genericobjectpool.java

爬虫

/*
 * Copyright 1999-2004 The Apache Software Foundation.
 * 
 * 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 org.apache.commons.pool.impl;

import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.LinkedList;
import java.util.ListIterator;
import java.util.Timer;
import java.util.TimerTask;

import org.apache.commons.pool.BaseObjectPool;
import org.apache.commons.pool.ObjectPool;
import org.apache.commons.pool.PoolableObjectFactory;
import org.apache.commons.pool.impl.GenericKeyedObjectPool.ObjectTimestampPair;

/**
 * A configurable {@link ObjectPool} implementation.
 * <p>
 * When coupled with the appropriate {@link PoolableObjectFactory},
 * <tt>GenericObjectPool</tt> provides robust pooling functionality for
 * arbitrary objects.
 * <p>
 * A <tt>GenericObjectPool</tt> provides a number of configurable parameters:
 * <ul>
 *  <li>
 *    {@link #setMaxActive <i>maxActive</i>} controls the maximum number of objects that can
 *    be borrowed from the pool at one time.  When non-positive, there
 *    is no limit to the number of objects that may be active at one time.
 *    When {@link #setMaxActive <i>maxActive</i>} is exceeded, the pool is said to be exhausted.
 *  </li>
 *  <li>
 *    {@link #setMaxIdle <i>maxIdle</i>} controls the maximum number of objects that can
 *    sit idle in the pool at any time.  When negative, there
 *    is no limit to the number of objects that may be idle at one time.
 *  </li>
 *  <li>
 *    {@link #setWhenExhaustedAction <i>whenExhaustedAction</i>} specifies the
 *    behaviour of the {@link #borrowObject} method when the pool is exhausted:
 *    <ul>
 *    <li>
 *      When {@link #setWhenExhaustedAction <i>whenExhaustedAction</i>} is
 *      {@link #WHEN_EXHAUSTED_FAIL}, {@link #borrowObject} will throw
 *      a {@link NoSuchElementException}
 *    </li>
 *    <li>
 *      When {@link #setWhenExhaustedAction <i>whenExhaustedAction</i>} is
 *      {@link #WHEN_EXHAUSTED_GROW}, {@link #borrowObject} will create a new
 *      object and return it(essentially making {@link #setMaxActive <i>maxActive</i>}
 *      meaningless.)
 *    </li>
 *    <li>
 *      When {@link #setWhenExhaustedAction <i>whenExhaustedAction</i>}
 *      is {@link #WHEN_EXHAUSTED_BLOCK}, {@link #borrowObject} will block
 *      (invoke {@link Object#wait} until a new or idle object is available.
 *      If a positive {@link #setMaxWait <i>maxWait</i>}
 *      value is supplied, the {@link #borrowObject} will block for at
 *      most that many milliseconds, after which a {@link NoSuchElementException}
 *      will be thrown.  If {@link #setMaxWait <i>maxWait</i>} is non-positive,
 *      the {@link #borrowObject} method will block indefinitely.
 *    </li>
 *    </ul>
 *  </li>
 *  <li>
 *    When {@link #setTestOnBorrow <i>testOnBorrow</i>} is set, the pool will
 *    attempt to validate each object before it is returned from the
 *    {@link #borrowObject} method. (Using the provided factory's
 *    {@link PoolableObjectFactory#validateObject} method.)  Objects that fail
 *    to validate will be dropped from the pool, and a different object will
 *    be borrowed.
 *  </li>
 *  <li>
 *    When {@link #setTestOnReturn <i>testOnReturn</i>} is set, the pool will
 *    attempt to validate each object before it is returned to the pool in the
 *    {@link #returnObject} method. (Using the provided factory's
 *    {@link PoolableObjectFactory#validateObject}
 *    method.)  Objects that fail to validate will be dropped from the pool.
 *  </li>
 * </ul>
 * <p>
 * Optionally, one may configure the pool to examine and possibly evict objects as they
 * sit idle in the pool.  This is performed by an "idle object eviction" thread, which
 * runs asychronously.  The idle object eviction thread may be configured using the
 * following attributes:
 * <ul>
 *  <li>
 *   {@link #setTimeBetweenEvictionRunsMillis <i>timeBetweenEvictionRunsMillis</i>}
 *   indicates how long the eviction thread should sleep before "runs" of examining
 *   idle objects.  When non-positive, no eviction thread will be launched.
 *  </li>
 *  <li>
 *   {@link #setMinEvictableIdleTimeMillis <i>minEvictableIdleTimeMillis</i>}
 *   specifies the minimum amount of time that an object may sit idle in the pool
 *   before it is eligable for eviction due to idle time.  When non-positive, no object
 *   will be dropped from the pool due to idle time alone.
 *  </li>
 *  <li>
 *   {@link #setTestWhileIdle <i>testWhileIdle</i>} indicates whether or not idle
 *   objects should be validated using the factory's
 *   {@link PoolableObjectFactory#validateObject} method.  Objects
 *   that fail to validate will be dropped from the pool.
 *  </li>
 * </ul>
 * <p>
 * GenericObjectPool is not usable without a {@link PoolableObjectFactory}.  A
 * non-<code>null</code> factory must be provided either as a constructor argument
 * or via a call to {@link #setFactory} before the pool is used.
 *
 * @see GenericKeyedObjectPool
 * @author Rodney Waldhoff
 * @author Dirk Verbeeck
 * @version $Revision: 1.2 $ $Date: 2006/05/16 01:31:42 $
 */
public class GenericObjectPool extends BaseObjectPool implements ObjectPool {

    //--- public constants -------------------------------------------

    /**
     * A "when exhausted action" type indicating that when the pool is
     * exhausted (i.e., the maximum number of active objects has
     * been reached), the {@link #borrowObject}
     * method should fail, throwing a {@link NoSuchElementException}.
     * @see #WHEN_EXHAUSTED_BLOCK
     * @see #WHEN_EXHAUSTED_GROW
     * @see #setWhenExhaustedAction
     */
    public static final byte WHEN_EXHAUSTED_FAIL   = 0;

    /**
     * A "when exhausted action" type indicating that when the pool
     * is exhausted (i.e., the maximum number
     * of active objects has been reached), the {@link #borrowObject}
     * method should block until a new object is available, or the
     * {@link #getMaxWait maximum wait time} has been reached.
     * @see #WHEN_EXHAUSTED_FAIL
     * @see #WHEN_EXHAUSTED_GROW
     * @see #setMaxWait
     * @see #getMaxWait
     * @see #setWhenExhaustedAction
     */
    public static final byte WHEN_EXHAUSTED_BLOCK  = 1;

    /**
     * A "when exhausted action" type indicating that when the pool is
     * exhausted (i.e., the maximum number
     * of active objects has been reached), the {@link #borrowObject}
     * method should simply create a new object anyway.
     * @see #WHEN_EXHAUSTED_FAIL
     * @see #WHEN_EXHAUSTED_GROW
     * @see #setWhenExhaustedAction
     */
    public static final byte WHEN_EXHAUSTED_GROW   = 2;

    /**
     * The default cap on the number of "sleeping" instances in the pool.
     * @see #getMaxIdle
     * @see #setMaxIdle
     */
    public static final int DEFAULT_MAX_IDLE  = 8;

    /**
     * The default minimum number of "sleeping" instances in the pool
     * before before the evictor thread (if active) spawns new objects.
     * @see #getMinIdle
     * @see #setMinIdle
     */
    public static final int DEFAULT_MIN_IDLE = 0;

    /**
     * The default cap on the total number of active instances from the pool.
     * @see #getMaxActive
     */
    public static final int DEFAULT_MAX_ACTIVE  = 8;

    /**
     * The default "when exhausted action" for the pool.
     * @see #WHEN_EXHAUSTED_BLOCK
     * @see #WHEN_EXHAUSTED_FAIL
     * @see #WHEN_EXHAUSTED_GROW
     * @see #setWhenExhaustedAction
     */
    public static final byte DEFAULT_WHEN_EXHAUSTED_ACTION = WHEN_EXHAUSTED_BLOCK;

    /**
     * The default maximum amount of time (in millis) the
     * {@link #borrowObject} method should block before throwing
     * an exception when the pool is exhausted and the
     * {@link #getWhenExhaustedAction "when exhausted" action} is
     * {@link #WHEN_EXHAUSTED_BLOCK}.
     * @see #getMaxWait
     * @see #setMaxWait
     */
    public static final long DEFAULT_MAX_WAIT = -1L;

    /**
     * The default "test on borrow" value.
     * @see #getTestOnBorrow
     * @see #setTestOnBorrow
     */
    public static final boolean DEFAULT_TEST_ON_BORROW = false;

    /**
     * The default "test on return" value.
     * @see #getTestOnReturn
     * @see #setTestOnReturn
     */
    public static final boolean DEFAULT_TEST_ON_RETURN = false;

    /**
     * The default "test while idle" value.
     * @see #getTestWhileIdle
     * @see #setTestWhileIdle
     * @see #getTimeBetweenEvictionRunsMillis
     * @see #setTimeBetweenEvictionRunsMillis
     */
    public static final boolean DEFAULT_TEST_WHILE_IDLE = false;

    /**
     * The default "time between eviction runs" value.
     * @see #getTimeBetweenEvictionRunsMillis
     * @see #setTimeBetweenEvictionRunsMillis
     */
    public static final long DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS = -1L;

    /**
     * The default number of objects to examine per run in the
     * idle object evictor.
     * @see #getNumTestsPerEvictionRun
     * @see #setNumTestsPerEvictionRun
     * @see #getTimeBetweenEvictionRunsMillis
     * @see #setTimeBetweenEvictionRunsMillis
     */
    public static final int DEFAULT_NUM_TESTS_PER_EVICTION_RUN = 3;

    /**
     * The default value for {@link #getMinEvictableIdleTimeMillis}.
     * @see #getMinEvictableIdleTimeMillis
     * @see #setMinEvictableIdleTimeMillis
     */
    public static final long DEFAULT_MIN_EVICTABLE_IDLE_TIME_MILLIS = 1000L * 60L * 30L;

    /**
     * The default value for {@link #getSoftMinEvictableIdleTimeMillis}.
     * @see #getSoftMinEvictableIdleTimeMillis
     * @see #setSoftMinEvictableIdleTimeMillis
     */
    public static final long DEFAULT_SOFT_MIN_EVICTABLE_IDLE_TIME_MILLIS = -1;

    //--- package constants -------------------------------------------

    /**
     * Idle object evition Timer. Shared between all {@link GenericObjectPool}s and {@link GenericKeyedObjectPool} s.
     */
    static final Timer EVICTION_TIMER = new Timer(true);

    //--- constructors -----------------------------------------------

    /**
     * Create a new <tt>GenericObjectPool</tt>.
     */
    public GenericObjectPool() {
        this(null,DEFAULT_MAX_ACTIVE,DEFAULT_WHEN_EXHAUSTED_ACTION,DEFAULT_MAX_WAIT,DEFAULT_MAX_IDLE,DEFAULT_MIN_IDLE,DEFAULT_TEST_ON_BORROW,DEFAULT_TEST_ON_RETURN,DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS,DEFAULT_NUM_TESTS_PER_EVICTION_RUN,DEFAULT_MIN_EVICTABLE_IDLE_TIME_MILLIS,DEFAULT_TEST_WHILE_IDLE);
    }

    /**
     * Create a new <tt>GenericObjectPool</tt> using the specified values.
     * @param factory the (possibly <tt>null</tt>)PoolableObjectFactory to use to create, validate and destroy objects
     */
    public GenericObjectPool(PoolableObjectFactory factory) {
        this(factory,DEFAULT_MAX_ACTIVE,DEFAULT_WHEN_EXHAUSTED_ACTION,DEFAULT_MAX_WAIT,DEFAULT_MAX_IDLE,DEFAULT_MIN_IDLE,DEFAULT_TEST_ON_BORROW,DEFAULT_TEST_ON_RETURN,DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS,DEFAULT_NUM_TESTS_PER_EVICTION_RUN,DEFAULT_MIN_EVICTABLE_IDLE_TIME_MILLIS,DEFAULT_TEST_WHILE_IDLE);
    }

    /**
     * Create a new <tt>GenericObjectPool</tt> using the specified values.
     * @param factory the (possibly <tt>null</tt>)PoolableObjectFactory to use to create, validate and destroy objects
     * @param config a non-<tt>null</tt> {@link GenericObjectPool.Config} describing my configuration
     */
    public GenericObjectPool(PoolableObjectFactory factory, GenericObjectPool.Config config) {
        this(factory,config.maxActive,config.whenExhaustedAction,config.maxWait,config.maxIdle,config.minIdle,config.testOnBorrow,config.testOnReturn,config.timeBetweenEvictionRunsMillis,config.numTestsPerEvictionRun,config.minEvictableIdleTimeMillis,config.testWhileIdle);
    }

    /**
     * Create a new <tt>GenericObjectPool</tt> using the specified values.
     * @param factory the (possibly <tt>null</tt>)PoolableObjectFactory to use to create, validate and destroy objects
     * @param maxActive the maximum number of objects that can be borrowed from me at one time (see {@link #setMaxActive})
     */
    public GenericObjectPool(PoolableObjectFactory factory, int maxActive) {
        this(factory,maxActive,DEFAULT_WHEN_EXHAUSTED_ACTION,DEFAULT_MAX_WAIT,DEFAULT_MAX_IDLE,DEFAULT_MIN_IDLE,DEFAULT_TEST_ON_BORROW,DEFAULT_TEST_ON_RETURN,DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS,DEFAULT_NUM_TESTS_PER_EVICTION_RUN,DEFAULT_MIN_EVICTABLE_IDLE_TIME_MILLIS,DEFAULT_TEST_WHILE_IDLE);
    }

    /**
     * Create a new <tt>GenericObjectPool</tt> using the specified values.
     * @param factory the (possibly <tt>null</tt>)PoolableObjectFactory to use to create, validate and destroy objects
     * @param maxActive the maximum number of objects that can be borrowed from me at one time (see {@link #setMaxActive})
     * @param whenExhaustedAction the action to take when the pool is exhausted (see {@link #getWhenExhaustedAction})
     * @param maxWait the maximum amount of time to wait for an idle object when the pool is exhausted an and <i>whenExhaustedAction</i> is {@link #WHEN_EXHAUSTED_BLOCK} (otherwise ignored) (see {@link #getMaxWait})
     */
    public GenericObjectPool(PoolableObjectFactory factory, int maxActive, byte whenExhaustedAction, long maxWait) {
        this(factory,maxActive,whenExhaustedAction,maxWait,DEFAULT_MAX_IDLE,DEFAULT_MIN_IDLE,DEFAULT_TEST_ON_BORROW,DEFAULT_TEST_ON_RETURN,DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS,DEFAULT_NUM_TESTS_PER_EVICTION_RUN,DEFAULT_MIN_EVICTABLE_IDLE_TIME_MILLIS,DEFAULT_TEST_WHILE_IDLE);
    }

    /**
     * Create a new <tt>GenericObjectPool</tt> using the specified values.
     * @param factory the (possibly <tt>null</tt>)PoolableObjectFactory to use to create, validate and destroy objects
     * @param maxActive the maximum number of objects that can be borrowed from me at one time (see {@link #setMaxActive})
     * @param whenExhaustedAction the action to take when the pool is exhausted (see {@link #getWhenExhaustedAction})
     * @param maxWait the maximum amount of time to wait for an idle object when the pool is exhausted an and <i>whenExhaustedAction</i> is {@link #WHEN_EXHAUSTED_BLOCK} (otherwise ignored) (see {@link #getMaxWait})
     * @param testOnBorrow whether or not to validate objects before they are returned by the {@link #borrowObject} method (see {@link #getTestOnBorrow})
     * @param testOnReturn whether or not to validate objects after they are returned to the {@link #returnObject} method (see {@link #getTestOnReturn})
     */
    public GenericObjectPool(PoolableObjectFactory factory, int maxActive, byte whenExhaustedAction, long maxWait, boolean testOnBorrow, boolean testOnReturn) {
        this(factory,maxActive,whenExhaustedAction,maxWait,DEFAULT_MAX_IDLE,DEFAULT_MIN_IDLE,testOnBorrow,testOnReturn,DEFAULT_TIME_BETWEEN_EVICTION_RUNS_MILLIS,DEFAULT_NUM_TESTS_PER_EVICTION_RUN,DEFAULT_MIN_EVICTABLE_IDLE_TIME_MILLIS,DEFAULT_TEST_WHILE_IDLE);
    }