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1   /*
2    *   Licensed to the Apache Software Foundation (ASF) under one
3    *   or more contributor license agreements.  See the NOTICE file
4    *   distributed with this work for additional information
5    *   regarding copyright ownership.  The ASF licenses this file
6    *   to you under the Apache License, Version 2.0 (the
7    *   "License"); you may not use this file except in compliance
8    *   with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   *   Unless required by applicable law or agreed to in writing,
13   *   software distributed under the License is distributed on an
14   *   "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   *   KIND, either express or implied.  See the License for the
16   *   specific language governing permissions and limitations
17   *   under the License.
18   *
19   */
20  package org.apache.directory.server.core.cursor;
21  
22  
23  /**
24   * A basic ClosureMonitor that simply uses a boolean for state and a cause 
25   * exception.
26   * 
27   * Note that we consciously chose not to synchronize close() operations with
28   * checks to see if the monitor state is closed because it costs to 
29   * synchronize and it's OK for the Cursor not to stop immediately when close()
30   * is called.
31   *
32   * @author <a href="mailto:dev@directory.apache.org">Apache Directory Project</a>
33   * @version $Rev$, $Date$
34   */
35  public class DefaultClosureMonitor implements ClosureMonitor
36  {
37      private boolean closed;
38      private Exception cause;
39  
40      
41      /* (non-Javadoc)
42       * @see org.apache.directory.server.core.cursor.ClosureMonitor#close()
43       */
44      public final void close()
45      {
46          // state check needed to "try" not to overwrite exception (lack of 
47          // synchronization may still allow overwriting but who cares that much
48          if ( ! closed )
49          {
50              // not going to sync because who cares if it takes a little longer 
51              // to stop but we need to set cause before toggling closed state 
52              // or else check for closure can throw null cause 
53              cause = new CursorClosedException();
54              closed = true;
55          }
56      }
57  
58  
59      /* (non-Javadoc)
60       * @see org.apache.directory.server.core.cursor.ClosureMonitor#close(java.lang.String)
61       */
62      public final void close( final String cause )
63      {
64          // state check needed to "try" not to overwrite exception (lack of 
65          // synchronization may still allow overwriting but who cares that much
66          if ( ! closed )
67          {
68              // not going to sync because who cares if it takes a little longer 
69              // to stop but we need to set cause before toggling closed state 
70              // or else check for closure can throw null cause 
71              this.cause = new CursorClosedException( cause );
72              closed = true;
73          }
74      }
75  
76  
77      /* (non-Javadoc)
78       * @see org.apache.directory.server.core.cursor.ClosureMonitor#close(java.lang.Exception)
79       */
80      public final void close( final Exception cause )
81      {
82          // state check needed to "try" not to overwrite exception (lack of 
83          // synchronization may still allow overwriting but who cares that much
84          if ( ! closed )
85          {
86              // not going to sync because who cares if it takes a little longer 
87              // to stop but we need to set cause before toggling closed state 
88              // or else check for closure can throw null cause 
89              this.cause = cause;
90              closed = true;
91          }
92      }
93  
94  
95      /* (non-Javadoc)
96       * @see org.apache.directory.server.core.cursor.ClosureMonitor#getCause()
97       */
98      public final Exception getCause()
99      {
100         return cause;
101     }
102 
103 
104     /* (non-Javadoc)
105      * @see org.apache.directory.server.core.cursor.ClosureMonitor#isClosed()
106      */
107     public final boolean isClosed()
108     {
109         return closed;
110     }
111 
112 
113     /*
114      * (non-Javadoc)
115      * @see org.apache.directory.server.core.cursor.ClosureMonitor#checkNotClosed()
116      */
117     public void checkNotClosed() throws Exception
118     {
119         // lack of synchronization may cause pass but eventually it will work
120         if ( closed )
121         {
122             throw cause;
123         }
124     }
125 }