/* * Copyright (c) 2002, 2011, 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 * or visit www.oracle.com if you need additional information or have any * questions. */ package com.sun.jndi.ldap.pool; import java.util.ArrayList; import java.util.Map; import java.util.WeakHashMap; import java.util.Collection; import java.util.Collections; 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 experimentation, cleanup of resources using the * ReferenceQueue mechanism is reliable and has more immediate 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); if (debug) { synchronized (map) { 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 = 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) { Collection copy; synchronized (map) { copy = new ArrayList<>(map.values()); } ArrayList removed = new ArrayList<>(); Connections conns; for (ConnectionsRef ref : copy) { conns = ref.getConnections(); if (conns.expire(threshold)) { d("expire(): removing ", conns); removed.add(ref); } } synchronized (map) { map.values().removeAll(removed); } 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) { 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); synchronized (map) { out.println("current pool size: " + map.size()); for (Map.Entry entry : map.entrySet()) { id = entry.getKey(); conns = entry.getValue().getConnections(); out.println(" " + id + ":" + conns.getStats()); } } out.println("====== Pool end ====================="); } public String toString() { synchronized (map) { 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); } } }