/*
    * 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
    *
    *      https://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.NoSuchElementException;
  import java.util.Set;
  import java.util.concurrent.ConcurrentHashMap;
  import java.util.concurrent.atomic.AtomicLong;
  import java.util.stream.Collectors;
  
  import org.apache.commons.pool2.DestroyMode;
  import org.apache.commons.pool2.ObjectPool;
  import org.apache.commons.pool2.PoolUtils;
  import org.apache.commons.pool2.PooledObject;
  import org.apache.commons.pool2.PooledObjectFactory;
  import org.apache.commons.pool2.PooledObjectState;
  import org.apache.commons.pool2.SwallowedExceptionListener;
  import org.apache.commons.pool2.TrackedUse;
  import org.apache.commons.pool2.UsageTracking;
  
  /**
   * A configurable {@link ObjectPool} implementation.
   * <p>
   * When coupled with the appropriate {@link PooledObjectFactory},
   * {@code GenericObjectPool} provides robust pooling functionality for
   * arbitrary objects.
   * </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 are available. 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>
   * The pool can also be configured to detect and remove "abandoned" objects,
   * i.e. objects that have been checked out of the pool but neither used nor
   * returned before the configured
   * {@link AbandonedConfig#getRemoveAbandonedTimeoutDuration() removeAbandonedTimeout}.
   * Abandoned object removal can be configured to happen when
   * {@code borrowObject} is invoked and the pool is close to starvation, or
   * it can be executed by the idle object evictor, or both. If pooled objects
   * implement the {@link TrackedUse} interface, their last use will be queried
   * using the {@code getLastUsed} method on that interface; otherwise
   * abandonment is determined by how long an object has been checked out from
   * the pool.
   * </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 GenericKeyedObjectPool
   * @param <T> Type of element pooled in this pool.
   * @since 2.0
   */
  public class GenericObjectPool<T> extends BaseGenericObjectPool<T>
          implements ObjectPool<T>, GenericObjectPoolMXBean, UsageTracking<T> {
  
      // JMX specific attributes
      private static final String ONAME_BASE =
          "org.apache.commons.pool2:type=GenericObjectPool,name=";
  
      private volatile String factoryType;
  
      private volatile int maxIdle = GenericObjectPoolConfig.DEFAULT_MAX_IDLE;
  
      private volatile int minIdle = GenericObjectPoolConfig.DEFAULT_MIN_IDLE;
  
      private final PooledObjectFactory<T> factory;
  
      /*
       * All of the objects currently associated with this pool in any state. It
       * excludes objects that have been destroyed. The size of
       * {@link #allObjects} will always be less than or equal to {@link
       * #getMaxTotal()}. Map keys are pooled objects, values are the PooledObject
      * wrappers used internally by the pool.
      */
     private final ConcurrentHashMap<IdentityWrapper<T>, PooledObject<T>> allObjects = new ConcurrentHashMap<>();
 
     /*
      * The combined count of the currently created objects and those in the
      * process of being created. Under load, it may exceed {@link #getMaxTotal()}
      * if multiple threads try and create a new object at the same time but
      * {@link #create()} will ensure that there are never more than
      * {@link #getMaxTotal()} objects created at any one time.
      */
     private final AtomicLong createCount = new AtomicLong();
 
     private long makeObjectCount;
 
     private final Object makeObjectCountLock = new Object();
 
     private final LinkedBlockingDeque<PooledObject<T>> idleObjects;
 
     /**
      * Creates a new {@code GenericObjectPool} using defaults from
      * {@link GenericObjectPoolConfig}.
      *
      * @param factory The object factory to be used to create object instances
      *                used by this pool
      */
     public GenericObjectPool(final PooledObjectFactory<T> factory) {
         this(factory, new GenericObjectPoolConfig<>());
     }
 
     /**
      * Creates a new {@code GenericObjectPool} using a specific
      * configuration.
      *
      * @param factory   The object factory to be used to create object instances
      *                  used by this pool
      * @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 GenericObjectPool(final PooledObjectFactory<T> factory,
             final GenericObjectPoolConfig<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;
 
         idleObjects = new LinkedBlockingDeque<>(config.getFairness());
 
         setConfig(config);
     }
 
     /**
      * Creates a new {@code GenericObjectPool} 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.
      */
     public GenericObjectPool(final PooledObjectFactory<T> factory,
             final GenericObjectPoolConfig<T> config, final AbandonedConfig abandonedConfig) {
         this(factory, config);
         setAbandonedConfig(abandonedConfig);
     }
 
     /**
      * Adds the provided wrapped pooled object to the set of idle objects for
      * this pool. The object must already be part of the pool.  If {@code p}
      * is null, this is a no-op (no exception, but no impact on the pool).
      *
      * @param p The object to make idle
      * @throws Exception If the factory fails to passivate the object
      */
     private void addIdleObject(final PooledObject<T> p) throws Exception {
         if (PooledObject.nonNull(p)) {
             factory.passivateObject(p);
             if (getLifo()) {
                 idleObjects.addFirst(p);
             } else {
                 idleObjects.addLast(p);
             }
         }
     }
 
     /**
      * Creates an object, and places it into the pool. addObject() is useful for
      * "pre-loading" a pool with idle objects.
      * <p>
      * If there is no capacity available to add to the pool, or there are already
      * {@link #getMaxIdle()} idle instances in 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. If there is no factory set (factory == null), an {@code IllegalStateException}
      * is thrown.
      * </p>
      */
     @Override
     public void addObject() throws Exception {
         assertOpen();
         if (factory == null) {
             throw new IllegalStateException("Cannot add objects without a factory.");
         }
         final int localMaxIdle = getMaxIdle();
         final int localMaxTotal = getMaxTotal();
         if ((localMaxIdle < 0 || getNumIdle() < localMaxIdle) &&
                 (localMaxTotal < 0 || createCount.get() < localMaxTotal)) {
             addIdleObject(create(getMaxWaitDuration()));
         }
     }
 
     /**
      * Equivalent to <code>{@link #borrowObject(Duration)
      * borrowObject}({@link #getMaxWaitDuration()})</code>.
      *
      * {@inheritDoc}
      */
     @Override
     public T borrowObject() throws Exception {
         return borrowObject(getMaxWaitDuration());
     }
 
     /**
      * Borrows an object from the pool using the specific waiting time which only
      * applies if {@link #getBlockWhenExhausted()} is true.
      * <p>
      * If there is one or more idle instance available in the pool, 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 pool, behavior depends on
      * the {@link #getMaxTotal() maxTotal}, (if applicable)
      * {@link #getBlockWhenExhausted()} and the value passed in the
      * {@code maxWaitDuration} parameter. If the number of instances
      * checked out from the pool 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}
      * is thrown. If the factory returns null when creating an instance,
      * a {@code NullPointerException} is thrown.
      * </p>
      * <p>
      * If the pool is exhausted (no available idle instances and no capacity to
      * create new ones), this method will either block (if
      * {@link #getBlockWhenExhausted()} is true) or throw a
      * {@code NoSuchElementException} (if
      * {@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 maxWaitDuration}
      * parameter. Passing a negative duration will cause this method to block
      * indefinitely until an object becomes available.
      * </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 maxWaitDuration The time to wait for an object to become available, not null.
      * @return object instance from the pool
      * @throws NoSuchElementException if an instance cannot be returned
      * @throws Exception if an object instance cannot be returned due to an error
      * @since 2.10.0
      */
     public T borrowObject(final Duration maxWaitDuration) throws Exception {
         assertOpen();
         final Instant startInstant = Instant.now();
         final boolean negativeDuration = maxWaitDuration.isNegative();
         Duration remainingWaitDuration = maxWaitDuration;
         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;
         while (p == null) {
             remainingWaitDuration = maxWaitDuration.minus(durationSince(startInstant));
             create = false;
             p = idleObjects.pollFirst();
             if (p == null) {
                 p = create(remainingWaitDuration);
                 if (PooledObject.nonNull(p)) {
                     create = true;
                 }
             }
             if (blockWhenExhausted) {
                 if (PooledObject.isNull(p)) {
                     remainingWaitDuration = maxWaitDuration.minus(durationSince(startInstant));
                     p = negativeDuration ? idleObjects.takeFirst() : idleObjects.pollFirst(remainingWaitDuration);
                 }
                 if (PooledObject.isNull(p)) {
                     throw new NoSuchElementException(appendStats("Timeout waiting for idle object, maxWaitDuration=" + remainingWaitDuration));
                 }
             } else if (PooledObject.isNull(p)) {
                 throw new NoSuchElementException(appendStats("Pool exhausted"));
             }
             if (!p.allocate()) {
                 p = null;
             }
             if (!PooledObject.isNull(p)) {
                 try {
                     factory.activateObject(p);
                 } catch (final Exception e) {
                     try {
                         destroy(p, 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(p);
                     } catch (final Throwable t) {
                         PoolUtils.checkRethrow(t);
                         validationThrowable = t;
                     }
                     if (!validate) {
                         try {
                             destroy(p, 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;
                         }
                     }
                 }
             }
         }
         updateStatsBorrow(p, durationSince(startInstant));
         return p.getObject();
     }
 
     /**
      * Borrows an object from the pool using the specific waiting time which only
      * applies if {@link #getBlockWhenExhausted()} is true.
      * <p>
      * If there is one or more idle instance available in the pool, 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 pool, behavior depends on
      * the {@link #getMaxTotal() maxTotal}, (if applicable)
      * {@link #getBlockWhenExhausted()} and the value passed in to the
      * {@code maxWaitMillis} parameter. If the number of instances
      * checked out from the pool 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}
      * is thrown. If the factory returns null when creating an instance,
      * a {@code NullPointerException} is thrown.
      * </p>
      * <p>
      * If the pool is exhausted (no available idle instances and no capacity to
      * create new ones), this method will either block (if
      * {@link #getBlockWhenExhausted()} is true) or throw a
      * {@code NoSuchElementException} (if
      * {@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 maxWaitMillis}
      * parameter.  Passing a negative duration will cause this method to block
      * indefinitely until an object becomes available.
      * </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 maxWaitMillis The time to wait in milliseconds for an object
      *                            to become available
      * @return object instance from the pool
      * @throws NoSuchElementException if an instance cannot be returned
      * @throws Exception if an object instance cannot be returned due to an
      *                   error
      * @deprecated Use {@link #borrowObject(Duration)}.
      */
     @Deprecated
     public T borrowObject(final long maxWaitMillis) throws Exception {
         return borrowObject(Duration.ofMillis(maxWaitMillis));
     }
 
     /**
      * Clears any objects sitting idle in the pool by removing them from the
      * idle instance pool and then invoking the configured
      * {@link PooledObjectFactory#destroyObject(PooledObject)} method on each
      * idle instance.
      * <p>
      * Implementation notes:
      * </p>
      * <ul>
      * <li>This method does not destroy or effect in any way instances that are
      * checked out of the pool 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() {
         PooledObject<T> p = idleObjects.poll();
 
         while (p != null) {
             try {
                 destroy(p, DestroyMode.NORMAL);
             } catch (final Exception e) {
                 swallowException(e);
             }
             p = idleObjects.poll();
         }
     }
 
     /**
      * Closes the pool. Once the pool is closed, {@link #borrowObject()} will
      * fail with IllegalStateException, but {@link #returnObject(Object)} and
      * {@link #invalidateObject(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
             idleObjects.interruptTakeWaiters();
         }
     }
 
     /**
      * Attempts to create a new wrapped pooled object.
      * <p>
      * If there are {@link #getMaxTotal()} objects already in circulation or in process of being created, this method
      * returns null.
      * </p>
      * <p>
      * If the factory makeObject returns null, this method throws a NullPointerException.
      * </p>
      *
      * @param maxWaitDurationRequest The time to wait for capacity to create.
      * @return The new wrapped pooled object or null.
      * @throws Exception if the object factory's {@code makeObject} fails.
      */
     private PooledObject<T> create(final Duration maxWaitDurationRequest) throws Exception {
         final Instant startInstant = Instant.now();
         final Duration maxWaitDuration = maxWaitDurationRequest.isNegative() ? Duration.ZERO : maxWaitDurationRequest;
         int localMaxTotal = getMaxTotal();
         // This simplifies the code later in this method
         if (localMaxTotal < 0) {
             localMaxTotal = Integer.MAX_VALUE;
         }
         final Instant localStartInstant = Instant.now();
         // 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) {
             // remainingWaitDuration handles spurious wakeup from wait().
             final Duration remainingWaitDuration = maxWaitDuration.minus(durationSince(startInstant));
             synchronized (makeObjectCountLock) {
                 final long newCreateCount = createCount.incrementAndGet();
                 if (newCreateCount > localMaxTotal) {
                     // The pool is currently at capacity or in the process of
                     // making enough new objects to take it to capacity.
                     createCount.decrementAndGet();
                     if (makeObjectCount == 0) {
                         // There are no makeObject() calls in progress so the
                         // pool 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.
                         wait(makeObjectCountLock, remainingWaitDuration);
                     }
                 } else {
                     // The pool is not at capacity. Create a new object.
                     makeObjectCount++;
                     create = Boolean.TRUE;
                 }
             }
             // Do not block more if remainingWaitDuration > 0.
             if (create == null && remainingWaitDuration.compareTo(Duration.ZERO) > 0 &&
                     durationSince(localStartInstant).compareTo(remainingWaitDuration) >= 0) {
                 create = Boolean.FALSE;
             }
         }
 
         if (!create.booleanValue()) {
             return null;
         }
 
         final PooledObject<T> p;
         try {
             p = factory.makeObject();
             if (PooledObject.isNull(p)) {
                 createCount.decrementAndGet();
                 throw new NullPointerException(String.format("%s.makeObject() = null", factory.getClass().getSimpleName()));
             }
             if (getTestOnCreate() && !factory.validateObject(p)) {
                 createCount.decrementAndGet();
                 return null;
             }
         } catch (final Throwable e) {
             createCount.decrementAndGet();
             throw e;
         } finally {
             synchronized (makeObjectCountLock) {
                 makeObjectCount--;
                 makeObjectCountLock.notifyAll();
             }
         }
 
         final AbandonedConfig ac = this.abandonedConfig;
         if (ac != null && ac.getLogAbandoned()) {
             p.setLogAbandoned(true);
             p.setRequireFullStackTrace(ac.getRequireFullStackTrace());
         }
 
         createdCount.incrementAndGet();
         allObjects.put(IdentityWrapper.unwrap(p), p);
         return p;
     }
 
     /**
      * Destroys a wrapped pooled object.
      *
      * @param toDestroy The wrapped pooled object to destroy
      * @param destroyMode DestroyMode context provided to the factory
      * @throws Exception If the factory fails to destroy the pooled object
      *                   cleanly
      */
     private void destroy(final PooledObject<T> toDestroy, final DestroyMode destroyMode) throws Exception {
         toDestroy.invalidate();
         idleObjects.remove(toDestroy);
         allObjects.remove(IdentityWrapper.unwrap(toDestroy));
         try {
             factory.destroyObject(toDestroy, destroyMode);
         } finally {
             destroyedCount.incrementAndGet();
             createCount.decrementAndGet();
         }
     }
 
 
     /**
      * Tries to ensure that {@code idleCount} idle instances exist in the pool.
      * <p>
      * Creates and adds idle instances until either {@link #getNumIdle()} reaches {@code idleCount}
      * or the total number of objects (idle, checked out, or being created) reaches
      * {@link #getMaxTotal()}. If {@code always} is false, no instances are created unless
      * there are threads waiting to check out instances from the pool.
      * </p>
      * <p>
      * If the factory returns null when creating an instance, a {@code NullPointerException}
      * is thrown.
      * </p>
      *
      * @param idleCount the number of idle instances desired
      * @param always true means create instances even if the pool has no threads waiting
      * @throws Exception if the factory's makeObject throws
      */
     private void ensureIdle(final int idleCount, final boolean always) throws Exception {
         if (idleCount < 1 || isClosed() || !always && !idleObjects.hasTakeWaiters()) {
             return;
         }
 
         while (idleObjects.size() < idleCount) {
             final PooledObject<T> p = create(getMaxWaitDuration());
             if (PooledObject.isNull(p)) {
                 // Can't create objects, no reason to think another call to
                 // create will work. Give up.
                 break;
             }
             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();
         }
     }
 
     @Override
     void ensureMinIdle() throws Exception {
         ensureIdle(getMinIdle(), true);
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * Successive activations of this method examine objects in sequence,
      * cycling through objects in oldest-to-youngest order.
      * </p>
      */
     @Override
     public void evict() throws Exception {
         assertOpen();
 
         if (!idleObjects.isEmpty()) {
 
             PooledObject<T> underTest = null;
             final EvictionPolicy<T> evictionPolicy = getEvictionPolicy();
 
             synchronized (evictionLock) {
                 final EvictionConfig evictionConfig = new EvictionConfig(
                         getMinEvictableIdleDuration(),
                         getSoftMinEvictableIdleDuration(),
                         getMinIdle());
 
                 final boolean testWhileIdle = getTestWhileIdle();
 
                 for (int i = 0, m = getNumTests(); i < m; i++) {
                     if (evictionIterator == null || !evictionIterator.hasNext()) {
                         evictionIterator = new EvictionIterator(idleObjects);
                     }
                     if (!evictionIterator.hasNext()) {
                         // Pool exhausted, nothing to do here
                         return;
                     }
 
                     try {
                         underTest = evictionIterator.next();
                     } 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,
                                 idleObjects.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(underTest, DestroyMode.NORMAL);
                         destroyedByEvictorCount.incrementAndGet();
                     } else {
                         if (testWhileIdle) {
                             boolean active = false;
                             try {
                                 factory.activateObject(underTest);
                                 active = true;
                             } catch (final Exception e) {
                                 destroy(underTest, DestroyMode.NORMAL);
                                 destroyedByEvictorCount.incrementAndGet();
                             }
                             if (active) {
                                 boolean validate = false;
                                 Throwable validationThrowable = null;
                                 try {
                                     validate = factory.validateObject(underTest);
                                 } catch (final Throwable t) {
                                     PoolUtils.checkRethrow(t);
                                     validationThrowable = t;
                                 }
                                 if (!validate) {
                                     destroy(underTest, DestroyMode.NORMAL);
                                     destroyedByEvictorCount.incrementAndGet();
                                     if (validationThrowable != null) {
                                         if (validationThrowable instanceof RuntimeException) {
                                             throw (RuntimeException) validationThrowable;
                                         }
                                         throw (Error) validationThrowable;
                                     }
                                 } else {
                                     try {
                                         factory.passivateObject(underTest);
                                     } catch (final Exception e) {
                                         destroy(underTest, DestroyMode.NORMAL);
                                         destroyedByEvictorCount.incrementAndGet();
                                     }
                                 }
                             }
                         }
                         underTest.endEvictionTest(idleObjects);
                     }
                 }
             }
         }
         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 PooledObjectFactory<T> getFactory() {
         return factory;
     }
 
     /**
      * Gets the type - including the specific type rather than the generic -
      * of the factory.
      *
      * @return A string representation of the factory type
      */
     @Override
     public String getFactoryType() {
         // Not thread safe. Accept that there may be multiple evaluations.
         if (factoryType == null) {
             final StringBuilder result = new StringBuilder();
             result.append(factory.getClass().getName());
             result.append('<');
             final Class<?> pooledObjectType =
                     PoolImplUtils.getFactoryType(factory.getClass());
             result.append(pooledObjectType.getName());
             result.append('>');
             factoryType = result.toString();
         }
         return factoryType;
     }
 
     /**
      * Gets the cap on the number of "idle" instances in the pool. If maxIdle
      * 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 maxIdle. The best value for maxIdle 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 the
      *         pool or a negative value if there is no limit
      * @see #setMaxIdle
      */
     @Override
     public int getMaxIdle() {
         return maxIdle;
     }
 
     /**
      * Gets the target for the minimum number of idle objects to maintain in
      * the pool. 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 the pool has the required
      * minimum number of instances during idle object eviction runs.
      * <p>
      * If the configured value of minIdle is greater than the configured value
      * for maxIdle then the value of maxIdle will be used instead.
      * </p>
      *
      * @return The minimum number of objects.
      * @see #setMinIdle(int)
      * @see #setMaxIdle(int)
      * @see #setDurationBetweenEvictionRuns(Duration)
      */
     @Override
     public int getMinIdle() {
         final int maxIdleSave = getMaxIdle();
         return Math.min(this.minIdle, maxIdleSave);
     }
 
     @Override
     public int getNumActive() {
         return allObjects.size() - idleObjects.size();
     }
 
     @Override
     public int getNumIdle() {
         return idleObjects.size();
     }
 
     /**
      * Calculates 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 numTestsPerEvictionRun = getNumTestsPerEvictionRun();
         if (numTestsPerEvictionRun >= 0) {
             return Math.min(numTestsPerEvictionRun, idleObjects.size());
         }
         return (int) Math.ceil(idleObjects.size() /
                 Math.abs((double) numTestsPerEvictionRun));
     }
 
     /**
      * 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()) {
             return idleObjects.getTakeQueueLength();
         }
         return 0;
     }
 
     PooledObject<T> getPooledObject(final T obj) {
         return allObjects.get(new IdentityWrapper<>(obj));
     }
 
     @Override
     String getStatsString() {
         // Simply listed in AB order.
         return super.getStatsString() +
                 String.format(", createdCount=%,d, makeObjectCount=%,d, maxIdle=%,d, minIdle=%,d",
                         createdCount.get(), makeObjectCount, maxIdle, minIdle);
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * Activation of this method decrements the active count and attempts to destroy the instance, using the default
      * (NORMAL) {@link DestroyMode}.
      * </p>
      *
      * @throws Exception if an exception occurs destroying the
      * @throws IllegalStateException if obj does not belong to this pool
      */
     @Override
     public void invalidateObject(final T obj) throws Exception {
         invalidateObject(obj, DestroyMode.NORMAL);
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * Activation of this method decrements the active count and attempts to destroy the instance, using the provided
      * {@link DestroyMode}. To ensure liveness of the pool, {@link #addObject()} is called to replace the invalidated
      * instance.
      * </p>
      *
      * @throws Exception if an exception occurs destroying the object
      * @throws IllegalStateException if obj does not belong to this pool
      * @since 2.9.0
      */
     @Override
     public void invalidateObject(final T obj, final DestroyMode destroyMode) throws Exception {
         final PooledObject<T> p = getPooledObject(obj);
         if (p == null) {
             if (isAbandonedConfig()) {
                 return;
             }
             throw new IllegalStateException("Invalidated object not currently part of this pool");
         }
         synchronized (p) {
             if (p.getState() != PooledObjectState.INVALID) {
                 destroy(p, destroyMode);
             }
         }
         if (!isClosed()) {
              addObject();
         }
     }
 
     /**
      * 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 on all the objects in the pool
      */
     @Override
     public Set<DefaultPooledObjectInfo> listAllObjects() {
         return allObjects.values().stream().map(DefaultPooledObjectInfo::new).collect(Collectors.toSet());
     }
 
     /**
      * Tries to ensure that {@link #getMinIdle()} idle instances are available
      * in the pool.
      *
      * @throws Exception If the associated factory throws an exception.
      * @since 2.4
      */
     public void preparePool() throws Exception {
         if (getMinIdle() < 1) {
             return;
         }
         ensureMinIdle();
     }
 
     /**
      * Recovers abandoned objects which have been checked out but
      * not used since longer than the removeAbandonedTimeout. For each object
      * deemed abandoned, {@link #invalidateObject(Object)} is called. This
      * results in the object being destroyed and then {@link #addObject()} is
      * called to try to replace it.
      *
      * @param abandonedConfig The configuration to use to identify abandoned objects
      */
     @SuppressWarnings("resource") // PrintWriter is managed elsewhere
     private void removeAbandoned(final AbandonedConfig abandonedConfig) {
         // Generate a list of abandoned objects to remove
         final ArrayList<PooledObject<T>> remove = createRemoveList(abandonedConfig, allObjects);
         // Now remove the abandoned objects
         remove.forEach(pooledObject -> {
             if (abandonedConfig.getLogAbandoned()) {
                 pooledObject.printStackTrace(abandonedConfig.getLogWriter());
             }
             try {
                 invalidateObject(pooledObject.getObject(), DestroyMode.ABANDONED);
             } catch (final Exception e) {
                 swallowException(e);
             }
         });
     }
 
     /**
      * {@inheritDoc}
      * <p>
      * If {@link #getMaxIdle() maxIdle} is set to a positive value and the
      * number of idle instances 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 pool. 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>
      */
     @Override
     public void returnObject(final T obj) {
         final PooledObject<T> p = getPooledObject(obj);
 
         if (p == null) {
             if (!isAbandonedConfig()) {
                 throw new IllegalStateException(
                         "Returned object not currently part of this pool");
             }
             return; // Object was abandoned and removed
         }
         synchronized (p) {
             markReturningState(p);
 
             final Duration activeTime = p.getActiveDuration();
 
             if (getTestOnReturn() && !factory.validateObject(p)) {
                 try {
                     destroy(p, DestroyMode.NORMAL);
                 } catch (final Exception e) {
                     swallowException(e);
                 }
                 try {
                     ensureIdle(1, false);
                 } catch (final Exception e) {
                     swallowException(e);
                 }
                 updateStatsReturn(activeTime);
                 return;
             }
 
             try {
                 factory.passivateObject(p);
             } catch (final Exception e1) {
                 swallowException(e1);
                 try {
                     destroy(p, DestroyMode.NORMAL);
                 } catch (final Exception e) {
                     swallowException(e);
                 }
                 try {
                     ensureIdle(1, false);
                 } catch (final Exception e) {
                     swallowException(e);
                 }
                 updateStatsReturn(activeTime);
                 return;
             }
 
             if (!p.deallocate()) {
                 throw new IllegalStateException(
                         "Object has already been returned to this pool or is invalid");
             }
 
             final int maxIdleSave = getMaxIdle();
             if (isClosed() || maxIdleSave > -1 && maxIdleSave <= idleObjects.size()) {
                 try {
                     destroy(p, DestroyMode.NORMAL);
                 } catch (final Exception e) {
                     swallowException(e);
                 }
                 try {
                     ensureIdle(1, false);
                 } 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();
                 }
             }
             updateStatsReturn(activeTime);
         }
     }
 
     /**
      * Sets the base pool configuration.
      *
      * @param conf the new configuration to use. This is used by value.
      * @see GenericObjectPoolConfig
      */
     public void setConfig(final GenericObjectPoolConfig<T> conf) {
         super.setConfig(conf);
         setMaxIdle(conf.getMaxIdle());
         setMinIdle(conf.getMinIdle());
         setMaxTotal(conf.getMaxTotal());
     }
 
     /**
      * Sets the cap on the number of "idle" instances in the pool. If maxIdle
      * 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 maxIdle. The best value for maxIdle for heavily
      * loaded system will vary but the default is a good starting point.
      *
      * @param maxIdle
      *            The cap on the number of "idle" instances in the pool. Use a
      *            negative value to indicate an unlimited number of idle
      *            instances
      * @see #getMaxIdle
      */
     public void setMaxIdle(final int maxIdle) {
         this.maxIdle = maxIdle;
     }
 
     /**
      * Sets the target for the minimum number of idle objects to maintain in
      * the pool. 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 the pool has the required
      * minimum number of instances during idle object eviction runs.
      * <p>
      * If the configured value of minIdle is greater than the configured value
      * for maxIdle then the value of maxIdle will be used instead.
      * </p>
      *
      * @param minIdle
      *            The minimum number of objects.
      * @see #getMinIdle()
      * @see #getMaxIdle()
      * @see #getDurationBetweenEvictionRuns()
      */
     public void setMinIdle(final int minIdle) {
         this.minIdle = minIdle;
     }
 
     @Override
     protected void toStringAppendFields(final StringBuilder builder) {
         super.toStringAppendFields(builder);
         builder.append(", factoryType=");
         builder.append(factoryType);
         builder.append(", maxIdle=");
         builder.append(maxIdle);
         builder.append(", minIdle=");
         builder.append(minIdle);
         builder.append(", factory=");
         builder.append(factory);
         builder.append(", allObjects=");
         builder.append(allObjects);
         builder.append(", createCount=");
         builder.append(createCount);
         builder.append(", idleObjects=");
         builder.append(idleObjects);
         builder.append(", abandonedConfig=");
         builder.append(abandonedConfig);
     }
 
     @Override
     public void use(final T pooledObject) {
         final AbandonedConfig abandonedCfg = this.abandonedConfig;
         if (abandonedCfg != null && abandonedCfg.getUseUsageTracking()) {
             final PooledObject<T> po = getPooledObject(pooledObject);
             if (po != null) {
                 po.use();
             }
         }
     }
 
 }