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1   /**
2    * JDBM LICENSE v1.00
3    *
4    * Redistribution and use of this software and associated documentation
5    * ("Software"), with or without modification, are permitted provided
6    * that the following conditions are met:
7    *
8    * 1. Redistributions of source code must retain copyright
9    *    statements and notices.  Redistributions must also contain a
10   *    copy of this document.
11   *
12   * 2. Redistributions in binary form must reproduce the
13   *    above copyright notice, this list of conditions and the
14   *    following disclaimer in the documentation and/or other
15   *    materials provided with the distribution.
16   *
17   * 3. The name "JDBM" must not be used to endorse or promote
18   *    products derived from this Software without prior written
19   *    permission of Cees de Groot.  For written permission,
20   *    please contact cg@cdegroot.com.
21   *
22   * 4. Products derived from this Software may not be called "JDBM"
23   *    nor may "JDBM" appear in their names without prior written
24   *    permission of Cees de Groot. 
25   *
26   * 5. Due credit should be given to the JDBM Project
27   *    (http://jdbm.sourceforge.net/).
28   *
29   * THIS SOFTWARE IS PROVIDED BY THE JDBM PROJECT AND CONTRIBUTORS
30   * ``AS IS'' AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT
31   * NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
32   * FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL
33   * CEES DE GROOT OR ANY CONTRIBUTORS BE LIABLE FOR ANY DIRECT,
34   * INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
35   * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
36   * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
37   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
38   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
39   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
40   * OF THE POSSIBILITY OF SUCH DAMAGE.
41   *
42   * Copyright 2000 (C) Cees de Groot. All Rights Reserved.
43   * Contributions are Copyright (C) 2000 by their associated contributors.
44   *
45   * $Id: FreeLogicalRowIdPageManager.java,v 1.1 2000/05/06 00:00:31 boisvert Exp $
46   */
47  
48  package jdbm.recman;
49  
50  import java.io.IOException;
51  
52  /**
53   *  This class manages free Logical rowid pages and provides methods
54   *  to free and allocate Logical rowids on a high level.
55   */
56  final class FreeLogicalRowIdPageManager {
57      // our record file
58      private RecordFile file;
59      // our page manager
60      private PageManager pageman;
61  
62      /**
63       *  Creates a new instance using the indicated record file and
64       *  page manager.
65       */
66      FreeLogicalRowIdPageManager(RecordFile file,
67                                  PageManager pageman) throws IOException {
68          this.file = file;
69          this.pageman = pageman;
70      }
71  
72      /**
73       *  Returns a free Logical rowid, or
74       *  null if nothing was found.
75       */
76      Location get() throws IOException {
77    
78          // Loop through the free Logical rowid list until we find
79          // the first rowid.
80          Location retval = null;
81          PageCursor curs = new PageCursor(pageman, Magic.FREELOGIDS_PAGE);
82          while (curs.next() != 0) {
83              FreeLogicalRowIdPage fp = FreeLogicalRowIdPage
84                  .getFreeLogicalRowIdPageView(file.get(curs.getCurrent()));
85              int slot = fp.getFirstAllocated();
86              if (slot != -1) {
87                  // got one!
88                  retval =
89                      new Location(fp.get(slot));
90                  fp.free(slot);
91                  if (fp.getCount() == 0) {
92                      // page became empty - free it
93                      file.release(curs.getCurrent(), false);
94                      pageman.free(Magic.FREELOGIDS_PAGE, curs.getCurrent());
95                  }
96                  else
97                      file.release(curs.getCurrent(), true);
98                  
99                  return retval;
100             }
101             else {
102                 // no luck, go to next page
103                 file.release(curs.getCurrent(), false);
104             }     
105         }
106         return null;
107     }
108 
109     /**
110      *  Puts the indicated rowid on the free list
111      */
112     void put(Location rowid)
113     throws IOException {
114         
115         PhysicalRowId free = null;
116         PageCursor curs = new PageCursor(pageman, Magic.FREELOGIDS_PAGE);
117         long freePage = 0;
118         while (curs.next() != 0) {
119             freePage = curs.getCurrent();
120             BlockIo curBlock = file.get(freePage);
121             FreeLogicalRowIdPage fp = FreeLogicalRowIdPage
122                 .getFreeLogicalRowIdPageView(curBlock);
123             int slot = fp.getFirstFree();
124             if (slot != -1) {
125                 free = fp.alloc(slot);
126                 break;
127             }
128             
129             file.release(curBlock);
130         }
131         if (free == null) {
132             // No more space on the free list, add a page.
133             freePage = pageman.allocate(Magic.FREELOGIDS_PAGE);
134             BlockIo curBlock = file.get(freePage);
135             FreeLogicalRowIdPage fp = 
136                 FreeLogicalRowIdPage.getFreeLogicalRowIdPageView(curBlock);
137             free = fp.alloc(0);
138         }
139         free.setBlock(rowid.getBlock());
140         free.setOffset(rowid.getOffset());
141         file.release(freePage, true);
142     }
143 }