| 1 | /* |
| 2 | |
| 3 | Derby - Class org.apache.derby.impl.services.cache.CachedItem |
| 4 | |
| 5 | Copyright 1997, 2004 The Apache Software Foundation or its licensors, as applicable. |
| 6 | |
| 7 | Licensed under the Apache License, Version 2.0 (the "License"); |
| 8 | you may not use this file except in compliance with the License. |
| 9 | You may obtain a copy of the License at |
| 10 | |
| 11 | http://www.apache.org/licenses/LICENSE-2.0 |
| 12 | |
| 13 | Unless required by applicable law or agreed to in writing, software |
| 14 | distributed under the License is distributed on an "AS IS" BASIS, |
| 15 | WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 16 | See the License for the specific language governing permissions and |
| 17 | limitations under the License. |
| 18 | |
| 19 | */ |
| 20 | |
| 21 | package org.apache.derby.impl.services.cache; |
| 22 | |
| 23 | import org.apache.derby.iapi.services.cache.Cacheable; |
| 24 | import org.apache.derby.iapi.services.cache.CacheableFactory; |
| 25 | import org.apache.derby.iapi.services.cache.CacheManager; |
| 26 | import org.apache.derby.iapi.error.StandardException; |
| 27 | |
| 28 | import org.apache.derby.iapi.services.sanity.SanityManager; |
| 29 | import org.apache.derby.iapi.services.context.ContextService; |
| 30 | |
| 31 | /** |
| 32 | A generic class to represent the cache related infomation of a cached object (Cacheable). |
| 33 | <P><PRE> |
| 34 | The relationship between isValid and settingIdentity can be explain by the |
| 35 | following life cycle of a cached item. |
| 36 | |
| 37 | Stage 1 2 3 |
| 38 | ---------------------- |
| 39 | isValid F T T |
| 40 | settingIdentity X T F |
| 41 | |
| 42 | In Stage 1, the CachedItem is created but it is invalid and has an entry |
| 43 | that is just a holder object with no identity. |
| 44 | |
| 45 | In Stage 2, the identity has been set and the item is being created or |
| 46 | being faulted into the cache. |
| 47 | |
| 48 | In Stage 3, the item found in the CachedItem entry |
| 49 | </PRE> <P> |
| 50 | Remove is set if this item is being removed out of existance, not just |
| 51 | being evicted from the cache. When the last referece to it release it from |
| 52 | the cache, it will be removed. |
| 53 | <BR> |
| 54 | RecentlyUsed is set whenever this item is accessed (via a keep() call). |
| 55 | It is reset by the clockHand as it sweeps around the cache looking for |
| 56 | victims to evict. |
| 57 | |
| 58 | <P>MT - must be MT-safe and work with cache manager. Every method that |
| 59 | access (set or get) instance variables is synchronized on the cached item |
| 60 | object. The following method waits so it should not be called by the cache |
| 61 | manager inside a sync block: clean(), waitFor(), create(), remove(). |
| 62 | (RESOLVE: need to move these from the cache manager to here) |
| 63 | |
| 64 | @see org.apache.derby.impl.services.cache |
| 65 | @see Cacheable |
| 66 | */ |
| 67 | public final class CachedItem { |
| 68 | |
| 69 | private static final int VALID = 0x00000001; |
| 70 | private static final int REMOVE_REQUESTED = 0x00000002; |
| 71 | private static final int SETTING_IDENTITY = 0x00000004; |
| 72 | private static final int REMOVE_OK = 0x00000008; |
| 73 | |
| 74 | private static final int RECENTLY_USED = 0x00000010; |
| 75 | |
| 76 | /* |
| 77 | ** Fields |
| 78 | */ |
| 79 | |
| 80 | /** |
| 81 | Does entry (the Cacheable) have an identity. |
| 82 | |
| 83 | <BR> MT - single thread required : synchronization provided by cache manager. |
| 84 | */ |
| 85 | private int state; |
| 86 | |
| 87 | /** |
| 88 | The current keep count on the entry. |
| 89 | |
| 90 | <BR> MT - single thread required : synchronization provided by cache manager. |
| 91 | |
| 92 | */ |
| 93 | private int keepCount; |
| 94 | |
| 95 | /** |
| 96 | The Cacheable object being represented. |
| 97 | |
| 98 | <BR> Mutable - content dynamic |
| 99 | */ |
| 100 | private Cacheable entry; |
| 101 | |
| 102 | /** |
| 103 | Create a CachedItem in the not valid state. |
| 104 | */ |
| 105 | public CachedItem() { |
| 106 | } |
| 107 | |
| 108 | /** |
| 109 | Keep the cached object after a search. |
| 110 | |
| 111 | */ |
| 112 | public void keepAfterSearch() { |
| 113 | keepCount++; |
| 114 | setUsed(true); |
| 115 | } |
| 116 | |
| 117 | public void keepForCreate() { |
| 118 | if (SanityManager.DEBUG) { |
| 119 | SanityManager.ASSERT(!isKept()); |
| 120 | SanityManager.ASSERT(!isValid()); |
| 121 | } |
| 122 | keepCount = 1; |
| 123 | state |= SETTING_IDENTITY; |
| 124 | } |
| 125 | |
| 126 | public void unkeepForCreate( ) |
| 127 | { |
| 128 | settingIdentityComplete(); |
| 129 | unkeep(); |
| 130 | } |
| 131 | |
| 132 | public void keepForClean() { |
| 133 | if (SanityManager.DEBUG) { |
| 134 | SanityManager.ASSERT(isValid()); |
| 135 | } |
| 136 | keepCount++; |
| 137 | } |
| 138 | |
| 139 | |
| 140 | |
| 141 | /** |
| 142 | Unkeep the cached object. |
| 143 | |
| 144 | <P>MT - not synchronized, only modified single threaded by the cache manager |
| 145 | |
| 146 | @return if the object is still kept after this call. |
| 147 | */ |
| 148 | public synchronized boolean unkeep() { |
| 149 | boolean unkept = --keepCount == 0; |
| 150 | |
| 151 | if (SanityManager.DEBUG) { |
| 152 | SanityManager.ASSERT(keepCount >= 0); |
| 153 | } |
| 154 | return unkept && ((state & REMOVE_REQUESTED) != 0); |
| 155 | } |
| 156 | |
| 157 | /** |
| 158 | Is the cached object kept? |
| 159 | |
| 160 | <P>MT - not synchronized, only accessed single threaded by the cache manager |
| 161 | */ |
| 162 | public final boolean isKept() { |
| 163 | |
| 164 | return keepCount != 0; |
| 165 | } |
| 166 | |
| 167 | /** |
| 168 | Clean the cached object |
| 169 | |
| 170 | <P>MT - <BR> |
| 171 | The wait will not release the lock on the cache manager, so the |
| 172 | cache manager should not waitfor clean inside a sync block or |
| 173 | the whole cache will freeze |
| 174 | |
| 175 | @param forRemove if true, get rid of the backend persistent store object |
| 176 | @exception StandardException error thrown while writing cacheable |
| 177 | object to disk |
| 178 | */ |
| 179 | public void clean(boolean forRemove) throws StandardException |
| 180 | { |
| 181 | entry.clean(forRemove); |
| 182 | } |
| 183 | |
| 184 | /** |
| 185 | Set the state of the to-be removed flag. |
| 186 | */ |
| 187 | public synchronized void setRemoveState() { |
| 188 | state |= REMOVE_REQUESTED; |
| 189 | } |
| 190 | |
| 191 | /** |
| 192 | Does the cached object have a valid identity. |
| 193 | */ |
| 194 | public final synchronized boolean isValid() { |
| 195 | return (state & VALID) != 0; |
| 196 | } |
| 197 | |
| 198 | /** |
| 199 | Set the valid state of the cached object. |
| 200 | */ |
| 201 | public synchronized void setValidState(boolean flag) { |
| 202 | |
| 203 | if (flag) |
| 204 | state |= VALID; |
| 205 | else |
| 206 | state &= ~VALID; |
| 207 | |
| 208 | state &= ~(REMOVE_REQUESTED | REMOVE_OK); |
| 209 | |
| 210 | setUsed(flag); |
| 211 | } |
| 212 | |
| 213 | /** |
| 214 | Get the cached object. |
| 215 | */ |
| 216 | public Cacheable getEntry() { |
| 217 | return entry; |
| 218 | } |
| 219 | |
| 220 | /** |
| 221 | Make entry (the Cacheable) take on a new identity. |
| 222 | */ |
| 223 | public Cacheable takeOnIdentity(CacheManager cm, CacheableFactory holderFactory, |
| 224 | Object key, boolean forCreate, Object createParameter) |
| 225 | throws StandardException { |
| 226 | |
| 227 | // tell the object it needs to create itself |
| 228 | Cacheable oldEntry = entry; |
| 229 | if (oldEntry == null) |
| 230 | oldEntry = holderFactory.newCacheable(cm); |
| 231 | |
| 232 | if (forCreate) { |
| 233 | entry = oldEntry.createIdentity(key, createParameter); |
| 234 | } else { |
| 235 | entry = oldEntry.setIdentity(key); |
| 236 | } |
| 237 | |
| 238 | if (entry != null) { |
| 239 | // item was found or created |
| 240 | if (SanityManager.DEBUG) { |
| 241 | SanityManager.ASSERT(entry.getIdentity().equals(key)); |
| 242 | } |
| 243 | |
| 244 | return entry; |
| 245 | } |
| 246 | |
| 247 | entry = oldEntry; |
| 248 | return null; |
| 249 | } |
| 250 | |
| 251 | public synchronized void settingIdentityComplete() { |
| 252 | // notify all waiters that this item has finished setting its identity, |
| 253 | // successfully or not. |
| 254 | state &= ~SETTING_IDENTITY; |
| 255 | |
| 256 | notifyAll(); |
| 257 | } |
| 258 | |
| 259 | /** |
| 260 | Allow use of the cacheable entry. |
| 261 | */ |
| 262 | |
| 263 | public synchronized Cacheable use() throws StandardException { |
| 264 | |
| 265 | while ((state & SETTING_IDENTITY) != 0) { |
| 266 | try { |
| 267 | if (SanityManager.DEBUG) { |
| 268 | SanityManager.DEBUG("CacheTrace", |
| 269 | "trying to use a cached item that is taking on an identity"); |
| 270 | } |
| 271 | |
| 272 | wait(); |
| 273 | |
| 274 | } catch (InterruptedException ie) { |
| 275 | throw StandardException.interrupt(ie); |
| 276 | } |
| 277 | } |
| 278 | |
| 279 | // see if the setting of this identity failed ... |
| 280 | if (!isValid()) |
| 281 | return null; |
| 282 | |
| 283 | if (SanityManager.DEBUG) |
| 284 | { |
| 285 | if (SanityManager.DEBUG_ON("CacheTrace")) |
| 286 | SanityManager.DEBUG( |
| 287 | "CacheTrace", "item keep count is " + keepCount); |
| 288 | } |
| 289 | |
| 290 | |
| 291 | return entry; |
| 292 | } |
| 293 | |
| 294 | /** |
| 295 | */ |
| 296 | public void remove(boolean removeNow) throws StandardException { |
| 297 | |
| 298 | if (!removeNow) { |
| 299 | |
| 300 | synchronized (this) { |
| 301 | while ((state & REMOVE_OK) == 0) { |
| 302 | try { |
| 303 | wait(); |
| 304 | } catch (InterruptedException ie) { |
| 305 | throw StandardException.interrupt(ie); |
| 306 | } |
| 307 | } |
| 308 | } |
| 309 | } |
| 310 | |
| 311 | clean(true); |
| 312 | } |
| 313 | |
| 314 | public synchronized void notifyRemover() { |
| 315 | |
| 316 | if (SanityManager.DEBUG) { |
| 317 | SanityManager.ASSERT((state & REMOVE_REQUESTED) != 0); |
| 318 | SanityManager.ASSERT(isKept()); |
| 319 | } |
| 320 | |
| 321 | state |= REMOVE_OK; |
| 322 | notifyAll(); |
| 323 | } |
| 324 | |
| 325 | /** |
| 326 | The clock hand has swept past this entry. |
| 327 | */ |
| 328 | public synchronized void setUsed(boolean flag) |
| 329 | { |
| 330 | if (flag) |
| 331 | state |= RECENTLY_USED; |
| 332 | else |
| 333 | state &= ~RECENTLY_USED; |
| 334 | } |
| 335 | |
| 336 | /** |
| 337 | Has the cached object been referenced (kept) since the last sweep of |
| 338 | the clock hand? |
| 339 | */ |
| 340 | public synchronized boolean recentlyUsed() { |
| 341 | return (state & RECENTLY_USED) != 0; |
| 342 | } |
| 343 | } |
| 344 | |
| 345 | |
| 346 | |