStateException
    072     *              after {@link #close} has been called on this pool.
    073     * @throws UnsupportedOperationException
    074     *              when this pool cannot add new idle objects.
    075     */
    076    void addObject() throws Exception;
    077
    078    /**
    079     * Calls {@link ObjectPool#addObject()} {@code count}
    080     * number of times.
    081     *
    082     * @param count
    083     *            the number of idle objects to add.
    084     * @throws Exception See {@link ObjectPool#addObject()}.
    085     * @since 2.8.0
    086     */
    087    default void addObjects(final int count) throws Exception {
    088        for (int i = 0; i < count; i++) {
    089            addObject();
    090        }
    091    }
    092
    093    /**
    094     * Borrows an instance from this pool.
    095     * <p>
    096     * Instances returned from this method will have been either newly created
    097     * with {@link PooledObjectFactory#makeObject} or will be a previously
    098     * idle object and have been activated with
    099     * {@link PooledObjectFactory#activateObject} and then validated with
    100     * {@link PooledObjectFactory#validateObject}.
    101     * </p>
    102     * <p>
    103     * By contract, clients <strong>must</strong> return the borrowed instance
    104     * using {@link #returnObject}, {@link #invalidateObject}, or a related
    105     * method as defined in an implementation or sub-interface.
    106     * </p>
    107     * <p>
    108     * The behavior of this method when the pool has been exhausted
    109     * is not strictly specified (although it may be specified by
    110     * implementations).
    111     * </p>
    112     *
    113     * @return an instance from this pool.
    114     *
    115     * @throws IllegalStateException
    116     *              after {@link #close close} has been called on this pool.
    117     * @throws Exception
    118     *              when {@link PooledObjectFactory#makeObject} throws an
    119     *              exception.
    120     * @throws NoSuchElementException
    121     *              when the pool is exhausted and cannot or will not return
    122     *              another instance.
    123     */
    124    T borrowObject() throws Exception;
    125
    126    /**
    127     * Clears any objects sitting idle in the pool, releasing any associated
    128     * resources (optional operation). Idle objects cleared must be
    129     * {@link PooledObjectFactory#destroyObject(PooledObject)}.
    130     *
    131     * @throws UnsupportedOperationException
    132     *              if this implementation does not support the operation
    133     *
    134     * @throws Exception if the pool cannot be cleared
    135     */
    136    void clear() throws Exception;
    137
    138    /**
    139     * Closes this pool, and free any resources associated with it.
    140     * <p>
    141     * Calling {@link #addObject} or {@link #borrowObject} after invoking this
    142     * method on a pool will cause them to throw an {@link IllegalStateException}.
    143     * </p>
    144     * <p>
    145     * Implementations should silently fail if not all resources can be freed.
    146     * </p>
    147     */
    148    @Override
    149    void close();
    150
    151    /**
    152     * Gets the number of instances currently borrowed from this pool. Returns
    153     * a negative value if this information is not available.
    154     * @return the number of instances currently borrowed from this pool.
    155     */
    156    int getNumActive();
    157
    158    /**
    159     * Gets the number of instances currently idle in this pool. This may be
    160     * considered an approximation of the number of objects that can be
    161     * {@link #borrowObject borrowed} without creating any new instances.
    162     * Returns a negative value if this information is not available.
    163     * @return the number of instances currently idle in this pool.
    164     */
    165    int getNumIdle();
    166
    167    /**
    168     * Invalidates an object from the pool.
    169     * <p>
    170     * By contract, {@code obj} <strong>must</strong> have been obtained
    171     * using {@link #borrowObject} or a related method as defined in an
    172     * implementation or sub-interface.
    173     * </p>
    174     * <p>
    175     * This method should be used when an object that has been borrowed is
    176     * determined (due to an exception or other problem) to be invalid.
    177     * </p>
    178     *
    179     * @param obj a {@link #borrowObject borrowed} instance to be disposed.
    180     *
    181     * @throws Exception if the instance cannot be invalidated
    182     */
    183    void invalidateObject(T obj) throws Exception;
    184
    185    /**
    186     * Invalidates an object from the pool, using the provided
    187     * {@link DestroyMode}
    188     * <p>
    189     * By contract, {@code obj} <strong>must</strong> have been obtained
    190     * using {@link #borrowObject} or a related method as defined in an
    191     * implementation or sub-interface.
    192     * </p>
    193     * <p>
    194     * This method should be used when an object that has been borrowed is
    195     * determined (due to an exception or other problem) to be invalid.
    196     * </p>
    197     *
    198     * @param obj a {@link #borrowObject borrowed} instance to be disposed.
    199     * @param destroyMode destroy activation context provided to the factory
    200     * @throws Exception if the instance cannot be invalidated
    201     * @since 2.9.0
    202     */
    203    default void invalidateObject(final T obj, final DestroyMode destroyMode) throws Exception {
    204        invalidateObject(obj);
    205    }
    206
    207    /**
    208     * Returns an instance to the pool. By contract, {@code obj}
    209     * <strong>must</strong> have been obtained using {@link #borrowObject()} or
    210     * a related method as defined in an implementation or sub-interface.
    211     *
    212     * @param obj a {@link #borrowObject borrowed} instance to be returned.
    213     *
    214     * @throws IllegalStateException
    215     *              if an attempt is made to return an object to the pool that
    216     *              is in any state other than allocated (i.e. borrowed).
    217     *              Attempting to return an object more than once or attempting
    218     *              to return an object that was never borrowed from the pool
    219     *              will trigger this exception.
    220     *
    221     * @throws Exception if an instance cannot be returned to the pool
    222     */
    223    void returnObject(T obj) throws Exception;
    224
    225}