1 /*
2 Copyright (c) 2007 Health Market Science, Inc.
3
4 This library is free software; you can redistribute it and/or
5 modify it under the terms of the GNU Lesser General Public
6 License as published by the Free Software Foundation; either
7 version 2.1 of the License, or (at your option) any later version.
8
9 This library is distributed in the hope that it will be useful,
10 but WITHOUT ANY WARRANTY; without even the implied warranty of
11 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
12 Lesser General Public License for more details.
13
14 You should have received a copy of the GNU Lesser General Public
15 License along with this library; if not, write to the Free Software
16 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307
17 USA
18
19 You can contact Health Market Science at info@healthmarketscience.com
20 or at the following address:
21
22 Health Market Science
23 2700 Horizon Drive
24 Suite 200
25 King of Prussia, PA 19406
26 */
27
28 package com.healthmarketscience.jackcess;
29
30 import java.io.IOException;
31 import java.nio.ByteBuffer;
32
33 /**
34 * Manages a reference to a page buffer.
35 *
36 * @author James Ahlborn
37 */
38 public final class TempPageHolder {
39
40 private int _pageNumber = PageChannel.INVALID_PAGE_NUMBER;
41 private final TempBufferHolder _buffer;
42 /** the last "modification" count of the buffer that this holder observed.
43 this is tracked so that the page data can be re-read if the underlying
44 buffer has been discarded since the last page read */
45 private int _bufferModCount;
46
47 private TempPageHolder(TempBufferHolder.Type type) {
48 _buffer = TempBufferHolder.newHolder(type, false);
49 _bufferModCount = _buffer.getModCount();
50 }
51
52 /**
53 * Creates a new TempPageHolder.
54 * @param type the type of reference desired for any create page buffers
55 */
56 public static TempPageHolder newHolder(TempBufferHolder.Type type) {
57 return new TempPageHolder(type);
58 }
59
60 /**
61 * @return the currently set page number
62 */
63 public int getPageNumber() {
64 return _pageNumber;
65 }
66
67 /**
68 * @return the page for the current page number, reading as necessary,
69 * position and limit are unchanged
70 */
71 public ByteBuffer getPage(PageChannel pageChannel)
72 throws IOException
73 {
74 return setPage(pageChannel, _pageNumber, false);
75 }
76
77 /**
78 * Sets the current page number and returns that page
79 * @return the page for the new page number, reading as necessary, resets
80 * position
81 */
82 public ByteBuffer setPage(PageChannel pageChannel, int pageNumber)
83 throws IOException
84 {
85 return setPage(pageChannel, pageNumber, true);
86 }
87
88 private ByteBuffer setPage(PageChannel pageChannel, int pageNumber,
89 boolean rewind)
90 throws IOException
91 {
92 ByteBuffer buffer = _buffer.getPageBuffer(pageChannel);
93 int modCount = _buffer.getModCount();
94 if((pageNumber != _pageNumber) || (_bufferModCount != modCount)) {
95 _pageNumber = pageNumber;
96 _bufferModCount = modCount;
97 pageChannel.readPage(buffer, _pageNumber);
98 } else if(rewind) {
99 buffer.rewind();
100 }
101
102 return buffer;
103 }
104
105 /**
106 * Allocates a new buffer in the database (with undefined data) and returns
107 * a new empty buffer.
108 */
109 public ByteBuffer setNewPage(PageChannel pageChannel)
110 throws IOException
111 {
112 // ditch any current data
113 clear();
114 // allocate a new page in the database
115 _pageNumber = pageChannel.allocateNewPage();
116 // return a new buffer
117 return _buffer.getPageBuffer(pageChannel);
118 }
119
120 /**
121 * Forces any current page data to be disregarded (any
122 * <code>getPage</code>/<code>setPage</code> call must reload page data).
123 * Does not necessarily release any memory.
124 */
125 public void invalidate() {
126 possiblyInvalidate(_pageNumber, null);
127 }
128
129 /**
130 * Forces any current page data to be disregarded if it matches the given
131 * page number (any <code>getPage</code>/<code>setPage</code> call must
132 * reload page data) and is not the given buffer. Does not necessarily
133 * release any memory.
134 */
135 public void possiblyInvalidate(int modifiedPageNumber,
136 ByteBuffer modifiedBuffer) {
137 if(modifiedBuffer == _buffer.getExistingBuffer()) {
138 // no worries, our buffer was the one modified (or is null, either way
139 // we'll need to reload)
140 return;
141 }
142 if(modifiedPageNumber == _pageNumber) {
143 _pageNumber = PageChannel.INVALID_PAGE_NUMBER;
144 }
145 }
146
147 /**
148 * Forces any current page data to be disregarded (any
149 * <code>getPage</code>/<code>setPage</code> call must reload page data) and
150 * releases any referenced memory.
151 */
152 public void clear() {
153 invalidate();
154 _buffer.clear();
155 }
156
157 }