Source Code Cross Referenced for ResourceCache.java in  » Sevlet-Container » tomcat-catalina » org » apache » naming » resources » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Sevlet Container » tomcat catalina » org.apache.naming.resources 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * Copyright 1999,2004 The Apache Software Foundation.
003:         * 
004:         * Licensed under the Apache License, Version 2.0 (the "License");
005:         * you may not use this file except in compliance with the License.
006:         * You may obtain a copy of the License at
007:         * 
008:         *      http://www.apache.org/licenses/LICENSE-2.0
009:         * 
010:         * Unless required by applicable law or agreed to in writing, software
011:         * distributed under the License is distributed on an "AS IS" BASIS,
012:         * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013:         * See the License for the specific language governing permissions and
014:         * limitations under the License.
015:         */
016:
017:        package org.apache.naming.resources;
018:
019:        import java.util.HashMap;
020:
021:        /**
022:         * Implements a special purpose cache.
023:         * 
024:         * @author <a href="mailto:remm@apache.org">Remy Maucherat</a>
025:         * @version $Revision: 1.3 $
026:         */
027:        public class ResourceCache {
028:
029:            // ----------------------------------------------------------- Constructors
030:
031:            public ResourceCache() {
032:            }
033:
034:            // ----------------------------------------------------- Instance Variables
035:
036:            /**
037:             * Cache.
038:             * Path -> Cache entry.
039:             */
040:            protected CacheEntry[] cache = new CacheEntry[0];
041:
042:            /**
043:             * Not found cache.
044:             */
045:            protected HashMap notFoundCache = new HashMap();
046:
047:            /**
048:             * Max size of resources which will have their content cached.
049:             */
050:            protected int cacheMaxSize = 10240; // 10 MB
051:
052:            /**
053:             * Max amount of removals during a make space.
054:             */
055:            protected int maxAllocateIterations = 20;
056:
057:            /**
058:             * Entry hit ratio at which an entry will never be removed from the cache.
059:             * Compared with entry.access / hitsCount
060:             */
061:            protected long desiredEntryAccessRatio = 3;
062:
063:            /**
064:             * Spare amount of not found entries.
065:             */
066:            protected int spareNotFoundEntries = 500;
067:
068:            /**
069:             * Current cache size in KB.
070:             */
071:            protected int cacheSize = 0;
072:
073:            /**
074:             * Number of accesses to the cache.
075:             */
076:            protected long accessCount = 0;
077:
078:            /**
079:             * Number of cache hits.
080:             */
081:            protected long hitsCount = 0;
082:
083:            // ------------------------------------------------------------- Properties
084:
085:            /**
086:             * Return the access count.
087:             * Note: Update is not synced, so the number may not be completely 
088:             * accurate.
089:             */
090:            public long getAccessCount() {
091:                return accessCount;
092:            }
093:
094:            /**
095:             * Return the maximum size of the cache in KB.
096:             */
097:            public int getCacheMaxSize() {
098:                return cacheMaxSize;
099:            }
100:
101:            /**
102:             * Set the maximum size of the cache in KB.
103:             */
104:            public void setCacheMaxSize(int cacheMaxSize) {
105:                this .cacheMaxSize = cacheMaxSize;
106:            }
107:
108:            /**
109:             * Return the current cache size in KB.
110:             */
111:            public int getCacheSize() {
112:                return cacheSize;
113:            }
114:
115:            /**
116:             * Return desired entry access ratio.
117:             */
118:            public long getDesiredEntryAccessRatio() {
119:                return desiredEntryAccessRatio;
120:            }
121:
122:            /**
123:             * Set the desired entry access ratio.
124:             */
125:            public void setDesiredEntryAccessRatio(long desiredEntryAccessRatio) {
126:                this .desiredEntryAccessRatio = desiredEntryAccessRatio;
127:            }
128:
129:            /**
130:             * Return the number of cache hits.
131:             * Note: Update is not synced, so the number may not be completely 
132:             * accurate.
133:             */
134:            public long getHitsCount() {
135:                return hitsCount;
136:            }
137:
138:            /**
139:             * Return the maximum amount of iterations during a space allocation.
140:             */
141:            public int getMaxAllocateIterations() {
142:                return maxAllocateIterations;
143:            }
144:
145:            /**
146:             * Set the maximum amount of iterations during a space allocation.
147:             */
148:            public void setMaxAllocateIterations(int maxAllocateIterations) {
149:                this .maxAllocateIterations = maxAllocateIterations;
150:            }
151:
152:            /**
153:             * Return the amount of spare not found entries.
154:             */
155:            public int getSpareNotFoundEntries() {
156:                return spareNotFoundEntries;
157:            }
158:
159:            /**
160:             * Set the amount of spare not found entries.
161:             */
162:            public void setSpareNotFoundEntries(int spareNotFoundEntries) {
163:                this .spareNotFoundEntries = spareNotFoundEntries;
164:            }
165:
166:            // --------------------------------------------------------- Public Methods
167:
168:            public boolean allocate(int space) {
169:
170:                int toFree = space - (cacheMaxSize - cacheSize);
171:
172:                if (toFree <= 0) {
173:                    return true;
174:                }
175:
176:                // Increase the amount to free so that allocate won't have to run right
177:                // away again
178:                toFree += (cacheMaxSize / 20);
179:
180:                int size = notFoundCache.size();
181:                if (size > spareNotFoundEntries) {
182:                    notFoundCache.clear();
183:                    cacheSize -= size;
184:                    toFree -= size;
185:                }
186:
187:                if (toFree <= 0) {
188:                    return true;
189:                }
190:
191:                int attempts = 0;
192:                int entriesFound = 0;
193:                long totalSpace = 0;
194:                int[] toRemove = new int[maxAllocateIterations];
195:                while (toFree > 0) {
196:                    if (attempts == maxAllocateIterations) {
197:                        // Give up, no changes are made to the current cache
198:                        return false;
199:                    }
200:                    if (toFree > 0) {
201:                        // Randomly select an entry in the array
202:                        int entryPos = -1;
203:                        boolean unique = false;
204:                        int count = 0;
205:                        while (!unique) {
206:                            unique = true;
207:                            entryPos = (int) Math.floor(Math.random()
208:                                    * (cache.length - 1));
209:                            // Guarantee uniqueness
210:                            for (int i = 0; i < entriesFound; i++) {
211:                                if (toRemove[i] == entryPos) {
212:                                    unique = false;
213:                                }
214:                            }
215:                        }
216:                        long entryAccessRatio = ((cache[entryPos].accessCount * 100) / accessCount);
217:                        if (entryAccessRatio < desiredEntryAccessRatio) {
218:                            toRemove[entriesFound] = entryPos;
219:                            totalSpace += cache[entryPos].size;
220:                            toFree -= cache[entryPos].size;
221:                            entriesFound++;
222:                        }
223:                    }
224:                    attempts++;
225:                }
226:
227:                // Now remove the selected entries
228:                java.util.Arrays.sort(toRemove, 0, entriesFound);
229:                CacheEntry[] newCache = new CacheEntry[cache.length
230:                        - entriesFound];
231:                int pos = 0;
232:                int n = -1;
233:                if (entriesFound > 0) {
234:                    n = toRemove[0];
235:                    for (int i = 0; i < cache.length; i++) {
236:                        if (i == n) {
237:                            if ((pos + 1) < entriesFound) {
238:                                n = toRemove[pos + 1];
239:                                pos++;
240:                            } else {
241:                                pos++;
242:                                n = -1;
243:                            }
244:                        } else {
245:                            newCache[i - pos] = cache[i];
246:                        }
247:                    }
248:                }
249:                cache = newCache;
250:                cacheSize -= totalSpace;
251:
252:                return true;
253:
254:            }
255:
256:            public CacheEntry lookup(String name) {
257:
258:                CacheEntry cacheEntry = null;
259:                accessCount++;
260:                int pos = find(cache, name);
261:                if ((pos != -1) && (name.equals(cache[pos].name))) {
262:                    cacheEntry = cache[pos];
263:                }
264:                if (cacheEntry == null) {
265:                    try {
266:                        cacheEntry = (CacheEntry) notFoundCache.get(name);
267:                    } catch (Exception e) {
268:                        // Ignore: the reliability of this lookup is not critical
269:                    }
270:                }
271:                if (cacheEntry != null) {
272:                    hitsCount++;
273:                }
274:                return cacheEntry;
275:
276:            }
277:
278:            public void load(CacheEntry entry) {
279:                if (entry.exists) {
280:                    insertCache(entry);
281:                } else {
282:                    notFoundCache.put(entry.name, entry);
283:                }
284:                cacheSize += entry.size;
285:            }
286:
287:            public boolean unload(String name) {
288:                CacheEntry removedEntry = removeCache(name);
289:                if (removedEntry != null) {
290:                    cacheSize -= removedEntry.size;
291:                    return true;
292:                } else if (notFoundCache.remove(name) != null) {
293:                    cacheSize--;
294:                    return true;
295:                }
296:                return false;
297:            }
298:
299:            /**
300:             * Find a map elemnt given its name in a sorted array of map elements.
301:             * This will return the index for the closest inferior or equal item in the
302:             * given array.
303:             */
304:            private static final int find(CacheEntry[] map, String name) {
305:
306:                int a = 0;
307:                int b = map.length - 1;
308:
309:                // Special cases: -1 and 0
310:                if (b == -1) {
311:                    return -1;
312:                }
313:                if (name.compareTo(map[0].name) < 0) {
314:                    return -1;
315:                }
316:                if (b == 0) {
317:                    return 0;
318:                }
319:
320:                int i = 0;
321:                while (true) {
322:                    i = (b + a) / 2;
323:                    int result = name.compareTo(map[i].name);
324:                    if (result > 0) {
325:                        a = i;
326:                    } else if (result == 0) {
327:                        return i;
328:                    } else {
329:                        b = i;
330:                    }
331:                    if ((b - a) == 1) {
332:                        int result2 = name.compareTo(map[b].name);
333:                        if (result2 < 0) {
334:                            return a;
335:                        } else {
336:                            return b;
337:                        }
338:                    }
339:                }
340:
341:            }
342:
343:            /**
344:             * Insert into the right place in a sorted MapElement array, and prevent
345:             * duplicates.
346:             */
347:            private final boolean insertCache(CacheEntry newElement) {
348:                CacheEntry[] oldCache = cache;
349:                int pos = find(oldCache, newElement.name);
350:                if ((pos != -1) && (newElement.name.equals(oldCache[pos].name))) {
351:                    return false;
352:                }
353:                CacheEntry[] newCache = new CacheEntry[cache.length + 1];
354:                System.arraycopy(oldCache, 0, newCache, 0, pos + 1);
355:                newCache[pos + 1] = newElement;
356:                System.arraycopy(oldCache, pos + 1, newCache, pos + 2,
357:                        oldCache.length - pos - 1);
358:                cache = newCache;
359:                return true;
360:            }
361:
362:            /**
363:             * Insert into the right place in a sorted MapElement array.
364:             */
365:            private final CacheEntry removeCache(String name) {
366:                CacheEntry[] oldCache = cache;
367:                int pos = find(oldCache, name);
368:                if ((pos != -1) && (name.equals(oldCache[pos].name))) {
369:                    CacheEntry[] newCache = new CacheEntry[cache.length - 1];
370:                    System.arraycopy(oldCache, 0, newCache, 0, pos);
371:                    System.arraycopy(oldCache, pos + 1, newCache, pos,
372:                            oldCache.length - pos - 1);
373:                    cache = newCache;
374:                    return oldCache[pos];
375:                }
376:                return null;
377:            }
378:
379:        }
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