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/*
* Filename: AbstractPool.java
*
* Copyright 2000-2001 by iPlanet/Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of iPlanet/Sun Microsystems, Inc. ("Confidential Information").
* You shall not disclose such Confidential Information and shall
* use it only in accordance with the terms of the license
* agreement you entered into with iPlanet/Sun Microsystems.
*/
/**
* <BR> <I>$Source: /cvs/glassfish/appserv-commons/src/java/com/sun/enterprise/util/pool/AbstractPool.java,v $</I>
* @author $Author: tcfujii $
* @version $Revision: 1.5 $ $Date: 2007/05/05 05:32:16 $
*/
package com.sun.enterprise.util.pool;
import java.util.Collection;
import java.util.ArrayList;
import com.sun.enterprise.util.scheduler.PeriodicallyServicable;
import com.sun.enterprise.util.scheduler.PeriodicEventScheduler;
import com.sun.enterprise.util.ApproximateClock;
//Bug 4677074 begin
import java.util.logging.Logger;
import java.util.logging.Level;
import com.sun.logging.LogDomains;
//Bug 4677074 end
/**
* <p>Abstract pool provides the basic implementation of an object pool. The implementation
* uses a linked list to maintain a collection of (available) objects. If the pool is
* empty it simply creates one using the ObjectFactory instance. Subclasses can change
* this behaviour by overriding getObject(...) and returnObject(....) methods. This
* class provides basic support for synchronization, event notification, pool shutdown
* and pool object recycling. It also does some very basic bookkeeping like the
* number of objects created, number of threads waiting for object.
* <p> Subclasses can make use of these book-keeping data to provide complex pooling
* mechanism like LRU / MRU / Random. Also, note that AbstractPool does not have a
* notion of pool limit. It is upto to the derived classes to implement these features.
*/
public abstract class AbstractPool
implements Pool
{
//Bug 4677074 begin
static Logger _logger=LogDomains.getLogger(LogDomains.UTIL_LOGGER);
//Bug 4677074 end
protected boolean bDebug=false;
protected Collection collection;
protected ArrayList listeners;
protected ObjectFactory factory = null;
protected int waitCount = 0;
protected int createdCount = 0;
protected Object onHold = null;
protected Object closed = null;
protected static final ApproximateClock _clock = new ApproximateClock(15000);
protected PeriodicEventScheduler scheduler;
protected AbstractPool() {
scheduler = PeriodicEventScheduler.getInstance();
}
/**
* Get an object. Application can use pool.getObject() to get an object
* instead of using new XXX().
* @param canWait Must be true if the calling thread is willing to wait for infinite time
* to get an object, false if the calling thread does not want to wait at all.
* @exception Throws InterruptedException if the thread was interrupted while waiting
*/
public Object getObject(boolean canWait, Object param)
throws InterruptedException, PoolException
{
Object object;
if (closed != null) {
throw new PoolException("Pool closed. Cannot obtain object");
}
synchronized (collection) {
while (true) {
if (collection.size() > 0) {
if ( (object = checkout(param)) != null) {
return object;
}
} else if (canCreate()) {
createdCount++;
break;
}
if (canWait) {
try {
waitCount++;
beforeWait(param);
collection.wait();
afterNotify(param);
waitCount--;
} catch (InterruptedException inEx) {
throw new RequestInterruptedException("InterruptedException", inEx);
}
} else {
return null;
}
}
}
try {
object = factory.create(param);
} catch (PoolException poolEx) {
synchronized (collection) {
createdCount--;
}
throw poolEx;
}
afterCreate(object);
return object;
}
/**
* Get an object. Application can use pool.getObject() to get an object
* instead of using new XXX(). The method throws TimedoutException
* if an object could not be returned in 'waitForMillis' millisecond.
* @param waitFor the amount of time the thread is willing to wait.
* @exception Throws InterruptedException if the thread was interrupted while waiting
* @exception Throws TimedoutException if an object could not be obtained from the pool
* within the specified time.
*/
public Object getObject(long waitFor, Object param)
throws InterruptedException, PoolException
{
if (closed != null) {
throw new PoolException("Pool closed. Cannot obtain object");
}
long now = _clock.getTime();
long timeLeft = waitFor;
long startTime = now;
Object object;
synchronized (collection) {
while (true) {
if (collection.size() > 0) {
if ( (object = checkout(param)) != null) {
return object;
}
} else if (canCreate()) {
createdCount++;
break;
}
if (timeLeft > 0) {
try {
waitCount++;
beforeWait(param);
collection.wait();
afterNotify(param);
waitCount--;
} catch (InterruptedException inEx) {
throw new RequestInterruptedException("InterruptedException", inEx);
}
} else {
return null;
}
now = _clock.getTime();
timeLeft = now - startTime;
startTime = now;
}
}
try {
object = factory.create(param);
} catch (PoolException poolEx) {
synchronized (collection) {
createdCount--;
}
throw poolEx;
}
afterCreate(object);
return object;
}
/**
* Return an object back to the pool. An object that is obtained through
* getObject() must always be returned back to the pool using either
* returnObject(obj) or through destroyObject(obj).
*/
public void returnObject(Object object) {
synchronized (collection) {
if (closed != null) {
if (waitCount == 0) {
destroyObject(object);
return;
}
}
checkin(object);
if (waitCount > 0) {
collection.notify();
}
}
}
/**
* Destroys an Object. Note that applications should not ignore the reference
* to the object that they got from getObject(). An object that is obtained through
* getObject() must always be returned back to the pool using either
* returnObject(obj) or through destroyObject(obj). This method tells that the
* object should be destroyed and cannot be reused.
*/
public void destroyObject(Object object) {
beforeDestroy(object);
factory.destroy(object);
synchronized (collection) {
createdCount--;
if (waitCount > 0) {
collection.notify();
}
}
}
/**
* Notification when an object is put back into the pool (checkin).
* @param The object to be returned back to the pool.
* @return Any non null value can be returned to signal that the object
* was indeed added to the pool. This class always adds the object to the
* pool (at the end of the collection), it returns non-null value.
* Subclasses can override this behaviour.
*/
protected abstract Object checkin(Object object);
/**
* Notification when an object is given out from the pool (checout).
* @return The object that has to be returned to the application. A null
* value must be returned if no object can be returned to the application. Since this
* class always returns the last node from the collection, it returns non-null value.
* Subclasses can override this behaviour.
*/
protected abstract Object checkout(Object param);
/**
* Add a PoolListener
* @param listener The pool listener
*/
public boolean addPoolListener(PoolListener listener) {
synchronized (this) {
if (listeners == null) {
listeners = new ArrayList();
listeners.add(listener);
return true;
}
if (listeners.indexOf(listener) == -1) {
listeners.add(listener);
return true;
} else {
return false;
}
}
}
/**
* Add a PoolListener
* @param listener The pool listener
*/
public boolean removePoolListener(PoolListener listener) {
synchronized (this) {
if (listeners == null) {
return false;
} else {
return listeners.remove(listener);
}
}
}
protected abstract boolean canCreate();
/**
* Preload the pool with objects.
* @param count the number of objects to be added.
*/
public void preload(int count) {
if (count <= 0) {
return;
}
ArrayList tempList = new ArrayList(count);
for (int i=0; i<count; i++) {
try {
tempList.add(factory.create(null));
} catch (PoolException poolEx) {
}
}
count = tempList.size();
synchronized (collection) {
for (int i=0; i<count; i++) {
checkin(tempList.get(i));
}
createdCount += count;
}
//Bug 4677074 if(bDebug) System.out.println("After preload(" + count + "): Size: " + collection.size());
//Bug 4677074 begin
if(com.sun.enterprise.util.logging.Debug.enabled) _logger.log(Level.FINE,"After preload(" + count + "): Size: " + collection.size());
//Bug 4677074 end
}
public int size() {
return collection.size();
}
/**
* Destroy the available objects in the pool.
*/
public int destroyPoolObjects() {
return destroyPoolObjects(collection.size());
}
/**
* Destroy 'count' available objects in the pool.
*/
public int destroyPoolObjects(int count) {
if (count <= 0) {
return 0;
}
Object[] array = collection.toArray();
ArrayList arrayList = null;
synchronized (collection) {
if (count > collection.size()) {
count = collection.size();
}
arrayList = new ArrayList(count);
for (int i=0; i<count; i++) {
arrayList.add(checkout(null));
}
count = arrayList.size();
createdCount -= count;
}
for (int i=0; i<count; i++) {
factory.destroy(arrayList.get(i));
}
return count;
}
/**
* Closes the current pool. No further getObject(....)s are allowed, while
* returnObject() and destroyObjects() are allowed.
*/
public void close() {
//first clean up all objects
onClose();
synchronized (collection) {
closed = "__Closed__";
int diff = collection.size() - this.waitCount;
destroyPoolObjects(diff);
//We do not need to change the factory as all fresh getObject()
// requests are blocked well before the synchronized access to the
// collection (or pool).
//this.factory = new ClosedObjectFactory(this.factory);
}
}
/**
* Test if the pool is closed or not
* @return True if the pool is closed, false if not.
*/
public boolean isClosed() {
return (closed != null);
}
//Event Notification
/**
* Called after an object is created using factory.create(....)
* @param The created object.
*/
public void afterCreate(Object object) {
if (listeners != null) {
int size = listeners.size();
for (int i=0; i<size; i++) {
((PoolListener) listeners.get(i)).afterCreate(object);
}
}
}
/**
* Called before an object is destroyed using factory.destroy(object)
* @param The object to be destroyed.
*/
public void beforeDestroy(Object object) {
if (listeners != null) {
int size = listeners.size();
for (int i=0; i<size; i++) {
((PoolListener) listeners.get(i)).beforeDestroy(object);
}
}
}
/**
* Called by the thread that is about to wait.
*/
public void beforeWait(Object object) {
if (listeners != null) {
int size = listeners.size();
for (int i=0; i<size; i++) {
((PoolListener) listeners.get(i)).beforeWait(object);
}
}
}
/**
* Called by the thread that has been notified.
*/
public void afterNotify(Object object) {
if (listeners != null) {
int size = listeners.size();
for (int i=0; i<size; i++) {
((PoolListener) listeners.get(i)).afterNotify(object);
}
}
}
/**
* Called when the pool is closed.
*/
public void onClose() {
if (listeners != null) {
int size = listeners.size();
for (int i=0; i<size; i++) {
((PoolListener) listeners.get(i)).onClose();
}
}
}
}
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