/*
 * 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.commons.pool2.impl;

import java.util.ArrayList;
import java.util.Deque;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NoSuchElementException;
import java.util.TreeMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

import org.apache.commons.pool2.KeyedObjectPool;
import org.apache.commons.pool2.KeyedPooledObjectFactory;
import org.apache.commons.pool2.PoolUtils;
import org.apache.commons.pool2.PooledObject;
import org.apache.commons.pool2.PooledObjectState;
import org.apache.commons.pool2.SwallowedExceptionListener;

A configurable KeyedObjectPool implementation.
 When coupled with the appropriate KeyedPooledObjectFactory, GenericKeyedObjectPool provides robust pooling functionality for
keyed objects. A GenericKeyedObjectPool can be viewed as a map of sub-pools, keyed on the (unique) key values provided to the preparePool, addObject or borrowObject methods. Each time a new key value is provided to one of these methods, a sub-new pool is created under the given key to be managed by the containing GenericKeyedObjectPool.

Note that the current implementation uses a ConcurrentHashMap which uses
equals() to compare keys.
This means that distinct instance keys must be distinguishable using equals.

Optionally, one may configure the pool to examine and possibly evict objects
as they sit idle in the pool and to ensure that a minimum number of idle
objects is maintained for each key. This is performed by an "idle object
eviction" thread, which runs asynchronously. Caution should be used when
configuring this optional feature. Eviction runs contend with client threads
for access to objects in the pool, so if they run too frequently performance
issues may result.

Implementation note: To prevent possible deadlocks, care has been taken to
ensure that no call to a factory method will occur within a synchronization
block. See POOL-125 and DBCP-44 for more information.

This class is intended to be thread-safe.
Type parameters:
<K> – The type of keys maintained by this pool.
<T> – Type of element pooled in this pool.
See Also:
GenericObjectPool
Since:
2.0/**
 * A configurable <code>KeyedObjectPool</code> implementation.
 * <p>
 * When coupled with the appropriate {@link KeyedPooledObjectFactory},
 * <code>GenericKeyedObjectPool</code> provides robust pooling functionality for
 * keyed objects. A <code>GenericKeyedObjectPool</code> can be viewed as a map
 * of sub-pools, keyed on the (unique) key values provided to the
 * {@link #preparePool preparePool}, {@link #addObject addObject} or
 * {@link #borrowObject borrowObject} methods. Each time a new key value is
 * provided to one of these methods, a sub-new pool is created under the given
 * key to be managed by the containing <code>GenericKeyedObjectPool.</code>
 * <p>
 * Note that the current implementation uses a ConcurrentHashMap which uses
 * equals() to compare keys.
 * This means that distinct instance keys must be distinguishable using equals.
 * <p>
 * Optionally, one may configure the pool to examine and possibly evict objects
 * as they sit idle in the pool and to ensure that a minimum number of idle
 * objects is maintained for each key. This is performed by an "idle object
 * eviction" thread, which runs asynchronously. Caution should be used when
 * configuring this optional feature. Eviction runs contend with client threads
 * for access to objects in the pool, so if they run too frequently performance
 * issues may result.
 * <p>
 * Implementation note: To prevent possible deadlocks, care has been taken to
 * ensure that no call to a factory method will occur within a synchronization
 * block. See POOL-125 and DBCP-44 for more information.
 * <p>
 * This class is intended to be thread-safe.
 *
 * @see GenericObjectPool
 *
 * @param <K> The type of keys maintained by this pool.
 * @param <T> Type of element pooled in this pool.
 *
 * @since 2.0
 */
public class GenericKeyedObjectPool<K, T> extends BaseGenericObjectPool<T>
        implements KeyedObjectPool<K, T>, GenericKeyedObjectPoolMXBean<K> {

    
Create a new GenericKeyedObjectPool using defaults from GenericKeyedObjectPoolConfig. 
Params:
factory – the factory to be used to create entries/**
     * Create a new <code>GenericKeyedObjectPool</code> using defaults from
     * {@link GenericKeyedObjectPoolConfig}.
     * @param factory the factory to be used to create entries
     */
    public GenericKeyedObjectPool(final KeyedPooledObjectFactory<K,T> factory) {
        this(factory, new GenericKeyedObjectPoolConfig<T>());
    }

    
Create a new GenericKeyedObjectPool using a specific
configuration.
Params:
factory – the factory to be used to create entries
config –    The configuration to use for this pool instance. The
                 configuration is used by value. Subsequent changes to
                 the configuration object will not be reflected in the
                 pool./**
     * Create a new <code>GenericKeyedObjectPool</code> using a specific
     * configuration.
     *
     * @param factory the factory to be used to create entries
     * @param config    The configuration to use for this pool instance. The
     *                  configuration is used by value. Subsequent changes to
     *                  the configuration object will not be reflected in the
     *                  pool.
     */
    public GenericKeyedObjectPool(final KeyedPooledObjectFactory<K, T> factory,
            final GenericKeyedObjectPoolConfig<T> config) {

        super(config, ONAME_BASE, config.getJmxNamePrefix());

        if (factory == null) {
            jmxUnregister(); // tidy up
            throw new IllegalArgumentException("factory may not be null");
        }
        this.factory = factory;
        this.fairness = config.getFairness();

        setConfig(config);
    }

    
Returns the limit on the number of object instances allocated by the pool
(checked out or idle), per key. When the limit is reached, the sub-pool
is said to be exhausted. A negative value indicates no limit.
See Also:
setMaxTotalPerKey
Returns:
the limit on the number of active instances per key/**
     * Returns the limit on the number of object instances allocated by the pool
     * (checked out or idle), per key. When the limit is reached, the sub-pool
     * is said to be exhausted. A negative value indicates no limit.
     *
     * @return the limit on the number of active instances per key
     *
     * @see #setMaxTotalPerKey
     */
    @Override
    public int getMaxTotalPerKey() {
        return maxTotalPerKey;
    }

    
Sets the limit on the number of object instances allocated by the pool
(checked out or idle), per key. When the limit is reached, the sub-pool
is said to be exhausted. A negative value indicates no limit.
Params:
maxTotalPerKey – the limit on the number of active instances per key
See Also:
getMaxTotalPerKey/**
     * Sets the limit on the number of object instances allocated by the pool
     * (checked out or idle), per key. When the limit is reached, the sub-pool
     * is said to be exhausted. A negative value indicates no limit.
     *
     * @param maxTotalPerKey the limit on the number of active instances per key
     *
     * @see #getMaxTotalPerKey
     */
    public void setMaxTotalPerKey(final int maxTotalPerKey) {
        this.maxTotalPerKey = maxTotalPerKey;
    }


    
Returns the cap on the number of "idle" instances per key in the pool.
If maxIdlePerKey is set too low on heavily loaded systems it is possible
you will see objects being destroyed and almost immediately new objects
being created. This is a result of the active threads momentarily
returning objects faster than they are requesting them, causing the
number of idle objects to rise above maxIdlePerKey. The best value for
maxIdlePerKey for heavily loaded system will vary but the default is a
good starting point.
See Also:
setMaxIdlePerKey
Returns:
the maximum number of "idle" instances that can be held in a
        given keyed sub-pool or a negative value if there is no limit/**
     * Returns the cap on the number of "idle" instances per key in the pool.
     * If maxIdlePerKey is set too low on heavily loaded systems it is possible
     * you will see objects being destroyed and almost immediately new objects
     * being created. This is a result of the active threads momentarily
     * returning objects faster than they are requesting them, causing the
     * number of idle objects to rise above maxIdlePerKey. The best value for
     * maxIdlePerKey for heavily loaded system will vary but the default is a
     * good starting point.
     *
     * @return the maximum number of "idle" instances that can be held in a
     *         given keyed sub-pool or a negative value if there is no limit
     *
     * @see #setMaxIdlePerKey
     */
    @Override
    public int getMaxIdlePerKey() {
        return maxIdlePerKey;
    }

    
Sets the cap on the number of "idle" instances per key in the pool.
If maxIdlePerKey is set too low on heavily loaded systems it is possible
you will see objects being destroyed and almost immediately new objects
being created. This is a result of the active threads momentarily
returning objects faster than they are requesting them, causing the
number of idle objects to rise above maxIdlePerKey. The best value for
maxIdlePerKey for heavily loaded system will vary but the default is a
good starting point.
Params:
maxIdlePerKey – the maximum number of "idle" instances that can be
                     held in a given keyed sub-pool. Use a negative value
                     for no limit
See Also:
getMaxIdlePerKey/**
     * Sets the cap on the number of "idle" instances per key in the pool.
     * If maxIdlePerKey is set too low on heavily loaded systems it is possible
     * you will see objects being destroyed and almost immediately new objects
     * being created. This is a result of the active threads momentarily
     * returning objects faster than they are requesting them, causing the
     * number of idle objects to rise above maxIdlePerKey. The best value for
     * maxIdlePerKey for heavily loaded system will vary but the default is a
     * good starting point.
     *
     * @param maxIdlePerKey the maximum number of "idle" instances that can be
     *                      held in a given keyed sub-pool. Use a negative value
     *                      for no limit
     *
     * @see #getMaxIdlePerKey
     */
    public void setMaxIdlePerKey(final int maxIdlePerKey) {
        this.maxIdlePerKey = maxIdlePerKey;
    }

    
Sets the target for the minimum number of idle objects to maintain in each of the keyed sub-pools. This setting only has an effect if it is positive and BaseGenericObjectPool.getTimeBetweenEvictionRunsMillis() is greater than zero. If this is the case, an attempt is made to ensure that each sub-pool has the required minimum number of instances during idle object eviction runs. 

If the configured value of minIdlePerKey is greater than the configured
value for maxIdlePerKey then the value of maxIdlePerKey will be used
instead.
Params:
minIdlePerKey – The minimum size of the each keyed pool
See Also:
getMinIdlePerKey
getMaxIdlePerKey()
BaseGenericObjectPool.setTimeBetweenEvictionRunsMillis/**
     * Sets the target for the minimum number of idle objects to maintain in
     * each of the keyed sub-pools. This setting only has an effect if it is
     * positive and {@link #getTimeBetweenEvictionRunsMillis()} is greater than
     * zero. If this is the case, an attempt is made to ensure that each
     * sub-pool has the required minimum number of instances during idle object
     * eviction runs.
     * <p>
     * If the configured value of minIdlePerKey is greater than the configured
     * value for maxIdlePerKey then the value of maxIdlePerKey will be used
     * instead.
     *
     * @param minIdlePerKey The minimum size of the each keyed pool
     *
     * @see #getMinIdlePerKey
     * @see #getMaxIdlePerKey()
     * @see #setTimeBetweenEvictionRunsMillis
     */
    public void setMinIdlePerKey(final int minIdlePerKey) {
        this.minIdlePerKey = minIdlePerKey;
    }

    
Returns the target for the minimum number of idle objects to maintain in each of the keyed sub-pools. This setting only has an effect if it is positive and BaseGenericObjectPool.getTimeBetweenEvictionRunsMillis() is greater than zero. If this is the case, an attempt is made to ensure that each sub-pool has the required minimum number of instances during idle object eviction runs. 

If the configured value of minIdlePerKey is greater than the configured
value for maxIdlePerKey then the value of maxIdlePerKey will be used
instead.
See Also:
BaseGenericObjectPool.setTimeBetweenEvictionRunsMillis
Returns:
minimum size of the each keyed pool/**
     * Returns the target for the minimum number of idle objects to maintain in
     * each of the keyed sub-pools. This setting only has an effect if it is
     * positive and {@link #getTimeBetweenEvictionRunsMillis()} is greater than
     * zero. If this is the case, an attempt is made to ensure that each
     * sub-pool has the required minimum number of instances during idle object
     * eviction runs.
     * <p>
     * If the configured value of minIdlePerKey is greater than the configured
     * value for maxIdlePerKey then the value of maxIdlePerKey will be used
     * instead.
     *
     * @return minimum size of the each keyed pool
     *
     * @see #setTimeBetweenEvictionRunsMillis
     */
    @Override
    public int getMinIdlePerKey() {
        final int maxIdlePerKeySave = getMaxIdlePerKey();
        if (this.minIdlePerKey > maxIdlePerKeySave) {
            return maxIdlePerKeySave;
        }
        return minIdlePerKey;
    }

    
Sets the configuration.
Params:
conf – the new configuration to use. This is used by value.
See Also:
GenericKeyedObjectPoolConfig/**
     * Sets the configuration.
     *
     * @param conf the new configuration to use. This is used by value.
     *
     * @see GenericKeyedObjectPoolConfig
     */
    public void setConfig(final GenericKeyedObjectPoolConfig<T> conf) {
        super.setConfig(conf);
        setMaxIdlePerKey(conf.getMaxIdlePerKey());
        setMaxTotalPerKey(conf.getMaxTotalPerKey());
        setMaxTotal(conf.getMaxTotal());
        setMinIdlePerKey(conf.getMinIdlePerKey());
    }

    
Obtain a reference to the factory used to create, destroy and validate
the objects used by this pool.
Returns:
the factory/**
     * Obtain a reference to the factory used to create, destroy and validate
     * the objects used by this pool.
     *
     * @return the factory
     */
    public KeyedPooledObjectFactory<K, T> getFactory() {
        return factory;
    }

    
Equivalent to borrowObject(key, BaseGenericObjectPool.getMaxWaitMillis()).

{@inheritDoc}
/**
     * Equivalent to <code>{@link #borrowObject(Object, long) borrowObject}(key,
     * {@link #getMaxWaitMillis()})</code>.
     * <p>
     * {@inheritDoc}
     */
    @Override
    public T borrowObject(final K key) throws Exception {
        return borrowObject(key, getMaxWaitMillis());
    }

    
Borrows an object from the sub-pool associated with the given key using the specified waiting time which only applies if BaseGenericObjectPool.getBlockWhenExhausted() is true. 
 If there is one or more idle instances available in the sub-pool associated with the given key, then an idle instance will be selected based on the value of BaseGenericObjectPool.getLifo(), activated and returned. If activation fails, or testOnBorrow is set to true and validation fails, the instance is destroyed and the
next available instance is examined.  This continues until either a valid
instance is returned or there are no more idle instances available.
 If there are no idle instances available in the sub-pool associated with the given key, behavior depends on the 
maxTotalPerKey, maxTotal, and (if applicable) BaseGenericObjectPool.getBlockWhenExhausted() and the value passed in to the borrowMaxWaitMillis parameter. If the number of instances checked
out from the sub-pool under the given key is less than
maxTotalPerKey and the total number of instances in
circulation (under all keys) is less than maxTotal, a new
instance is created, activated and (if applicable) validated and returned
to the caller. If validation fails, a NoSuchElementException
will be thrown.
 If the associated sub-pool is exhausted (no available idle instances and no capacity to create new ones), this method will either block (BaseGenericObjectPool.getBlockWhenExhausted() is true) or throw a NoSuchElementException (BaseGenericObjectPool.getBlockWhenExhausted() is false). The length of time that this method will block when BaseGenericObjectPool.getBlockWhenExhausted() is true is determined by the value passed in to the borrowMaxWait parameter.

When maxTotal is set to a positive value and this method is
invoked when at the limit with no idle instances available under the requested
key, an attempt is made to create room by clearing the oldest 15% of the
elements from the keyed sub-pools.

When the pool is exhausted, multiple calling threads may be
simultaneously blocked waiting for instances to become available. A
"fairness" algorithm has been implemented to ensure that threads receive
available instances in request arrival order.
Params:
key – pool key
borrowMaxWaitMillis – The time to wait in milliseconds for an object
                           to become available
Throws:
NoSuchElementException – if a keyed object instance cannot be
                               returned because the pool is exhausted.
Exception – if a keyed object instance cannot be returned due to an
                  error
Returns:
object instance from the keyed pool/**
     * Borrows an object from the sub-pool associated with the given key using
     * the specified waiting time which only applies if
     * {@link #getBlockWhenExhausted()} is true.
     * <p>
     * If there is one or more idle instances available in the sub-pool
     * associated with the given key, then an idle instance will be selected
     * based on the value of {@link #getLifo()}, activated and returned.  If
     * activation fails, or {@link #getTestOnBorrow() testOnBorrow} is set to
     * <code>true</code> and validation fails, the instance is destroyed and the
     * next available instance is examined.  This continues until either a valid
     * instance is returned or there are no more idle instances available.
     * <p>
     * If there are no idle instances available in the sub-pool associated with
     * the given key, behavior depends on the {@link #getMaxTotalPerKey()
     * maxTotalPerKey}, {@link #getMaxTotal() maxTotal}, and (if applicable)
     * {@link #getBlockWhenExhausted()} and the value passed in to the
     * <code>borrowMaxWaitMillis</code> parameter. If the number of instances checked
     * out from the sub-pool under the given key is less than
     * <code>maxTotalPerKey</code> and the total number of instances in
     * circulation (under all keys) is less than <code>maxTotal</code>, a new
     * instance is created, activated and (if applicable) validated and returned
     * to the caller. If validation fails, a <code>NoSuchElementException</code>
     * will be thrown.
     * <p>
     * If the associated sub-pool is exhausted (no available idle instances and
     * no capacity to create new ones), this method will either block
     * ({@link #getBlockWhenExhausted()} is true) or throw a
     * <code>NoSuchElementException</code>
     * ({@link #getBlockWhenExhausted()} is false).
     * The length of time that this method will block when
     * {@link #getBlockWhenExhausted()} is true is determined by the value
     * passed in to the <code>borrowMaxWait</code> parameter.
     * <p>
     * When <code>maxTotal</code> is set to a positive value and this method is
     * invoked when at the limit with no idle instances available under the requested
     * key, an attempt is made to create room by clearing the oldest 15% of the
     * elements from the keyed sub-pools.
     * <p>
     * When the pool is exhausted, multiple calling threads may be
     * simultaneously blocked waiting for instances to become available. A
     * "fairness" algorithm has been implemented to ensure that threads receive
     * available instances in request arrival order.
     *
     * @param key pool key
     * @param borrowMaxWaitMillis The time to wait in milliseconds for an object
     *                            to become available
     *
     * @return object instance from the keyed pool
     *
     * @throws NoSuchElementException if a keyed object instance cannot be
     *                                returned because the pool is exhausted.
     *
     * @throws Exception if a keyed object instance cannot be returned due to an
     *                   error
     */
    public T borrowObject(final K key, final long borrowMaxWaitMillis) throws Exception {
        assertOpen();

        PooledObject<T> p = null;

        // Get local copy of current config so it is consistent for entire
        // method execution
        final boolean blockWhenExhausted = getBlockWhenExhausted();

        boolean create;
        final long waitTime = System.currentTimeMillis();
        final ObjectDeque<T> objectDeque = register(key);

        try {
            while (p == null) {
                create = false;
                p = objectDeque.getIdleObjects().pollFirst();
                if (p == null) {
                    p = create(key);
                    if (p != null) {
                        create = true;
                    }
                }
                if (blockWhenExhausted) {
                    if (p == null) {
                        if (borrowMaxWaitMillis < 0) {
                            p = objectDeque.getIdleObjects().takeFirst();
                        } else {
                            p = objectDeque.getIdleObjects().pollFirst(
                                    borrowMaxWaitMillis, TimeUnit.MILLISECONDS);
                        }
                    }
                    if (p == null) {
                        throw new NoSuchElementException(
                                "Timeout waiting for idle object");
                    }
                } else {
                    if (p == null) {
                        throw new NoSuchElementException("Pool exhausted");
                    }
                }
                if (!p.allocate()) {
                    p = null;
                }

                if (p != null) {
                    try {
                        factory.activateObject(key, p);
                    } catch (final Exception e) {
                        try {
                            destroy(key, p, true);
                        } catch (final Exception e1) {
                            // Ignore - activation failure is more important
                        }
                        p = null;
                        if (create) {
                            final NoSuchElementException nsee = new NoSuchElementException(
                                    "Unable to activate object");
                            nsee.initCause(e);
                            throw nsee;
                        }
                    }
                    if (p != null && getTestOnBorrow()) {
                        boolean validate = false;
                        Throwable validationThrowable = null;
                        try {
                            validate = factory.validateObject(key, p);
                        } catch (final Throwable t) {
                            PoolUtils.checkRethrow(t);
                            validationThrowable = t;
                        }
                        if (!validate) {
                            try {
                                destroy(key, p, true);
                                destroyedByBorrowValidationCount.incrementAndGet();
                            } catch (final Exception e) {
                                // Ignore - validation failure is more important
                            }
                            p = null;
                            if (create) {
                                final NoSuchElementException nsee = new NoSuchElementException(
                                        "Unable to validate object");
                                nsee.initCause(validationThrowable);
                                throw nsee;
                            }
                        }
                    }
                }
            }
        } finally {
            deregister(key);
        }

        updateStatsBorrow(p, System.currentTimeMillis() - waitTime);

        return p.getObject();
    }


    
Returns an object to a keyed sub-pool.
 If maxIdle is set to a positive value and the number of idle instances under the given key has reached this value, the returning instance is destroyed. 
 If testOnReturn == true, the returning instance is validated before being returned to the idle instance sub-pool under the given key. In this case, if validation fails, the instance is destroyed. 
 Exceptions encountered destroying objects for any reason are swallowed but notified via a SwallowedExceptionListener. 
Params:
key – pool key
obj – instance to return to the keyed pool
Throws:
IllegalStateException – if an object is returned to the pool that
                              was not borrowed from it or if an object is
                              returned to the pool multiple times/**
     * Returns an object to a keyed sub-pool.
     * <p>
     * If {@link #getMaxIdlePerKey() maxIdle} is set to a positive value and the
     * number of idle instances under the given key has reached this value, the
     * returning instance is destroyed.
     * <p>
     * If {@link #getTestOnReturn() testOnReturn} == true, the returning
     * instance is validated before being returned to the idle instance sub-pool
     * under the given key. In this case, if validation fails, the instance is
     * destroyed.
     * <p>
     * Exceptions encountered destroying objects for any reason are swallowed
     * but notified via a {@link SwallowedExceptionListener}.
     *
     * @param key pool key
     * @param obj instance to return to the keyed pool
     *
     * @throws IllegalStateException if an object is returned to the pool that
     *                               was not borrowed from it or if an object is
     *                               returned to the pool multiple times
     */
    @Override
    public void returnObject(final K key, final T obj) {

        final ObjectDeque<T> objectDeque = poolMap.get(key);

        final PooledObject<T> p = objectDeque.getAllObjects().get(new IdentityWrapper<>(obj));

        if (p == null) {
            throw new IllegalStateException(
                    "Returned object not currently part of this pool");
        }

        markReturningState(p);

        final long activeTime = p.getActiveTimeMillis();

        try {
            if (getTestOnReturn() && !factory.validateObject(key, p)) {
                try {
                    destroy(key, p, true);
                } catch (final Exception e) {
                    swallowException(e);
                }
                whenWaitersAddObject(key, objectDeque.idleObjects);
                return;
            }

            try {
                factory.passivateObject(key, p);
            } catch (final Exception e1) {
                swallowException(e1);
                try {
                    destroy(key, p, true);
                } catch (final Exception e) {
                    swallowException(e);
                }
                whenWaitersAddObject(key, objectDeque.idleObjects);
                return;
            }

            if (!p.deallocate()) {
                throw new IllegalStateException(
                        "Object has already been returned to this pool");
            }

            final int maxIdle = getMaxIdlePerKey();
            final LinkedBlockingDeque<PooledObject<T>> idleObjects =
                    objectDeque.getIdleObjects();

            if (isClosed() || maxIdle > -1 && maxIdle <= idleObjects.size()) {
                try {
                    destroy(key, p, true);
                } catch (final Exception e) {
                    swallowException(e);
                }
            } else {
                if (getLifo()) {
                    idleObjects.addFirst(p);
                } else {
                    idleObjects.addLast(p);
                }
                if (isClosed()) {
                    // Pool closed while object was being added to idle objects.
                    // Make sure the returned object is destroyed rather than left
                    // in the idle object pool (which would effectively be a leak)
                    clear(key);
                }
            }
        } finally {
            if (hasBorrowWaiters()) {
                reuseCapacity();
            }
            updateStatsReturn(activeTime);
        }
    }

    
Whether there is at least one thread waiting on this deque, add an pool object.
Params:
key – pool key.
idleObjects – list of idle pool objects./**
     * Whether there is at least one thread waiting on this deque, add an pool object.
     * @param key pool key.
     * @param idleObjects list of idle pool objects.
     */
    private void whenWaitersAddObject(final K key, final LinkedBlockingDeque<PooledObject<T>> idleObjects) {
        if (idleObjects.hasTakeWaiters()) {
            try {
                addObject(key);
            } catch (final Exception e) {
                swallowException(e);
            }
        }
    }

    
{@inheritDoc}

Activation of this method decrements the active count associated with
the given keyed pool and attempts to destroy obj.
Params:
key – pool key
obj – instance to invalidate
Throws:
Exception –             if an exception occurs destroying the
                              object
IllegalStateException – if obj does not belong to the pool
                              under the given key/**
     * {@inheritDoc}
     * <p>
     * Activation of this method decrements the active count associated with
     * the given keyed pool and attempts to destroy <code>obj.</code>
     *
     * @param key pool key
     * @param obj instance to invalidate
     *
     * @throws Exception             if an exception occurs destroying the
     *                               object
     * @throws IllegalStateException if obj does not belong to the pool
     *                               under the given key
     */
    @Override
    public void invalidateObject(final K key, final T obj) throws Exception {

        final ObjectDeque<T> objectDeque = poolMap.get(key);

        final PooledObject<T> p = objectDeque.getAllObjects().get(new IdentityWrapper<>(obj));
        if (p == null) {
            throw new IllegalStateException(
                    "Object not currently part of this pool");
        }
        synchronized (p) {
            if (p.getState() != PooledObjectState.INVALID) {
                destroy(key, p, true);
            }
        }
        if (objectDeque.idleObjects.hasTakeWaiters()) {
            addObject(key);
        }
    }


    
Clears any objects sitting idle in the pool by removing them from the idle instance sub-pools and then invoking the configured PoolableObjectFactory's KeyedPooledObjectFactory.destroyObject(Object, PooledObject) method on each idle instance. 

Implementation notes:

This method does not destroy or effect in any way instances that are
checked out when it is invoked.
Invoking this method does not prevent objects being returned to the
idle instance pool, even during its execution. Additional instances may
be returned while removed items are being destroyed.
Exceptions encountered destroying idle instances are swallowed but notified via a SwallowedExceptionListener.

/**
     * Clears any objects sitting idle in the pool by removing them from the
     * idle instance sub-pools and then invoking the configured
     * PoolableObjectFactory's
     * {@link KeyedPooledObjectFactory#destroyObject(Object, PooledObject)}
     * method on each idle instance.
     * <p>
     * Implementation notes:
     * <ul>
     * <li>This method does not destroy or effect in any way instances that are
     * checked out when it is invoked.</li>
     * <li>Invoking this method does not prevent objects being returned to the
     * idle instance pool, even during its execution. Additional instances may
     * be returned while removed items are being destroyed.</li>
     * <li>Exceptions encountered destroying idle instances are swallowed
     * but notified via a {@link SwallowedExceptionListener}.</li>
     * </ul>
     */
    @Override
    public void clear() {
        final Iterator<K> iter = poolMap.keySet().iterator();

        while (iter.hasNext()) {
            clear(iter.next());
        }
    }


    
Clears the specified sub-pool, removing all pooled instances
corresponding to the given key. Exceptions encountered destroying idle instances are swallowed but notified via a SwallowedExceptionListener. 
Params:
key – the key to clear/**
     * Clears the specified sub-pool, removing all pooled instances
     * corresponding to the given <code>key</code>. Exceptions encountered
     * destroying idle instances are swallowed but notified via a
     * {@link SwallowedExceptionListener}.
     *
     * @param key the key to clear
     */
    @Override
    public void clear(final K key) {

        final ObjectDeque<T> objectDeque = register(key);

        try {
            final LinkedBlockingDeque<PooledObject<T>> idleObjects =
                    objectDeque.getIdleObjects();

            PooledObject<T> p = idleObjects.poll();

            while (p != null) {
                try {
                    destroy(key, p, true);
                } catch (final Exception e) {
                    swallowException(e);
                }
                p = idleObjects.poll();
            }
        } finally {
            deregister(key);
        }
    }


    @Override
    public int getNumActive() {
        return numTotal.get() - getNumIdle();
    }


    @Override
    public int getNumIdle() {
        final Iterator<ObjectDeque<T>> iter = poolMap.values().iterator();
        int result = 0;

        while (iter.hasNext()) {
            result += iter.next().getIdleObjects().size();
        }

        return result;
    }


    @Override
    public int getNumActive(final K key) {
        final ObjectDeque<T> objectDeque = poolMap.get(key);
        if (objectDeque != null) {
            return objectDeque.getAllObjects().size() -
                    objectDeque.getIdleObjects().size();
        }
        return 0;
    }


    @Override
    public int getNumIdle(final K key) {
        final ObjectDeque<T> objectDeque = poolMap.get(key);
        return objectDeque != null ? objectDeque.getIdleObjects().size() : 0;
    }


    
Closes the keyed object pool. Once the pool is closed, borrowObject(Object) will fail with IllegalStateException, but returnObject(Object, Object) and invalidateObject(Object, Object) will continue to work, with returned objects destroyed on return. 
 Destroys idle instances in the pool by invoking clear(). /**
     * Closes the keyed object pool. Once the pool is closed,
     * {@link #borrowObject(Object)} will fail with IllegalStateException, but
     * {@link #returnObject(Object, Object)} and
     * {@link #invalidateObject(Object, Object)} will continue to work, with
     * returned objects destroyed on return.
     * <p>
     * Destroys idle instances in the pool by invoking {@link #clear()}.
     */
    @Override
    public void close() {
        if (isClosed()) {
            return;
        }

        synchronized (closeLock) {
            if (isClosed()) {
                return;
            }

            // Stop the evictor before the pool is closed since evict() calls
            // assertOpen()
            stopEvictor();

            closed = true;
            // This clear removes any idle objects
            clear();

            jmxUnregister();

            // Release any threads that were waiting for an object
            final Iterator<ObjectDeque<T>> iter = poolMap.values().iterator();
            while (iter.hasNext()) {
                iter.next().getIdleObjects().interuptTakeWaiters();
            }
            // This clear cleans up the keys now any waiting threads have been
            // interrupted
            clear();
        }
    }


    
Clears oldest 15% of objects in pool.  The method sorts the objects into
a TreeMap and then iterates the first 15% for removal.
/**
     * Clears oldest 15% of objects in pool.  The method sorts the objects into
     * a TreeMap and then iterates the first 15% for removal.
     */
    public void clearOldest() {

        // build sorted map of idle objects
        final Map<PooledObject<T>, K> map = new TreeMap<>();

        for (final Map.Entry<K, ObjectDeque<T>> entry : poolMap.entrySet()) {
            final K k = entry.getKey();
            final ObjectDeque<T> deque = entry.getValue();
            // Protect against possible NPE if key has been removed in another
            // thread. Not worth locking the keys while this loop completes.
            if (deque != null) {
                final LinkedBlockingDeque<PooledObject<T>> idleObjects =
                        deque.getIdleObjects();
                for (final PooledObject<T> p : idleObjects) {
                    // each item into the map using the PooledObject object as the
                    // key. It then gets sorted based on the idle time
                    map.put(p, k);
                }
            }
        }

        // Now iterate created map and kill the first 15% plus one to account
        // for zero
        int itemsToRemove = ((int) (map.size() * 0.15)) + 1;
        final Iterator<Map.Entry<PooledObject<T>, K>> iter =
                map.entrySet().iterator();

        while (iter.hasNext() && itemsToRemove > 0) {
            final Map.Entry<PooledObject<T>, K> entry = iter.next();
            // kind of backwards on naming.  In the map, each key is the
            // PooledObject because it has the ordering with the timestamp
            // value.  Each value that the key references is the key of the
            // list it belongs to.
            final K key = entry.getValue();
            final PooledObject<T> p = entry.getKey();
            // Assume the destruction succeeds
            boolean destroyed = true;
            try {
                destroyed = destroy(key, p, false);
            } catch (final Exception e) {
                swallowException(e);
            }
            if (destroyed) {
                itemsToRemove--;
            }
        }
    }

    
Attempt to create one new instance to serve from the most heavily
loaded pool that can add a new instance.
This method exists to ensure liveness in the pool when threads are
parked waiting and capacity to create instances under the requested keys
subsequently becomes available.
This method is not guaranteed to create an instance and its selection
of the most loaded pool that can create an instance may not always be
correct, since it does not lock the pool and instances may be created,
borrowed, returned or destroyed by other threads while it is executing.
/**
     * Attempt to create one new instance to serve from the most heavily
     * loaded pool that can add a new instance.
     *
     * This method exists to ensure liveness in the pool when threads are
     * parked waiting and capacity to create instances under the requested keys
     * subsequently becomes available.
     *
     * This method is not guaranteed to create an instance and its selection
     * of the most loaded pool that can create an instance may not always be
     * correct, since it does not lock the pool and instances may be created,
     * borrowed, returned or destroyed by other threads while it is executing.
     */
    private void reuseCapacity() {
        final int maxTotalPerKeySave = getMaxTotalPerKey();

        // Find the most loaded pool that could take a new instance
        int maxQueueLength = 0;
        LinkedBlockingDeque<PooledObject<T>> mostLoaded = null;
        K loadedKey = null;
        for (final Map.Entry<K, ObjectDeque<T>> entry : poolMap.entrySet()) {
            final K k = entry.getKey();
            final ObjectDeque<T> deque = entry.getValue();
            if (deque != null) {
                final LinkedBlockingDeque<PooledObject<T>> pool = deque.getIdleObjects();
                final int queueLength = pool.getTakeQueueLength();
                if (getNumActive(k) < maxTotalPerKeySave && queueLength > maxQueueLength) {
                    maxQueueLength = queueLength;
                    mostLoaded = pool;
                    loadedKey = k;
                }
            }
        }

        // Attempt to add an instance to the most loaded pool
        if (mostLoaded != null) {
            register(loadedKey);
            try {
                final PooledObject<T> p = create(loadedKey);
                if (p != null) {
                    addIdleObject(loadedKey, p);
                }
            } catch (final Exception e) {
                swallowException(e);
            } finally {
                deregister(loadedKey);
            }
        }
    }

    
Checks to see if there are any threads currently waiting to borrow
objects but are blocked waiting for more objects to become available.
Returns:
true if there is at least one thread waiting otherwise false/**
     * Checks to see if there are any threads currently waiting to borrow
     * objects but are blocked waiting for more objects to become available.
     *
     * @return {@code true} if there is at least one thread waiting otherwise
     *         {@code false}
     */
    private boolean hasBorrowWaiters() {
        for (final Map.Entry<K, ObjectDeque<T>> entry : poolMap.entrySet()) {
            final ObjectDeque<T> deque = entry.getValue();
            if (deque != null) {
                final LinkedBlockingDeque<PooledObject<T>> pool =
                        deque.getIdleObjects();
                if(pool.hasTakeWaiters()) {
                    return true;
                }
            }
        }
        return false;
    }


    
{@inheritDoc}

Successive activations of this method examine objects in keyed sub-pools
in sequence, cycling through the keys and examining objects in
oldest-to-youngest order within the keyed sub-pools.
/**
     * {@inheritDoc}
     * <p>
     * Successive activations of this method examine objects in keyed sub-pools
     * in sequence, cycling through the keys and examining objects in
     * oldest-to-youngest order within the keyed sub-pools.
     */
    @Override
    public void evict() throws Exception {
        assertOpen();

        if (getNumIdle() == 0) {
            return;
        }

        PooledObject<T> underTest = null;
        final EvictionPolicy<T> evictionPolicy = getEvictionPolicy();

        synchronized (evictionLock) {
            final EvictionConfig evictionConfig = new EvictionConfig(
                    getMinEvictableIdleTimeMillis(),
                    getSoftMinEvictableIdleTimeMillis(),
                    getMinIdlePerKey());

            final boolean testWhileIdle = getTestWhileIdle();

            for (int i = 0, m = getNumTests(); i < m; i++) {
                if(evictionIterator == null || !evictionIterator.hasNext()) {
                    if (evictionKeyIterator == null ||
                            !evictionKeyIterator.hasNext()) {
                        final List<K> keyCopy = new ArrayList<>();
                        final Lock readLock = keyLock.readLock();
                        readLock.lock();
                        try {
                            keyCopy.addAll(poolKeyList);
                        } finally {
                            readLock.unlock();
                        }
                        evictionKeyIterator = keyCopy.iterator();
                    }
                    while (evictionKeyIterator.hasNext()) {
                        evictionKey = evictionKeyIterator.next();
                        final ObjectDeque<T> objectDeque = poolMap.get(evictionKey);
                        if (objectDeque == null) {
                            continue;
                        }

                        final Deque<PooledObject<T>> idleObjects = objectDeque.getIdleObjects();
                        evictionIterator = new EvictionIterator(idleObjects);
                        if (evictionIterator.hasNext()) {
                            break;
                        }
                        evictionIterator = null;
                    }
                }
                if (evictionIterator == null) {
                    // Pools exhausted
                    return;
                }
                final Deque<PooledObject<T>> idleObjects;
                try {
                    underTest = evictionIterator.next();
                    idleObjects = evictionIterator.getIdleObjects();
                } catch (final NoSuchElementException nsee) {
                    // Object was borrowed in another thread
                    // Don't count this as an eviction test so reduce i;
                    i--;
                    evictionIterator = null;
                    continue;
                }

                if (!underTest.startEvictionTest()) {
                    // Object was borrowed in another thread
                    // Don't count this as an eviction test so reduce i;
                    i--;
                    continue;
                }

                // User provided eviction policy could throw all sorts of
                // crazy exceptions. Protect against such an exception
                // killing the eviction thread.
                boolean evict;
                try {
                    evict = evictionPolicy.evict(evictionConfig, underTest,
                            poolMap.get(evictionKey).getIdleObjects().size());
                } catch (final Throwable t) {
                    // Slightly convoluted as SwallowedExceptionListener
                    // uses Exception rather than Throwable
                    PoolUtils.checkRethrow(t);
                    swallowException(new Exception(t));
                    // Don't evict on error conditions
                    evict = false;
                }

                if (evict) {
                    destroy(evictionKey, underTest, true);
                    destroyedByEvictorCount.incrementAndGet();
                } else {
                    if (testWhileIdle) {
                        boolean active = false;
                        try {
                            factory.activateObject(evictionKey, underTest);
                            active = true;
                        } catch (final Exception e) {
                            destroy(evictionKey, underTest, true);
                            destroyedByEvictorCount.incrementAndGet();
                        }
                        if (active) {
                            if (!factory.validateObject(evictionKey, underTest)) {
                                destroy(evictionKey, underTest, true);
                                destroyedByEvictorCount.incrementAndGet();
                            } else {
                                try {
                                    factory.passivateObject(evictionKey, underTest);
                                } catch (final Exception e) {
                                    destroy(evictionKey, underTest, true);
                                    destroyedByEvictorCount.incrementAndGet();
                                }
                            }
                        }
                    }
                    if (!underTest.endEvictionTest(idleObjects)) {
                        // TODO - May need to add code here once additional
                        // states are used
                    }
                }
            }
        }
    }

    
Create a new pooled object.
Params:
key – Key associated with new pooled object
Throws:
Exception – If the objection creation fails
Returns:
The new, wrapped pooled object/**
     * Create a new pooled object.
     *
     * @param key Key associated with new pooled object
     *
     * @return The new, wrapped pooled object
     *
     * @throws Exception If the objection creation fails
     */
    private PooledObject<T> create(final K key) throws Exception {
        int maxTotalPerKeySave = getMaxTotalPerKey(); // Per key
        if (maxTotalPerKeySave < 0) {
            maxTotalPerKeySave = Integer.MAX_VALUE;
        }
        final int maxTotal = getMaxTotal();   // All keys

        final ObjectDeque<T> objectDeque = poolMap.get(key);

        // Check against the overall limit
        boolean loop = true;

        while (loop) {
            final int newNumTotal = numTotal.incrementAndGet();
            if (maxTotal > -1 && newNumTotal > maxTotal) {
                numTotal.decrementAndGet();
                if (getNumIdle() == 0) {
                    return null;
                }
                clearOldest();
            } else {
                loop = false;
            }
        }

        // Flag that indicates if create should:
        // - TRUE:  call the factory to create an object
        // - FALSE: return null
        // - null:  loop and re-test the condition that determines whether to
        //          call the factory
        Boolean create = null;
        while (create == null) {
            synchronized (objectDeque.makeObjectCountLock) {
                final long newCreateCount = objectDeque.getCreateCount().incrementAndGet();
                // Check against the per key limit
                if (newCreateCount > maxTotalPerKeySave) {
                    // The key is currently at capacity or in the process of
                    // making enough new objects to take it to capacity.
                    objectDeque.getCreateCount().decrementAndGet();
                    if (objectDeque.makeObjectCount == 0) {
                        // There are no makeObject() calls in progress for this
                        // key so the key is at capacity. Do not attempt to
                        // create a new object. Return and wait for an object to
                        // be returned.
                        create = Boolean.FALSE;
                    } else {
                        // There are makeObject() calls in progress that might
                        // bring the pool to capacity. Those calls might also
                        // fail so wait until they complete and then re-test if
                        // the pool is at capacity or not.
                        objectDeque.makeObjectCountLock.wait();
                    }
                } else {
                    // The pool is not at capacity. Create a new object.
                    objectDeque.makeObjectCount++;
                    create = Boolean.TRUE;
                }
            }
        }

        if (!create.booleanValue()) {
            numTotal.decrementAndGet();
            return null;
        }

        PooledObject<T> p = null;
        try {
            p = factory.makeObject(key);
            if (getTestOnCreate() && !factory.validateObject(key, p)) {
                numTotal.decrementAndGet();
                objectDeque.getCreateCount().decrementAndGet();
                return null;
            }
        } catch (final Exception e) {
            numTotal.decrementAndGet();
            objectDeque.getCreateCount().decrementAndGet();
            throw e;
        } finally {
            synchronized (objectDeque.makeObjectCountLock) {
                objectDeque.makeObjectCount--;
                objectDeque.makeObjectCountLock.notifyAll();
            }
        }

        createdCount.incrementAndGet();
        objectDeque.getAllObjects().put(new IdentityWrapper<>(p.getObject()), p);
        return p;
    }

    
Destroy the wrapped, pooled object.
Params:
key – The key associated with the object to destroy.
toDestroy – The wrapped object to be destroyed
always – Should the object be destroyed even if it is not currently
              in the set of idle objects for the given key
Throws:
Exception – If the object destruction failed
Returns:
true if the object was destroyed, otherwise false/**
     * Destroy the wrapped, pooled object.
     *
     * @param key The key associated with the object to destroy.
     * @param toDestroy The wrapped object to be destroyed
     * @param always Should the object be destroyed even if it is not currently
     *               in the set of idle objects for the given key
     * @return {@code true} if the object was destroyed, otherwise {@code false}
     * @throws Exception If the object destruction failed
     */
    private boolean destroy(final K key, final PooledObject<T> toDestroy, final boolean always)
            throws Exception {

        final ObjectDeque<T> objectDeque = register(key);

        try {
            final boolean isIdle = objectDeque.getIdleObjects().remove(toDestroy);

            if (isIdle || always) {
                objectDeque.getAllObjects().remove(new IdentityWrapper<>(toDestroy.getObject()));
                toDestroy.invalidate();

                try {
                    factory.destroyObject(key, toDestroy);
                } finally {
                    objectDeque.getCreateCount().decrementAndGet();
                    destroyedCount.incrementAndGet();
                    numTotal.decrementAndGet();
                }
                return true;
            }
            return false;
        } finally {
            deregister(key);
        }
    }


    
Register the use of a key by an object.

register() and deregister() must always be used as a pair.
Params:
k – The key to register
Returns:
The objects currently associated with the given key. If this
        method returns without throwing an exception then it will never
        return null./**
     * Register the use of a key by an object.
     * <p>
     * register() and deregister() must always be used as a pair.
     *
     * @param k The key to register
     *
     * @return The objects currently associated with the given key. If this
     *         method returns without throwing an exception then it will never
     *         return null.
     */
    private ObjectDeque<T> register(final K k) {
        Lock lock = keyLock.readLock();
        ObjectDeque<T> objectDeque = null;
        try {
            lock.lock();
            objectDeque = poolMap.get(k);
            if (objectDeque == null) {
                // Upgrade to write lock
                lock.unlock();
                lock = keyLock.writeLock();
                lock.lock();
                objectDeque = poolMap.get(k);
                if (objectDeque == null) {
                    objectDeque = new ObjectDeque<>(fairness);
                    objectDeque.getNumInterested().incrementAndGet();
                    // NOTE: Keys must always be added to both poolMap and
                    //       poolKeyList at the same time while protected by
                    //       keyLock.writeLock()
                    poolMap.put(k, objectDeque);
                    poolKeyList.add(k);
                } else {
                    objectDeque.getNumInterested().incrementAndGet();
                }
            } else {
                objectDeque.getNumInterested().incrementAndGet();
            }
        } finally {
            lock.unlock();
        }
        return objectDeque;
    }

    
De-register the use of a key by an object.

register() and deregister() must always be used as a pair.
Params:
k – The key to de-register/**
     * De-register the use of a key by an object.
     * <p>
     * register() and deregister() must always be used as a pair.
     *
     * @param k The key to de-register
     */
    private void deregister(final K k) {
        Lock lock = keyLock.readLock();
        ObjectDeque<T> objectDeque;
        try {
            lock.lock();
            objectDeque = poolMap.get(k);
            final long numInterested = objectDeque.getNumInterested().decrementAndGet();
            if (numInterested == 0 && objectDeque.getCreateCount().get() == 0) {
                // Potential to remove key
                // Upgrade to write lock
                lock.unlock();
                lock = keyLock.writeLock();
                lock.lock();
                if (objectDeque.getCreateCount().get() == 0 && objectDeque.getNumInterested().get() == 0) {
                    // NOTE: Keys must always be removed from both poolMap and
                    //       poolKeyList at the same time while protected by
                    //       keyLock.writeLock()
                    poolMap.remove(k);
                    poolKeyList.remove(k);
                }
            }
        } finally {
            lock.unlock();
        }
    }

    @Override
    void ensureMinIdle() throws Exception {
        final int minIdlePerKeySave = getMinIdlePerKey();
        if (minIdlePerKeySave < 1) {
            return;
        }

        for (final K k : poolMap.keySet()) {
            ensureMinIdle(k);
        }
    }

    
Ensure that the configured number of minimum idle objects is available in
the pool for the given key.
Params:
key – The key to check for idle objects
Throws:
Exception – If a new object is required and cannot be created/**
     * Ensure that the configured number of minimum idle objects is available in
     * the pool for the given key.
     *
     * @param key The key to check for idle objects
     *
     * @throws Exception If a new object is required and cannot be created
     */
    private void ensureMinIdle(final K key) throws Exception {
        // Calculate current pool objects
        ObjectDeque<T> objectDeque = poolMap.get(key);

        // objectDeque == null is OK here. It is handled correctly by both
        // methods called below.

        // this method isn't synchronized so the
        // calculateDeficit is done at the beginning
        // as a loop limit and a second time inside the loop
        // to stop when another thread already returned the
        // needed objects
        final int deficit = calculateDeficit(objectDeque);

        for (int i = 0; i < deficit && calculateDeficit(objectDeque) > 0; i++) {
            addObject(key);
            // If objectDeque was null, it won't be any more. Obtain a reference
            // to it so the deficit can be correctly calculated. It needs to
            // take account of objects created in other threads.
            if (objectDeque == null) {
                objectDeque = poolMap.get(key);
            }
        }
    }

    
Create an object using the 
factory, passivate it, and then place it in the idle object pool. addObject is useful for "pre-loading" a pool with idle
objects.
Params:
key – the key a new instance should be added to
Throws:
Exception – when KeyedPooledObjectFactory.makeObject fails./**
     * Create an object using the {@link KeyedPooledObjectFactory#makeObject
     * factory}, passivate it, and then place it in the idle object pool.
     * <code>addObject</code> is useful for "pre-loading" a pool with idle
     * objects.
     *
     * @param key the key a new instance should be added to
     *
     * @throws Exception when {@link KeyedPooledObjectFactory#makeObject}
     *                   fails.
     */
    @Override
    public void addObject(final K key) throws Exception {
        assertOpen();
        register(key);
        try {
            final PooledObject<T> p = create(key);
            addIdleObject(key, p);
        } finally {
            deregister(key);
        }
    }

    
Add an object to the set of idle objects for a given key.
Params:
key – The key to associate with the idle object
p – The wrapped object to add.
Throws:
Exception – If the associated factory fails to passivate the object/**
     * Add an object to the set of idle objects for a given key.
     *
     * @param key The key to associate with the idle object
     * @param p The wrapped object to add.
     *
     * @throws Exception If the associated factory fails to passivate the object
     */
    private void addIdleObject(final K key, final PooledObject<T> p) throws Exception {

        if (p != null) {
            factory.passivateObject(key, p);
            final LinkedBlockingDeque<PooledObject<T>> idleObjects =
                    poolMap.get(key).getIdleObjects();
            if (getLifo()) {
                idleObjects.addFirst(p);
            } else {
                idleObjects.addLast(p);
            }
        }
    }

    
Registers a key for pool control and ensures that getMinIdlePerKey() idle instances are created. 
Params:
key – - The key to register for pool control.
Throws:
Exception – If the associated factory throws an exception/**
     * Registers a key for pool control and ensures that
     * {@link #getMinIdlePerKey()} idle instances are created.
     *
     * @param key - The key to register for pool control.
     *
     * @throws Exception If the associated factory throws an exception
     */
    public void preparePool(final K key) throws Exception {
        final int minIdlePerKeySave = getMinIdlePerKey();
        if (minIdlePerKeySave < 1) {
            return;
        }
        ensureMinIdle(key);
    }

    
Calculate the number of objects to test in a run of the idle object
evictor.
Returns:
The number of objects to test for validity/**
     * Calculate the number of objects to test in a run of the idle object
     * evictor.
     *
     * @return The number of objects to test for validity
     */
    private int getNumTests() {
        final int totalIdle = getNumIdle();
        final int numTests = getNumTestsPerEvictionRun();
        if (numTests >= 0) {
            return Math.min(numTests, totalIdle);
        }
        return(int)(Math.ceil(totalIdle/Math.abs((double)numTests)));
    }

    
Calculate the number of objects that need to be created to attempt to
maintain the minimum number of idle objects while not exceeded the limits
on the maximum number of objects either per key or totally.
Params:
objectDeque –   The set of objects to check
Returns:
The number of new objects to create/**
     * Calculate the number of objects that need to be created to attempt to
     * maintain the minimum number of idle objects while not exceeded the limits
     * on the maximum number of objects either per key or totally.
     *
     * @param objectDeque   The set of objects to check
     *
     * @return The number of new objects to create
     */
    private int calculateDeficit(final ObjectDeque<T> objectDeque) {

        if (objectDeque == null) {
            return getMinIdlePerKey();
        }

        // Used more than once so keep a local copy so the value is consistent
        final int maxTotal = getMaxTotal();
        final int maxTotalPerKeySave = getMaxTotalPerKey();

        int objectDefecit = 0;

        // Calculate no of objects needed to be created, in order to have
        // the number of pooled objects < maxTotalPerKey();
        objectDefecit = getMinIdlePerKey() - objectDeque.getIdleObjects().size();
        if (maxTotalPerKeySave > 0) {
            final int growLimit = Math.max(0,
                    maxTotalPerKeySave - objectDeque.getIdleObjects().size());
            objectDefecit = Math.min(objectDefecit, growLimit);
        }

        // Take the maxTotal limit into account
        if (maxTotal > 0) {
            final int growLimit = Math.max(0, maxTotal - getNumActive() - getNumIdle());
            objectDefecit = Math.min(objectDefecit, growLimit);
        }

        return objectDefecit;
    }


    //--- JMX support ----------------------------------------------------------

    @Override
    public Map<String,Integer> getNumActivePerKey() {
        final HashMap<String,Integer> result = new HashMap<>();

        final Iterator<Entry<K,ObjectDeque<T>>> iter = poolMap.entrySet().iterator();
        while (iter.hasNext()) {
            final Entry<K,ObjectDeque<T>> entry = iter.next();
            if (entry != null) {
                final K key = entry.getKey();
                final ObjectDeque<T> objectDequeue = entry.getValue();
                if (key != null && objectDequeue != null) {
                    result.put(key.toString(), Integer.valueOf(
                            objectDequeue.getAllObjects().size() -
                            objectDequeue.getIdleObjects().size()));
                }
            }
        }
        return result;
    }

    
Return an estimate of the number of threads currently blocked waiting for
an object from the pool. This is intended for monitoring only, not for
synchronization control.
Returns:
The estimate of the number of threads currently blocked waiting
        for an object from the pool/**
     * Return an estimate of the number of threads currently blocked waiting for
     * an object from the pool. This is intended for monitoring only, not for
     * synchronization control.
     *
     * @return The estimate of the number of threads currently blocked waiting
     *         for an object from the pool
     */
    @Override
    public int getNumWaiters() {
        int result = 0;

        if (getBlockWhenExhausted()) {
            final Iterator<ObjectDeque<T>> iter = poolMap.values().iterator();

            while (iter.hasNext()) {
                // Assume no overflow
                result += iter.next().getIdleObjects().getTakeQueueLength();
            }
        }

        return result;
    }

    
Return an estimate of the number of threads currently blocked waiting for
an object from the pool for each key. This is intended for
monitoring only, not for synchronization control.
Returns:
The estimate of the number of threads currently blocked waiting
        for an object from the pool for each key/**
     * Return an estimate of the number of threads currently blocked waiting for
     * an object from the pool for each key. This is intended for
     * monitoring only, not for synchronization control.
     *
     * @return The estimate of the number of threads currently blocked waiting
     *         for an object from the pool for each key
     */
    @Override
    public Map<String,Integer> getNumWaitersByKey() {
        final Map<String,Integer> result = new HashMap<>();

        for (final Map.Entry<K, ObjectDeque<T>> entry : poolMap.entrySet()) {
            final K k = entry.getKey();
            final ObjectDeque<T> deque = entry.getValue();
            if (deque != null) {
                if (getBlockWhenExhausted()) {
                    result.put(k.toString(), Integer.valueOf(
                            deque.getIdleObjects().getTakeQueueLength()));
                } else {
                    result.put(k.toString(), Integer.valueOf(0));
                }
            }
        }
        return result;
    }

    
Provides information on all the objects in the pool, both idle (waiting
to be borrowed) and active (currently borrowed).

Note: This is named listAllObjects so it is presented as an operation via
JMX. That means it won't be invoked unless the explicitly requested
whereas all attributes will be automatically requested when viewing the
attributes for an object in a tool like JConsole.
Returns:
Information grouped by key on all the objects in the pool/**
     * Provides information on all the objects in the pool, both idle (waiting
     * to be borrowed) and active (currently borrowed).
     * <p>
     * Note: This is named listAllObjects so it is presented as an operation via
     * JMX. That means it won't be invoked unless the explicitly requested
     * whereas all attributes will be automatically requested when viewing the
     * attributes for an object in a tool like JConsole.
     *
     * @return Information grouped by key on all the objects in the pool
     */
    @Override
    public Map<String,List<DefaultPooledObjectInfo>> listAllObjects() {
        final Map<String,List<DefaultPooledObjectInfo>> result =
                new HashMap<>();

        for (final Map.Entry<K, ObjectDeque<T>> entry : poolMap.entrySet()) {
            final K k = entry.getKey();
            final ObjectDeque<T> deque = entry.getValue();
            if (deque != null) {
                final List<DefaultPooledObjectInfo> list =
                        new ArrayList<>();
                result.put(k.toString(), list);
                for (final PooledObject<T> p : deque.getAllObjects().values()) {
                    list.add(new DefaultPooledObjectInfo(p));
                }
            }
        }
        return result;
    }


    //--- inner classes ----------------------------------------------

    
Maintains information on the per key queue for a given key.
Type parameters:
<S> – type of objects in the pool/**
     * Maintains information on the per key queue for a given key.
     *
     * @param <S> type of objects in the pool
     */
    private class ObjectDeque<S> {

        private final LinkedBlockingDeque<PooledObject<S>> idleObjects;

        /*
         * Number of instances created - number destroyed.
         * Invariant: createCount <= maxTotalPerKey
         */
        private final AtomicInteger createCount = new AtomicInteger(0);

        private long makeObjectCount = 0;
        private final Object makeObjectCountLock = new Object();

        /*
         * The map is keyed on pooled instances, wrapped to ensure that
         * they work properly as keys.
         */
        private final Map<IdentityWrapper<S>, PooledObject<S>> allObjects =
                new ConcurrentHashMap<>();

        /*
         * Number of threads with registered interest in this key.
         * register(K) increments this counter and deRegister(K) decrements it.
         * Invariant: empty keyed pool will not be dropped unless numInterested
         *            is 0.
         */
        private final AtomicLong numInterested = new AtomicLong(0);

        
Create a new ObjecDeque with the given fairness policy.
Params:
fairness – true means client threads waiting to borrow / return instances
will be served as if waiting in a FIFO queue./**
         * Create a new ObjecDeque with the given fairness policy.
         * @param fairness true means client threads waiting to borrow / return instances
         * will be served as if waiting in a FIFO queue.
         */
        public ObjectDeque(final boolean fairness) {
            idleObjects = new LinkedBlockingDeque<>(fairness);
        }

        
Obtain the idle objects for the current key.
Returns:
The idle objects/**
         * Obtain the idle objects for the current key.
         *
         * @return The idle objects
         */
        public LinkedBlockingDeque<PooledObject<S>> getIdleObjects() {
            return idleObjects;
        }

        
Obtain the count of the number of objects created for the current
key.
Returns:
The number of objects created for this key/**
         * Obtain the count of the number of objects created for the current
         * key.
         *
         * @return The number of objects created for this key
         */
        public AtomicInteger getCreateCount() {
            return createCount;
        }

        
Obtain the number of threads with an interest registered in this key.
Returns:
The number of threads with a registered interest in this key/**
         * Obtain the number of threads with an interest registered in this key.
         *
         * @return The number of threads with a registered interest in this key
         */
        public AtomicLong getNumInterested() {
            return numInterested;
        }

        
Obtain all the objects for the current key.
Returns:
All the objects/**
         * Obtain all the objects for the current key.
         *
         * @return All the objects
         */
        public Map<IdentityWrapper<S>, PooledObject<S>> getAllObjects() {
            return allObjects;
        }

        @Override
        public String toString() {
            final StringBuilder builder = new StringBuilder();
            builder.append("ObjectDeque [idleObjects=");
            builder.append(idleObjects);
            builder.append(", createCount=");
            builder.append(createCount);
            builder.append(", allObjects=");
            builder.append(allObjects);
            builder.append(", numInterested=");
            builder.append(numInterested);
            builder.append("]");
            return builder.toString();
        }

    }

    //--- configuration attributes ---------------------------------------------
    private volatile int maxIdlePerKey =
            GenericKeyedObjectPoolConfig.DEFAULT_MAX_IDLE_PER_KEY;
    private volatile int minIdlePerKey =
            GenericKeyedObjectPoolConfig.DEFAULT_MIN_IDLE_PER_KEY;
    private volatile int maxTotalPerKey =
            GenericKeyedObjectPoolConfig.DEFAULT_MAX_TOTAL_PER_KEY;
    private final KeyedPooledObjectFactory<K,T> factory;
    private final boolean fairness;


    //--- internal attributes --------------------------------------------------

    /*
     * My hash of sub-pools (ObjectQueue). The list of keys <b>must</b> be kept
     * in step with {@link #poolKeyList} using {@link #keyLock} to ensure any
     * changes to the list of current keys is made in a thread-safe manner.
     */
    private final Map<K,ObjectDeque<T>> poolMap =
            new ConcurrentHashMap<>(); // @GuardedBy("keyLock") for write access (and some read access)
    /*
     * List of pool keys - used to control eviction order. The list of keys
     * <b>must</b> be kept in step with {@link #poolMap} using {@link #keyLock}
     * to ensure any changes to the list of current keys is made in a
     * thread-safe manner.
     */
    private final List<K> poolKeyList = new ArrayList<>(); // @GuardedBy("keyLock")
    private final ReadWriteLock keyLock = new ReentrantReadWriteLock(true);
    /*
     * The combined count of the currently active objects for all keys and those
     * in the process of being created. Under load, it may exceed
     * {@link #maxTotal} but there will never be more than {@link #maxTotal}
     * created at any one time.
     */
    private final AtomicInteger numTotal = new AtomicInteger(0);
    private Iterator<K> evictionKeyIterator = null; // @GuardedBy("evictionLock")
    private K evictionKey = null; // @GuardedBy("evictionLock")

    // JMX specific attributes
    private static final String ONAME_BASE =
            "org.apache.commons.pool2:type=GenericKeyedObjectPool,name=";

    @Override
    protected void toStringAppendFields(final StringBuilder builder) {
        super.toStringAppendFields(builder);
        builder.append(", maxIdlePerKey=");
        builder.append(maxIdlePerKey);
        builder.append(", minIdlePerKey=");
        builder.append(minIdlePerKey);
        builder.append(", maxTotalPerKey=");
        builder.append(maxTotalPerKey);
        builder.append(", factory=");
        builder.append(factory);
        builder.append(", fairness=");
        builder.append(fairness);
        builder.append(", poolMap=");
        builder.append(poolMap);
        builder.append(", poolKeyList=");
        builder.append(poolKeyList);
        builder.append(", keyLock=");
        builder.append(keyLock);
        builder.append(", numTotal=");
        builder.append(numTotal);
        builder.append(", evictionKeyIterator=");
        builder.append(evictionKeyIterator);
        builder.append(", evictionKey=");
        builder.append(evictionKey);
    }
}