GenericKeyedObjectPool.java
/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.tomcat.dbcp.pool2.impl;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Deque;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.NoSuchElementException;
import java.util.TreeMap;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import org.apache.tomcat.dbcp.pool2.DestroyMode;
import org.apache.tomcat.dbcp.pool2.KeyedObjectPool;
import org.apache.tomcat.dbcp.pool2.KeyedPooledObjectFactory;
import org.apache.tomcat.dbcp.pool2.PoolUtils;
import org.apache.tomcat.dbcp.pool2.PooledObject;
import org.apache.tomcat.dbcp.pool2.PooledObjectState;
/**
* A configurable {@code KeyedObjectPool} implementation.
* <p>
* When coupled with the appropriate {@link KeyedPooledObjectFactory},
* {@code GenericKeyedObjectPool} provides robust pooling functionality for
* keyed objects. A {@code GenericKeyedObjectPool} can be viewed as a map
* of sub-pools, keyed on the (unique) key values provided to the
* {@link #preparePool preparePool}, {@link #addObject addObject} or
* {@link #borrowObject borrowObject} methods. Each time a new key value is
* provided to one of these methods, a sub-new pool is created under the given
* key to be managed by the containing {@code GenericKeyedObjectPool.}
* </p>
* <p>
* Note that the current implementation uses a ConcurrentHashMap which uses
* equals() to compare keys.
* This means that distinct instance keys must be distinguishable using equals.
* </p>
* <p>
* Optionally, one may configure the pool to examine and possibly evict objects
* as they sit idle in the pool and to ensure that a minimum number of idle
* objects is maintained for each key. This is performed by an "idle object
* eviction" thread, which runs asynchronously. Caution should be used when
* configuring this optional feature. Eviction runs contend with client threads
* for access to objects in the pool, so if they run too frequently performance
* issues may result.
* </p>
* <p>
* Implementation note: To prevent possible deadlocks, care has been taken to
* ensure that no call to a factory method will occur within a synchronization
* block. See POOL-125 and DBCP-44 for more information.
* </p>
* <p>
* This class is intended to be thread-safe.
* </p>
*
* @see GenericObjectPool
*
* @param <K> The type of keys maintained by this pool.
* @param <T> Type of element pooled in this pool.
*
* @since 2.0
*/
public class GenericKeyedObjectPool<K, T> extends BaseGenericObjectPool<T>
implements KeyedObjectPool<K, T>, GenericKeyedObjectPoolMXBean<K> {
/**
* Create a new {@code GenericKeyedObjectPool} using defaults from
* {@link GenericKeyedObjectPoolConfig}.
* @param factory the factory to be used to create entries
*/
public GenericKeyedObjectPool(final KeyedPooledObjectFactory<K, T> factory) {
this(factory, new GenericKeyedObjectPoolConfig<T>());
}
/**
* Create a new {@code GenericKeyedObjectPool} using a specific
* configuration.
*
* @param factory the factory to be used to create entries
* @param config The configuration to use for this pool instance. The
* configuration is used by value. Subsequent changes to
* the configuration object will not be reflected in the
* pool.
*/
public GenericKeyedObjectPool(final KeyedPooledObjectFactory<K, T> factory,
final GenericKeyedObjectPoolConfig<T> config) {
super(config, ONAME_BASE, config.getJmxNamePrefix());
if (factory == null) {
jmxUnregister(); // tidy up
throw new IllegalArgumentException("factory may not be null");
}
this.factory = factory;
this.fairness = config.getFairness();
setConfig(config);
}
/**
* Returns the limit on the number of object instances allocated by the pool
* (checked out or idle), per key. When the limit is reached, the sub-pool
* is said to be exhausted. A negative value indicates no limit.
*
* @return the limit on the number of active instances per key
*
* @see #setMaxTotalPerKey
*/
@Override
public int getMaxTotalPerKey() {
return maxTotalPerKey;
}
/**
* Sets the limit on the number of object instances allocated by the pool
* (checked out or idle), per key. When the limit is reached, the sub-pool
* is said to be exhausted. A negative value indicates no limit.
*
* @param maxTotalPerKey the limit on the number of active instances per key
*
* @see #getMaxTotalPerKey
*/
public void setMaxTotalPerKey(final int maxTotalPerKey) {
this.maxTotalPerKey = maxTotalPerKey;
}
/**
* Returns the cap on the number of "idle" instances per key in the pool.
* If maxIdlePerKey is set too low on heavily loaded systems it is possible
* you will see objects being destroyed and almost immediately new objects
* being created. This is a result of the active threads momentarily
* returning objects faster than they are requesting them, causing the
* number of idle objects to rise above maxIdlePerKey. The best value for
* maxIdlePerKey for heavily loaded system will vary but the default is a
* good starting point.
*
* @return the maximum number of "idle" instances that can be held in a
* given keyed sub-pool or a negative value if there is no limit
*
* @see #setMaxIdlePerKey
*/
@Override
public int getMaxIdlePerKey() {
return maxIdlePerKey;
}
/**
* Sets the cap on the number of "idle" instances per key in the pool.
* If maxIdlePerKey is set too low on heavily loaded systems it is possible
* you will see objects being destroyed and almost immediately new objects
* being created. This is a result of the active threads momentarily
* returning objects faster than they are requesting them, causing the
* number of idle objects to rise above maxIdlePerKey. The best value for
* maxIdlePerKey for heavily loaded system will vary but the default is a
* good starting point.
*
* @param maxIdlePerKey the maximum number of "idle" instances that can be
* held in a given keyed sub-pool. Use a negative value
* for no limit
*
* @see #getMaxIdlePerKey
*/
public void setMaxIdlePerKey(final int maxIdlePerKey) {
this.maxIdlePerKey = maxIdlePerKey;
}
/**
* Sets the target for the minimum number of idle objects to maintain in
* each of the keyed sub-pools. This setting only has an effect if it is
* positive and {@link #getTimeBetweenEvictionRunsMillis()} is greater than
* zero. If this is the case, an attempt is made to ensure that each
* sub-pool has the required minimum number of instances during idle object
* eviction runs.
* <p>
* If the configured value of minIdlePerKey is greater than the configured
* value for maxIdlePerKey then the value of maxIdlePerKey will be used
* instead.
*
* @param minIdlePerKey The minimum size of the each keyed pool
*
* @see #getMinIdlePerKey
* @see #getMaxIdlePerKey()
* @see #setTimeBetweenEvictionRunsMillis
*/
public void setMinIdlePerKey(final int minIdlePerKey) {
this.minIdlePerKey = minIdlePerKey;
}
/**
* Returns the target for the minimum number of idle objects to maintain in
* each of the keyed sub-pools. This setting only has an effect if it is
* positive and {@link #getTimeBetweenEvictionRunsMillis()} is greater than
* zero. If this is the case, an attempt is made to ensure that each
* sub-pool has the required minimum number of instances during idle object
* eviction runs.
* <p>
* If the configured value of minIdlePerKey is greater than the configured
* value for maxIdlePerKey then the value of maxIdlePerKey will be used
* instead.
*
* @return minimum size of the each keyed pool
*
* @see #setTimeBetweenEvictionRunsMillis
*/
@Override
public int getMinIdlePerKey() {
final int maxIdlePerKeySave = getMaxIdlePerKey();
if (this.minIdlePerKey > maxIdlePerKeySave) {
return maxIdlePerKeySave;
}
return minIdlePerKey;
}
/**
* Sets the configuration.
*
* @param conf the new configuration to use. This is used by value.
*
* @see GenericKeyedObjectPoolConfig
*/
public void setConfig(final GenericKeyedObjectPoolConfig<T> conf) {
super.setConfig(conf);
setMaxIdlePerKey(conf.getMaxIdlePerKey());
setMaxTotalPerKey(conf.getMaxTotalPerKey());
setMaxTotal(conf.getMaxTotal());
setMinIdlePerKey(conf.getMinIdlePerKey());
}
/**
* Obtain a reference to the factory used to create, destroy and validate
* the objects used by this pool.
*
* @return the factory
*/
public KeyedPooledObjectFactory<K, T> getFactory() {
return factory;
}
/**
* Equivalent to <code>{@link #borrowObject(Object, long) borrowObject}(key,
* {@link #getMaxWaitMillis()})</code>.
* <p>
* {@inheritDoc}
*/
@Override
public T borrowObject(final K key) throws Exception {
return borrowObject(key, getMaxWaitMillis());
}
/**
* Borrows an object from the sub-pool associated with the given key using
* the specified waiting time which only applies if
* {@link #getBlockWhenExhausted()} is true.
* <p>
* If there is one or more idle instances available in the sub-pool
* associated with the given key, then an idle instance will be selected
* based on the value of {@link #getLifo()}, activated and returned. If
* activation fails, or {@link #getTestOnBorrow() testOnBorrow} is set to
* {@code true} and validation fails, the instance is destroyed and the
* next available instance is examined. This continues until either a valid
* instance is returned or there are no more idle instances available.
* <p>
* If there are no idle instances available in the sub-pool associated with
* the given key, behavior depends on the {@link #getMaxTotalPerKey()
* maxTotalPerKey}, {@link #getMaxTotal() maxTotal}, and (if applicable)
* {@link #getBlockWhenExhausted()} and the value passed in to the
* {@code borrowMaxWaitMillis} parameter. If the number of instances checked
* out from the sub-pool under the given key is less than
* {@code maxTotalPerKey} and the total number of instances in
* circulation (under all keys) is less than {@code maxTotal}, a new
* instance is created, activated and (if applicable) validated and returned
* to the caller. If validation fails, a {@code NoSuchElementException}
* will be thrown.
* <p>
* If the associated sub-pool is exhausted (no available idle instances and
* no capacity to create new ones), this method will either block
* ({@link #getBlockWhenExhausted()} is true) or throw a
* {@code NoSuchElementException}
* ({@link #getBlockWhenExhausted()} is false).
* The length of time that this method will block when
* {@link #getBlockWhenExhausted()} is true is determined by the value
* passed in to the {@code borrowMaxWait} parameter.
* <p>
* When {@code maxTotal} is set to a positive value and this method is
* invoked when at the limit with no idle instances available under the requested
* key, an attempt is made to create room by clearing the oldest 15% of the
* elements from the keyed sub-pools.
* <p>
* When the pool is exhausted, multiple calling threads may be
* simultaneously blocked waiting for instances to become available. A
* "fairness" algorithm has been implemented to ensure that threads receive
* available instances in request arrival order.
*
* @param key pool key
* @param borrowMaxWaitMillis The time to wait in milliseconds for an object
* to become available
*
* @return object instance from the keyed pool
*
* @throws NoSuchElementException if a keyed object instance cannot be
* returned because the pool is exhausted.
*
* @throws Exception if a keyed object instance cannot be returned due to an
* error
*/
public T borrowObject(final K key, final long borrowMaxWaitMillis) throws Exception {
assertOpen();
PooledObject<T> p = null;
// Get local copy of current config so it is consistent for entire
// method execution
final boolean blockWhenExhausted = getBlockWhenExhausted();
boolean create;
final long waitTimeMillis = System.currentTimeMillis();
final ObjectDeque<T> objectDeque = register(key);
try {
while (p == null) {
create = false;
p = objectDeque.getIdleObjects().pollFirst();
if (p == null) {
p = create(key);
if (p != null) {
create = true;
}
}
if (blockWhenExhausted) {
if (p == null) {
if (borrowMaxWaitMillis < 0) {
p = objectDeque.getIdleObjects().takeFirst();
} else {
p = objectDeque.getIdleObjects().pollFirst(
borrowMaxWaitMillis, TimeUnit.MILLISECONDS);
}
}
if (p == null) {
throw new NoSuchElementException(
"Timeout waiting for idle object");
}
} else {
if (p == null) {
throw new NoSuchElementException("Pool exhausted");
}
}
if (!p.allocate()) {
p = null;
}
if (p != null) {
try {
factory.activateObject(key, p);
} catch (final Exception e) {
try {
destroy(key, p, true, DestroyMode.NORMAL);
} catch (final Exception e1) {
// Ignore - activation failure is more important
}
p = null;
if (create) {
final NoSuchElementException nsee = new NoSuchElementException(
"Unable to activate object");
nsee.initCause(e);
throw nsee;
}
}
if (p != null && getTestOnBorrow()) {
boolean validate = false;
Throwable validationThrowable = null;
try {
validate = factory.validateObject(key, p);
} catch (final Throwable t) {
PoolUtils.checkRethrow(t);
validationThrowable = t;
}
if (!validate) {
try {
destroy(key, p, true, DestroyMode.NORMAL);
destroyedByBorrowValidationCount.incrementAndGet();
} catch (final Exception e) {
// Ignore - validation failure is more important
}
p = null;
if (create) {
final NoSuchElementException nsee = new NoSuchElementException(
"Unable to validate object");
nsee.initCause(validationThrowable);
throw nsee;
}
}
}
}
}
} finally {
deregister(key);
}
updateStatsBorrow(p, System.currentTimeMillis() - waitTimeMillis);
return p.getObject();
}
/**
* Returns an object to a keyed sub-pool.
* <p>
* If {@link #getMaxIdlePerKey() maxIdle} is set to a positive value and the
* number of idle instances under the given key has reached this value, the
* returning instance is destroyed.
* <p>
* If {@link #getTestOnReturn() testOnReturn} == true, the returning
* instance is validated before being returned to the idle instance sub-pool
* under the given key. In this case, if validation fails, the instance is
* destroyed.
* <p>
* Exceptions encountered destroying objects for any reason are swallowed
* but notified via a
* {@link org.apache.tomcat.dbcp.pool2.SwallowedExceptionListener}.
*
* @param key pool key
* @param obj instance to return to the keyed pool
*
* @throws IllegalStateException if an object is returned to the pool that
* was not borrowed from it or if an object is
* returned to the pool multiple times
*/
@Override
public void returnObject(final K key, final T obj) {
final ObjectDeque<T> objectDeque = poolMap.get(key);
if (objectDeque == null) {
throw new IllegalStateException(
"No keyed pool found under the given key.");
}
final PooledObject<T> p = objectDeque.getAllObjects().get(new IdentityWrapper<>(obj));
if (p == null) {
throw new IllegalStateException(
"Returned object not currently part of this pool");
}
markReturningState(p);
final long activeTime = p.getActiveTimeMillis();
try {
if (getTestOnReturn() && !factory.validateObject(key, p)) {
try {
destroy(key, p, true, DestroyMode.NORMAL);
} catch (final Exception e) {
swallowException(e);
}
whenWaitersAddObject(key, objectDeque.idleObjects);
return;
}
try {
factory.passivateObject(key, p);
} catch (final Exception e1) {
swallowException(e1);
try {
destroy(key, p, true, DestroyMode.NORMAL);
} catch (final Exception e) {
swallowException(e);
}
whenWaitersAddObject(key, objectDeque.idleObjects);
return;
}
if (!p.deallocate()) {
throw new IllegalStateException(
"Object has already been returned to this pool");
}
final int maxIdle = getMaxIdlePerKey();
final LinkedBlockingDeque<PooledObject<T>> idleObjects =
objectDeque.getIdleObjects();
if (isClosed() || maxIdle > -1 && maxIdle <= idleObjects.size()) {
try {
destroy(key, p, true, DestroyMode.NORMAL);
} catch (final Exception e) {
swallowException(e);
}
} else {
if (getLifo()) {
idleObjects.addFirst(p);
} else {
idleObjects.addLast(p);
}
if (isClosed()) {
// Pool closed while object was being added to idle objects.
// Make sure the returned object is destroyed rather than left
// in the idle object pool (which would effectively be a leak)
clear(key);
}
}
} finally {
if (hasBorrowWaiters()) {
reuseCapacity();
}
updateStatsReturn(activeTime);
}
}
/**
* Whether there is at least one thread waiting on this deque, add an pool object.
* @param key pool key.
* @param idleObjects list of idle pool objects.
*/
private void whenWaitersAddObject(final K key, final LinkedBlockingDeque<PooledObject<T>> idleObjects) {
if (idleObjects.hasTakeWaiters()) {
try {
addObject(key);
} catch (final Exception e) {
swallowException(e);
}
}
}
/**
* {@inheritDoc}
* <p>
* Activation of this method decrements the active count associated with
* the given keyed pool and attempts to destroy {@code obj.}
*
* @param key pool key
* @param obj instance to invalidate
*
* @throws Exception if an exception occurs destroying the
* object
* @throws IllegalStateException if obj does not belong to the pool
* under the given key
*/
@Override
public void invalidateObject(final K key, final T obj) throws Exception {
invalidateObject(key, obj, DestroyMode.NORMAL);
}
/**
* {@inheritDoc}
* <p>
* Activation of this method decrements the active count associated with
* the given keyed pool and attempts to destroy {@code obj.}
*
* @param key pool key
* @param obj instance to invalidate
* @param mode DestroyMode context provided to factory
*
* @throws Exception if an exception occurs destroying the
* object
* @throws IllegalStateException if obj does not belong to the pool
* under the given key
* @since 2.9.0
*/
@Override
public void invalidateObject(final K key, final T obj, final DestroyMode mode) throws Exception {
final ObjectDeque<T> objectDeque = poolMap.get(key);
final PooledObject<T> p = objectDeque.getAllObjects().get(new IdentityWrapper<>(obj));
if (p == null) {
throw new IllegalStateException(
"Object not currently part of this pool");
}
synchronized (p) {
if (p.getState() != PooledObjectState.INVALID) {
destroy(key, p, true, mode);
}
}
if (objectDeque.idleObjects.hasTakeWaiters()) {
addObject(key);
}
}
/**
* Clears any objects sitting idle in the pool by removing them from the
* idle instance sub-pools and then invoking the configured
* PoolableObjectFactory's
* {@link KeyedPooledObjectFactory#destroyObject(Object, PooledObject)}
* method on each idle instance.
* <p>
* Implementation notes:
* <ul>
* <li>This method does not destroy or effect in any way instances that are
* checked out when it is invoked.</li>
* <li>Invoking this method does not prevent objects being returned to the
* idle instance pool, even during its execution. Additional instances may
* be returned while removed items are being destroyed.</li>
* <li>Exceptions encountered destroying idle instances are swallowed
* but notified via a
* {@link org.apache.tomcat.dbcp.pool2.SwallowedExceptionListener}.</li>
* </ul>
*/
@Override
public void clear() {
for (K k : poolMap.keySet()) {
clear(k);
}
}
/**
* Clears the specified sub-pool, removing all pooled instances
* corresponding to the given {@code key}. Exceptions encountered
* destroying idle instances are swallowed but notified via a
* {@link org.apache.tomcat.dbcp.pool2.SwallowedExceptionListener}.
*
* @param key the key to clear
*/
@Override
public void clear(final K key) {
final ObjectDeque<T> objectDeque = register(key);
try {
final LinkedBlockingDeque<PooledObject<T>> idleObjects =
objectDeque.getIdleObjects();
PooledObject<T> p = idleObjects.poll();
while (p != null) {
try {
destroy(key, p, true, DestroyMode.NORMAL);
} catch (final Exception e) {
swallowException(e);
}
p = idleObjects.poll();
}
} finally {
deregister(key);
}
}
@Override
public int getNumActive() {
return numTotal.get() - getNumIdle();
}
@Override
public int getNumIdle() {
final Iterator<ObjectDeque<T>> iter = poolMap.values().iterator();
int result = 0;
while (iter.hasNext()) {
result += iter.next().getIdleObjects().size();
}
return result;
}
@Override
public int getNumActive(final K key) {
final ObjectDeque<T> objectDeque = poolMap.get(key);
if (objectDeque != null) {
return objectDeque.getAllObjects().size() -
objectDeque.getIdleObjects().size();
}
return 0;
}
@Override
public int getNumIdle(final K key) {
final ObjectDeque<T> objectDeque = poolMap.get(key);
return objectDeque != null ? objectDeque.getIdleObjects().size() : 0;
}
/**
* Closes the keyed object pool. Once the pool is closed,
* {@link #borrowObject(Object)} will fail with IllegalStateException, but
* {@link #returnObject(Object, Object)} and
* {@link #invalidateObject(Object, Object)} will continue to work, with
* returned objects destroyed on return.
* <p>
* Destroys idle instances in the pool by invoking {@link #clear()}.
*/
@Override
public void close() {
if (isClosed()) {
return;
}
synchronized (closeLock) {
if (isClosed()) {
return;
}
// Stop the evictor before the pool is closed since evict() calls
// assertOpen()
stopEvictor();
closed = true;
// This clear removes any idle objects
clear();
jmxUnregister();
// Release any threads that were waiting for an object
for (ObjectDeque<T> tObjectDeque : poolMap.values()) {
tObjectDeque.getIdleObjects().interuptTakeWaiters();
}
// This clear cleans up the keys now any waiting threads have been
// interrupted
clear();
}
}
/**
* Clears oldest 15% of objects in pool. The method sorts the objects into
* a TreeMap and then iterates the first 15% for removal.
*/
public void clearOldest() {
// build sorted map of idle objects
final Map<PooledObject<T>, K> map = new TreeMap<>();
for (final Map.Entry<K, ObjectDeque<T>> entry : poolMap.entrySet()) {
final K k = entry.getKey();
final ObjectDeque<T> deque = entry.getValue();
// Protect against possible NPE if key has been removed in another
// thread. Not worth locking the keys while this loop completes.
if (deque != null) {
final LinkedBlockingDeque<PooledObject<T>> idleObjects =
deque.getIdleObjects();
for (final PooledObject<T> p : idleObjects) {
// each item into the map using the PooledObject object as the
// key. It then gets sorted based on the idle time
map.put(p, k);
}
}
}
// Now iterate created map and kill the first 15% plus one to account
// for zero
int itemsToRemove = ((int) (map.size() * 0.15)) + 1;
final Iterator<Map.Entry<PooledObject<T>, K>> iter =
map.entrySet().iterator();
while (iter.hasNext() && itemsToRemove > 0) {
final Map.Entry<PooledObject<T>, K> entry = iter.next();
// kind of backwards on naming. In the map, each key is the
// PooledObject because it has the ordering with the timestamp
// value. Each value that the key references is the key of the
// list it belongs to.
final K key = entry.getValue();
final PooledObject<T> p = entry.getKey();
// Assume the destruction succeeds
boolean destroyed = true;
try {
destroyed = destroy(key, p, false, DestroyMode.NORMAL);
} catch (final Exception e) {
swallowException(e);
}
if (destroyed) {
itemsToRemove--;
}
}
}
/**
* Attempt to create one new instance to serve from the most heavily
* loaded pool that can add a new instance.
*
* This method exists to ensure liveness in the pool when threads are
* parked waiting and capacity to create instances under the requested keys
* subsequently becomes available.
*
* This method is not guaranteed to create an instance and its selection
* of the most loaded pool that can create an instance may not always be
* correct, since it does not lock the pool and instances may be created,
* borrowed, returned or destroyed by other threads while it is executing.
*/
private void reuseCapacity() {
final int maxTotalPerKeySave = getMaxTotalPerKey();
// Find the most loaded pool that could take a new instance
int maxQueueLength = 0;
LinkedBlockingDeque<PooledObject<T>> mostLoaded = null;
K loadedKey = null;
for (final Map.Entry<K, ObjectDeque<T>> entry : poolMap.entrySet()) {
final K k = entry.getKey();
final ObjectDeque<T> deque = entry.getValue();
if (deque != null) {
final LinkedBlockingDeque<PooledObject<T>> pool = deque.getIdleObjects();
final int queueLength = pool.getTakeQueueLength();
if (getNumActive(k) < maxTotalPerKeySave && queueLength > maxQueueLength) {
maxQueueLength = queueLength;
mostLoaded = pool;
loadedKey = k;
}
}
}
// Attempt to add an instance to the most loaded pool
if (mostLoaded != null) {
register(loadedKey);
try {
final PooledObject<T> p = create(loadedKey);
if (p != null) {
addIdleObject(loadedKey, p);
}
} catch (final Exception e) {
swallowException(e);
} finally {
deregister(loadedKey);
}
}
}
/**
* Checks to see if there are any threads currently waiting to borrow
* objects but are blocked waiting for more objects to become available.
*
* @return {@code true} if there is at least one thread waiting otherwise
* {@code false}
*/
private boolean hasBorrowWaiters() {
for (final Map.Entry<K, ObjectDeque<T>> entry : poolMap.entrySet()) {
final ObjectDeque<T> deque = entry.getValue();
if (deque != null) {
final LinkedBlockingDeque<PooledObject<T>> pool =
deque.getIdleObjects();
if(pool.hasTakeWaiters()) {
return true;
}
}
}
return false;
}
/**
* {@inheritDoc}
* <p>
* Successive activations of this method examine objects in keyed sub-pools
* in sequence, cycling through the keys and examining objects in
* oldest-to-youngest order within the keyed sub-pools.
*/
@Override
public void evict() throws Exception {
assertOpen();
if (getNumIdle() == 0) {
return;
}
PooledObject<T> underTest = null;
final EvictionPolicy<T> evictionPolicy = getEvictionPolicy();
synchronized (evictionLock) {
final EvictionConfig evictionConfig = new EvictionConfig(
getMinEvictableIdleTimeMillis(),
getSoftMinEvictableIdleTimeMillis(),
getMinIdlePerKey());
final boolean testWhileIdle = getTestWhileIdle();
for (int i = 0, m = getNumTests(); i < m; i++) {
if(evictionIterator == null || !evictionIterator.hasNext()) {
if (evictionKeyIterator == null ||
!evictionKeyIterator.hasNext()) {
final List<K> keyCopy;
final Lock readLock = keyLock.readLock();
readLock.lock();
try {
keyCopy = new ArrayList<>(poolKeyList);
} finally {
readLock.unlock();
}
evictionKeyIterator = keyCopy.iterator();
}
while (evictionKeyIterator.hasNext()) {
evictionKey = evictionKeyIterator.next();
final ObjectDeque<T> objectDeque = poolMap.get(evictionKey);
if (objectDeque == null) {
continue;
}
final Deque<PooledObject<T>> idleObjects = objectDeque.getIdleObjects();
evictionIterator = new EvictionIterator(idleObjects);
if (evictionIterator.hasNext()) {
break;
}
evictionIterator = null;
}
}
if (evictionIterator == null) {
// Pools exhausted
return;
}
final Deque<PooledObject<T>> idleObjects;
try {
underTest = evictionIterator.next();
idleObjects = evictionIterator.getIdleObjects();
} catch (final NoSuchElementException nsee) {
// Object was borrowed in another thread
// Don't count this as an eviction test so reduce i;
i--;
evictionIterator = null;
continue;
}
if (!underTest.startEvictionTest()) {
// Object was borrowed in another thread
// Don't count this as an eviction test so reduce i;
i--;
continue;
}
// User provided eviction policy could throw all sorts of
// crazy exceptions. Protect against such an exception
// killing the eviction thread.
boolean evict;
try {
evict = evictionPolicy.evict(evictionConfig, underTest,
poolMap.get(evictionKey).getIdleObjects().size());
} catch (final Throwable t) {
// Slightly convoluted as SwallowedExceptionListener
// uses Exception rather than Throwable
PoolUtils.checkRethrow(t);
swallowException(new Exception(t));
// Don't evict on error conditions
evict = false;
}
if (evict) {
destroy(evictionKey, underTest, true, DestroyMode.NORMAL);
destroyedByEvictorCount.incrementAndGet();
} else {
if (testWhileIdle) {
boolean active = false;
try {
factory.activateObject(evictionKey, underTest);
active = true;
} catch (final Exception e) {
destroy(evictionKey, underTest, true, DestroyMode.NORMAL);
destroyedByEvictorCount.incrementAndGet();
}
if (active) {
if (!factory.validateObject(evictionKey, underTest)) {
destroy(evictionKey, underTest, true, DestroyMode.NORMAL);
destroyedByEvictorCount.incrementAndGet();
} else {
try {
factory.passivateObject(evictionKey, underTest);
} catch (final Exception e) {
destroy(evictionKey, underTest, true, DestroyMode.NORMAL);
destroyedByEvictorCount.incrementAndGet();
}
}
}
}
if (!underTest.endEvictionTest(idleObjects)) {
// TODO - May need to add code here once additional
// states are used
}
}
}
}
}
/**
* Create a new pooled object.
*
* @param key Key associated with new pooled object
*
* @return The new, wrapped pooled object
*
* @throws Exception If the objection creation fails
*/
private PooledObject<T> create(final K key) throws Exception {
int maxTotalPerKeySave = getMaxTotalPerKey(); // Per key
if (maxTotalPerKeySave < 0) {
maxTotalPerKeySave = Integer.MAX_VALUE;
}
final int maxTotal = getMaxTotal(); // All keys
final ObjectDeque<T> objectDeque = poolMap.get(key);
// Check against the overall limit
boolean loop = true;
while (loop) {
final int newNumTotal = numTotal.incrementAndGet();
if (maxTotal > -1 && newNumTotal > maxTotal) {
numTotal.decrementAndGet();
if (getNumIdle() == 0) {
return null;
}
clearOldest();
} else {
loop = false;
}
}
// Flag that indicates if create should:
// - TRUE: call the factory to create an object
// - FALSE: return null
// - null: loop and re-test the condition that determines whether to
// call the factory
Boolean create = null;
while (create == null) {
synchronized (objectDeque.makeObjectCountLock) {
final long newCreateCount = objectDeque.getCreateCount().incrementAndGet();
// Check against the per key limit
if (newCreateCount > maxTotalPerKeySave) {
// The key is currently at capacity or in the process of
// making enough new objects to take it to capacity.
objectDeque.getCreateCount().decrementAndGet();
if (objectDeque.makeObjectCount == 0) {
// There are no makeObject() calls in progress for this
// key so the key is at capacity. Do not attempt to
// create a new object. Return and wait for an object to
// be returned.
create = Boolean.FALSE;
} else {
// There are makeObject() calls in progress that might
// bring the pool to capacity. Those calls might also
// fail so wait until they complete and then re-test if
// the pool is at capacity or not.
objectDeque.makeObjectCountLock.wait();
}
} else {
// The pool is not at capacity. Create a new object.
objectDeque.makeObjectCount++;
create = Boolean.TRUE;
}
}
}
if (!create.booleanValue()) {
numTotal.decrementAndGet();
return null;
}
PooledObject<T> p = null;
try {
p = factory.makeObject(key);
if (getTestOnCreate() && !factory.validateObject(key, p)) {
numTotal.decrementAndGet();
objectDeque.getCreateCount().decrementAndGet();
return null;
}
} catch (final Exception e) {
numTotal.decrementAndGet();
objectDeque.getCreateCount().decrementAndGet();
throw e;
} finally {
synchronized (objectDeque.makeObjectCountLock) {
objectDeque.makeObjectCount--;
objectDeque.makeObjectCountLock.notifyAll();
}
}
createdCount.incrementAndGet();
objectDeque.getAllObjects().put(new IdentityWrapper<>(p.getObject()), p);
return p;
}
/**
* Destroy the wrapped, pooled object.
*
* @param key The key associated with the object to destroy.
* @param toDestroy The wrapped object to be destroyed
* @param always Should the object be destroyed even if it is not currently
* in the set of idle objects for the given key
* @param mode DestroyMode context provided to the factory
*
* @return {@code true} if the object was destroyed, otherwise {@code false}
* @throws Exception If the object destruction failed
*/
private boolean destroy(final K key, final PooledObject<T> toDestroy, final boolean always, final DestroyMode mode)
throws Exception {
final ObjectDeque<T> objectDeque = register(key);
try {
boolean isIdle;
synchronized(toDestroy) {
// Check idle state directly
isIdle = toDestroy.getState().equals(PooledObjectState.IDLE);
// If idle, not under eviction test, or always is true, remove instance,
// updating isIdle if instance is found in idle objects
if (isIdle || always) {
isIdle = objectDeque.getIdleObjects().remove(toDestroy);
}
}
if (isIdle || always) {
objectDeque.getAllObjects().remove(new IdentityWrapper<>(toDestroy.getObject()));
toDestroy.invalidate();
try {
factory.destroyObject(key, toDestroy, mode);
} finally {
objectDeque.getCreateCount().decrementAndGet();
destroyedCount.incrementAndGet();
numTotal.decrementAndGet();
}
return true;
}
return false;
} finally {
deregister(key);
}
}
/**
* Register the use of a key by an object.
* <p>
* register() and deregister() must always be used as a pair.
*
* @param k The key to register
*
* @return The objects currently associated with the given key. If this
* method returns without throwing an exception then it will never
* return null.
*/
private ObjectDeque<T> register(final K k) {
Lock lock = keyLock.readLock();
ObjectDeque<T> objectDeque = null;
try {
lock.lock();
objectDeque = poolMap.get(k);
if (objectDeque == null) {
// Upgrade to write lock
lock.unlock();
lock = keyLock.writeLock();
lock.lock();
objectDeque = poolMap.get(k);
if (objectDeque == null) {
objectDeque = new ObjectDeque<>(fairness);
objectDeque.getNumInterested().incrementAndGet();
// NOTE: Keys must always be added to both poolMap and
// poolKeyList at the same time while protected by
// keyLock.writeLock()
poolMap.put(k, objectDeque);
poolKeyList.add(k);
} else {
objectDeque.getNumInterested().incrementAndGet();
}
} else {
objectDeque.getNumInterested().incrementAndGet();
}
} finally {
lock.unlock();
}
return objectDeque;
}
/**
* De-register the use of a key by an object.
* <p>
* register() and deregister() must always be used as a pair.
*
* @param k The key to de-register
*/
private void deregister(final K k) {
Lock lock = keyLock.readLock();
try {
lock.lock();
final ObjectDeque<T> objectDeque = poolMap.get(k);
final long numInterested = objectDeque.getNumInterested().decrementAndGet();
if (numInterested == 0 && objectDeque.getCreateCount().get() == 0) {
// Potential to remove key
// Upgrade to write lock
lock.unlock();
lock = keyLock.writeLock();
lock.lock();
if (objectDeque.getCreateCount().get() == 0 && objectDeque.getNumInterested().get() == 0) {
// NOTE: Keys must always be removed from both poolMap and
// poolKeyList at the same time while protected by
// keyLock.writeLock()
poolMap.remove(k);
poolKeyList.remove(k);
}
}
} finally {
lock.unlock();
}
}
@Override
void ensureMinIdle() throws Exception {
final int minIdlePerKeySave = getMinIdlePerKey();
if (minIdlePerKeySave < 1) {
return;
}
for (final K k : poolMap.keySet()) {
ensureMinIdle(k);
}
}
/**
* Ensure that the configured number of minimum idle objects is available in
* the pool for the given key.
*
* @param key The key to check for idle objects
*
* @throws Exception If a new object is required and cannot be created
*/
private void ensureMinIdle(final K key) throws Exception {
// Calculate current pool objects
ObjectDeque<T> objectDeque = poolMap.get(key);
// objectDeque == null is OK here. It is handled correctly by both
// methods called below.
// this method isn't synchronized so the
// calculateDeficit is done at the beginning
// as a loop limit and a second time inside the loop
// to stop when another thread already returned the
// needed objects
final int deficit = calculateDeficit(objectDeque);
for (int i = 0; i < deficit && calculateDeficit(objectDeque) > 0; i++) {
addObject(key);
// If objectDeque was null, it won't be any more. Obtain a reference
// to it so the deficit can be correctly calculated. It needs to
// take account of objects created in other threads.
if (objectDeque == null) {
objectDeque = poolMap.get(key);
}
}
}
/**
* Create an object using the {@link KeyedPooledObjectFactory#makeObject
* factory}, passivate it, and then place it in the idle object pool.
* {@code addObject} is useful for "pre-loading" a pool with idle
* objects.
*
* @param key the key a new instance should be added to
*
* @throws Exception when {@link KeyedPooledObjectFactory#makeObject}
* fails.
*/
@Override
public void addObject(final K key) throws Exception {
assertOpen();
register(key);
try {
final PooledObject<T> p = create(key);
addIdleObject(key, p);
} finally {
deregister(key);
}
}
/**
* Calls {@link KeyedObjectPool#addObject(Object)} with each
* key in <code>keys</code> for <code>count</code> number of times. This has
* the same effect as calling {@link #addObjects(Object, int)}
* for each key in the <code>keys</code> collection.
*
* @param keys
* {@link Collection} of keys to add objects for.
* @param count
* the number of idle objects to add for each <code>key</code>.
* @throws Exception
* when {@link KeyedObjectPool#addObject(Object)} fails.
* @throws IllegalArgumentException
* when <code>keyedPool</code>, <code>keys</code>, or any value
* in <code>keys</code> is <code>null</code>.
* @see #addObjects(Object, int)
*/
@Override
public void addObjects(final Collection<K> keys, final int count) throws Exception, IllegalArgumentException {
if (keys == null) {
throw new IllegalArgumentException(PoolUtils.MSG_NULL_KEYS);
}
final Iterator<K> iter = keys.iterator();
while (iter.hasNext()) {
addObjects(iter.next(), count);
}
}
/**
* Calls {@link KeyedObjectPool#addObject(Object)}
* <code>key</code> <code>count</code> number of times.
*
* @param key
* the key to add objects for.
* @param count
* the number of idle objects to add for <code>key</code>.
* @throws Exception
* when {@link KeyedObjectPool#addObject(Object)} fails.
* @throws IllegalArgumentException
* when <code>key</code> is <code>null</code>.
* @since 2.8.0
*/
@Override
public void addObjects(final K key, final int count) throws Exception, IllegalArgumentException {
if (key == null) {
throw new IllegalArgumentException(PoolUtils.MSG_NULL_KEY);
}
for (int i = 0; i < count; i++) {
addObject(key);
}
}
/**
* Add an object to the set of idle objects for a given key.
*
* @param key The key to associate with the idle object
* @param p The wrapped object to add.
*
* @throws Exception If the associated factory fails to passivate the object
*/
private void addIdleObject(final K key, final PooledObject<T> p) throws Exception {
if (p != null) {
factory.passivateObject(key, p);
final LinkedBlockingDeque<PooledObject<T>> idleObjects =
poolMap.get(key).getIdleObjects();
if (getLifo()) {
idleObjects.addFirst(p);
} else {
idleObjects.addLast(p);
}
}
}
/**
* Registers a key for pool control and ensures that
* {@link #getMinIdlePerKey()} idle instances are created.
*
* @param key - The key to register for pool control.
*
* @throws Exception If the associated factory throws an exception
*/
public void preparePool(final K key) throws Exception {
final int minIdlePerKeySave = getMinIdlePerKey();
if (minIdlePerKeySave < 1) {
return;
}
ensureMinIdle(key);
}
/**
* Calculate the number of objects to test in a run of the idle object
* evictor.
*
* @return The number of objects to test for validity
*/
private int getNumTests() {
final int totalIdle = getNumIdle();
final int numTests = getNumTestsPerEvictionRun();
if (numTests >= 0) {
return Math.min(numTests, totalIdle);
}
return(int)(Math.ceil(totalIdle/Math.abs((double)numTests)));
}
/**
* Calculate the number of objects that need to be created to attempt to
* maintain the minimum number of idle objects while not exceeded the limits
* on the maximum number of objects either per key or totally.
*
* @param objectDeque The set of objects to check
*
* @return The number of new objects to create
*/
private int calculateDeficit(final ObjectDeque<T> objectDeque) {
if (objectDeque == null) {
return getMinIdlePerKey();
}
// Used more than once so keep a local copy so the value is consistent
final int maxTotal = getMaxTotal();
final int maxTotalPerKeySave = getMaxTotalPerKey();
int objectDefecit = 0;
// Calculate no of objects needed to be created, in order to have
// the number of pooled objects < maxTotalPerKey();
objectDefecit = getMinIdlePerKey() - objectDeque.getIdleObjects().size();
if (maxTotalPerKeySave > 0) {
final int growLimit = Math.max(0,
maxTotalPerKeySave - objectDeque.getIdleObjects().size());
objectDefecit = Math.min(objectDefecit, growLimit);
}
// Take the maxTotal limit into account
if (maxTotal > 0) {
final int growLimit = Math.max(0, maxTotal - getNumActive() - getNumIdle());
objectDefecit = Math.min(objectDefecit, growLimit);
}
return objectDefecit;
}
//--- JMX support ----------------------------------------------------------
@Override
public Map<String,Integer> getNumActivePerKey() {
final HashMap<String,Integer> result = new HashMap<>();
for (Entry<K, ObjectDeque<T>> entry : poolMap.entrySet()) {
if (entry != null) {
final K key = entry.getKey();
final ObjectDeque<T> objectDequeue = entry.getValue();
if (key != null && objectDequeue != null) {
result.put(key.toString(), Integer.valueOf(
objectDequeue.getAllObjects().size() -
objectDequeue.getIdleObjects().size()));
}
}
}
return result;
}
/**
* Return an estimate of the number of threads currently blocked waiting for
* an object from the pool. This is intended for monitoring only, not for
* synchronization control.
*
* @return The estimate of the number of threads currently blocked waiting
* for an object from the pool
*/
@Override
public int getNumWaiters() {
int result = 0;
if (getBlockWhenExhausted()) {
for (ObjectDeque<T> tObjectDeque : poolMap.values()) {
// Assume no overflow
result += tObjectDeque.getIdleObjects().getTakeQueueLength();
}
}
return result;
}
/**
* Return an estimate of the number of threads currently blocked waiting for
* an object from the pool for each key. This is intended for
* monitoring only, not for synchronization control.
*
* @return The estimate of the number of threads currently blocked waiting
* for an object from the pool for each key
*/
@Override
public Map<String,Integer> getNumWaitersByKey() {
final Map<String,Integer> result = new HashMap<>();
for (final Map.Entry<K, ObjectDeque<T>> entry : poolMap.entrySet()) {
final K k = entry.getKey();
final ObjectDeque<T> deque = entry.getValue();
if (deque != null) {
if (getBlockWhenExhausted()) {
result.put(k.toString(), Integer.valueOf(
deque.getIdleObjects().getTakeQueueLength()));
} else {
result.put(k.toString(), Integer.valueOf(0));
}
}
}
return result;
}
/**
* Provides information on all the objects in the pool, both idle (waiting
* to be borrowed) and active (currently borrowed).
* <p>
* Note: This is named listAllObjects so it is presented as an operation via
* JMX. That means it won't be invoked unless the explicitly requested
* whereas all attributes will be automatically requested when viewing the
* attributes for an object in a tool like JConsole.
*
* @return Information grouped by key on all the objects in the pool
*/
@Override
public Map<String,List<DefaultPooledObjectInfo>> listAllObjects() {
final Map<String,List<DefaultPooledObjectInfo>> result =
new HashMap<>();
for (final Map.Entry<K, ObjectDeque<T>> entry : poolMap.entrySet()) {
final K k = entry.getKey();
final ObjectDeque<T> deque = entry.getValue();
if (deque != null) {
final List<DefaultPooledObjectInfo> list =
new ArrayList<>();
result.put(k.toString(), list);
for (final PooledObject<T> p : deque.getAllObjects().values()) {
list.add(new DefaultPooledObjectInfo(p));
}
}
}
return result;
}
//--- inner classes ----------------------------------------------
/**
* Maintains information on the per key queue for a given key.
*
* @param <S> type of objects in the pool
*/
private class ObjectDeque<S> {
private final LinkedBlockingDeque<PooledObject<S>> idleObjects;
/*
* Number of instances created - number destroyed.
* Invariant: createCount <= maxTotalPerKey
*/
private final AtomicInteger createCount = new AtomicInteger(0);
private long makeObjectCount = 0;
private final Object makeObjectCountLock = new Object();
/*
* The map is keyed on pooled instances, wrapped to ensure that
* they work properly as keys.
*/
private final Map<IdentityWrapper<S>, PooledObject<S>> allObjects =
new ConcurrentHashMap<>();
/*
* Number of threads with registered interest in this key.
* register(K) increments this counter and deRegister(K) decrements it.
* Invariant: empty keyed pool will not be dropped unless numInterested
* is 0.
*/
private final AtomicLong numInterested = new AtomicLong(0);
/**
* Create a new ObjecDeque with the given fairness policy.
* @param fairness true means client threads waiting to borrow / return instances
* will be served as if waiting in a FIFO queue.
*/
ObjectDeque(final boolean fairness) {
idleObjects = new LinkedBlockingDeque<>(fairness);
}
/**
* Obtain the idle objects for the current key.
*
* @return The idle objects
*/
public LinkedBlockingDeque<PooledObject<S>> getIdleObjects() {
return idleObjects;
}
/**
* Obtain the count of the number of objects created for the current
* key.
*
* @return The number of objects created for this key
*/
public AtomicInteger getCreateCount() {
return createCount;
}
/**
* Obtain the number of threads with an interest registered in this key.
*
* @return The number of threads with a registered interest in this key
*/
public AtomicLong getNumInterested() {
return numInterested;
}
/**
* Obtain all the objects for the current key.
*
* @return All the objects
*/
public Map<IdentityWrapper<S>, PooledObject<S>> getAllObjects() {
return allObjects;
}
@Override
public String toString() {
final StringBuilder builder = new StringBuilder();
builder.append("ObjectDeque [idleObjects=");
builder.append(idleObjects);
builder.append(", createCount=");
builder.append(createCount);
builder.append(", allObjects=");
builder.append(allObjects);
builder.append(", numInterested=");
builder.append(numInterested);
builder.append("]");
return builder.toString();
}
}
//--- configuration attributes ---------------------------------------------
private volatile int maxIdlePerKey =
GenericKeyedObjectPoolConfig.DEFAULT_MAX_IDLE_PER_KEY;
private volatile int minIdlePerKey =
GenericKeyedObjectPoolConfig.DEFAULT_MIN_IDLE_PER_KEY;
private volatile int maxTotalPerKey =
GenericKeyedObjectPoolConfig.DEFAULT_MAX_TOTAL_PER_KEY;
private final KeyedPooledObjectFactory<K, T> factory;
private final boolean fairness;
//--- internal attributes --------------------------------------------------
/*
* My hash of sub-pools (ObjectQueue). The list of keys <b>must</b> be kept
* in step with {@link #poolKeyList} using {@link #keyLock} to ensure any
* changes to the list of current keys is made in a thread-safe manner.
*/
private final Map<K, ObjectDeque<T>> poolMap =
new ConcurrentHashMap<>(); // @GuardedBy("keyLock") for write access (and some read access)
/*
* List of pool keys - used to control eviction order. The list of keys
* <b>must</b> be kept in step with {@link #poolMap} using {@link #keyLock}
* to ensure any changes to the list of current keys is made in a
* thread-safe manner.
*/
private final List<K> poolKeyList = new ArrayList<>(); // @GuardedBy("keyLock")
private final ReadWriteLock keyLock = new ReentrantReadWriteLock(true);
/*
* The combined count of the currently active objects for all keys and those
* in the process of being created. Under load, it may exceed
* {@link #maxTotal} but there will never be more than {@link #maxTotal}
* created at any one time.
*/
private final AtomicInteger numTotal = new AtomicInteger(0);
private Iterator<K> evictionKeyIterator = null; // @GuardedBy("evictionLock")
private K evictionKey = null; // @GuardedBy("evictionLock")
// JMX specific attributes
private static final String ONAME_BASE =
"org.apache.tomcat.dbcp.pool2:type=GenericKeyedObjectPool,name=";
@Override
protected void toStringAppendFields(final StringBuilder builder) {
super.toStringAppendFields(builder);
builder.append(", maxIdlePerKey=");
builder.append(maxIdlePerKey);
builder.append(", minIdlePerKey=");
builder.append(minIdlePerKey);
builder.append(", maxTotalPerKey=");
builder.append(maxTotalPerKey);
builder.append(", factory=");
builder.append(factory);
builder.append(", fairness=");
builder.append(fairness);
builder.append(", poolMap=");
builder.append(poolMap);
builder.append(", poolKeyList=");
builder.append(poolKeyList);
builder.append(", keyLock=");
builder.append(keyLock);
builder.append(", numTotal=");
builder.append(numTotal);
builder.append(", evictionKeyIterator=");
builder.append(evictionKeyIterator);
builder.append(", evictionKey=");
builder.append(evictionKey);
}
}