Source Code Cross Referenced for IdentityTable.java in  » Science » Cougaar12_4 » org » cougaar » core » persist » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Science » Cougaar12_4 » org.cougaar.core.persist 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * <copyright>
003:         *  
004:         *  Copyright 1997-2004 BBNT Solutions, LLC
005:         *  under sponsorship of the Defense Advanced Research Projects
006:         *  Agency (DARPA).
007:         * 
008:         *  You can redistribute this software and/or modify it under the
009:         *  terms of the Cougaar Open Source License as published on the
010:         *  Cougaar Open Source Website (www.cougaar.org).
011:         * 
012:         *  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
013:         *  "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
014:         *  LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
015:         *  A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
016:         *  OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
017:         *  SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
018:         *  LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
019:         *  DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
020:         *  THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
021:         *  (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
022:         *  OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
023:         *  
024:         * </copyright>
025:         */
026:
027:        package org.cougaar.core.persist;
028:
029:        import java.lang.ref.ReferenceQueue;
030:        import java.util.ArrayList;
031:        import java.util.Collection;
032:        import java.util.Iterator;
033:
034:        import org.cougaar.util.log.Logger;
035:        import org.cougaar.util.GC;
036:
037:        /**
038:         * Identifies all objects that have been (or are about to be) written
039:         * to persistence media. This purpose of this table is to remember
040:         * objects that have persisted in previous persistence snapshots so
041:         * that references to such objects in subsequent persistence deltas
042:         * can be replaced with references to the previously persisted
043:         * objects. This is similar to the wire handle of the Java
044:         * serialization process (ObjectOutputStream), but applies across
045:         * persistence snapshots whereas the wire handle applies within a
046:         * single snapshot.
047:         * <p>
048:         * This class is essentially a hash table implementation. It differs
049:         * from the java.util versions of hash tables in that the values are
050:         * {@link WeakReference}s so that values to which there are no longer
051:         * any references get removed from the table. WeakHashMap has weak
052:         * keys, not weak values.
053:         */
054:        class IdentityTable {
055:            static class MyArrayList extends ArrayList {
056:                /**
057:                 * Strangely enough, ArrayLists cannot be resized; this extension
058:                 * adds setSize(). 
059:                 * @param newSize the new size.  
060:                 */
061:                public void setSize(int newSize) {
062:                    while (this .size() < newSize) {
063:                        this .add(null);
064:                    }
065:                    while (this .size() > newSize) {
066:                        this .remove(this .size() - 1);
067:                    }
068:                }
069:            }
070:
071:            private int nextId = 0;
072:
073:            private PersistenceAssociation[] table = new PersistenceAssociation[123];
074:
075:            private int count = 0;
076:
077:            private ReferenceQueue referenceQueue = new ReferenceQueue();
078:
079:            private Collection rehydrationCollection = null;
080:
081:            private Logger logger;
082:
083:            /**
084:             * This list keeps all the PersistenceAssociation objects indexed
085:             * by their refId. Only the first encountered (last written) version
086:             * is kept.
087:             */
088:            private MyArrayList persistentObjects = new MyArrayList();
089:
090:            IdentityTable(Logger logger) {
091:                this .logger = logger;
092:            }
093:
094:            private void processQueue() {
095:                PersistenceAssociation pAssoc;
096:                while ((pAssoc = (PersistenceAssociation) referenceQueue.poll()) != null) {
097:                    if (logger.isDetailEnabled())
098:                        logger.detail("processQueue removing " + pAssoc);
099:                    int hashIndex = (pAssoc.hash & 0x7fffffff) % table.length;
100:                    for (PersistenceAssociation x = table[hashIndex], prev = null;; prev = x, x = x.next) {
101:                        if (x == null) {
102:                            break; // Not found due to "clear()"
103:                        }
104:                        if (x == pAssoc) {
105:                            if (prev == null) {
106:                                table[hashIndex] = pAssoc.next;
107:                            } else {
108:                                prev.next = pAssoc.next;
109:                            }
110:                            count--;
111:                            break;
112:                        }
113:                    }
114:                    persistentObjects.set(pAssoc.getReferenceId().intValue(),
115:                            null);
116:                }
117:            }
118:
119:            public void setRehydrationCollection(Collection list) {
120:                rehydrationCollection = list;
121:                if (list == null) {
122:                    GC.gc();
123:                }
124:            }
125:
126:            public int getNextId() {
127:                return nextId;
128:            }
129:
130:            public void setNextId(int newNextId) {
131:                nextId = newNextId;
132:            }
133:
134:            /**
135:             * Find the PersistenceAssociation for an object.
136:             * @param object the object
137:             * @return the PersistenceAssociation for the object
138:             * @return null if the object has no current association
139:             */
140:            public PersistenceAssociation find(Object object) {
141:                processQueue();
142:                int hash = System.identityHashCode(object);
143:                int hashIndex = (hash & 0x7fffffff) % table.length;
144:                PersistenceAssociation pAssoc;
145:                for (pAssoc = table[hashIndex]; pAssoc != null; pAssoc = pAssoc.next) {
146:                    if (pAssoc.get() == object) {
147:                        return pAssoc;
148:                    }
149:                }
150:                return null;
151:            }
152:
153:            private void rehash() {
154:                PersistenceAssociation[] oldTable = table;
155:                int newLength = table.length * 2 + 1;
156:                table = new PersistenceAssociation[newLength];
157:                for (int i = 0; i < oldTable.length; i++) {
158:                    PersistenceAssociation p = oldTable[i];
159:                    while (p != null) {
160:                        PersistenceAssociation n = p.next;
161:                        int hashIndex = (p.hash & 0x7fffffff) % newLength;
162:                        p.next = table[hashIndex];
163:                        table[hashIndex] = p;
164:                        p = n;
165:                    }
166:                }
167:            }
168:
169:            /**
170:             * Create a new PersistenceAssociation and enter it into the table.
171:             * @param o the object of the PersistenceAssociation
172:             * @param ref The PersistenceReference of the object.
173:             * @return the new PersistenceAssociation
174:             */
175:            public PersistenceAssociation create(Object o,
176:                    PersistenceReference ref) {
177:                if (count > table.length * 3 / 4) {
178:                    rehash();
179:                }
180:                PersistenceAssociation pAssoc = new PersistenceAssociation(o,
181:                        ref, referenceQueue);
182:                if (rehydrationCollection != null) {
183:                    rehydrationCollection.add(o); // Make sure there is a reference to the object
184:                }
185:                int hashIndex = (pAssoc.hash & 0x7fffffff) % table.length;
186:                pAssoc.next = table[hashIndex];
187:                table[hashIndex] = pAssoc;
188:                int ix = ref.intValue();
189:                if (persistentObjects.size() <= ix)
190:                    persistentObjects.setSize(ix + 1);
191:                if (persistentObjects.get(ix) != null) {
192:                    throw new IllegalArgumentException("Slot full: "
193:                            + persistentObjects.get(ix) + "<-" + pAssoc);
194:                }
195:                persistentObjects.set(ix, pAssoc);
196:                count++;
197:                return pAssoc;
198:            }
199:
200:            /**
201:             * Assign an identity to the given object. Makes an entry in the
202:             * identityTable if not already there and marks the entry as
203:             * "needing to be written".  The next time the
204:             * ObjectOutputStream.replaceObject method is called for the object
205:             * it will be written. Thereafter, a reference object will be
206:             * written.
207:             */
208:            public PersistenceAssociation findOrCreate(Object o) {
209:                PersistenceAssociation pAssoc = find(o);
210:                if (pAssoc != null) {
211:                    return pAssoc;
212:                }
213:                return create(o, new PersistenceReference(nextId++));
214:            }
215:
216:            /**
217:             * Get the PersistenceAssociation corresponding to a PersistenceReference.
218:             * @param ref the PersistenceReference
219:             * @return the corresponding PersistenceAssociation
220:             * @return null if the is no corresponding PersistenceAssociation
221:             */
222:            public PersistenceAssociation get(PersistenceReference ref) {
223:                return get(ref.intValue());
224:            }
225:
226:            /**
227:             * Get the PersistenceAssociation at a particular index.
228:             * @param ix the index
229:             * @return the corresponding PersistenceAssociation
230:             * @return null if the is no corresponding PersistenceAssociation
231:             */
232:            public PersistenceAssociation get(int ix) {
233:                processQueue();
234:                if (ix < 0 || ix >= persistentObjects.size())
235:                    return null;
236:                return (PersistenceAssociation) persistentObjects.get(ix);
237:            }
238:
239:            public int size() {
240:                return persistentObjects.size();
241:            }
242:
243:            public Iterator iterator() {
244:                processQueue();
245:                return new Iterator() {
246:                    Iterator iter = persistentObjects.iterator();
247:                    Object nextObject = null;
248:
249:                    public boolean hasNext() {
250:                        while (nextObject == null) {
251:                            if (!iter.hasNext()) {
252:                                return false;
253:                            }
254:                            nextObject = iter.next();
255:                        }
256:                        return true;
257:                    }
258:
259:                    public Object next() {
260:                        if (nextObject == null) {
261:                            return iter.next();
262:                        }
263:                        Object result = nextObject;
264:                        nextObject = null;
265:                        return result;
266:                    }
267:
268:                    public void remove() {
269:                        throw new UnsupportedOperationException(
270:                                "remove not supported");
271:                    }
272:                };
273:            }
274:
275:            public void clear() {
276:                table = new PersistenceAssociation[123];
277:                count = 0;
278:                setRehydrationCollection(null);
279:            }
280:        }
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