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}