/*
* 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;
import java.util.NoSuchElementException;
/**
* A pooling interface.
* <p>
* <code>ObjectPool</code> defines a trivially simple pooling interface. The only
* required methods are {@link #borrowObject borrowObject}, {@link #returnObject returnObject}
* and {@link #invalidateObject invalidateObject}.
* </p>
* <p>
* Example of use:
* <pre style="border:solid thin; padding: 1ex;"
* > Object obj = <code style="color:#00C">null</code>;
*
* <code style="color:#00C">try</code> {
* obj = pool.borrowObject();
* <code style="color:#00C">try</code> {
* <code style="color:#0C0">//...use the object...</code>
* } <code style="color:#00C">catch</code>(Exception e) {
* <code style="color:#0C0">// invalidate the object</code>
* pool.invalidateObject(obj);
* <code style="color:#0C0">// do not return the object to the pool twice</code>
* obj = <code style="color:#00C">null</code>;
* } <code style="color:#00C">finally</code> {
* <code style="color:#0C0">// make sure the object is returned to the pool</code>
* <code style="color:#00C">if</code>(<code style="color:#00C">null</code> != obj) {
* pool.returnObject(obj);
* }
* }
* } <code style="color:#00C">catch</code>(Exception e) {
* <code style="color:#0C0">// failed to borrow an object</code>
* }</pre>
* </p>
*
* <p>See {@link BaseObjectPool} for a simple base implementation.</p>
*
* @param <T> the type of objects held in this pool
*
* @author Rodney Waldhoff
* @author Sandy McArthur
* @version $Revision: 1222396 $ $Date: 2011-12-22 14:02:25 -0500 (Thu, 22 Dec 2011) $
* @see PoolableObjectFactory
* @see ObjectPoolFactory
* @see KeyedObjectPool
* @see BaseObjectPool
* @since Pool 1.0
*/
public interface ObjectPool<T> {
/**
* Obtains an instance from this pool.
* <p>
* Instances returned from this method will have been either newly created with
* {@link PoolableObjectFactory#makeObject makeObject} or will be a previously idle object and
* have been activated with {@link PoolableObjectFactory#activateObject activateObject} and
* then validated with {@link PoolableObjectFactory#validateObject validateObject}.
* </p>
* <p>
* By contract, clients <strong>must</strong> return the borrowed instance using
* {@link #returnObject returnObject}, {@link #invalidateObject invalidateObject}, or a related method
* as defined in an implementation or sub-interface.
* </p>
* <p>
* The behaviour of this method when the pool has been exhausted
* is not strictly specified (although it may be specified by implementations).
* Older versions of this method would return <code>null</code> to indicate exhaustion,
* newer versions are encouraged to throw a {@link NoSuchElementException}.
* </p>
*
* @return an instance from this pool.
* @throws IllegalStateException after {@link #close close} has been called on this pool.
* @throws Exception when {@link PoolableObjectFactory#makeObject makeObject} throws an exception.
* @throws NoSuchElementException when the pool is exhausted and cannot or will not return another instance.
*/
T borrowObject() throws Exception, NoSuchElementException, IllegalStateException;
/**
* Return an instance to the pool.
* By contract, <code>obj</code> <strong>must</strong> have been obtained
* using {@link #borrowObject() borrowObject}
* or a related method as defined in an implementation
* or sub-interface.
*
* @param obj a {@link #borrowObject borrowed} instance to be returned.
* @throws Exception
*/
void returnObject(T obj) throws Exception;
/**
* <p>Invalidates an object from the pool.</p>
*
* <p>By contract, <code>obj</code> <strong>must</strong> have been obtained
* using {@link #borrowObject borrowObject} or a related method as defined in
* an implementation or sub-interface.</p>
*
* <p>This method should be used when an object that has been borrowed
* is determined (due to an exception or other problem) to be invalid.</p>
*
* @param obj a {@link #borrowObject borrowed} instance to be disposed.
* @throws Exception
*/
void invalidateObject(T obj) throws Exception;
/**
* Create an object using the {@link PoolableObjectFactory factory} or other
* implementation dependent mechanism, passivate it, and then place it in the idle object pool.
* <code>addObject</code> is useful for "pre-loading" a pool with idle objects.
* (Optional operation).
*
* @throws Exception when {@link PoolableObjectFactory#makeObject} fails.
* @throws IllegalStateException after {@link #close} has been called on this pool.
* @throws UnsupportedOperationException when this pool cannot add new idle objects.
*/
void addObject() throws Exception, IllegalStateException, UnsupportedOperationException;
/**
* Return the number of instances
* currently idle in this pool (optional operation).
* This may be considered an approximation of the number
* of objects that can be {@link #borrowObject borrowed}
* without creating any new instances.
* Returns a negative value if this information is not available.
*
* @return the number of instances currently idle in this pool or a negative value if unsupported
* @throws UnsupportedOperationException <strong>deprecated</strong>: if this implementation does not support the operation
*/
int getNumIdle() throws UnsupportedOperationException;
/**
* Return the number of instances
* currently borrowed from this pool
* (optional operation).
* Returns a negative value if this information is not available.
*
* @return the number of instances currently borrowed from this pool or a negative value if unsupported
* @throws UnsupportedOperationException <strong>deprecated</strong>: if this implementation does not support the operation
*/
int getNumActive() throws UnsupportedOperationException;
/**
* Clears any objects sitting idle in the pool, releasing any
* associated resources (optional operation).
* Idle objects cleared must be {@link PoolableObjectFactory#destroyObject(Object) destroyed}.
*
* @throws UnsupportedOperationException if this implementation does not support the operation
*/
void clear() throws Exception, UnsupportedOperationException;
/**
* Close this pool, and free any resources associated with it.
* <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 <strong>deprecated</strong>: implementations should silently fail if not all resources can be freed.
*/
void close() throws Exception;
/**
* Sets the {@link PoolableObjectFactory factory} this pool uses
* to create new instances (optional operation). Trying to change
* the <code>factory</code> after a pool has been used will frequently
* throw an {@link UnsupportedOperationException}. It is up to the pool
* implementation to determine when it is acceptable to call this method.
*
* @param factory the {@link PoolableObjectFactory} used to create new instances.
* @throws IllegalStateException when the factory cannot be set at this time
* @throws UnsupportedOperationException if this implementation does not support the operation
* @deprecated to be removed in pool 2.0
*/
@Deprecated
void setFactory(PoolableObjectFactory<T> factory) throws IllegalStateException, UnsupportedOperationException;
}