    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.pool2.impl;
    018
    019import java.time.Duration;
    020import java.util.ArrayList;
    021import java.util.Map;
    022import java.util.NoSuchElementException;
    023import java.util.Set;
    024import java.util.concurrent.ConcurrentHashMap;
    025import java.util.concurrent.atomic.AtomicLong;
    026import java.util.stream.Collectors;
    027
    028import org.apache.commons.pool2.DestroyMode;
    029import org.apache.commons.pool2.ObjectPool;
    030import org.apache.commons.pool2.PoolUtils;
    031import org.apache.commons.pool2.PooledObject;
    032import org.apache.commons.pool2.PooledObjectFactory;
    033import org.apache.commons.pool2.PooledObjectState;
    034import org.apache.commons.pool2.SwallowedExceptionListener;
    035import org.apache.commons.pool2.TrackedUse;
    036import org.apache.commons.pool2.UsageTracking;
    037
    038/**
    039 * A configurable {@link ObjectPool} implementation.
    040 * <p>
    041 * When coupled with the appropriate {@link PooledObjectFactory},
    042 * {@code GenericObjectPool} provides robust pooling functionality for
    043 * arbitrary objects.
    044 * </p>
    045 * <p>
    046 * Optionally, one may configure the pool to examine and possibly evict objects
    047 * as they sit idle in the pool and to ensure that a minimum number of idle
    048 * objects are available. This is performed by an "idle object eviction" thread,
    049 * which runs asynchronously. Caution should be used when configuring this
    050 * optional feature. Eviction runs contend with client threads for access to
    051 * objects in the pool, so if they run too frequently performance issues may
    052 * result.
    053 * </p>
    054 * <p>
    055 * The pool can also be configured to detect and remove "abandoned" objects,
    056 * i.e. objects that have been checked out of the pool but neither used nor
    057 * returned before the configured
    058 * {@link AbandonedConfig#getRemoveAbandonedTimeoutDuration() removeAbandonedTimeout}.
    059 * Abandoned object removal can be configured to happen when
    060 * {@code borrowObject} is invoked and the pool is close to starvation, or
    061 * it can be executed by the idle object evictor, or both. If pooled objects
    062 * implement the {@link TrackedUse} interface, their last use will be queried
    063 * using the {@code getLastUsed} method on that interface; otherwise
    064 * abandonment is determined by how long an object has been checked out from
    065 * the pool.
    066 * </p>
    067 * <p>
    068 * Implementation note: To prevent possible deadlocks, care has been taken to
    069 * ensure that no call to a factory method will occur within a synchronization
    070 * block. See POOL-125 and DBCP-44 for more information.
    071 * </p>
    072 * <p>
    073 * This class is intended to be thread-safe.
    074 * </p>
    075 *
    076 * @see GenericKeyedObjectPool
    077 *
    078 * @param <T> Type of element pooled in this pool.
    079 *
    080 * @since 2.0
    081 */
    082public class GenericObjectPool<T> extends BaseGenericObjectPool<T>
    083        implements ObjectPool<T>, GenericObjectPoolMXBean, UsageTracking<T> {
    084
    085    // JMX specific attributes
    086    private static final String ONAME_BASE =
    087        "org.apache.commons.pool2:type=GenericObjectPool,name=";
    088
    089    private volatile String factoryType;
    090
    091    private volatile int maxIdle = GenericObjectPoolConfig.DEFAULT_MAX_IDLE;
    092
    093    private volatile int minIdle = GenericObjectPoolConfig.DEFAULT_MIN_IDLE;
    094
    095    private final PooledObjectFactory<T> factory;
    096
    097    /*
    098     * All of the objects currently associated with this pool in any state. It
    099     * excludes objects that have been destroyed. The size of
    100     * {@link #allObjects} will always be less than or equal to {@link
    101     * #_maxActive}. Map keys are pooled objects, values are the PooledObject
    102     * wrappers used internally by the pool.
    103     */
    104    private final Map<IdentityWrapper<T>, PooledObject<T>> allObjects =
    105        new ConcurrentHashMap<>();
    106
    107    /*
    108     * The combined count of the currently created objects and those in the
    109     * process of being created. Under load, it may exceed {@link #_maxActive}
    110     * if multiple threads try and create a new object at the same time but
    111     * {@link #create()} will ensure that there are never more than
    112     * {@link #_maxActive} objects created at any one time.
    113     */
    114    private final AtomicLong createCount = new AtomicLong();
    115
    116    private long makeObjectCount;
    117
    118    private final Object makeObjectCountLock = new Object();
    119
    120    private final LinkedBlockingDeque<PooledObject<T>> idleObjects;
    121
    122    /**
    123     * Creates a new {@code GenericObjectPool} using defaults from
    124     * {@link GenericObjectPoolConfig}.
    125     *
    126     * @param factory The object factory to be used to create object instances
    127     *                used by this pool
    128     */
    129    public GenericObjectPool(final PooledObjectFactory<T> factory) {
    130        this(factory, new GenericObjectPoolConfig<>());
    131    }
    132
    133    /**
    134     * Creates a new {@code GenericObjectPool} using a specific
    135     * configuration.
    136     *
    137     * @param factory   The object factory to be used to create object instances
    138     *                  used by this pool
    139     * @param config    The configuration to use for this pool instance. The
    140     *                  configuration is used by value. Subsequent changes to
    141     *                  the configuration object will not be reflected in the
    142     *                  pool.
    143     */
    144    public GenericObjectPool(final PooledObjectFactory<T> factory,
    145            final GenericObjectPoolConfig<T> config) {
    146
    147        super(config, ONAME_BASE, config.getJmxNamePrefix());
    148
    149        if (factory == null) {
    150            jmxUnregister(); // tidy up
    151            throw new IllegalArgumentException("Factory may not be null");
    152        }
    153        this.factory = factory;
    154
    155        idleObjects = new LinkedBlockingDeque<>(config.getFairness());
    156
    157        setConfig(config);
    158    }
    159
    160    /**
    161     * Creates a new {@code GenericObjectPool} that tracks and destroys
    162     * objects that are checked out, but never returned to the pool.
    163     *
    164     * @param factory   The object factory to be used to create object instances
    165     *                  used by this pool
    166     * @param config    The base pool configuration to use for this pool instance.
    167     *                  The configuration is used by value. Subsequent changes to
    168     *                  the configuration object will not be reflected in the
    169     *                  pool.
    170     * @param abandonedConfig  Configuration for abandoned object identification
    171     *                         and removal.  The configuration is used by value.
    172     */
    173    public GenericObjectPool(final PooledObjectFactory<T> factory,
    174            final GenericObjectPoolConfig<T> config, final AbandonedConfig abandonedConfig) {
    175        this(factory, config);
    176        setAbandonedConfig(abandonedConfig);
    177    }
    178
    179    /**
    180     * Adds the provided wrapped pooled object to the set of idle objects for
    181     * this pool. The object must already be part of the pool.  If {@code p}
    182     * is null, this is a no-op (no exception, but no impact on the pool).
    183     *
    184     * @param p The object to make idle
    185     *
    186     * @throws Exception If the factory fails to passivate the object
    187     */
    188    private void addIdleObject(final PooledObject<T> p) throws Exception {
    189        if (p != null) {
    190            factory.passivateObject(p);
    191            if (getLifo()) {
    192                idleObjects.addFirst(p);
    193            } else {
    194                idleObjects.addLast(p);
    195            }
    196        }
    197    }
    198
    199    /**
    200     * Creates an object, and place it into the pool. addObject() is useful for
    201     * "pre-loading" a pool with idle objects.
    202     * <p>
    203     * If there is no capacity available to add to the pool, this is a no-op
    204     * (no exception, no impact to the pool). </p>
    205     */
    206    @Override
    207    public void addObject() throws Exception {
    208        assertOpen();
    209        if (factory == null) {
    210            throw new IllegalStateException("Cannot add objects without a factory.");
    211        }
    212        addIdleObject(create());
    213    }
    214
    215    /**
    216     * Equivalent to <code>{@link #borrowObject(long)
    217     * borrowObject}({@link #getMaxWaitDuration()})</code>.
    218     *
    219     * {@inheritDoc}
    220     */
    221    @Override
    222    public T borrowObject() throws Exception {
    223        return borrowObject(getMaxWaitDuration());
    224    }
    225
    226    /**
    227     * Borrows an object from the pool using the specific waiting time which only
    228     * applies if {@link #getBlockWhenExhausted()} is true.
    229     * <p>
    230     * If there is one or more idle instance available in the pool, then an
    231     * idle instance will be selected based on the value of {@link #getLifo()},
    232     * activated and returned. If activation fails, or {@link #getTestOnBorrow()
    233     * testOnBorrow} is set to {@code true} and validation fails, the
    234     * instance is destroyed and the next available instance is examined. This
    235     * continues until either a valid instance is returned or there are no more
    236     * idle instances available.
    237     * </p>
    238     * <p>
    239     * If there are no idle instances available in the pool, behavior depends on
    240     * the {@link #getMaxTotal() maxTotal}, (if applicable)
    241     * {@link #getBlockWhenExhausted()} and the value passed in to the
    242     * {@code borrowMaxWaitMillis} parameter. If the number of instances
    243     * checked out from the pool is less than {@code maxTotal,} a new
    244     * instance is created, activated and (if applicable) validated and returned
    245     * to the caller. If validation fails, a {@code NoSuchElementException}
    246     * is thrown.
    247     * </p>
    248     * <p>
    249     * If the pool is exhausted (no available idle instances and no capacity to
    250     * create new ones), this method will either block (if
    251     * {@link #getBlockWhenExhausted()} is true) or throw a
    252     * {@code NoSuchElementException} (if
    253     * {@link #getBlockWhenExhausted()} is false). The length of time that this
    254     * method will block when {@link #getBlockWhenExhausted()} is true is
    255     * determined by the value passed in to the {@code borrowMaxWaitMillis}
    256     * parameter.
    257     * </p>
    258     * <p>
    259     * When the pool is exhausted, multiple calling threads may be
    260     * simultaneously blocked waiting for instances to become available. A
    261     * "fairness" algorithm has been implemented to ensure that threads receive
    262     * available instances in request arrival order.
    263     * </p>
    264     *
    265     * @param borrowMaxWaitDuration The time to wait for an object
    266     *                            to become available
    267     *
    268     * @return object instance from the pool
    269     *
    270     * @throws NoSuchElementException if an instance cannot be returned
    271     *
    272     * @throws Exception if an object instance cannot be returned due to an
    273     *                   error
    274     * @since 2.10.0
    275     */
    276    public T borrowObject(final Duration borrowMaxWaitDuration) throws Exception {
    277        assertOpen();
    278
    279        final AbandonedConfig ac = this.abandonedConfig;
    280        if (ac != null && ac.getRemoveAbandonedOnBorrow() && (getNumIdle() < 2) &&
    281                (getNumActive() > getMaxTotal() - 3)) {
    282            removeAbandoned(ac);
    283        }
    284
    285        PooledObject<T> p = null;
    286
    287        // Get local copy of current config so it is consistent for entire
    288        // method execution
    289        final boolean blockWhenExhausted = getBlockWhenExhausted();
    290
    291        boolean create;
    292        final long waitTimeMillis = System.currentTimeMillis();
    293
    294        while (p == null) {
    295            create = false;
    296            p = idleObjects.pollFirst();
    297            if (p == null) {
    298                p = create();
    299                if (p != null) {
    300                    create = true;
    301                }
    302            }
    303            if (blockWhenExhausted) {
    304                if (p == null) {
    305                    if (borrowMaxWaitDuration.isNegative()) {
    306                        p = idleObjects.takeFirst();
    307                    } else {
    308                        p = idleObjects.pollFirst(borrowMaxWaitDuration);
    309                    }
    310                }
    311                if (p == null) {
    312                    throw new NoSuchElementException(appendStats(
    313                            "Timeout waiting for idle object, borrowMaxWaitMillis=" + borrowMaxWaitDuration));
    314                }
    315            } else if (p == null) {
    316                throw new NoSuchElementException(appendStats("Pool exhausted"));
    317            }
    318            if (!p.allocate()) {
    319                p = null;
    320            }
    321
    322            if (p != null) {
    323                try {
    324                    factory.activateObject(p);
    325                } catch (final Exception e) {
    326                    try {
    327                        destroy(p, DestroyMode.NORMAL);
    328                    } catch (final Exception e1) {
    329                        // Ignore - activation failure is more important
    330                    }
    331                    p = null;
    332                    if (create) {
    333                        final NoSuchElementException nsee = new NoSuchElementException(
    334                                appendStats("Unable to activate object"));
    335                        nsee.initCause(e);
    336                        throw nsee;
    337                    }
    338                }
    339                if (p != null && getTestOnBorrow()) {
    340                    boolean validate = false;
    341                    Throwable validationThrowable = null;
    342                    try {
    343                        validate = factory.validateObject(p);
    344                    } catch (final Throwable t) {
    345                        PoolUtils.checkRethrow(t);
    346                        validationThrowable = t;
    347                    }
    348                    if (!validate) {
    349                        try {
    350                            destroy(p, DestroyMode.NORMAL);
    351                            destroyedByBorrowValidationCount.incrementAndGet();
    352                        } catch (final Exception e) {
    353                            // Ignore - validation failure is more important
    354                        }
    355                        p = null;
    356                        if (create) {
    357                            final NoSuchElementException nsee = new NoSuchElementException(
    358                                    appendStats("Unable to validate object"));
    359                            nsee.initCause(validationThrowable);
    360                            throw nsee;
    361                        }
    362                    }
    363                }
    364            }
    365        }
    366
    367        updateStatsBorrow(p, Duration.ofMillis(System.currentTimeMillis() - waitTimeMillis));
    368
    369        return p.getObject();
    370    }
    371
    372    @Override
    373    String getStatsString() {
    374        // Simply listed in AB order.
    375        return super.getStatsString() +
    376                String.format(", createdCount=%,d, makeObjectCount=%,d, maxIdle=%,d, minIdle=%,d",
    377                        createdCount.get(), makeObjectCount, maxIdle, minIdle);
    378    }
    379
    380    /**
    381     * Borrows an object from the pool using the specific waiting time which only
    382     * applies if {@link #getBlockWhenExhausted()} is true.
    383     * <p>
    384     * If there is one or more idle instance available in the pool, then an
    385     * idle instance will be selected based on the value of {@link #getLifo()},
    386     * activated and returned. If activation fails, or {@link #getTestOnBorrow()
    387     * testOnBorrow} is set to {@code true} and validation fails, the
    388     * instance is destroyed and the next available instance is examined. This
    389     * continues until either a valid instance is returned or there are no more
    390     * idle instances available.
    391     * </p>
    392     * <p>
    393     * If there are no idle instances available in the pool, behavior depends on
    394     * the {@link #getMaxTotal() maxTotal}, (if applicable)
    395     * {@link #getBlockWhenExhausted()} and the value passed in to the
    396     * {@code borrowMaxWaitMillis} parameter. If the number of instances
    397     * checked out from the pool is less than {@code maxTotal,} a new
    398     * instance is created, activated and (if applicable) validated and returned
    399     * to the caller. If validation fails, a {@code NoSuchElementException}
    400     * is thrown.
    401     * </p>
    402     * <p>
    403     * If the pool is exhausted (no available idle instances and no capacity to
    404     * create new ones), this method will either block (if
    405     * {@link #getBlockWhenExhausted()} is true) or throw a
    406     * {@code NoSuchElementException} (if
    407     * {@link #getBlockWhenExhausted()} is false). The length of time that this
    408     * method will block when {@link #getBlockWhenExhausted()} is true is
    409     * determined by the value passed in to the {@code borrowMaxWaitMillis}
    410     * parameter.
    411     * </p>
    412     * <p>
    413     * When the pool is exhausted, multiple calling threads may be
    414     * simultaneously blocked waiting for instances to become available. A
    415     * "fairness" algorithm has been implemented to ensure that threads receive
    416     * available instances in request arrival order.
    417     * </p>
    418     *
    419     * @param borrowMaxWaitMillis The time to wait in milliseconds for an object
    420     *                            to become available
    421     *
    422     * @return object instance from the pool
    423     *
    424     * @throws NoSuchElementException if an instance cannot be returned
    425     *
    426     * @throws Exception if an object instance cannot be returned due to an
    427     *                   error
    428     */
    429    public T borrowObject(final long borrowMaxWaitMillis) throws Exception {
    430        return borrowObject(Duration.ofMillis(borrowMaxWaitMillis));
    431    }
    432
    433    /**
    434     * Clears any objects sitting idle in the pool by removing them from the
    435     * idle instance pool and then invoking the configured
    436     * {@link PooledObjectFactory#destroyObject(PooledObject)} method on each
    437     * idle instance.
    438     * <p>
    439     * Implementation notes:
    440     * </p>
    441     * <ul>
    442     * <li>This method does not destroy or effect in any way instances that are
    443     * checked out of the pool when it is invoked.</li>
    444     * <li>Invoking this method does not prevent objects being returned to the
    445     * idle instance pool, even during its execution. Additional instances may
    446     * be returned while removed items are being destroyed.</li>
    447     * <li>Exceptions encountered destroying idle instances are swallowed
    448     * but notified via a {@link SwallowedExceptionListener}.</li>
    449     * </ul>
    450     */
    451    @Override
    452    public void clear() {
    453        PooledObject<T> p = idleObjects.poll();
    454
    455        while (p != null) {
    456            try {
    457                destroy(p, DestroyMode.NORMAL);
    458            } catch (final Exception e) {
    459                swallowException(e);
    460            }
    461            p = idleObjects.poll();
    462        }
    463    }
    464
    465    /**
    466     * Closes the pool. Once the pool is closed, {@link #borrowObject()} will
    467     * fail with IllegalStateException, but {@link #returnObject(Object)} and
    468     * {@link #invalidateObject(Object)} will continue to work, with returned
    469     * objects destroyed on return.
    470     * <p>
    471     * Destroys idle instances in the pool by invoking {@link #clear()}.
    472     * </p>
    473     */
    474    @Override
    475    public void close() {
    476        if (isClosed()) {
    477            return;
    478        }
    479
    480        synchronized (closeLock) {
    481            if (isClosed()) {
    482                return;
    483            }
    484
    485            // Stop the evictor before the pool is closed since evict() calls
    486            // assertOpen()
    487            stopEvictor();
    488
    489            closed = true;
    490            // This clear removes any idle objects
    491            clear();
    492
    493            jmxUnregister();
    494
    495            // Release any threads that were waiting for an object
    496            idleObjects.interuptTakeWaiters();
    497        }
    498    }
    499
    500    /**
    501     * Attempts to create a new wrapped pooled object.
    502     * <p>
    503     * If there are {@link #getMaxTotal()} objects already in circulation
    504     * or in process of being created, this method returns null.
    505     * </p>
    506     *
    507     * @return The new wrapped pooled object
    508     *
    509     * @throws Exception if the object factory's {@code makeObject} fails
    510     */
    511    private PooledObject<T> create() throws Exception {
    512        int localMaxTotal = getMaxTotal();
    513        // This simplifies the code later in this method
    514        if (localMaxTotal < 0) {
    515            localMaxTotal = Integer.MAX_VALUE;
    516        }
    517
    518        final long localStartTimeMillis = System.currentTimeMillis();
    519        final long localMaxWaitTimeMillis = Math.max(getMaxWaitDuration().toMillis(), 0);
    520
    521        // Flag that indicates if create should:
    522        // - TRUE:  call the factory to create an object
    523        // - FALSE: return null
    524        // - null:  loop and re-test the condition that determines whether to
    525        //          call the factory
    526        Boolean create = null;
    527        while (create == null) {
    528            synchronized (makeObjectCountLock) {
    529                final long newCreateCount = createCount.incrementAndGet();
    530                if (newCreateCount > localMaxTotal) {
    531                    // The pool is currently at capacity or in the process of
    532                    // making enough new objects to take it to capacity.
    533                    createCount.decrementAndGet();
    534                    if (makeObjectCount == 0) {
    535                        // There are no makeObject() calls in progress so the
    536                        // pool is at capacity. Do not attempt to create a new
    537                        // object. Return and wait for an object to be returned
    538                        create = Boolean.FALSE;
    539                    } else {
    540                        // There are makeObject() calls in progress that might
    541                        // bring the pool to capacity. Those calls might also
    542                        // fail so wait until they complete and then re-test if
    543                        // the pool is at capacity or not.
    544                        makeObjectCountLock.wait(localMaxWaitTimeMillis);
    545                    }
    546                } else {
    547                    // The pool is not at capacity. Create a new object.
    548                    makeObjectCount++;
    549                    create = Boolean.TRUE;
    550                }
    551            }
    552
    553            // Do not block more if maxWaitTimeMillis is set.
    554            if (create == null &&
    555                (localMaxWaitTimeMillis > 0 &&
    556                 System.currentTimeMillis() - localStartTimeMillis >= localMaxWaitTimeMillis)) {
    557                create = Boolean.FALSE;
    558            }
    559        }
    560
    561        if (!create.booleanValue()) {
    562            return null;
    563        }
    564
    565        final PooledObject<T> p;
    566        try {
    567            p = factory.makeObject();
    568            if (getTestOnCreate() && !factory.validateObject(p)) {
    569                createCount.decrementAndGet();
    570                return null;
    571            }
    572        } catch (final Throwable e) {
    573            createCount.decrementAndGet();
    574            throw e;
    575        } finally {
    576            synchronized (makeObjectCountLock) {
    577                makeObjectCount--;
    578                makeObjectCountLock.notifyAll();
    579            }
    580        }
    581
    582        final AbandonedConfig ac = this.abandonedConfig;
    583        if (ac != null && ac.getLogAbandoned()) {
    584            p.setLogAbandoned(true);
    585            p.setRequireFullStackTrace(ac.getRequireFullStackTrace());
    586        }
    587
    588        createdCount.incrementAndGet();
    589        allObjects.put(new IdentityWrapper<>(p.getObject()), p);
    590        return p;
    591    }
    592
    593    /**
    594     * Destroys a wrapped pooled object.
    595     *
    596     * @param toDestroy The wrapped pooled object to destroy
    597     * @param destroyMode DestroyMode context provided to the factory
    598     *
    599     * @throws Exception If the factory fails to destroy the pooled object
    600     *                   cleanly
    601     */
    602    private void destroy(final PooledObject<T> toDestroy, final DestroyMode destroyMode) throws Exception {
    603        toDestroy.invalidate();
    604        idleObjects.remove(toDestroy);
    605        allObjects.remove(new IdentityWrapper<>(toDestroy.getObject()));
    606        try {
    607            factory.destroyObject(toDestroy, destroyMode);
    608        } finally {
    609            destroyedCount.incrementAndGet();
    610            createCount.decrementAndGet();
    611        }
    612    }
    613
    614    /**
    615     * Tries to ensure that {@code idleCount} idle instances exist in the pool.
    616     * <p>
    617     * Creates and adds idle instances until either {@link #getNumIdle()} reaches {@code idleCount}
    618     * or the total number of objects (idle, checked out, or being created) reaches
    619     * {@link #getMaxTotal()}. If {@code always} is false, no instances are created unless
    620     * there are threads waiting to check out instances from the pool.
    621     * </p>
    622     *
    623     * @param idleCount the number of idle instances desired
    624     * @param always true means create instances even if the pool has no threads waiting
    625     * @throws Exception if the factory's makeObject throws
    626     */
    627    private void ensureIdle(final int idleCount, final boolean always) throws Exception {
    628        if (idleCount < 1 || isClosed() || (!always && !idleObjects.hasTakeWaiters())) {
    629            return;
    630        }
    631
    632        while (idleObjects.size() < idleCount) {
    633            final PooledObject<T> p = create();
    634            if (p == null) {
    635                // Can't create objects, no reason to think another call to
    636                // create will work. Give up.
    637                break;
    638            }
    639            if (getLifo()) {
    640                idleObjects.addFirst(p);
    641            } else {
    642                idleObjects.addLast(p);
    643            }
    644        }
    645        if (isClosed()) {
    646            // Pool closed while object was being added to idle objects.
    647            // Make sure the returned object is destroyed rather than left
    648            // in the idle object pool (which would effectively be a leak)
    649            clear();
    650        }
    651    }
    652
    653    @Override
    654    void ensureMinIdle() throws Exception {
    655        ensureIdle(getMinIdle(), true);
    656    }
    657
    658    /**
    659     * {@inheritDoc}
    660     * <p>
    661     * Successive activations of this method examine objects in sequence,
    662     * cycling through objects in oldest-to-youngest order.
    663     * </p>
    664     */
    665    @Override
    666    public void evict() throws Exception {
    667        assertOpen();
    668
    669        if (!idleObjects.isEmpty()) {
    670
    671            PooledObject<T> underTest = null;
    672            final EvictionPolicy<T> evictionPolicy = getEvictionPolicy();
    673
    674            synchronized (evictionLock) {
    675                final EvictionConfig evictionConfig = new EvictionConfig(
    676                        getMinEvictableIdleDuration(),
    677                        getSoftMinEvictableIdleDuration(),
    678                        getMinIdle());
    679
    680                final boolean testWhileIdle = getTestWhileIdle();
    681
    682                for (int i = 0, m = getNumTests(); i < m; i++) {
    683                    if (evictionIterator == null || !evictionIterator.hasNext()) {
    684                        evictionIterator = new EvictionIterator(idleObjects);
    685                    }
    686                    if (!evictionIterator.hasNext()) {
    687                        // Pool exhausted, nothing to do here
    688                        return;
    689                    }
    690
    691                    try {
    692                        underTest = evictionIterator.next();
    693                    } catch (final NoSuchElementException nsee) {
    694                        // Object was borrowed in another thread
    695                        // Don't count this as an eviction test so reduce i;
    696                        i--;
    697                        evictionIterator = null;
    698                        continue;
    699                    }
    700
    701                    if (!underTest.startEvictionTest()) {
    702                        // Object was borrowed in another thread
    703                        // Don't count this as an eviction test so reduce i;
    704                        i--;
    705                        continue;
    706                    }
    707
    708                    // User provided eviction policy could throw all sorts of
    709                    // crazy exceptions. Protect against such an exception
    710                    // killing the eviction thread.
    711                    boolean evict;
    712                    try {
    713                        evict = evictionPolicy.evict(evictionConfig, underTest,
    714                                idleObjects.size());
    715                    } catch (final Throwable t) {
    716                        // Slightly convoluted as SwallowedExceptionListener
    717                        // uses Exception rather than Throwable
    718                        PoolUtils.checkRethrow(t);
    719                        swallowException(new Exception(t));
    720                        // Don't evict on error conditions
    721                        evict = false;
    722                    }
    723
    724                    if (evict) {
    725                        destroy(underTest, DestroyMode.NORMAL);
    726                        destroyedByEvictorCount.incrementAndGet();
    727                    } else {
    728                        if (testWhileIdle) {
    729                            boolean active = false;
    730                            try {
    731                                factory.activateObject(underTest);
    732                                active = true;
    733                            } catch (final Exception e) {
    734                                destroy(underTest, DestroyMode.NORMAL);
    735                                destroyedByEvictorCount.incrementAndGet();
    736                            }
    737                            if (active) {
    738                                boolean validate = false;
    739                                Throwable validationThrowable = null;
    740                                try {
    741                                    validate = factory.validateObject(underTest);
    742                                } catch (final Throwable t) {
    743                                    PoolUtils.checkRethrow(t);
    744                                    validationThrowable = t;
    745                                }
    746                                if (!validate) {
    747                                    destroy(underTest, DestroyMode.NORMAL);
    748                                    destroyedByEvictorCount.incrementAndGet();
    749                                    if (validationThrowable != null) {
    750                                        if (validationThrowable instanceof RuntimeException) {
    751                                            throw (RuntimeException) validationThrowable;
    752                                        }
    753                                        throw (Error) validationThrowable;
    754                                    }
    755                                } else {
    756                                    try {
    757                                        factory.passivateObject(underTest);
    758                                    } catch (final Exception e) {
    759                                        destroy(underTest, DestroyMode.NORMAL);
    760                                        destroyedByEvictorCount.incrementAndGet();
    761                                    }
    762                                }
    763                            }
    764                        }
    765                        if (!underTest.endEvictionTest(idleObjects)) {
    766                            // TODO - May need to add code here once additional
    767                            // states are used
    768                        }
    769                    }
    770                }
    771            }
    772        }
    773        final AbandonedConfig ac = this.abandonedConfig;
    774        if (ac != null && ac.getRemoveAbandonedOnMaintenance()) {
    775            removeAbandoned(ac);
    776        }
    777    }
    778
    779    /**
    780     * Gets a reference to the factory used to create, destroy and validate
    781     * the objects used by this pool.
    782     *
    783     * @return the factory
    784     */
    785    public PooledObjectFactory<T> getFactory() {
    786        return factory;
    787    }
    788
    789    /**
    790     * Gets the type - including the specific type rather than the generic -
    791     * of the factory.
    792     *
    793     * @return A string representation of the factory type
    794     */
    795    @Override
    796    public String getFactoryType() {
    797        // Not thread safe. Accept that there may be multiple evaluations.
    798        if (factoryType == null) {
    799            final StringBuilder result = new StringBuilder();
    800            result.append(factory.getClass().getName());
    801            result.append('<');
    802            final Class<?> pooledObjectType =
    803                    PoolImplUtils.getFactoryType(factory.getClass());
    804            result.append(pooledObjectType.getName());
    805            result.append('>');
    806            factoryType = result.toString();
    807        }
    808        return factoryType;
    809    }
    810
    811    /**
    812     * Gets the cap on the number of "idle" instances in the pool. If maxIdle
    813     * is set too low on heavily loaded systems it is possible you will see
    814     * objects being destroyed and almost immediately new objects being created.
    815     * This is a result of the active threads momentarily returning objects
    816     * faster than they are requesting them, causing the number of idle
    817     * objects to rise above maxIdle. The best value for maxIdle for heavily
    818     * loaded system will vary but the default is a good starting point.
    819     *
    820     * @return the maximum number of "idle" instances that can be held in the
    821     *         pool or a negative value if there is no limit
    822     *
    823     * @see #setMaxIdle
    824     */
    825    @Override
    826    public int getMaxIdle() {
    827        return maxIdle;
    828    }
    829
    830    /**
    831     * Gets the target for the minimum number of idle objects to maintain in
    832     * the pool. This setting only has an effect if it is positive and
    833     * {@link #getDurationBetweenEvictionRuns()} is greater than zero. If this
    834     * is the case, an attempt is made to ensure that the pool has the required
    835     * minimum number of instances during idle object eviction runs.
    836     * <p>
    837     * If the configured value of minIdle is greater than the configured value
    838     * for maxIdle then the value of maxIdle will be used instead.
    839     * </p>
    840     *
    841     * @return The minimum number of objects.
    842     *
    843     * @see #setMinIdle(int)
    844     * @see #setMaxIdle(int)
    845     * @see #setTimeBetweenEvictionRuns(Duration)
    846     */
    847    @Override
    848    public int getMinIdle() {
    849        final int maxIdleSave = getMaxIdle();
    850        if (this.minIdle > maxIdleSave) {
    851            return maxIdleSave;
    852        }
    853        return minIdle;
    854    }
    855
    856    @Override
    857    public int getNumActive() {
    858        return allObjects.size() - idleObjects.size();
    859    }
    860
    861    @Override
    862    public int getNumIdle() {
    863        return idleObjects.size();
    864    }
    865
    866    /**
    867     * Calculates the number of objects to test in a run of the idle object
    868     * evictor.
    869     *
    870     * @return The number of objects to test for validity
    871     */
    872    private int getNumTests() {
    873        final int numTestsPerEvictionRun = getNumTestsPerEvictionRun();
    874        if (numTestsPerEvictionRun >= 0) {
    875            return Math.min(numTestsPerEvictionRun, idleObjects.size());
    876        }
    877        return (int) (Math.ceil(idleObjects.size() /
    878                Math.abs((double) numTestsPerEvictionRun)));
    879    }
    880
    881    /**
    882     * Gets an estimate of the number of threads currently blocked waiting for
    883     * an object from the pool. This is intended for monitoring only, not for
    884     * synchronization control.
    885     *
    886     * @return The estimate of the number of threads currently blocked waiting
    887     *         for an object from the pool
    888     */
    889    @Override
    890    public int getNumWaiters() {
    891        if (getBlockWhenExhausted()) {
    892            return idleObjects.getTakeQueueLength();
    893        }
    894        return 0;
    895    }
    896
    897    /**
    898     * {@inheritDoc}
    899     * <p>
    900     * Activation of this method decrements the active count and attempts to
    901     * destroy the instance, using the default (NORMAL) {@link DestroyMode}.
    902     * </p>
    903     *
    904     * @throws Exception             if an exception occurs destroying the
    905     *                               object
    906     * @throws IllegalStateException if obj does not belong to this pool
    907     */
    908    @Override
    909    public void invalidateObject(final T obj) throws Exception {
    910        invalidateObject(obj, DestroyMode.NORMAL);
    911    }
    912
    913    /**
    914     * {@inheritDoc}
    915     * <p>
    916     * Activation of this method decrements the active count and attempts to
    917     * destroy the instance, using the provided {@link DestroyMode}.
    918     * </p>
    919     *
    920     * @throws Exception             if an exception occurs destroying the
    921     *                               object
    922     * @throws IllegalStateException if obj does not belong to this pool
    923     * @since 2.9.0
    924     */
    925    @Override
    926    public void invalidateObject(final T obj, final DestroyMode destroyMode) throws Exception {
    927        final PooledObject<T> p = allObjects.get(new IdentityWrapper<>(obj));
    928        if (p == null) {
    929            if (isAbandonedConfig()) {
    930                return;
    931            }
    932            throw new IllegalStateException(
    933                    "Invalidated object not currently part of this pool");
    934        }
    935        synchronized (p) {
    936            if (p.getState() != PooledObjectState.INVALID) {
    937                destroy(p, destroyMode);
    938            }
    939        }
    940        ensureIdle(1, false);
    941    }
    942
    943    /**
    944     * Provides information on all the objects in the pool, both idle (waiting
    945     * to be borrowed) and active (currently borrowed).
    946     * <p>
    947     * Note: This is named listAllObjects so it is presented as an operation via
    948     * JMX. That means it won't be invoked unless the explicitly requested
    949     * whereas all attributes will be automatically requested when viewing the
    950     * attributes for an object in a tool like JConsole.
    951     * </p>
    952     *
    953     * @return Information grouped on all the objects in the pool
    954     */
    955    @Override
    956    public Set<DefaultPooledObjectInfo> listAllObjects() {
    957        return allObjects.values().stream().map(DefaultPooledObjectInfo::new).collect(Collectors.toSet());
    958    }
    959    /**
    960     * Tries to ensure that {@link #getMinIdle()} idle instances are available
    961     * in the pool.
    962     *
    963     * @throws Exception If the associated factory throws an exception
    964     * @since 2.4
    965     */
    966    public void preparePool() throws Exception {
    967        if (getMinIdle() < 1) {
    968            return;
    969        }
    970        ensureMinIdle();
    971    }
    972
    973    /**
    974     * Recovers abandoned objects which have been checked out but
    975     * not used since longer than the removeAbandonedTimeout.
    976     *
    977     * @param abandonedConfig The configuration to use to identify abandoned objects
    978     */
    979    @SuppressWarnings("resource") // PrintWriter is managed elsewhere
    980    private void removeAbandoned(final AbandonedConfig abandonedConfig) {
    981        // Generate a list of abandoned objects to remove
    982        final ArrayList<PooledObject<T>> remove = createRemoveList(abandonedConfig, allObjects);
    983        // Now remove the abandoned objects
    984        remove.forEach(pooledObject -> {
    985            if (abandonedConfig.getLogAbandoned()) {
    986                pooledObject.printStackTrace(abandonedConfig.getLogWriter());
    987            }
    988            try {
    989                invalidateObject(pooledObject.getObject(), DestroyMode.ABANDONED);
    990            } catch (final Exception e) {
    991                swallowException(e);
    992            }
    993        });
    994    }
    995
    996    /**
    997     * {@inheritDoc}
    998     * <p>
    999     * If {@link #getMaxIdle() maxIdle} is set to a positive value and the
    1000     * number of idle instances has reached this value, the returning instance
    1001     * is destroyed.
    1002     * </p>
    1003     * <p>
    1004     * If {@link #getTestOnReturn() testOnReturn} == true, the returning
    1005     * instance is validated before being returned to the idle instance pool. In
    1006     * this case, if validation fails, the instance is destroyed.
    1007     * </p>
    1008     * <p>
    1009     * Exceptions encountered destroying objects for any reason are swallowed
    1010     * but notified via a {@link SwallowedExceptionListener}.
    1011     * </p>
    1012     */
    1013    @Override
    1014    public void returnObject(final T obj) {
    1015        final PooledObject<T> p = allObjects.get(new IdentityWrapper<>(obj));
    1016
    1017        if (p == null) {
    1018            if (!isAbandonedConfig()) {
    1019                throw new IllegalStateException(
    1020                        "Returned object not currently part of this pool");
    1021            }
    1022            return; // Object was abandoned and removed
    1023        }
    1024
    1025        markReturningState(p);
    1026
    1027        final Duration activeTime = p.getActiveDuration();
    1028
    1029        if (getTestOnReturn() && !factory.validateObject(p)) {
    1030            try {
    1031                destroy(p, DestroyMode.NORMAL);
    1032            } catch (final Exception e) {
    1033                swallowException(e);
    1034            }
    1035            try {
    1036                ensureIdle(1, false);
    1037            } catch (final Exception e) {
    1038                swallowException(e);
    1039            }
    1040            updateStatsReturn(activeTime);
    1041            return;
    1042        }
    1043
    1044        try {
    1045            factory.passivateObject(p);
    1046        } catch (final Exception e1) {
    1047            swallowException(e1);
    1048            try {
    1049                destroy(p, DestroyMode.NORMAL);
    1050            } catch (final Exception e) {
    1051                swallowException(e);
    1052            }
    1053            try {
    1054                ensureIdle(1, false);
    1055            } catch (final Exception e) {
    1056                swallowException(e);
    1057            }
    1058            updateStatsReturn(activeTime);
    1059            return;
    1060        }
    1061
    1062        if (!p.deallocate()) {
    1063            throw new IllegalStateException(
    1064                    "Object has already been returned to this pool or is invalid");
    1065        }
    1066
    1067        final int maxIdleSave = getMaxIdle();
    1068        if (isClosed() || maxIdleSave > -1 && maxIdleSave <= idleObjects.size()) {
    1069            try {
    1070                destroy(p, DestroyMode.NORMAL);
    1071            } catch (final Exception e) {
    1072                swallowException(e);
    1073            }
    1074            try {
    1075                ensureIdle(1, false);
    1076            } catch (final Exception e) {
    1077                swallowException(e);
    1078            }
    1079        } else {
    1080            if (getLifo()) {
    1081                idleObjects.addFirst(p);
    1082            } else {
    1083                idleObjects.addLast(p);
    1084            }
    1085            if (isClosed()) {
    1086                // Pool closed while object was being added to idle objects.
    1087                // Make sure the returned object is destroyed rather than left
    1088                // in the idle object pool (which would effectively be a leak)
    1089                clear();
    1090            }
    1091        }
    1092        updateStatsReturn(activeTime);
    1093    }
    1094
    1095    /**
    1096     * Sets the base pool configuration.
    1097     *
    1098     * @param conf the new configuration to use. This is used by value.
    1099     *
    1100     * @see GenericObjectPoolConfig
    1101     */
    1102    public void setConfig(final GenericObjectPoolConfig<T> conf) {
    1103        super.setConfig(conf);
    1104        setMaxIdle(conf.getMaxIdle());
    1105        setMinIdle(conf.getMinIdle());
    1106        setMaxTotal(conf.getMaxTotal());
    1107    }
    1108
    1109    /**
    1110     * Sets the cap on the number of "idle" instances in the pool. If maxIdle
    1111     * is set too low on heavily loaded systems it is possible you will see
    1112     * objects being destroyed and almost immediately new objects being created.
    1113     * This is a result of the active threads momentarily returning objects
    1114     * faster than they are requesting them, causing the number of idle
    1115     * objects to rise above maxIdle. The best value for maxIdle for heavily
    1116     * loaded system will vary but the default is a good starting point.
    1117     *
    1118     * @param maxIdle
    1119     *            The cap on the number of "idle" instances in the pool. Use a
    1120     *            negative value to indicate an unlimited number of idle
    1121     *            instances
    1122     *
    1123     * @see #getMaxIdle
    1124     */
    1125    public void setMaxIdle(final int maxIdle) {
    1126        this.maxIdle = maxIdle;
    1127    }
    1128
    1129    /**
    1130     * Sets the target for the minimum number of idle objects to maintain in
    1131     * the pool. This setting only has an effect if it is positive and
    1132     * {@link #getDurationBetweenEvictionRuns()} is greater than zero. If this
    1133     * is the case, an attempt is made to ensure that the pool has the required
    1134     * minimum number of instances during idle object eviction runs.
    1135     * <p>
    1136     * If the configured value of minIdle is greater than the configured value
    1137     * for maxIdle then the value of maxIdle will be used instead.
    1138     * </p>
    1139     *
    1140     * @param minIdle
    1141     *            The minimum number of objects.
    1142     *
    1143     * @see #getMinIdle()
    1144     * @see #getMaxIdle()
    1145     * @see #getDurationBetweenEvictionRuns()
    1146     */
    1147    public void setMinIdle(final int minIdle) {
    1148        this.minIdle = minIdle;
    1149    }
    1150
    1151    @Override
    1152    protected void toStringAppendFields(final StringBuilder builder) {
    1153        super.toStringAppendFields(builder);
    1154        builder.append(", factoryType=");
    1155        builder.append(factoryType);
    1156        builder.append(", maxIdle=");
    1157        builder.append(maxIdle);
    1158        builder.append(", minIdle=");
    1159        builder.append(minIdle);
    1160        builder.append(", factory=");
    1161        builder.append(factory);
    1162        builder.append(", allObjects=");
    1163        builder.append(allObjects);
    1164        builder.append(", createCount=");
    1165        builder.append(createCount);
    1166        builder.append(", idleObjects=");
    1167        builder.append(idleObjects);
    1168        builder.append(", abandonedConfig=");
    1169        builder.append(abandonedConfig);
    1170    }
    1171
    1172    @Override
    1173    public void use(final T pooledObject) {
    1174        final AbandonedConfig abandonedCfg = this.abandonedConfig;
    1175        if (abandonedCfg != null && abandonedCfg.getUseUsageTracking()) {
    1176            allObjects.get(new IdentityWrapper<>(pooledObject)).use();
    1177        }
    1178    }
    1179
    1180}