/*

 * Licensed to the Apache Software Foundation (ASF) under one or more

 * contributor license agreements.  See the NOTICE file distributed with

 * this work for additional information regarding copyright ownership.

 * The ASF licenses this file to You under the Apache License, Version 2.0

 * (the "License"); you may not use this file except in compliance with

 * the License.  You may obtain a copy of the License at

 *

 *      http://www.apache.org/licenses/LICENSE-2.0

 *

 * Unless required by applicable law or agreed to in writing, software

 * distributed under the License is distributed on an "AS IS" BASIS,

 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.

 * See the License for the specific language governing permissions and

 * limitations under the License.

 */

package org.apache.commons.pool.impl;

import java.util.Iterator;

import java.util.NoSuchElementException;

import java.util.Stack;

import org.apache.commons.pool.BaseObjectPool;

import org.apache.commons.pool.ObjectPool;

import org.apache.commons.pool.PoolUtils;

import org.apache.commons.pool.PoolableObjectFactory;

/**

 * A simple, {@link java.util.Stack Stack}-based {@link ObjectPool} implementation.

 * <p>

 * Given a {@link PoolableObjectFactory}, this class will maintain

 * a simple pool of instances.  A finite number of "sleeping"

 * or idle instances is enforced, but when the pool is

 * empty, new instances are created to support the new load.

 * Hence this class places no limit on the number of "active"

 * instances created by the pool, but is quite useful for

 * re-using <tt>Object</tt>s without introducing

 * artificial limits.

 *

 * @author Rodney Waldhoff

 * @author Dirk Verbeeck

 * @author Sandy McArthur

 * @since Pool 1.0

 */

public class StackObjectPool extends BaseObjectPool implements ObjectPool {

    /**

     * Create a new pool using no factory. Clients must first 

     * {@link #setFactory(PoolableObjectFactory) set the factory} or

     * else this pool will not behave correctly. Clients may first populate the pool

     * using {@link #returnObject(java.lang.Object)} before they can be {@link #borrowObject borrowed}

     * but this usage is <strong>discouraged</strong>.

     *

     * @see #StackObjectPool(PoolableObjectFactory)

     * @deprecated to be removed in pool 2.0 - use {@link #StackObjectPool(PoolableObjectFactory)}

     */

    public StackObjectPool() {

        this((PoolableObjectFactory)null,DEFAULT_MAX_SLEEPING,DEFAULT_INIT_SLEEPING_CAPACITY);

    }

    /**

     * Create a new pool using no factory.

     * Clients must first {@link #setFactory(PoolableObjectFactory) set the factory} or

     * else this pool will not behave correctly. Clients may first populate the pool

     * using {@link #returnObject(java.lang.Object)} before they can be {@link #borrowObject borrowed}

     * but this usage is <strong>discouraged</strong>.

     *

     * @param maxIdle cap on the number of "sleeping" instances in the pool

     * @see #StackObjectPool(PoolableObjectFactory, int)

     * @deprecated to be removed in pool 2.0 - use {@link #StackObjectPool(PoolableObjectFactory, int)}

     */

    public StackObjectPool(int maxIdle) {

        this((PoolableObjectFactory)null,maxIdle,DEFAULT_INIT_SLEEPING_CAPACITY);

    }

    /**

     * Create a new pool using no factory.

     * Clients must first {@link #setFactory(PoolableObjectFactory) set the factory} or

     * else this pool will not behave correctly. Clients may first populate the pool

     * using {@link #returnObject(java.lang.Object)} before they can be {@link #borrowObject borrowed}

     * but this usage is <strong>discouraged</strong>.

     *

     * @param maxIdle cap on the number of "sleeping" instances in the pool

     * @param initIdleCapacity initial size of the pool (this specifies the size of the container,

     *             it does not cause the pool to be pre-populated.)

     * @see #StackObjectPool(PoolableObjectFactory, int, int)

     * @deprecated to be removed in pool 2.0 - use {@link #StackObjectPool(PoolableObjectFactory, int, int)}

     */

    public StackObjectPool(int maxIdle, int initIdleCapacity) {

        this((PoolableObjectFactory)null,maxIdle,initIdleCapacity);

    }

    /**

     * Create a new <tt>StackObjectPool</tt> using the specified <i>factory</i> to create new instances.

     *

     * @param factory the {@link PoolableObjectFactory} used to populate the pool

     */

    public StackObjectPool(PoolableObjectFactory factory) {

        this(factory,DEFAULT_MAX_SLEEPING,DEFAULT_INIT_SLEEPING_CAPACITY);

    }

    /**

     * Create a new <tt>SimpleObjectPool</tt> using the specified <i>factory</i> to create new instances,

     * capping the number of "sleeping" instances to <i>maxIdle</i>.

     *

     * @param factory the {@link PoolableObjectFactory} used to populate the pool

     * @param maxIdle cap on the number of "sleeping" instances in the pool

     */

    public StackObjectPool(PoolableObjectFactory factory, int maxIdle) {

        this(factory,maxIdle,DEFAULT_INIT_SLEEPING_CAPACITY);

    }

    /**

     * <p>Create a new <tt>StackObjectPool</tt> using the specified <code>factory</code> to create new instances,

     * capping the number of "sleeping" instances to <code>maxIdle</code>, and initially allocating a container

     * capable of containing at least <code>initIdleCapacity</code> instances.  The pool is not pre-populated.

     * The <code>initIdleCapacity</code> parameter just determines the initial size of the underlying

     * container, which can increase beyond this value if <code>maxIdle &gt; initIdleCapacity.</code></p>

     * 

     * <p>Negative values of <code>maxIdle</code> are ignored (i.e., the pool is created using

     * {@link #DEFAULT_MAX_SLEEPING}) as are non-positive values for <code>initIdleCapacity.</code>

     *

     * @param factory the {@link PoolableObjectFactory} used to populate the pool

     * @param maxIdle cap on the number of "sleeping" instances in the pool

     * @param initIdleCapacity initial size of the pool (this specifies the size of the container,

     *             it does not cause the pool to be pre-populated.)

     */

    public StackObjectPool(PoolableObjectFactory factory, int maxIdle, int initIdleCapacity) {

        _factory = factory;

        _maxSleeping = (maxIdle < 0 ? DEFAULT_MAX_SLEEPING : maxIdle);

        int initcapacity = (initIdleCapacity < 1 ? DEFAULT_INIT_SLEEPING_CAPACITY : initIdleCapacity);

        _pool = new Stack();

        _pool.ensureCapacity( initcapacity > _maxSleeping ? _maxSleeping : initcapacity);

    }

    /**

     * <p>Borrows an object from the pool.  If there are idle instances available on the stack,

     * the top element of the stack is popped to activate, validate and return to the client.  If there

     * are no idle instances available, the {@link PoolableObjectFactory#makeObject() makeObject} 

     * method of the pool's {@link PoolableObjectFactory} is invoked to create a new instance.</p>

     * 

     * <p>All instances are {@link PoolableObjectFactory#activateObject(Object) activated} and

     * {@link PoolableObjectFactory#validateObject(Object) validated} before being returned to the

     * client.  If validation fails or an exception occurs activating or validating an instance 

     * popped from the idle instance stack, the failing instance is 

     * {@link PoolableObjectFactory#destroyObject(Object) destroyed} and the next instance on

     * the stack is popped, validated and activated.  This process continues until either the

     * stack is empty or an instance passes validation.  If the stack is empty on activation or

     * it does not contain any valid instances, the factory's <code>makeObject</code> method is used

     * to create a new instance.  If a null instance is returned by the factory or the created

     * instance either raises an exception on activation or fails validation, <code>NoSuchElementException</code>

     * is thrown. Exceptions thrown by <code>MakeObject</code> are propagated to the caller; but 

     * other than <code>ThreadDeath</code> or <code>VirtualMachineError</code>, exceptions generated by

     * activation, validation or destroy methods are swallowed silently.</p>

     * 

     * @return an instance from the pool

     */

    public synchronized Object borrowObject() throws Exception {

        assertOpen();

        Object obj = null;

        boolean newlyCreated = false;

        while (null == obj) {

            if (!_pool.empty()) {

                obj = _pool.pop();

            } else {

                if(null == _factory) {

                    throw new NoSuchElementException();

                } else {

                    obj = _factory.makeObject();

                    newlyCreated = true;

                  if (obj == null) {

                    throw new NoSuchElementException("PoolableObjectFactory.makeObject() returned null.");

                  }

                }

            }

            if (null != _factory && null != obj) {

                try {

                    _factory.activateObject(obj);

                    if (!_factory.validateObject(obj)) {

                        throw new Exception("ValidateObject failed");

                    }

                } catch (Throwable t) {

                    PoolUtils.checkRethrow(t);

                    try {

                        _factory.destroyObject(obj);

                    } catch (Throwable t2) {

                        PoolUtils.checkRethrow(t2);

                        // swallowed

                    } finally {

                        obj = null;

                    }

                    if (newlyCreated) {

                        throw new NoSuchElementException(

                            "Could not create a validated object, cause: " +

                            t.getMessage());

                    }

                }

            }

        }

        _numActive++;

        return obj;

    }

    /**

     * <p>Returns an instance to the pool, pushing it on top of the idle instance stack after successful

     * validation and passivation. The returning instance is destroyed if any of the following are true:<ul>

     *   <li>the pool is closed</li>

     *   <li>{@link PoolableObjectFactory#validateObject(Object) validation} fails</li>

     *   <li>{@link PoolableObjectFactory#passivateObject(Object) passivation} throws an exception</li>

     * </ul>

     * If adding a validated, passivated returning instance to the stack would cause

     * {@link #getMaxSleeping() maxSleeping} to be exceeded, the oldest (bottom) instance on the stack

     * is destroyed to make room for the returning instance, which is pushed on top of the stack.</p>

     * 

     * <p>Exceptions passivating or destroying instances are silently swallowed.  Exceptions validating

     * instances are propagated to the client.</p>

     * 

     * @param obj instance to return to the pool

     */

    public synchronized void returnObject(Object obj) throws Exception {

        boolean success = !isClosed();

        if(null != _factory) {

            if(!_factory.validateObject(obj)) {

                success = false;

            } else {

                try {

                    _factory.passivateObject(obj);

                } catch(Exception e) {

                    success = false;

                }

            }

        }

        boolean shouldDestroy = !success;

        _numActive--;

        if (success) {

            Object toBeDestroyed = null;

            if(_pool.size() >= _maxSleeping) {

                shouldDestroy = true;

                toBeDestroyed = _pool.remove(0); // remove the stalest object

            }

            _pool.push(obj);

            obj = toBeDestroyed; // swap returned obj with the stalest one so it can be destroyed

        }

        notifyAll(); // _numActive has changed

        if(shouldDestroy) { // by constructor, shouldDestroy is false when _factory is null

            try {

                _factory.destroyObject(obj);

            } catch(Exception e) {

                // ignored

            }

        }

    }

    /**

     * {@inheritDoc}

     */

    public synchronized void invalidateObject(Object obj) throws Exception {

        _numActive--;

        if (null != _factory) {

            _factory.destroyObject(obj);

        }

        notifyAll(); // _numActive has changed

    }

    /**

     * Return the number of instances

     * currently idle in this pool.

     *

     * @return the number of instances currently idle in this pool

     */

    public synchronized int getNumIdle() {

        return _pool.size();

    }

    /**

     * Return the number of instances currently borrowed from this pool.

     *

     * @return the number of instances currently borrowed from this pool

     */

    public synchronized int getNumActive() {

        return _numActive;

    }

    /**

     * Clears any objects sitting idle in the pool. Silently swallows any

     * exceptions thrown by {@link PoolableObjectFactory#destroyObject(Object)}.

     */

    public synchronized void clear() {

        if(null != _factory) {

            Iterator it = _pool.iterator();

            while(it.hasNext()) {

                try {

                    _factory.destroyObject(it.next());

                } catch(Exception e) {

                    // ignore error, keep destroying the rest

                }

            }

        }

        _pool.clear();

    }

    /**

     * <p>Close this pool, and free any resources associated with it. Invokes

     * {@link #clear()} to destroy and remove instances in the pool.</p>

     * 

     * <p>Calling {@link #addObject} or {@link #borrowObject} after invoking

     * this method on a pool will cause them to throw an

     * {@link IllegalStateException}.</p>

     *

     * @throws Exception never - exceptions clearing the pool are swallowed

     */

    public void close() throws Exception {

        super.close();

        clear();

    }

    /**

     * <p>Create an object, and place it on top of the stack.

     * This method is useful for "pre-loading" a pool with idle objects.</p>

     * 

     * <p>Before being added to the pool, the newly created instance is

     * {@link PoolableObjectFactory#validateObject(Object) validated} and 

     * {@link PoolableObjectFactory#passivateObject(Object) passivated}.  If validation

     * fails, the new instance is {@link PoolableObjectFactory#destroyObject(Object) destroyed}.

     * Exceptions generated by the factory <code>makeObject</code> or <code>passivate</code> are

     * propagated to the caller. Exceptions destroying instances are silently swallowed.</p>

     * 

     * <p>If a new instance is created and successfully validated and passivated and adding this

     * instance to the pool causes {@link #getMaxSleeping() maxSleeping} to be exceeded, the oldest

     * (bottom) instance in the pool is destroyed to make room for the newly created instance, which

     * is pushed on top of the stack.

     * 

     * @throws Exception when the {@link #getFactory() factory} has a problem creating or passivating an object.

     */

    public synchronized void addObject() throws Exception {

        assertOpen();

        if (_factory == null) {

            throw new IllegalStateException("Cannot add objects without a factory.");

        }

        Object obj = _factory.makeObject();

        boolean success = true;

        if(!_factory.validateObject(obj)) {

            success = false;

        } else {

            _factory.passivateObject(obj);

        }

        boolean shouldDestroy = !success;

        if (success) {

            Object toBeDestroyed = null;

            if(_pool.size() >= _maxSleeping) {

                shouldDestroy = true;

                toBeDestroyed = _pool.remove(0); // remove the stalest object

            }

            _pool.push(obj);

            obj = toBeDestroyed; // swap returned obj with the stalest one so it can be destroyed

        }

        notifyAll(); // _numIdle has changed

        if(shouldDestroy) { // by constructor, shouldDestroy is false when _factory is null

            try {

                _factory.destroyObject(obj);

            } catch(Exception e) {

                // ignored

            }

        }

    }

    /**

     * Sets the {@link PoolableObjectFactory factory} this pool uses

     * to create new instances. Trying to change

     * the <code>factory</code> while there are borrowed objects will

     * throw an {@link IllegalStateException}.

     *

     * @param factory the {@link PoolableObjectFactory} used to create new instances.

     * @throws IllegalStateException when the factory cannot be set at this time

     * @deprecated to be removed in pool 2.0

     */

    public synchronized void setFactory(PoolableObjectFactory factory) throws IllegalStateException {

        assertOpen();

        if(0 < getNumActive()) {

            throw new IllegalStateException("Objects are already active");

        } else {

            clear();

            _factory = factory;

        }

    }

    /**

     * The cap on the number of "sleeping" instances in the pool.

     */

    protected static final int DEFAULT_MAX_SLEEPING  = 8;

    /**

     * The default initial size of the pool

     * (this specifies the size of the container, it does not

     * cause the pool to be pre-populated.)

     */

    protected static final int DEFAULT_INIT_SLEEPING_CAPACITY = 4;

    /** 

     * My pool.

     * @deprecated to be made private in pool 2.0 

     */

    protected Stack _pool = null;

    /** 

     * My {@link PoolableObjectFactory}.

     * @deprecated to be made private in pool 2.0 - use {@link #getFactory()}

     */

    protected PoolableObjectFactory _factory = null;

    /** 

     * The cap on the number of "sleeping" instances in the pool. 

     * @deprecated to be made private in pool 2.0 - use {@link #getMaxSleeping()}

     */

    protected int _maxSleeping = DEFAULT_MAX_SLEEPING;

    /**

     * Number of objects borrowed but not yet returned to the pool.

     * @deprecated to be made private in pool 2.0 - use {@link #getNumActive()}

     */

    protected int _numActive = 0;

    /**

     * Returns the {@link PoolableObjectFactory} used by this pool to create and manage object instances.

     * 

     * @return the factory

     * @since 1.5.5

     */

    public synchronized PoolableObjectFactory getFactory() {

        return _factory;

    }

    /**

     * Returns the maximum number of idle instances in the pool.

     * 

     * @return maxSleeping

     * @since 1.5.5

     */

    public int getMaxSleeping() {

        return _maxSleeping;

    }

}