/*
    * 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.time.Duration;
  import java.time.Instant;
  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.Objects;
  import java.util.TreeMap;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.TimeUnit;
  import java.util.concurrent.atomic.AtomicBoolean;
  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 java.util.stream.Collectors;
  
  import org.apache.commons.pool2.DestroyMode;
  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;
  import org.apache.commons.pool2.UsageTracking;
  
  /**
   * A configurable {@code KeyedObjectPool} implementation.
   * <p>
   * When coupled with the appropriate {@link KeyedPooledObjectFactory},
   * {@code GenericKeyedObjectPool} provides robust pooling functionality for
   * keyed objects. A {@code GenericKeyedObjectPool} 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.}
   * </p>
   * <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>
   * <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>
   * <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>
   * <p>
   * This class is intended to be thread-safe.
   * </p>
   *
   * @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>, UsageTracking<T> {
  
      /**
       * Maintains information on the per key queue for a given key.
       *
       * @param <S> type of objects in the pool
       */
     private static 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;
         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();
 
         /**
          * Constructs a new ObjectDeque 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);
         }
 
         /**
          * Gets all the objects for the current key.
          *
          * @return All the objects
          */
         public Map<IdentityWrapper<S>, PooledObject<S>> getAllObjects() {
             return allObjects;
         }
 
         /**
          * Gets the number of instances created - number destroyed.
          * Should always be less than or equal to maxTotalPerKey.
          *
          * @return The net instance addition count for this deque
          */
         public AtomicInteger getCreateCount() {
             return createCount;
         }
 
         /**
          * Gets the idle objects for the current key.
          *
          * @return The idle objects
          */
         public LinkedBlockingDeque<PooledObject<S>> getIdleObjects() {
             return idleObjects;
         }
 
         /**
          * Gets 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;
         }
 
         @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();
         }
 
     }
 
     private static final Integer ZERO = Integer.valueOf(0);
 
     // JMX specific attributes
     private static final String ONAME_BASE =
             "org.apache.commons.pool2:type=GenericKeyedObjectPool,name=";
 
     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;
 
     /*
      * 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 ArrayList<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; // @GuardedBy("evictionLock")
 
 
     private K evictionKey; // @GuardedBy("evictionLock")
 
     /**
      * Constructs a new {@code GenericKeyedObjectPool} 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<>());
     }
 
     /**
      * Constructs a new {@code GenericKeyedObjectPool} 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);
     }
 
     /**
      * Creates a new {@code GenericKeyedObjectPool} that tracks and destroys
      * objects that are checked out, but never returned to the pool.
      *
      * @param factory   The object factory to be used to create object instances
      *                  used by this pool
      * @param config    The base pool 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.
      * @param abandonedConfig  Configuration for abandoned object identification
      *                         and removal.  The configuration is used by value.
      * @since 2.10.0
      */
     public GenericKeyedObjectPool(final KeyedPooledObjectFactory<K, T> factory,
             final GenericKeyedObjectPoolConfig<T> config, final AbandonedConfig abandonedConfig) {
         this(factory, config);
         setAbandonedConfig(abandonedConfig);
     }
 
     /**
      * Add an object to the set of idle objects for a given key.
      * If the object is null this is a no-op.
      *
      * @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 (!PooledObject.isNull(p)) {
             factory.passivateObject(key, p);
             final LinkedBlockingDeque<PooledObject<T>> idleObjects = poolMap.get(key).getIdleObjects();
             if (getLifo()) {
                 idleObjects.addFirst(p);
             } else {
                 idleObjects.addLast(p);
             }
         }
     }
 
     /**
      * Create an object using the {@link KeyedPooledObjectFactory#makeObject
      * factory}, passivate it, and then place it in the idle object pool.
      * {@code addObject} is useful for "pre-loading" a pool with idle
      * objects.
      * <p>
      * If there is no capacity available to add to the pool under the given key,
      * this is a no-op (no exception, no impact to the pool).
      * </p>
      * <p>
      * If the factory returns null when creating an instance,
      * a {@code NullPointerException} is thrown.
      * </p>
      *
      * @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 {
             addIdleObject(key, create(key));
         } finally {
             deregister(key);
         }
     }
 
     /**
      * Equivalent to <code>{@link #borrowObject(Object, long) borrowObject}(key,
      * {@link #getMaxWaitDuration()})</code>.
      *
      * {@inheritDoc}
      */
     @Override
     public T borrowObject(final K key) throws Exception {
         return borrowObject(key, getMaxWaitDuration().toMillis());
     }
 
     /**
      * 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} 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>
      * <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} parameter. If the number of instances checked
      * out from the sub-pool under the given key is less than
      * {@code maxTotalPerKey} and the total number of instances in
      * circulation (under all keys) is less than {@code maxTotal}, a new
      * instance is created, activated and (if applicable) validated and returned
      * to the caller. If validation fails, a {@code NoSuchElementException}
      * will be thrown. If the factory returns null when creating an instance,
      * a {@code NullPointerException} is thrown.
      * </p>
      * <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}
      * ({@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} parameter.
      * </p>
      * <p>
      * When {@code 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.
      * </p>
      * <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.
      * </p>
      *
      * @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();
 
         final AbandonedConfig ac = this.abandonedConfig;
         if (ac != null && ac.getRemoveAbandonedOnBorrow() && getNumIdle() < 2 &&
                 getNumActive() > getMaxTotal() - 3) {
             removeAbandoned(ac);
         }
 
         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 Instant waitTime = Instant.now();
         final ObjectDeque<T> objectDeque = register(key);
 
         try {
             while (p == null) {
                 create = false;
                 p = objectDeque.getIdleObjects().pollFirst();
                 if (p == null) {
                     p = create(key);
                     if (!PooledObject.isNull(p)) {
                         create = true;
                     }
                 }
                 if (blockWhenExhausted) {
                     if (PooledObject.isNull(p)) {
                         p = borrowMaxWaitMillis < 0 ? objectDeque.getIdleObjects().takeFirst():
                                 objectDeque.getIdleObjects().pollFirst(borrowMaxWaitMillis, TimeUnit.MILLISECONDS);
                     }
                     if (PooledObject.isNull(p)) {
                         throw new NoSuchElementException(appendStats(
                                 "Timeout waiting for idle object, borrowMaxWaitMillis=" + borrowMaxWaitMillis));
                     }
                 } else if (PooledObject.isNull(p)) {
                     throw new NoSuchElementException(appendStats("Pool exhausted"));
                 }
                 if (!p.allocate()) {
                     p = null;
                 }
 
                 if (!PooledObject.isNull(p)) {
                     try {
                         factory.activateObject(key, p);
                     } catch (final Exception e) {
                         try {
                             destroy(key, p, true, DestroyMode.NORMAL);
                         } catch (final Exception ignored) {
                             // ignored - activation failure is more important
                         }
                         p = null;
                         if (create) {
                             final NoSuchElementException nsee = new NoSuchElementException(appendStats("Unable to activate object"));
                             nsee.initCause(e);
                             throw nsee;
                         }
                     }
                     if (!PooledObject.isNull(p) && 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, DestroyMode.NORMAL);
                                 destroyedByBorrowValidationCount.incrementAndGet();
                             } catch (final Exception ignored) {
                                 // ignored - validation failure is more important
                             }
                             p = null;
                             if (create) {
                                 final NoSuchElementException nsee = new NoSuchElementException(
                                         appendStats("Unable to validate object"));
                                 nsee.initCause(validationThrowable);
                                 throw nsee;
                             }
                         }
                     }
                 }
             }
         } finally {
             deregister(key);
         }
 
         updateStatsBorrow(p, Duration.between(waitTime, Instant.now()));
 
         return p.getObject();
     }
 
     /**
      * 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();
 
         // Calculate no of objects needed to be created, in order to have
         // the number of pooled objects < maxTotalPerKey();
         int 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;
     }
 
     /**
      * 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() {
         poolMap.keySet().forEach(key -> clear(key, false));
     }
 
     /**
      * Clears the specified sub-pool, removing all pooled instances
      * corresponding to the given {@code key}. Exceptions encountered
      * destroying idle instances are swallowed but notified via a
      * {@link SwallowedExceptionListener}.
      * <p>
      * If there are clients waiting to borrow objects, this method will
      * attempt to reuse the capacity freed by this operation, adding
      * instances to the most loaded keyed pools.  To avoid triggering
      * possible object creation, use {@link #clear(Object, boolean)}.
      *
      * @param key the key to clear
      */
     @Override
     public void clear(final K key) {
         clear(key, true);
     }
 
     /**
      * Clears the specified sub-pool, removing all pooled instances
      * corresponding to the given {@code key}. Exceptions encountered
      * destroying idle instances are swallowed but notified via a
      * {@link SwallowedExceptionListener}.
      * <p>
      * If reuseCapacity is true and there are clients waiting to
      * borrow objects, this method will attempt to reuse the capacity freed
      * by this operation, adding instances to the most loaded keyed pools.
      * </p>
      *
      * @param key the key to clear
      * @param reuseCapacity whether or not to reuse freed capacity
      * @since 2.12.0
      */
     public void clear(final K key, final boolean reuseCapacity) {
         // Return immediately if there is no pool under this key.
         if (!poolMap.containsKey(key)) {
             return;
         }
         final ObjectDeque<T> objectDeque = register(key);
         int freedCapacity = 0;
         try {
             final LinkedBlockingDeque<PooledObject<T>> idleObjects = objectDeque.getIdleObjects();
             PooledObject<T> p = idleObjects.poll();
             while (p != null) {
                 try {
                     if (destroy(key, p, true, DestroyMode.NORMAL)) {
                         freedCapacity++;
                     }
                 } catch (final Exception e) {
                     swallowException(e);
                 }
                 p = idleObjects.poll();
             }
         } finally {
             deregister(key);
         }
         if (reuseCapacity) {
             reuseCapacity(freedCapacity);
         }
     }
 
     /**
      * 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 TreeMap<PooledObject<T>, K> map = new TreeMap<>();
 
         poolMap.forEach((key, value) -> {
             // Each item into the map using the PooledObject object as the
             // key. It then gets sorted based on the idle time
             value.getIdleObjects().forEach(p -> map.put(p, key));
         });
 
         // 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<Entry<PooledObject<T>, K>> iter = map.entrySet().iterator();
 
         while (iter.hasNext() && itemsToRemove > 0) {
             final 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, DestroyMode.NORMAL);
             } catch (final Exception e) {
                 swallowException(e);
             }
             if (destroyed) {
                 itemsToRemove--;
             }
         }
     }
 
 
     /**
      * 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()}.
      * </p>
      */
     @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
             poolMap.values().forEach(e -> e.getIdleObjects().interuptTakeWaiters());
             // This clear cleans up the keys now any waiting threads have been
             // interrupted
             clear();
         }
     }
 
 
     /**
      * Creates a new pooled object or null.
      *
      * @param key Key associated with new pooled object.
      *
      * @return The new, wrapped pooled object. May return null.
      *
      * @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 (PooledObject.isNull(p)) {
                 numTotal.decrementAndGet();
                 objectDeque.getCreateCount().decrementAndGet();
                 throw new NullPointerException(String.format("%s.makeObject() = null", factory.getClass().getSimpleName()));
             }
             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();
             }
         }
 
         final AbandonedConfig ac = this.abandonedConfig;
         if (ac != null && ac.getLogAbandoned()) {
             p.setLogAbandoned(true);
             p.setRequireFullStackTrace(ac.getRequireFullStackTrace());
         }
 
         createdCount.incrementAndGet();
         objectDeque.getAllObjects().put(new IdentityWrapper<>(p.getObject()), p);
         return p;
     }
 
     /**
      * De-register the use of a key by an object.
      * <p>
      * {@link #register(Object)} and {@link #deregister(Object)} must always be used as a pair.
      * </p>
      *
      * @param k The key to de-register
      */
     private void deregister(final K k) {
         Lock lock = keyLock.readLock();
         try {
             lock.lock();
             ObjectDeque<T> objectDeque = poolMap.get(k);
             if (objectDeque == null) {
                 throw new IllegalStateException("Attempt to de-register a key for a non-existent pool");
             }
             final long numInterested = objectDeque.getNumInterested().decrementAndGet();
             if (numInterested < 0) {
                 throw new IllegalStateException("numInterested count for key " + k + " is less than zero");
             }
             if (numInterested == 0 && objectDeque.getCreateCount().get() == 0) {
                 // Potential to remove key
                 // Upgrade to write lock
                 lock.unlock();
                 lock = keyLock.writeLock();
                 lock.lock();
                 // Pool may have changed since we released the read lock
                 // numInterested decrement could lead to removal while waiting for write lock
                 objectDeque = poolMap.get(k);
                 if (null != objectDeque && objectDeque.getNumInterested().get() == 0 && objectDeque.getCreateCount().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();
         }
     }
 
     /**
      * 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
      * @param destroyMode DestroyMode context provided to the factory
      *
      * @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, final DestroyMode destroyMode) throws Exception {
 
         final ObjectDeque<T> objectDeque = register(key);
 
         try {
             boolean isIdle;
             synchronized (toDestroy) {
                 // Check idle state directly
                 isIdle = toDestroy.getState().equals(PooledObjectState.IDLE);
                 // If idle, not under eviction test, or always is true, remove instance,
                 // updating isIdle if instance is found in idle objects
                 if (isIdle || always) {
                     isIdle = objectDeque.getIdleObjects().remove(toDestroy);
                 }
             }
             if (isIdle || always) {
                 objectDeque.getAllObjects().remove(new IdentityWrapper<>(toDestroy.getObject()));
                 toDestroy.invalidate();
 
                 try {
                     factory.destroyObject(key, toDestroy, destroyMode);
                 } finally {
                     objectDeque.getCreateCount().decrementAndGet();
                     destroyedCount.incrementAndGet();
                     numTotal.decrementAndGet();
                 }
                 return true;
             }
             return false;
         } finally {
             deregister(key);
         }
     }
 
 
     @Override
     void ensureMinIdle() throws Exception {
         final int minIdlePerKeySave = getMinIdlePerKey();
         if (minIdlePerKeySave < 1) {
             return;
         }
 
         for (final K k : poolMap.keySet()) {
             ensureMinIdle(k);
         }
     }
 
     /**
      * Try to ensure that the configured number of minimum idle objects is available in
      * the pool for the given key.
      * <p>
      * If there is no capacity available to add to the pool, this is a no-op
      * (no exception, no impact to the pool).
      * </p>
      * <p>
      * If the factory returns null when creating an object, a {@code NullPointerException}
      * is thrown.
      * </p>
      *
      * @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);
             }
         }
     }
 
     /**
      * {@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.
      * </p>
      */
     @Override
     public void evict() throws Exception {
         assertOpen();
 
         if (getNumIdle() > 0) {
 
             PooledObject<T> underTest = null;
             final EvictionPolicy<T> evictionPolicy = getEvictionPolicy();
 
             synchronized (evictionLock) {
                 final EvictionConfig evictionConfig = new EvictionConfig(
                         getMinEvictableIdleDuration(),
                         getSoftMinEvictableIdleDuration(),
                         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, DestroyMode.NORMAL);
                         destroyedByEvictorCount.incrementAndGet();
                     } else {
                         if (testWhileIdle) {
                             boolean active = false;
                             try {
                                 factory.activateObject(evictionKey, underTest);
                                 active = true;
                             } catch (final Exception e) {
                                 destroy(evictionKey, underTest, true, DestroyMode.NORMAL);
                                 destroyedByEvictorCount.incrementAndGet();
                             }
                             if (active) {
                                 boolean validate = false;
                                 Throwable validationThrowable = null;
                                 try {
                                     validate = factory.validateObject(evictionKey, underTest);
                                 } catch (final Throwable t) {
                                     PoolUtils.checkRethrow(t);
                                     validationThrowable = t;
                                 }
                                 if (!validate) {
                                     destroy(evictionKey, underTest, true, DestroyMode.NORMAL);
                                     destroyedByEvictorCount.incrementAndGet();
                                     if (validationThrowable != null) {
                                         if (validationThrowable instanceof RuntimeException) {
                                             throw (RuntimeException) validationThrowable;
                                         }
                                         throw (Error) validationThrowable;
                                     }
                                 } else {
                                     try {
                                         factory.passivateObject(evictionKey, underTest);
                                     } catch (final Exception e) {
                                         destroy(evictionKey, underTest, true, DestroyMode.NORMAL);
                                         destroyedByEvictorCount.incrementAndGet();
                                     }
                                 }
                             }
                         }
                         underTest.endEvictionTest(idleObjects);
                         // TODO - May need to add code here once additional
                         // states are used
                     }
                 }
             }
         }
         final AbandonedConfig ac = this.abandonedConfig;
         if (ac != null && ac.getRemoveAbandonedOnMaintenance()) {
             removeAbandoned(ac);
         }
     }
 
 
     /**
      * Gets 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;
     }
 
     /**
      * Gets a copy of the pool key list.
      *
      * @return a copy of the pool key list.
      * @since 2.12.0
      */
     @Override
     @SuppressWarnings("unchecked")
     public List<K> getKeys() {
         return (List<K>) poolKeyList.clone();
     }
 
     /**
      * Gets 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;
     }
 
     /**
      * Gets 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;
     }
 
     /**
      * Gets 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 #getDurationBetweenEvictionRuns()} 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.
      * </p>
      *
      * @return minimum size of the each keyed pool
      *
      * @see #setTimeBetweenEvictionRunsMillis
      */
     @Override
     public int getMinIdlePerKey() {
         final int maxIdlePerKeySave = getMaxIdlePerKey();
         return Math.min(this.minIdlePerKey, maxIdlePerKeySave);
     }
 
     @Override
     public int getNumActive() {
         return numTotal.get() - getNumIdle();
     }
 
     @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 Map<String, Integer> getNumActivePerKey() {
         return poolMap.entrySet().stream().collect(Collectors.toMap(
                 e -> e.getKey().toString(),
                 e -> Integer.valueOf(e.getValue().getAllObjects().size() - e.getValue().getIdleObjects().size()),
                 (t, u) -> u));
     }
 
     @Override
     public int getNumIdle() {
         return poolMap.values().stream().mapToInt(e -> e.getIdleObjects().size()).sum();
     }
 
     @Override
     public int getNumIdle(final K key) {
         final ObjectDeque<T> objectDeque = poolMap.get(key);
         return objectDeque != null ? objectDeque.getIdleObjects().size() : 0;
     }
 
     /**
      * Gets 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));
     }
 
     /**
      * Gets 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() {
         if (getBlockWhenExhausted()) {
             // Assume no overflow
             return poolMap.values().stream().mapToInt(e -> e.getIdleObjects().getTakeQueueLength()).sum();
         }
         return 0;
     }
 
     /**
      * Gets 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<>();
         poolMap.forEach((k, deque) -> result.put(k.toString(), getBlockWhenExhausted() ?
                 Integer.valueOf(deque.getIdleObjects().getTakeQueueLength()) :
                 ZERO));
         return result;
     }
 
     @Override
     String getStatsString() {
         // Simply listed in AB order.
         return super.getStatsString() +
                 String.format(", fairness=%s, maxIdlePerKey%,d, maxTotalPerKey=%,d, minIdlePerKey=%,d, numTotal=%,d",
                         fairness, maxIdlePerKey, maxTotalPerKey, minIdlePerKey, numTotal.get());
     }
 
     /**
      * Tests 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() {
         return getBlockWhenExhausted() && poolMap.values().stream().anyMatch(deque -> deque.getIdleObjects().hasTakeWaiters());
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * Activation of this method decrements the active count associated with
      * the given keyed pool and attempts to destroy {@code obj.}
      * </p>
      *
      * @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 {
         invalidateObject(key, obj, DestroyMode.NORMAL);
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * Activation of this method decrements the active count associated with
      * the given keyed pool and attempts to destroy {@code obj.}
      * </p>
      *
      * @param key pool key
      * @param obj instance to invalidate
      * @param destroyMode DestroyMode context provided to factory
      *
      * @throws Exception             if an exception occurs destroying the
      *                               object
      * @throws IllegalStateException if obj does not belong to the pool
      *                               under the given key
      * @since 2.9.0
      */
     @Override
     public void invalidateObject(final K key, final T obj, final DestroyMode destroyMode) throws Exception {
         final ObjectDeque<T> objectDeque = poolMap.get(key);
         final PooledObject<T> p = objectDeque != null ? objectDeque.getAllObjects().get(new IdentityWrapper<>(obj)) : null;
         if (p == null) {
             throw new IllegalStateException(appendStats("Object not currently part of this pool"));
         }
         synchronized (p) {
             if (p.getState() != PooledObjectState.INVALID) {
                 destroy(key, p, true, destroyMode);
                 reuseCapacity();
             }
         }
     }
 
     /**
      * 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.
      * </p>
      *
      * @return Information grouped by key on all the objects in the pool
      */
     @Override
     public Map<String, List<DefaultPooledObjectInfo>> listAllObjects() {
         return poolMap.entrySet().stream().collect(Collectors.toMap(e -> e.getKey().toString(), 
                 e -> e.getValue().getAllObjects().values().stream().map(DefaultPooledObjectInfo::new).collect(Collectors.toList())));
     }
 
     /**
      * 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);
     }
 
     /**
      * Register the use of a key by an object.
      * <p>
      * {@link #register(Object)} and {@link #deregister(Object)} must always be used as a pair.
      * </p>
      *
      * @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();
                 final AtomicBoolean allocated = new AtomicBoolean(); 
                 objectDeque = poolMap.computeIfAbsent(k, key -> {
                     allocated.set(true);
                     final ObjectDeque<T> deque = new ObjectDeque<>(fairness);
                     deque.getNumInterested().incrementAndGet();
                     // NOTE: Keys must always be added to both poolMap and
                     //       poolKeyList at the same time while protected by
                     //       the write lock
                     poolKeyList.add(k);
                     return deque;
                 });
                 if (!allocated.get()) {
                     // Another thread could have beaten us to creating the deque, while we were
                     // waiting for the write lock, so re-get it from the map.
                     objectDeque = poolMap.get(k);
                     objectDeque.getNumInterested().incrementAndGet();
                 }
             } else {
                 objectDeque.getNumInterested().incrementAndGet();
             }
         } finally {
             lock.unlock();
         }
         return objectDeque;
     }
 
     /**
      * Recovers abandoned objects which have been checked out but
      * not used since longer than the removeAbandonedTimeout.
      *
      * @param abandonedConfig The configuration to use to identify abandoned objects
      */
     @SuppressWarnings("resource") // The PrintWriter is managed elsewhere
     private void removeAbandoned(final AbandonedConfig abandonedConfig) {
         poolMap.forEach((key, value) -> {
             // Generate a list of abandoned objects to remove
             final ArrayList<PooledObject<T>> remove = createRemoveList(abandonedConfig, value.getAllObjects());
             // Now remove the abandoned objects
             remove.forEach(pooledObject -> {
                 if (abandonedConfig.getLogAbandoned()) {
                     pooledObject.printStackTrace(abandonedConfig.getLogWriter());
                 }
                 try {
                     invalidateObject(key, pooledObject.getObject(), DestroyMode.ABANDONED);
                 } catch (final Exception e) {
                     swallowException(e);
                 }
             });
         });
     }
 
     /**
      * 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>
      * <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>
      * <p>
      * Exceptions encountered destroying objects for any reason are swallowed
      * but notified via a {@link SwallowedExceptionListener}.
      * </p>
      *
      * @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);
 
         if (objectDeque == null) {
             throw new IllegalStateException("No keyed pool found under the given key.");
         }
 
         final PooledObject<T> p = objectDeque.getAllObjects().get(new IdentityWrapper<>(obj));
 
         if (PooledObject.isNull(p)) {
             throw new IllegalStateException("Returned object not currently part of this pool");
         }
 
         markReturningState(p);
 
         final Duration activeTime = p.getActiveDuration();
 
         try {
             if (getTestOnReturn() && !factory.validateObject(key, p)) {
                 try {
                     destroy(key, p, true, DestroyMode.NORMAL);
                 } 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, DestroyMode.NORMAL);
                 } 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, DestroyMode.NORMAL);
                 } 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);
         }
     }
 
     /**
      * 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();
         int maxQueueLength = 0;
         LinkedBlockingDeque<PooledObject<T>> mostLoadedPool = null;
         K mostLoadedKey = null;
 
         // Find the most loaded pool that could take a new instance
         for (final Map.Entry<K, ObjectDeque<T>> entry : poolMap.entrySet()) {
             final K k = entry.getKey();
             final LinkedBlockingDeque<PooledObject<T>> pool = entry.getValue().getIdleObjects();
             final int queueLength = pool.getTakeQueueLength();
             if (getNumActive(k) < maxTotalPerKeySave && queueLength > maxQueueLength) {
                 maxQueueLength = queueLength;
                 mostLoadedPool = pool;
                 mostLoadedKey = k;
             }
         }
 
         // Attempt to add an instance to the most loaded pool.
         if (mostLoadedPool != null) {
             register(mostLoadedKey);
             try {
                 // If there is no capacity to add, create will return null
                 // and addIdleObject will no-op.
                 addIdleObject(mostLoadedKey, create(mostLoadedKey));
             } catch (final Exception e) {
                 swallowException(e);
             } finally {
                 deregister(mostLoadedKey);
             }
         }
     }
 
     /**
      * Call {@link #reuseCapacity()} repeatedly.
      * <p>
      * Always activates {@link #reuseCapacity()} at least once.
      *
      * @param newCapacity number of new instances to attempt to create.
      */
     private void reuseCapacity(final int newCapacity) {
         final int bound = newCapacity < 1 ? 1 : newCapacity;
         for (int i = 0; i < bound; i++) {
             reuseCapacity();
         }
     }
 
     /**
      * 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());
     }
 
     /**
      * 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 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;
     }
 
     /**
      * 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 #getDurationBetweenEvictionRuns()} 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.
      * </p>
      *
      * @param minIdlePerKey The minimum size of the each keyed pool
      *
      * @see #getMinIdlePerKey()
      * @see #getMaxIdlePerKey()
      * @see #setDurationBetweenEvictionRuns(Duration)
      */
     public void setMinIdlePerKey(final int minIdlePerKey) {
         this.minIdlePerKey = minIdlePerKey;
     }
 
     @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);
         builder.append(", abandonedConfig=");
         builder.append(abandonedConfig);
     }
 
     /**
      * @since 2.10.0
      */
     @Override
     public void use(final T pooledObject) {
         final AbandonedConfig abandonedCfg = this.abandonedConfig;
         if (abandonedCfg != null && abandonedCfg.getUseUsageTracking()) {
             poolMap.values().stream()
                 .map(pool -> pool.getAllObjects().get(new IdentityWrapper<>(pooledObject)))
                 .filter(Objects::nonNull)
                 .findFirst()
                 .ifPresent(PooledObject::use);
         }
     }
 
     /**
      * When there is at least one thread waiting on the given deque, try to add an instance to pool under the given key.
      * NOTE: there is no check that the key corresponds to the deque (it is assumed that the key was used to get the deque
      * from the poolMap)
      *
      * @param key pool key.
      * @param idleObjects deque backing the pool under the given key
      */
     private void whenWaitersAddObject(final K key, final LinkedBlockingDeque<PooledObject<T>> idleObjects) {
         if (idleObjects.hasTakeWaiters()) {
             try {
                 addObject(key);
             } catch (final Exception e) {
                 swallowException(e);
             }
         }
     }
 
 }