/*
* Copyright (c) 2002, 2003, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package com.sun.jndi.ldap.pool;
import java.util.Map;
import java.util.WeakHashMap;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.Set;
import java.util.LinkedList;
import java.io.PrintStream;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import javax.naming.NamingException;
/**
* A map of pool ids to Connections.
* Key is an object that uniquely identifies a PooledConnection request
* (typically information needed to create the connection).
* The definitions of the key's equals() and hashCode() methods are
* vital to its unique identification in a Pool.
*
* Value is a ConnectionsRef, which is a reference to Connections,
* a list of equivalent connections.
*
* Supports methods that
* - retrieves (or creates as necessary) a connection from the pool
* - removes expired connections from the pool
*
* Connections cleanup:
* A WeakHashMap is used for mapping the pool ids and Connections.
* A SoftReference from the value to the key is kept to hold the map
* entry as long as possible. This allows the GC to remove Connections
* from the Pool under situations of VM running out of resources.
* To take an appropriate action of 'closing the connections' before the GC
* reclaims the ConnectionsRef objects, the ConnectionsRef objects are made
* weakly reachable through a list of weak references registered with
* a reference queue.
* Upon an entry gets removed from the WeakHashMap, the ConnectionsRef (value
* in the map) object is weakly reachable. When another sweep of
* clearing the weak references is made by the GC it puts the corresponding
* ConnectionsWeakRef object into the reference queue.
* The reference queue is monitored lazily for reclaimable Connections
* whenever a pooled connection is requested or a call to remove the expired
* connections is made. The monitoring is done regularly when idle connection
* timeout is set as the PoolCleaner removes expired connections periodically.
* As determined by the experiements, cleanup of resources using the
* ReferenceQueue mechanism is reliable and has immidiate effect than the
* finalizer approach.
*
* @author Rosanna Lee
*/
final public class Pool {
static final boolean debug = com.sun.jndi.ldap.LdapPoolManager.debug;
/*
* Used for connections cleanup
*/
private static final ReferenceQueue queue = new ReferenceQueue();
private static final Collection weakRefs =
Collections.synchronizedList(new LinkedList());
final private int maxSize; // max num of identical conn per pool
final private int prefSize; // preferred num of identical conn per pool
final private int initSize; // initial number of identical conn to create
final private Map map;
public Pool(int initSize, int prefSize, int maxSize) {
map = new WeakHashMap();
this.prefSize = prefSize;
this.maxSize = maxSize;
this.initSize = initSize;
}
/**
* Gets a pooled connection for id. The pooled connection might be
* newly created, as governed by the maxSize and prefSize settings.
* If a pooled connection is unavailable and cannot be created due
* to the maxSize constraint, this call blocks until the constraint
* is removed or until 'timeout' ms has elapsed.
*
* @param id identity of the connection to get
* @param timeout the number of milliseconds to wait before giving up
* @param factory the factory to use for creating the connection if
* creation is necessary
* @return a pooled connection
* @throws NamingException the connection could not be created due to
* an error.
*/
public PooledConnection getPooledConnection(Object id, long timeout,
PooledConnectionFactory factory) throws NamingException {
d("get(): ", id);
d("size: ", map.size());
expungeStaleConnections();
Connections conns;
synchronized (map) {
conns = getConnections(id);
if (conns == null) {
d("get(): creating new connections list for ", id);
// No connections for this id so create a new list
conns = new Connections(id, initSize, prefSize, maxSize,
factory);
ConnectionsRef connsRef = new ConnectionsRef(conns);
map.put(id, connsRef);
// Create a weak reference to ConnectionsRef
Reference weakRef = new ConnectionsWeakRef(connsRef, queue);
// Keep the weak reference through the element of a linked list
weakRefs.add(weakRef);
}
}
d("get(): size after: ", map.size());
return conns.get(timeout, factory); // get one connection from list
}
private Connections getConnections(Object id) {
ConnectionsRef ref = (ConnectionsRef) map.get(id);
return (ref != null) ? ref.getConnections() : null;
}
/**
* Goes through the connections in this Pool and expires ones that
* have been idle before 'threshold'. An expired connection is closed
* and then removed from the pool (removePooledConnection() will eventually
* be called, and the list of pools itself removed if it becomes empty).
*
* @param threshold connections idle before 'threshold' should be closed
* and removed.
*/
public void expire(long threshold) {
synchronized (map) {
Collection coll = map.values();
Iterator iter = coll.iterator();
Connections conns;
while (iter.hasNext()) {
conns = ((ConnectionsRef) (iter.next())).getConnections();
if (conns.expire(threshold)) {
d("expire(): removing ", conns);
iter.remove();
}
}
}
expungeStaleConnections();
}
/*
* Closes the connections contained in the ConnectionsRef object that
* is going to be reclaimed by the GC. Called by getPooledConnection()
* and expire() methods of this class.
*/
private static void expungeStaleConnections() {
ConnectionsWeakRef releaseRef = null;
while ((releaseRef = (ConnectionsWeakRef) queue.poll())
!= null) {
Connections conns = releaseRef.getConnections();
if (debug) {
System.err.println(
"weak reference cleanup: Closing Connections:" + conns);
}
// cleanup
conns.close();
weakRefs.remove(releaseRef);
releaseRef.clear();
}
}
public void showStats(PrintStream out) {
Map.Entry entry;
Object id;
Connections conns;
out.println("===== Pool start ======================");
out.println("maximum pool size: " + maxSize);
out.println("preferred pool size: " + prefSize);
out.println("initial pool size: " + initSize);
out.println("current pool size: " + map.size());
Set entries = map.entrySet();
Iterator iter = entries.iterator();
while (iter.hasNext()) {
entry = (Map.Entry) iter.next();
id = entry.getKey();
conns = ((ConnectionsRef) entry.getValue()).getConnections();
out.println(" " + id + ":" + conns.getStats());
}
out.println("====== Pool end =====================");
}
public String toString() {
return super.toString() + " " + map.toString();
}
private void d(String msg, int i) {
if (debug) {
System.err.println(this + "." + msg + i);
}
}
private void d(String msg, Object obj) {
if (debug) {
System.err.println(this + "." + msg + obj);
}
}
}