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1
5 package org.h2.util;
6
7 import java.sql.SQLException  ;
8
9 import org.h2.engine.Constants;
10 import org.h2.message.Message;
11
12
18 public class CacheLRU implements Cache {
19
20 public static final String TYPE_NAME = "LRU";
21
22 private int len;
23 private int maxSize;
24 private CacheObject[] values;
25 private int mask;
26 private CacheWriter writer;
27 private int sizeRecords;
28 private int sizeBlocks;
29 private CacheObject head = new CacheHead();
30
31 public CacheLRU(CacheWriter writer, int maxSize) {
32 this.writer = writer;
33 this.len = maxSize / 2;
34 this.mask = len - 1;
35 MathUtils.checkPowerOf2(len);
36 this.maxSize = maxSize;
37 clear();
38 }
39
40 public void put(CacheObject rec) throws SQLException {
41 if(Constants.CHECK) {
42 for(int i=0; i<rec.getBlockCount(); i++) {
43 CacheObject old = find(rec.getPos() + i);
44 if(old != null) {
45 throw Message.getInternalError("try to add a record twice i="+i);
46 }
47 }
48 }
49 int index = rec.getPos() & mask;
50 rec.chained = values[index];
51 values[index] = rec;
52 sizeRecords++;
53 sizeBlocks += rec.getBlockCount();
54 addToFront(rec);
55 removeOld();
56 }
57
58 public CacheObject update(int pos, CacheObject rec) throws SQLException {
59 CacheObject old = find(pos);
60 if(old == null) {
61 put(rec);
62 } else {
63 if(Constants.CHECK) {
64 if(old!=rec) {
65 throw Message.getInternalError("old != record old="+old+" new="+rec);
66 }
67 }
68 removeFromLinkedList(rec);
69 addToFront(rec);
70 }
71 return old;
72 }
73
74 private void removeOld() throws SQLException {
75 if(sizeBlocks < maxSize) {
76 return;
77 }
78 int i=0;
79 ObjectArray changed = new ObjectArray();
80 while (sizeBlocks*4 > maxSize*3 && sizeRecords > Constants.CACHE_MIN_RECORDS) {
81 CacheObject last = head.next;
82 if(i++ >= sizeRecords) {
83 break;
87 }
88 if(Constants.CHECK && last == head) {
89 throw Message.getInternalError("try to remove head");
90 }
91 if(!last.canRemove()) {
95 removeFromLinkedList(last);
96 addToFront(last);
97 continue;
98 }
99 remove(last.getPos());
100 if (last.isChanged()) {
101 changed.add(last);
102 }
103 }
104 if(changed.size() > 0) {
105 CacheObject.sort(changed);
106 for(i=0; i<changed.size(); i++) {
107 CacheObject rec = (CacheObject) changed.get(i);
108 writer.writeBack(rec);
109 }
110 }
111 }
112
113 private void addToFront(CacheObject rec) {
114 if(Constants.CHECK && rec == head) {
115 throw Message.getInternalError("try to move head");
116 }
117 rec.next = head;
118 rec.previous = head.previous;
119 rec.previous.next = rec;
120 head.previous = rec;
121 }
122
123 private void removeFromLinkedList(CacheObject rec) {
124 if(Constants.CHECK && rec == head) {
125 throw Message.getInternalError("try to remove head");
126 }
127 rec.previous.next = rec.next;
128 rec.next.previous = rec.previous;
129 rec.next = null;
131 rec.previous = null;
132 }
133
134 public void remove(int pos) {
135 int index = pos & mask;
136 CacheObject rec = values[index];
137 if(rec == null) {
138 return;
139 }
140 if(rec.getPos() == pos) {
141 values[index] = rec.chained;
142 } else {
143 CacheObject last;
144 do {
145 last = rec;
146 rec = rec.chained;
147 if(rec == null) {
148 return;
149 }
150 } while(rec.getPos() != pos);
151 last.chained = rec.chained;
152 }
153 sizeRecords--;
154 sizeBlocks -= rec.getBlockCount();
155 removeFromLinkedList(rec);
156 if(Constants.CHECK) {
157 rec.chained = null;
158 if(find(pos) != null) {
159 throw Message.getInternalError("not removed!");
160 }
161 }
162 }
163
164 public CacheObject find(int pos) {
165 CacheObject rec = values[pos & mask];
166 while(rec != null && rec.getPos() != pos) {
167 rec = rec.chained;
168 }
169 return rec;
170 }
171
172 public CacheObject get(int pos) {
173 CacheObject rec = find(pos);
174 if(rec != null) {
175 removeFromLinkedList(rec);
176 addToFront(rec);
177 }
178 return rec;
179 }
180
181
210 public ObjectArray getAllChanged() {
211 ObjectArray list = new ObjectArray();
216 for (int i = 0; i < len; i++) {
217 CacheObject rec = values[i];
218 while (rec != null) {
219 if(rec.isChanged()) {
220 list.add(rec);
221 if(list.size() >= sizeRecords) {
222 if(Constants.CHECK) {
223 if(list.size() > sizeRecords) {
224 throw Message.getInternalError("cache chain error");
225 }
226 } else {
227 break;
228 }
229 }
230 }
231 rec = rec.chained;
232 }
233 }
234 return list;
235 }
236
237 public void clear() {
238 head.next = head.previous = head;
239 values = new CacheObject[len];
240 sizeRecords = 0;
241 sizeBlocks = 0;
242 }
243
244 public void setMaxSize(int newSize) throws SQLException {
245 maxSize = newSize < 0 ? 0 : newSize;
246 removeOld();
247 }
248
249 public String getTypeName() {
250 return TYPE_NAME;
251 }
252
253 }
254
255
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