1 /*
   2  * Copyright (c) 2003, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 
  26 package com.sun.jndi.ldap.pool;
  27 
  28 import java.lang.ref.WeakReference;
  29 import java.lang.ref.ReferenceQueue;
  30 
  31 /*
  32  * This class defines a WeakReference to the ConnectionRef (the referent).
  33  *
  34  * The ConnectionRef enables to break the reference
  35  * cycle between Connection, LdapClient, Connections and ConnectionDesc,
  36  * shown in the figure below.
  37  *
  38  *        -------> Connections -----> ConnectionDesc
  39  *        |              ^                  |
  40  *        |              |                  |
  41  *        |              |                  |
  42  * ConnectionsRef    LdapClient <------------
  43  *        ^              |   ^
  44  *        :              |   |
  45  *        :              v   |
  46  * ConnectionsWeakRef  Connection
  47  *
  48  * The ConnectionsRef is for cleaning up the resources held by the
  49  * Connection thread by making them available to the GC. The pool
  50  * uses ConnectionRef to hold the pooled resources.
  51  *
  52  * This class in turn holds a WeakReference with a ReferenceQueue to the
  53  * ConnectionRef to track when the ConnectionRef becomes ready
  54  * for getting GC'ed. It extends from WeakReference in order to hold a
  55  * reference to Connections used for closing (which in turn terminates
  56  * the Connection thread) it by monitoring the ReferenceQueue.
  57  */
  58 class ConnectionsWeakRef extends WeakReference {
  59 
  60     private final Connections conns;
  61 
  62     ConnectionsWeakRef (ConnectionsRef connsRef, ReferenceQueue queue) {
  63         super(connsRef, queue);
  64         this.conns = connsRef.getConnections();
  65     }
  66 
  67     Connections getConnections() {
  68         return conns;
  69     }
  70 }