| 1 | /* |
| 2 | |
| 3 | Derby - Class org.apache.derby.impl.services.cache.Clock |
| 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.CacheManager; |
| 24 | import org.apache.derby.iapi.services.cache.Cacheable; |
| 25 | import org.apache.derby.iapi.services.cache.CacheableFactory; |
| 26 | import org.apache.derby.iapi.services.cache.SizedCacheable; |
| 27 | import org.apache.derby.iapi.services.context.ContextManager; |
| 28 | import org.apache.derby.iapi.services.daemon.DaemonService; |
| 29 | import org.apache.derby.iapi.services.daemon.Serviceable; |
| 30 | |
| 31 | import org.apache.derby.iapi.error.StandardException; |
| 32 | |
| 33 | import org.apache.derby.iapi.services.monitor.Monitor; |
| 34 | |
| 35 | import org.apache.derby.iapi.services.sanity.SanityManager; |
| 36 | |
| 37 | import org.apache.derby.iapi.services.cache.ClassSize; |
| 38 | import org.apache.derby.iapi.util.Matchable; |
| 39 | import org.apache.derby.iapi.util.Operator; |
| 40 | import org.apache.derby.iapi.reference.SQLState; |
| 41 | |
| 42 | import java.util.ArrayList; |
| 43 | import java.util.Hashtable; |
| 44 | import java.util.Properties; |
| 45 | |
| 46 | |
| 47 | /** |
| 48 | A cache manager that uses a Hashtable and a ArrayList. The ArrayList holds |
| 49 | CachedItem objects, each with a holder object. The Hashtable is keyed |
| 50 | by the identity of the holder object (Cacheable.getIdentity()) and |
| 51 | the data portion is a pointer to the CachedItem. CachedItems that have |
| 52 | holder objects with no identity do not have entries in the hashtable. |
| 53 | <P> |
| 54 | CachedItems can in various state. |
| 55 | <UL> |
| 56 | <LI>isValid - the entry has a valid identity |
| 57 | <LI>inCreate - the entry is being created or being faulted in from persistent store |
| 58 | <LI>inClean - the entry is being written out to persistent store |
| 59 | <LI>isKept - the entry is currently being looked at/updated, do not remove or |
| 60 | clean it. |
| 61 | </OL> |
| 62 | |
| 63 | <P>Multithreading considerations:<BR> |
| 64 | A clock cache manager must be MT-safe. |
| 65 | All member variables are accessed single threaded (synchronized on this) or |
| 66 | set once or readonly. Assumptions: holders size() and addElement must be |
| 67 | synchronized. |
| 68 | <BR> |
| 69 | CachedItem is never passed out of the clock cache manager, only the |
| 70 | Cacheable object is. The cachedItem is responsible for the setting and |
| 71 | clearing of its own member fields (RESOLVE: now they are done in cache |
| 72 | manager, need to be moved to the cachedItem). The cache manager will |
| 73 | following the following rules while accessing a cacheditem: |
| 74 | <UL> |
| 75 | <LI>invalid item is never returned from the cache |
| 76 | <LI>setValidState and isValid() is only called single threaded through the cache manager. |
| 77 | <LI>keep() and isKept() is only called single threaded through the cache |
| 78 | manager once the item has been added to the holders array |
| 79 | <LI>item that isKept() won't be cleaned or removed or invalidated from the cache. |
| 80 | <LI>item that is inClean() or inCreate(), the cache manager |
| 81 | will wait on the cachedItem to finish cleaning or creating before it |
| 82 | returns the cached item outside of the cache. |
| 83 | </UL> |
| 84 | <BR> |
| 85 | The cacheable must be cleaned thru the cache if it is managed by a cache. |
| 86 | On CacheItem, a inClean state is maintain to stablelize the content of the |
| 87 | cacheable while it is being cleaned. Only unkept items are cleaned. If an |
| 88 | item is found to be inClean, it will wait until it exits the inClean state. |
| 89 | If a cached item calls it own clean method without notifying the cache, it |
| 90 | has to stablize its content for the duration of the clean. |
| 91 | <BR> |
| 92 | It is assumed that the cacheable object maintain its own MT-safeness.<BR> |
| 93 | |
| 94 | @see CachedItem |
| 95 | @see Cacheable |
| 96 | |
| 97 | */ |
| 98 | |
| 99 | final class Clock extends Hashtable implements CacheManager, Serviceable { |
| 100 | |
| 101 | /* |
| 102 | ** Fields |
| 103 | */ |
| 104 | public final CacheStat stat; |
| 105 | private DaemonService cleaner; // the background worker thread who is going to |
| 106 | // do pre-flush for this cache. |
| 107 | private final ArrayList holders; |
| 108 | private int validItemCount = 0; |
| 109 | private long maximumSize; |
| 110 | private boolean useByteCount; // regulate the total byte count or the entry count |
| 111 | private long currentByteCount = 0; |
| 112 | /* currentByteCount should be the sum of entry.getSize() for all entries in the cache. |
| 113 | * That is, it should be the sum of getItemSize( item, false) for each item in the holders |
| 114 | * vector. |
| 115 | */ |
| 116 | |
| 117 | private static final int ITEM_OVERHEAD = ClassSize.estimateBaseFromCatalog( CachedItem.class) |
| 118 | + ClassSize.getRefSize() // one ref per item in the holder ArrayList |
| 119 | + ClassSize.estimateHashEntrySize(); |
| 120 | |
| 121 | private final CacheableFactory holderFactory; |
| 122 | |
| 123 | private boolean active; // true if active for find/create |
| 124 | private String name; // name of the cache, mainly for debugging purposes. |
| 125 | private int clockHand; // the sweep of the clock hand |
| 126 | |
| 127 | |
| 128 | private int myClientNumber; // use this number to talk to cleaner service |
| 129 | private boolean wokenToClean; // true if the client was woken to clean, false if to shrink |
| 130 | private boolean cleanerRunning; |
| 131 | private boolean needService; |
| 132 | |
| 133 | /** |
| 134 | Construct a new clock cache manager. |
| 135 | |
| 136 | <P>MT - not needed for constructor. |
| 137 | |
| 138 | @param holderFactory the cacheable object class |
| 139 | @param name the name of the cache |
| 140 | @param initialSize the initial number of cachable object this cache |
| 141 | holds. |
| 142 | @param maximumSize the maximum size of the cache. The cache may grow |
| 143 | from initialSize to maximumSize if the cache policy notices that there |
| 144 | is not enough free buffers availiable. Once the cache hits maximumSize |
| 145 | it will not grow. If the cache is full, an exception will be thrown |
| 146 | |
| 147 | */ |
| 148 | Clock(CacheableFactory holderFactory, |
| 149 | String name, |
| 150 | int initialSize, |
| 151 | long maximumSize, |
| 152 | boolean useByteCount) |
| 153 | { |
| 154 | super(initialSize, (float) 0.95); |
| 155 | this.maximumSize = maximumSize; |
| 156 | this.holderFactory = holderFactory; |
| 157 | this.useByteCount = useByteCount; |
| 158 | |
| 159 | if (SanityManager.DEBUG) { |
| 160 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) { |
| 161 | SanityManager.DEBUG(ClockFactory.CacheTrace, "initializing " + name + " cache to size " + initialSize); |
| 162 | } |
| 163 | } |
| 164 | |
| 165 | //int delta = initialSize / 2; |
| 166 | //if (delta < 5) |
| 167 | // delta = 5; |
| 168 | |
| 169 | holders = new ArrayList(initialSize); |
| 170 | this.name = name; |
| 171 | active = true; |
| 172 | |
| 173 | this.stat = new CacheStat(); |
| 174 | stat.initialSize = initialSize; |
| 175 | stat.maxSize = maximumSize; |
| 176 | } |
| 177 | |
| 178 | /** |
| 179 | Find the object or materialize one in the cache. If it has not been |
| 180 | created in the persistent store yet, return null. |
| 181 | |
| 182 | <P>MT - must be MT-safe. The cache is single threaded through finding |
| 183 | the item in cache and finding a free item if it is not in cache, thus |
| 184 | preventing another thread from creating the same item while is is being |
| 185 | faulted in. (RESOLVE - this is really low performance if the cache |
| 186 | cleaner cannot keep a steady supply of free items and we have to do an |
| 187 | I/O while blocking the cache). If it needs to be faulted in, the |
| 188 | inCreate bit is set. The item is kept before it exits the sync block. |
| 189 | <BR> |
| 190 | If the item is in cache but in the middle of being faulted in or |
| 191 | cleaned, it needs to wait until this is done being before returning. |
| 192 | <BR> |
| 193 | The keep status prevents other threads from removing this item. |
| 194 | The inCreate status prevents other threads from looking at or writing |
| 195 | out this item while it is being faulted in. |
| 196 | (RESOLVE: need to handle the case where the object is marked for |
| 197 | removal and being waited on) |
| 198 | |
| 199 | @param key the key to the object |
| 200 | @return a cacheable object that is kept in the cache. |
| 201 | @exception StandardException Cloudscape Standard error policy |
| 202 | */ |
| 203 | public Cacheable find(Object key) throws StandardException { |
| 204 | CachedItem item; |
| 205 | boolean add; |
| 206 | |
| 207 | /* |
| 208 | ** We will only loop if someone else tried to add the |
| 209 | ** same key as we did and they failed. In this case |
| 210 | ** we start all over. An example of this would be an |
| 211 | ** attempt to cache an object that failed due to a |
| 212 | ** transient error (e.g. deadlock), which should not |
| 213 | ** prevent another thread from trying to add the |
| 214 | ** key to the cache (e.g. it might be the one holding |
| 215 | ** the lock that caused the other thread to deadlock). |
| 216 | */ |
| 217 | while (true) |
| 218 | { |
| 219 | add = false; |
| 220 | |
| 221 | synchronized (this) { |
| 222 | |
| 223 | if (!active) |
| 224 | return null; |
| 225 | |
| 226 | item = (CachedItem) get(key); |
| 227 | |
| 228 | if (item != null) { |
| 229 | item.keepAfterSearch(); |
| 230 | |
| 231 | stat.findHit++; |
| 232 | |
| 233 | if (SanityManager.DEBUG) { |
| 234 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) |
| 235 | { |
| 236 | SanityManager.DEBUG(ClockFactory.CacheTrace, name + ": Found key " + |
| 237 | key + " already in cache, item " + item); |
| 238 | } |
| 239 | } |
| 240 | } |
| 241 | } |
| 242 | |
| 243 | // no entry was found, need to add one |
| 244 | if (item == null) { |
| 245 | |
| 246 | // get a free item |
| 247 | item = findFreeItem(); |
| 248 | |
| 249 | stat.findMiss++; |
| 250 | |
| 251 | if (SanityManager.DEBUG) { |
| 252 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) |
| 253 | { |
| 254 | SanityManager.DEBUG(ClockFactory.CacheTrace, name + ": Find key " + |
| 255 | key + " Not in cache, get free item " + item); |
| 256 | } |
| 257 | } |
| 258 | |
| 259 | |
| 260 | if (SanityManager.DEBUG) |
| 261 | SanityManager.ASSERT(item != null, "found null item"); |
| 262 | |
| 263 | synchronized (this) { |
| 264 | CachedItem inCacheItem = (CachedItem) get(key); |
| 265 | |
| 266 | if (inCacheItem != null) { |
| 267 | // some-one beat us to adding an item into the cache, |
| 268 | // just use that one |
| 269 | item.unkeepForCreate(); |
| 270 | |
| 271 | item = inCacheItem; |
| 272 | item.keepAfterSearch(); |
| 273 | } else { |
| 274 | // yes, we really are the ones to add it |
| 275 | put(key, item); |
| 276 | add = true; |
| 277 | if (SanityManager.DEBUG) { |
| 278 | |
| 279 | if (SanityManager.DEBUG_ON("memoryLeakTrace")) { |
| 280 | |
| 281 | if (size() > ((11 * maximumSize) / 10)) |
| 282 | System.out.println("memoryLeakTrace:Cache:" + name + " " + size()); |
| 283 | } |
| 284 | } |
| 285 | } |
| 286 | } |
| 287 | } |
| 288 | |
| 289 | if (add) { |
| 290 | |
| 291 | if (SanityManager.DEBUG) { |
| 292 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) |
| 293 | { |
| 294 | SanityManager.DEBUG(ClockFactory.CacheTrace, name + " Added " + |
| 295 | key + " to cache, item " + item); |
| 296 | } |
| 297 | } |
| 298 | |
| 299 | stat.findFault++; |
| 300 | |
| 301 | return addEntry(item, key, false, (Object) null); |
| 302 | } |
| 303 | |
| 304 | Cacheable entry = item.use(); |
| 305 | if (entry == null) { |
| 306 | // item was not added by the other user successfully ... |
| 307 | synchronized (this) { |
| 308 | item.unkeep(); |
| 309 | } |
| 310 | |
| 311 | // try to hash the key again (see |
| 312 | // comment at head of loop) |
| 313 | continue; |
| 314 | } |
| 315 | |
| 316 | return entry; |
| 317 | } |
| 318 | } |
| 319 | |
| 320 | |
| 321 | /** |
| 322 | Find an object in the cache. Do not fault in or create the object if |
| 323 | is is not found in the cache. |
| 324 | |
| 325 | <P>MT - must be MT-safe. The cache is single threaded through finding |
| 326 | the item in cache. If it needs to wait for it to be faulted in or |
| 327 | cleaned it is synchronized/waited on the cached item itself. |
| 328 | |
| 329 | @param key the key to the object |
| 330 | @return a cacheable object that is kept in the cache. |
| 331 | */ |
| 332 | |
| 333 | public Cacheable findCached(Object key) throws StandardException { |
| 334 | |
| 335 | |
| 336 | CachedItem item; |
| 337 | |
| 338 | synchronized (this) { |
| 339 | |
| 340 | if (!active) |
| 341 | return null; |
| 342 | |
| 343 | item = (CachedItem) get(key); |
| 344 | |
| 345 | if (item == null) { |
| 346 | stat.findCachedMiss++; |
| 347 | return null; |
| 348 | } else |
| 349 | stat.findCachedHit++; |
| 350 | |
| 351 | item.keepAfterSearch(); |
| 352 | } |
| 353 | |
| 354 | Cacheable entry = item.use(); |
| 355 | if (entry == null) { |
| 356 | // item was not added by the other user successfully ... |
| 357 | synchronized (this) { |
| 358 | item.unkeep(); |
| 359 | } |
| 360 | } |
| 361 | |
| 362 | return entry; |
| 363 | } |
| 364 | |
| 365 | |
| 366 | /** |
| 367 | * Mark a set of entries as having been used. Normally this is done as a side effect |
| 368 | * of find() or findCached. Entries that are no longer in the cache are ignored. |
| 369 | * |
| 370 | * @param keys the key of the used entry. |
| 371 | */ |
| 372 | public void setUsed( Object[] keys) |
| 373 | { |
| 374 | CachedItem item; |
| 375 | |
| 376 | for( int i = 0; i < keys.length;) |
| 377 | { |
| 378 | // Do not hold the synchronization lock for too long. |
| 379 | synchronized (this) |
| 380 | { |
| 381 | if (!active) |
| 382 | return; |
| 383 | |
| 384 | int endIdx = i + 32; |
| 385 | if( endIdx > keys.length) |
| 386 | endIdx = keys.length; |
| 387 | for( ; i < endIdx; i++) |
| 388 | { |
| 389 | if( keys[i] == null) |
| 390 | return; |
| 391 | |
| 392 | item = (CachedItem) get(keys[i]); |
| 393 | if( null != item) |
| 394 | item.setUsed( true); |
| 395 | } |
| 396 | } |
| 397 | } |
| 398 | } // end of setUsed |
| 399 | |
| 400 | /** |
| 401 | Create a new object with the said key. |
| 402 | |
| 403 | <P>MT - must be MT-safe. Single thread thru verifying no such item |
| 404 | exist in cache and finding a free item, keep the item and set inCreate |
| 405 | state. The actual creating of the object is done outside |
| 406 | the sync block and is protected by the isKept and inCreate bits. |
| 407 | |
| 408 | @param key the key to the object |
| 409 | @return a cacheable object that is kept in the cache. |
| 410 | |
| 411 | @exception StandardException Cloudscape Standard error policy |
| 412 | */ |
| 413 | public Cacheable create(Object key, Object createParameter) throws StandardException { |
| 414 | |
| 415 | // assume the item is not already in the cache |
| 416 | CachedItem item = findFreeItem(); |
| 417 | |
| 418 | stat.create++; |
| 419 | |
| 420 | synchronized (this) { |
| 421 | |
| 422 | if (!active) |
| 423 | return null; |
| 424 | |
| 425 | if (get(key) != null) { |
| 426 | |
| 427 | item.unkeepForCreate(); |
| 428 | |
| 429 | throw StandardException.newException(SQLState.OBJECT_EXISTS_IN_CACHE, this.name, key); |
| 430 | } |
| 431 | |
| 432 | put(key, item); |
| 433 | |
| 434 | if (SanityManager.DEBUG) { |
| 435 | |
| 436 | if (SanityManager.DEBUG_ON("memoryLeakTrace")) { |
| 437 | |
| 438 | if (size() > ((11 * maximumSize) / 10)) |
| 439 | System.out.println("memoryLeakTrace:Cache:" + name + " " + size()); |
| 440 | } |
| 441 | } |
| 442 | } |
| 443 | |
| 444 | Cacheable entry = addEntry(item, key, true, createParameter); |
| 445 | |
| 446 | if (SanityManager.DEBUG) { |
| 447 | if (entry != null) |
| 448 | SanityManager.ASSERT(item.getEntry() == entry); |
| 449 | } |
| 450 | |
| 451 | return entry; |
| 452 | } |
| 453 | |
| 454 | |
| 455 | /** |
| 456 | The caller is no longer looking at or updating the entry. Since there |
| 457 | could be more than one piece of code looking at this entry, release |
| 458 | does not mean nobody is looking at or updating the entry, just one |
| 459 | less. If the cacheable is marked for remove (someone is waiting to |
| 460 | remove the persistent object once nobody is looking at it), then notify |
| 461 | the waiter if this is the last one looking at it. |
| 462 | <BR> |
| 463 | Unless there is a good reason to do otherwise, release should be used |
| 464 | to release a cachable and not directly call cachedItem unkeep, since |
| 465 | unkeep does not handle the case of remove. |
| 466 | |
| 467 | |
| 468 | <P>MT - must be MT-safe. Getting and deleteing item from the hashtable |
| 469 | is in the same synchronized block. If the cacheable object is waiting |
| 470 | to be removed, that is synchronized thru the cachedItem itself |
| 471 | (RESOLVE: need to move this sync block to cachedItem instead) |
| 472 | |
| 473 | @param entry the cached entry |
| 474 | |
| 475 | */ |
| 476 | public void release(Cacheable entry) { |
| 477 | boolean removeItem; |
| 478 | CachedItem item; |
| 479 | long toShrink = 0; |
| 480 | |
| 481 | synchronized (this) { |
| 482 | |
| 483 | item = (CachedItem) get(entry.getIdentity()); |
| 484 | |
| 485 | if (SanityManager.DEBUG) { |
| 486 | SanityManager.ASSERT(item != null, "item null"); |
| 487 | SanityManager.ASSERT(item.getEntry() == entry, "entry not equals keyed entry"); |
| 488 | SanityManager.ASSERT(item.isKept(), "item is not kept in release(Cachable)"); |
| 489 | } |
| 490 | |
| 491 | removeItem = item.unkeep(); |
| 492 | |
| 493 | if (removeItem) { |
| 494 | |
| 495 | remove(entry.getIdentity()); |
| 496 | |
| 497 | // we keep the item here to stop another thread trying to evict it |
| 498 | // while we are destroying it. |
| 499 | item.keepForClean(); |
| 500 | } |
| 501 | |
| 502 | if (cleaner == null) { |
| 503 | // try to shrink the cache on a release |
| 504 | toShrink = shrinkSize( getCurrentSize()); |
| 505 | } |
| 506 | } |
| 507 | |
| 508 | if (removeItem) { |
| 509 | |
| 510 | item.notifyRemover(); |
| 511 | } |
| 512 | |
| 513 | if (toShrink > 0) |
| 514 | performWork(true /* shrink only */); |
| 515 | } |
| 516 | |
| 517 | protected void release(CachedItem item) { |
| 518 | |
| 519 | boolean removeItem; |
| 520 | |
| 521 | synchronized (this) { |
| 522 | |
| 523 | if (SanityManager.DEBUG) { |
| 524 | SanityManager.ASSERT(item.isKept(), "item is not kept in released(CachedItem)"); |
| 525 | } |
| 526 | |
| 527 | removeItem = item.unkeep(); |
| 528 | |
| 529 | if (removeItem) { |
| 530 | |
| 531 | remove(item.getEntry().getIdentity()); |
| 532 | |
| 533 | // we keep the item here to stop another thread trying to evict it |
| 534 | // while we are destroying it. |
| 535 | item.keepForClean(); |
| 536 | } |
| 537 | } |
| 538 | |
| 539 | if (removeItem) { |
| 540 | |
| 541 | item.notifyRemover(); |
| 542 | } |
| 543 | } |
| 544 | |
| 545 | /** |
| 546 | Remove an object from the cache. The item will be placed into the NoIdentity |
| 547 | state through clean() (if required) and clearIdentity(). The removal of the |
| 548 | object will be delayed until it is not kept by anyone. |
| 549 | |
| 550 | After this call the caller must throw away the reference to item. |
| 551 | |
| 552 | <P>MT - must be MT-safe. Single thread thru finding and setting the |
| 553 | remove state of the item, the actual removal of the cacheable is |
| 554 | synchronized on the cachedItem itself. |
| 555 | |
| 556 | @exception StandardException Standard Cloudscape error policy. |
| 557 | */ |
| 558 | public void remove(Cacheable entry) throws StandardException { |
| 559 | |
| 560 | boolean removeNow; |
| 561 | CachedItem item; |
| 562 | long origItemSize = 0; |
| 563 | |
| 564 | stat.remove++; |
| 565 | |
| 566 | synchronized (this) { |
| 567 | |
| 568 | |
| 569 | |
| 570 | item = (CachedItem) get(entry.getIdentity()); |
| 571 | |
| 572 | if (SanityManager.DEBUG) { |
| 573 | SanityManager.ASSERT(item != null); |
| 574 | SanityManager.ASSERT(item.getEntry() == entry); |
| 575 | SanityManager.ASSERT(item.isKept()); |
| 576 | } |
| 577 | if( useByteCount) |
| 578 | origItemSize = getItemSize( item); |
| 579 | |
| 580 | item.setRemoveState(); |
| 581 | removeNow = item.unkeep(); |
| 582 | |
| 583 | if (removeNow) { |
| 584 | remove(entry.getIdentity()); |
| 585 | item.keepForClean(); |
| 586 | } |
| 587 | } |
| 588 | |
| 589 | try { |
| 590 | // if removeNow is false then this thread may sleep |
| 591 | item.remove(removeNow); |
| 592 | |
| 593 | } finally { |
| 594 | |
| 595 | synchronized (this) |
| 596 | { |
| 597 | // in the case where this thread didn't call keepForClean() the thread |
| 598 | // that woke us would have called keepForClean. |
| 599 | item.unkeep(); |
| 600 | item.setValidState(false); |
| 601 | validItemCount--; |
| 602 | item.getEntry().clearIdentity(); |
| 603 | if( useByteCount) |
| 604 | currentByteCount += getItemSize( item) - origItemSize; |
| 605 | } |
| 606 | } |
| 607 | |
| 608 | } |
| 609 | |
| 610 | /** |
| 611 | Clean all objects in the cache. |
| 612 | */ |
| 613 | public void cleanAll() throws StandardException { |
| 614 | stat.cleanAll++; |
| 615 | cleanCache((Matchable) null); |
| 616 | } |
| 617 | |
| 618 | /** |
| 619 | Clean all objects that match a partial key. |
| 620 | */ |
| 621 | public void clean(Matchable partialKey) throws StandardException { |
| 622 | |
| 623 | cleanCache(partialKey); |
| 624 | } |
| 625 | |
| 626 | /** |
| 627 | Age as many objects as possible out of the cache. |
| 628 | |
| 629 | <BR>MT - thread safe |
| 630 | |
| 631 | @see CacheManager#ageOut |
| 632 | */ |
| 633 | public void ageOut() { |
| 634 | |
| 635 | stat.ageOut++; |
| 636 | synchronized (this) { |
| 637 | |
| 638 | int size = holders.size(); |
| 639 | long toShrink = shrinkSize( getCurrentSize()); |
| 640 | boolean shrunk = false; |
| 641 | |
| 642 | for (int position = 0; position < size; position++) { |
| 643 | CachedItem item = (CachedItem) holders.get(position); |
| 644 | |
| 645 | if (item.isKept()) |
| 646 | continue; |
| 647 | if (!item.isValid()) |
| 648 | continue; |
| 649 | |
| 650 | if (item.getEntry().isDirty()) { |
| 651 | continue; |
| 652 | } |
| 653 | |
| 654 | long itemSize = removeIdentity(item); |
| 655 | |
| 656 | if (toShrink > 0) { |
| 657 | |
| 658 | if (SanityManager.DEBUG) { |
| 659 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) { |
| 660 | SanityManager.DEBUG(ClockFactory.CacheTrace, name + |
| 661 | " shrinking item " + item + " at position " + position); |
| 662 | } |
| 663 | } |
| 664 | |
| 665 | toShrink -= itemSize; |
| 666 | shrunk = true; |
| 667 | } |
| 668 | |
| 669 | } // end of for loop |
| 670 | |
| 671 | if (shrunk) |
| 672 | trimToSize(); |
| 673 | |
| 674 | } // out of sync block |
| 675 | } // end of ageOut |
| 676 | |
| 677 | /** |
| 678 | MT - synchronization provided by caller |
| 679 | |
| 680 | @exception StandardException Standard Cloudscape error policy. |
| 681 | */ |
| 682 | public void shutdown() throws StandardException { |
| 683 | |
| 684 | if (cleaner != null) { |
| 685 | cleaner.unsubscribe(myClientNumber); |
| 686 | cleaner = null; |
| 687 | } |
| 688 | |
| 689 | synchronized (this) { |
| 690 | active = false; |
| 691 | } |
| 692 | |
| 693 | ageOut(); |
| 694 | cleanAll(); |
| 695 | ageOut(); |
| 696 | } |
| 697 | |
| 698 | /** |
| 699 | MT - synchronization provided by caller |
| 700 | |
| 701 | can use this Daemomn service if needed |
| 702 | */ |
| 703 | public void useDaemonService(DaemonService daemon) |
| 704 | { |
| 705 | // if we were using another cleaner, unsubscribe first |
| 706 | if (cleaner != null) |
| 707 | cleaner.unsubscribe(myClientNumber); |
| 708 | |
| 709 | cleaner = daemon; |
| 710 | myClientNumber = cleaner.subscribe(this, true /* onDemandOnly */); |
| 711 | } |
| 712 | /** |
| 713 | Discard all objects that match the partial key. |
| 714 | |
| 715 | <BR>MT - thread safe |
| 716 | */ |
| 717 | public boolean discard(Matchable partialKey) { |
| 718 | |
| 719 | // we miss something because it was kept |
| 720 | boolean noMisses = true; |
| 721 | |
| 722 | synchronized (this) { |
| 723 | |
| 724 | int size = holders.size(); |
| 725 | long toShrink = shrinkSize( getCurrentSize()); |
| 726 | boolean shrunk = false; |
| 727 | |
| 728 | for (int position = 0; position < size; position++) { |
| 729 | CachedItem item = (CachedItem) holders.get(position); |
| 730 | |
| 731 | if (!item.isValid()) |
| 732 | continue; |
| 733 | |
| 734 | Object key = item.getEntry().getIdentity(); |
| 735 | |
| 736 | if (partialKey != null && !partialKey.match(key)) |
| 737 | continue; |
| 738 | |
| 739 | if (item.isKept()) |
| 740 | { |
| 741 | noMisses = false; |
| 742 | continue; |
| 743 | } |
| 744 | |
| 745 | long itemSize = removeIdentity(item); |
| 746 | |
| 747 | if (toShrink > 0) { |
| 748 | |
| 749 | if (SanityManager.DEBUG) { |
| 750 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) { |
| 751 | SanityManager.DEBUG(ClockFactory.CacheTrace, name + |
| 752 | " shrinking item " + item + " at position " + position); |
| 753 | } |
| 754 | } |
| 755 | |
| 756 | // and we shrunk one item |
| 757 | toShrink -= itemSize; |
| 758 | shrunk = true; |
| 759 | } |
| 760 | } |
| 761 | |
| 762 | if (shrunk) |
| 763 | trimToSize(); |
| 764 | } |
| 765 | |
| 766 | return noMisses; |
| 767 | } |
| 768 | |
| 769 | /** |
| 770 | Add a new CachedItem and a holder object to the cache. The holder object |
| 771 | is returned kept. |
| 772 | |
| 773 | <P>MT - need to be MT-safe. The insertion of the key into the hash |
| 774 | table is synchronized on this. |
| 775 | |
| 776 | */ |
| 777 | private Cacheable addEntry(CachedItem item, Object key, boolean forCreate, Object createParameter) |
| 778 | throws StandardException { |
| 779 | |
| 780 | Cacheable entry = null; |
| 781 | long origEntrySize = 0; |
| 782 | if( useByteCount) |
| 783 | origEntrySize = getItemSize( item); |
| 784 | |
| 785 | try |
| 786 | { |
| 787 | if (SanityManager.DEBUG) { |
| 788 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) |
| 789 | { |
| 790 | SanityManager.DEBUG(ClockFactory.CacheTrace, name + |
| 791 | " item " + item + " take on identity " + key); |
| 792 | } |
| 793 | } |
| 794 | |
| 795 | // tell the object it needs to create itself |
| 796 | entry = item.takeOnIdentity(this, holderFactory, key, forCreate, createParameter); |
| 797 | } |
| 798 | finally |
| 799 | { |
| 800 | boolean notifyWaiters; |
| 801 | synchronized (this) { |
| 802 | |
| 803 | Object removed = remove(key); |
| 804 | if (SanityManager.DEBUG) { |
| 805 | SanityManager.ASSERT(removed == item); |
| 806 | } |
| 807 | |
| 808 | if (entry != null) { |
| 809 | // put the actual key into the hash table, not the one that was passed in |
| 810 | // for the find or create. This is because the caller may re-use the key |
| 811 | // for another cache operation, which would corrupt our hashtable |
| 812 | put(entry.getIdentity(), item); |
| 813 | if( useByteCount) |
| 814 | currentByteCount += ((SizedCacheable) entry).getSize() - origEntrySize; |
| 815 | item.setValidState(true); |
| 816 | validItemCount++; |
| 817 | notifyWaiters = true; |
| 818 | } else { |
| 819 | item.unkeep(); |
| 820 | notifyWaiters = item.isKept(); |
| 821 | } |
| 822 | } |
| 823 | |
| 824 | // whatever the outcome, we have to notify waiters ... |
| 825 | if (notifyWaiters) |
| 826 | item.settingIdentityComplete(); |
| 827 | } |
| 828 | |
| 829 | return entry; |
| 830 | } |
| 831 | |
| 832 | |
| 833 | protected CachedItem findFreeItem() throws StandardException { |
| 834 | |
| 835 | // Need to avoid thrashing the cache when we start out |
| 836 | // so if the cache is smaller than its maximum size |
| 837 | // then that's a good indication we should grow. |
| 838 | |
| 839 | long currentSize = getCurrentSize(); |
| 840 | |
| 841 | |
| 842 | if (currentSize >= maximumSize) { |
| 843 | // look at 20% |
| 844 | CachedItem item = rotateClock(0.2f); |
| 845 | if (item != null) |
| 846 | return item; |
| 847 | } |
| 848 | |
| 849 | // However, if the cache contains a large number of invalid |
| 850 | // items then we should see if we can avoid growing. |
| 851 | // This avoids simple use of Cloudscape looking like |
| 852 | // a memory leak, as the page cache fills the holders array |
| 853 | // with page objects including the 4k (or 32k) pages. |
| 854 | // size() is the number of valid entries in the hash table |
| 855 | |
| 856 | |
| 857 | // no need to sync on getting the sizes since if they are |
| 858 | // wrong we will discover it in the loop. |
| 859 | if (validItemCount < holders.size()) { |
| 860 | |
| 861 | synchronized (this) { |
| 862 | |
| 863 | // 1) find out how many invalid items there are in the |
| 864 | // cache |
| 865 | // 2) search for a free invalid item |
| 866 | // 3) stop searching when there are no more invalid |
| 867 | // items to find |
| 868 | |
| 869 | int invalidItems = holders.size() - validItemCount; |
| 870 | |
| 871 | // Invalid items might occur in the cache when |
| 872 | // a) a new item is created in growCache(), but it |
| 873 | // is not in use yet, or |
| 874 | // b) an item is deleted (usually when a table is |
| 875 | // dropped) |
| 876 | |
| 877 | // It is critical to break out of the loop as soon as |
| 878 | // possible since we are blocking others trying to |
| 879 | // access the page cache. New items are added to the |
| 880 | // end of the page cache, so the search for invalid |
| 881 | // items should start from the end. |
| 882 | |
| 883 | for (int i = holders.size() - 1; (invalidItems > 0) && (i >= 0) ; i--) { |
| 884 | CachedItem item = (CachedItem) holders.get(i); |
| 885 | |
| 886 | if (item.isKept()) { |
| 887 | if (!item.isValid()) invalidItems--; |
| 888 | continue; |
| 889 | } |
| 890 | |
| 891 | // found a free item, just use it |
| 892 | if (!item.isValid()) { |
| 893 | item.keepForCreate(); |
| 894 | return item; |
| 895 | } |
| 896 | } |
| 897 | } |
| 898 | } |
| 899 | |
| 900 | |
| 901 | return growCache(); |
| 902 | } |
| 903 | |
| 904 | /** |
| 905 | Go through the list of holder objects and find a free one. |
| 906 | <P>MT - must be MT-safe. The moving of the clockHand and finding of an |
| 907 | eviction candidate is synchronized. The cleaning of the cachable is |
| 908 | handled by the cacheable itself. |
| 909 | */ |
| 910 | protected CachedItem rotateClock(float percentOfClock) throws StandardException |
| 911 | { |
| 912 | // statistics -- only used in debug |
| 913 | int evictions = 0; |
| 914 | int cleaned = 0; |
| 915 | int resetUsed = 0; |
| 916 | int iskept = 0; |
| 917 | |
| 918 | // When we are managing the entry count (useByteCount == false) this method just |
| 919 | // has to find or manufacture an available item (a cache slot). When we are managing |
| 920 | // the total byte count then this method must find both available space and an |
| 921 | // available item. |
| 922 | CachedItem availableItem = null; |
| 923 | |
| 924 | boolean kickCleaner = false; |
| 925 | |
| 926 | try { |
| 927 | |
| 928 | |
| 929 | // this can be approximate |
| 930 | int itemCount = holders.size(); |
| 931 | int itemsToCheck; |
| 932 | if (itemCount < 20) |
| 933 | itemsToCheck = 2 * itemCount; |
| 934 | else |
| 935 | itemsToCheck = (int) (((float) itemCount) * percentOfClock); |
| 936 | |
| 937 | |
| 938 | // if we can grow then shrinking is OK too, if we can't grow |
| 939 | // then shrinking the cache won't help us find an item. |
| 940 | long toShrink = shrinkSize(getCurrentSize()); |
| 941 | |
| 942 | restartClock: |
| 943 | for (; itemsToCheck > 0;) { |
| 944 | |
| 945 | CachedItem item = null; |
| 946 | |
| 947 | synchronized (this) { |
| 948 | |
| 949 | if (SanityManager.DEBUG) { |
| 950 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) |
| 951 | { |
| 952 | SanityManager.DEBUG(ClockFactory.CacheTrace, name + " rotateClock starting " + |
| 953 | clockHand + " itemsToCheck " + itemsToCheck); |
| 954 | } |
| 955 | } |
| 956 | |
| 957 | // size of holders cannot change while in the synchronized block. |
| 958 | int size = holders.size(); |
| 959 | for (; itemsToCheck > 0; item = null, itemsToCheck--, incrClockHand()) |
| 960 | { |
| 961 | // |
| 962 | // This uses a very simple clock algorithm. |
| 963 | // |
| 964 | // The cache consist of a circular list of cachedItems. Each cached item |
| 965 | // has a 'recentlyUsed' bit which is set every time that item is kept. |
| 966 | // Each clock cache manager keeps a global variable clockHand which |
| 967 | // refers to the item that is most recently replaced. |
| 968 | // |
| 969 | // to find a free item, the clock Hand moves to the next cached Item. |
| 970 | // If it is kept, or in the middle of being created, the clock hand |
| 971 | // moves on. |
| 972 | // If it is recentlyUsed, clear the recently used bit and moves on. |
| 973 | // If it is not recentlyUsed, clean the item and use |
| 974 | // |
| 975 | // If all the cached item is kept, then create a new entry. |
| 976 | // So it is possible, although very unlikely, that, in time, the cache |
| 977 | // will grow beyond the maximum size. |
| 978 | |
| 979 | |
| 980 | |
| 981 | if (clockHand >= size) { |
| 982 | if (size == 0) |
| 983 | break; |
| 984 | clockHand = 0; |
| 985 | } |
| 986 | |
| 987 | item = (CachedItem) holders.get(clockHand); |
| 988 | |
| 989 | if (item.isKept()) |
| 990 | { |
| 991 | if (SanityManager.DEBUG) // stats only in debug mode |
| 992 | iskept++; |
| 993 | continue; |
| 994 | } |
| 995 | |
| 996 | if (!item.isValid()) // found a free item, just use it |
| 997 | { |
| 998 | if( null != availableItem) |
| 999 | // We have found an available item, now we are looking for bytes |
| 1000 | continue; |
| 1001 | if (SanityManager.DEBUG) { |
| 1002 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) |
| 1003 | { |
| 1004 | SanityManager.DEBUG(ClockFactory.CacheTrace, |
| 1005 | name + " found free item at " + clockHand + " item " + item); |
| 1006 | } |
| 1007 | } |
| 1008 | |
| 1009 | item.keepForCreate(); |
| 1010 | if( useByteCount && getCurrentSize() > maximumSize) |
| 1011 | { |
| 1012 | availableItem = item; |
| 1013 | // now look for bytes. |
| 1014 | continue; |
| 1015 | } |
| 1016 | // since we are using this item, move the clock past it. |
| 1017 | incrClockHand(); |
| 1018 | |
| 1019 | return item; |
| 1020 | } |
| 1021 | |
| 1022 | if (item.recentlyUsed()) |
| 1023 | { |
| 1024 | |
| 1025 | if (SanityManager.DEBUG) // stats only in debug mode |
| 1026 | resetUsed++; |
| 1027 | item.setUsed(false); |
| 1028 | continue; |
| 1029 | } |
| 1030 | |
| 1031 | |
| 1032 | if (toShrink > 0) { |
| 1033 | if (!cleanerRunning) { |
| 1034 | |
| 1035 | // try an get the cleaner to shrink the cache |
| 1036 | kickCleaner = true; |
| 1037 | cleanerRunning = true; |
| 1038 | needService = true; |
| 1039 | } |
| 1040 | } |
| 1041 | |
| 1042 | // we are seeing valid, not recently used buffers. Evict this. |
| 1043 | if (SanityManager.DEBUG) { |
| 1044 | evictions++; |
| 1045 | |
| 1046 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) |
| 1047 | { |
| 1048 | SanityManager.DEBUG(ClockFactory.CacheTrace, |
| 1049 | name + " evicting item at " + |
| 1050 | clockHand + " item " + item); |
| 1051 | } |
| 1052 | } |
| 1053 | |
| 1054 | if (!item.getEntry().isDirty()) { |
| 1055 | |
| 1056 | if (SanityManager.DEBUG) { |
| 1057 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) |
| 1058 | { |
| 1059 | SanityManager.DEBUG(ClockFactory.CacheTrace, |
| 1060 | name + " Evicting Item " + |
| 1061 | item + ", not dirty"); |
| 1062 | } |
| 1063 | } |
| 1064 | |
| 1065 | // a valid, unkept, clean item, clear its identity |
| 1066 | // and use it. |
| 1067 | long itemSize = removeIdentity(item); |
| 1068 | |
| 1069 | if( useByteCount) |
| 1070 | { |
| 1071 | toShrink -= itemSize; |
| 1072 | if( getCurrentSize() > maximumSize && 0 < toShrink) |
| 1073 | { |
| 1074 | if( null == availableItem) |
| 1075 | { |
| 1076 | item.keepForCreate(); |
| 1077 | availableItem = item; |
| 1078 | } |
| 1079 | continue; |
| 1080 | } |
| 1081 | } |
| 1082 | // since we are using it move the clock past it |
| 1083 | incrClockHand(); |
| 1084 | |
| 1085 | if( null != availableItem) |
| 1086 | return availableItem; |
| 1087 | |
| 1088 | // item is kept but not valid when returned |
| 1089 | item.keepForCreate(); |
| 1090 | return item; |
| 1091 | } |
| 1092 | // item is valid, unkept, and dirty. clean it. |
| 1093 | if ((cleaner != null) && !cleanerRunning) { |
| 1094 | kickCleaner = true; |
| 1095 | wokenToClean = true; |
| 1096 | cleanerRunning = true; // at least it soon will be |
| 1097 | } |
| 1098 | item.keepForClean(); |
| 1099 | |
| 1100 | // leave the clock hand where it is so that we will pick it |
| 1101 | // up if no-one else uses the cache. Other hunters will |
| 1102 | // skip over it as it is kept, and thus move the clock |
| 1103 | // hand past it. |
| 1104 | break; |
| 1105 | } |
| 1106 | if (item == null) { |
| 1107 | return availableItem; |
| 1108 | } |
| 1109 | |
| 1110 | } // out of synchronized block |
| 1111 | |
| 1112 | // clean the entry outside of a sync block |
| 1113 | try |
| 1114 | { |
| 1115 | if ( SanityManager.DEBUG) { |
| 1116 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) { |
| 1117 | SanityManager.DEBUG(ClockFactory.CacheTrace,name + " cleaning item " + item); |
| 1118 | } |
| 1119 | } |
| 1120 | |
| 1121 | item.clean(false); |
| 1122 | |
| 1123 | if (SanityManager.DEBUG) // stats only in debug mode |
| 1124 | { |
| 1125 | cleaned++; |
| 1126 | } |
| 1127 | } |
| 1128 | finally { |
| 1129 | release(item); |
| 1130 | item = null; |
| 1131 | } |
| 1132 | |
| 1133 | // at this point the item we cleaned could be in any state |
| 1134 | // so we can't just re-use it. Continue searching |
| 1135 | continue restartClock; |
| 1136 | } |
| 1137 | return availableItem; |
| 1138 | } finally { |
| 1139 | |
| 1140 | |
| 1141 | if (SanityManager.DEBUG) |
| 1142 | { |
| 1143 | // report statistics |
| 1144 | if ( |
| 1145 | SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) |
| 1146 | SanityManager.DEBUG(ClockFactory.CacheTrace, name + " evictions " + evictions + |
| 1147 | ", cleaned " + cleaned + |
| 1148 | ", resetUsed " + resetUsed + |
| 1149 | ", isKept " + iskept + |
| 1150 | ", size " + holders.size()); |
| 1151 | } |
| 1152 | |
| 1153 | if (kickCleaner && (cleaner != null)) |
| 1154 | { |
| 1155 | if (SanityManager.DEBUG) { |
| 1156 | if (SanityManager.DEBUG_ON(DaemonService.DaemonTrace)) { |
| 1157 | SanityManager.DEBUG(DaemonService.DaemonTrace, name + " client # " + myClientNumber + " calling cleaner "); |
| 1158 | } |
| 1159 | } |
| 1160 | |
| 1161 | cleaner.serviceNow(myClientNumber); |
| 1162 | |
| 1163 | if (SanityManager.DEBUG) { |
| 1164 | if (SanityManager.DEBUG_ON(DaemonService.DaemonTrace)) { |
| 1165 | SanityManager.DEBUG(DaemonService.DaemonTrace, name + Thread.currentThread().getName() + " cleaner called"); |
| 1166 | } |
| 1167 | } |
| 1168 | } |
| 1169 | } |
| 1170 | } // end of rotateClock |
| 1171 | |
| 1172 | /** |
| 1173 | Synchronously increment clock hand position |
| 1174 | */ |
| 1175 | private int incrClockHand() |
| 1176 | { |
| 1177 | if (++clockHand >= holders.size()) |
| 1178 | clockHand = 0; |
| 1179 | return clockHand; |
| 1180 | } |
| 1181 | |
| 1182 | /* |
| 1183 | * Serviceable methods |
| 1184 | */ |
| 1185 | |
| 1186 | public int performWork(ContextManager contextMgr /* ignored */) { |
| 1187 | |
| 1188 | int ret = performWork(false); |
| 1189 | synchronized (this) { |
| 1190 | cleanerRunning = false; |
| 1191 | } |
| 1192 | return ret; |
| 1193 | } |
| 1194 | |
| 1195 | |
| 1196 | /** |
| 1197 | <P>MT - read only. |
| 1198 | */ |
| 1199 | public boolean serviceASAP() |
| 1200 | { |
| 1201 | return needService; |
| 1202 | } |
| 1203 | |
| 1204 | |
| 1205 | // @return true, if this work needs to be done on a user thread immediately |
| 1206 | public boolean serviceImmediately() |
| 1207 | { |
| 1208 | return false; |
| 1209 | } |
| 1210 | |
| 1211 | |
| 1212 | public synchronized int getNumberInUse() { |
| 1213 | |
| 1214 | int size = holders.size(); |
| 1215 | int inUse = 0; |
| 1216 | |
| 1217 | for (int position = 0; position < size; position++) { |
| 1218 | |
| 1219 | CachedItem item = (CachedItem) holders.get(position); |
| 1220 | |
| 1221 | if (item.isValid()) { |
| 1222 | inUse++; |
| 1223 | } |
| 1224 | |
| 1225 | } |
| 1226 | return inUse; |
| 1227 | } |
| 1228 | /* |
| 1229 | public int getNumberKept() { |
| 1230 | |
| 1231 | synchronized (this) { |
| 1232 | |
| 1233 | int size = holders.size(); |
| 1234 | int inUse = 0; |
| 1235 | |
| 1236 | for (int position = 0; position < size; position++) { |
| 1237 | |
| 1238 | CachedItem item = (CachedItem) holders.get(position); |
| 1239 | |
| 1240 | if (item.isValid() && item.isKept()) { |
| 1241 | inUse++; |
| 1242 | } |
| 1243 | |
| 1244 | } |
| 1245 | return inUse; |
| 1246 | } |
| 1247 | } |
| 1248 | */ |
| 1249 | |
| 1250 | /** |
| 1251 | Grow the cache and return a unused, kept item. |
| 1252 | |
| 1253 | @exception StandardException Thrown if the cache cannot be grown. |
| 1254 | */ |
| 1255 | |
| 1256 | private CachedItem growCache() { |
| 1257 | |
| 1258 | CachedItem item = new CachedItem(); |
| 1259 | item.keepForCreate(); |
| 1260 | |
| 1261 | // if we run out of memory below here we don't |
| 1262 | // know what state the holders could be in |
| 1263 | // so don't trap it |
| 1264 | synchronized (this) { |
| 1265 | holders.add(item); |
| 1266 | // Do not adjust currentByteCount until we put the entry into the CachedItem. |
| 1267 | } |
| 1268 | |
| 1269 | return item; |
| 1270 | } |
| 1271 | |
| 1272 | |
| 1273 | /** |
| 1274 | Clear an item's identity. Item must be |
| 1275 | unkept and valid. This is called for |
| 1276 | dirty items from the discard code. |
| 1277 | |
| 1278 | Caller must hold the cache synchronization. |
| 1279 | |
| 1280 | @return the amount by which this shrinks the cache. |
| 1281 | */ |
| 1282 | protected long removeIdentity(CachedItem item) { |
| 1283 | |
| 1284 | long shrink = 1; |
| 1285 | |
| 1286 | if (SanityManager.DEBUG) { |
| 1287 | SanityManager.ASSERT(!item.isKept(), "item is kept"); |
| 1288 | SanityManager.ASSERT(item.isValid(), "item is not valid"); |
| 1289 | |
| 1290 | } |
| 1291 | |
| 1292 | if( useByteCount) |
| 1293 | shrink = ((SizedCacheable) item.getEntry()).getSize(); |
| 1294 | remove(item.getEntry().getIdentity()); |
| 1295 | item.setValidState(false); |
| 1296 | validItemCount--; |
| 1297 | item.getEntry().clearIdentity(); |
| 1298 | if( useByteCount) |
| 1299 | { |
| 1300 | shrink -= ((SizedCacheable) item.getEntry()).getSize(); |
| 1301 | currentByteCount -= shrink; |
| 1302 | } |
| 1303 | return shrink; |
| 1304 | } |
| 1305 | |
| 1306 | /** |
| 1307 | Write out all dirty buffers. |
| 1308 | |
| 1309 | <P>MT - must be MT safe. |
| 1310 | Single thread on the part that finds the next dirty buffer to write |
| 1311 | out, the synchronization of cleaning of the individual cachable is |
| 1312 | provided by the cacheable itself. |
| 1313 | */ |
| 1314 | protected void cleanCache(Matchable partialKey) throws StandardException { |
| 1315 | |
| 1316 | int position; |
| 1317 | |
| 1318 | synchronized(this) |
| 1319 | { |
| 1320 | // this is at many dirty buffers as the cleaner is ever going to |
| 1321 | // see |
| 1322 | position = holders.size() - 1; |
| 1323 | } |
| 1324 | |
| 1325 | |
| 1326 | outerscan: |
| 1327 | for (;;) { |
| 1328 | |
| 1329 | CachedItem item = null; |
| 1330 | |
| 1331 | synchronized (this) { |
| 1332 | |
| 1333 | // the cache may have shrunk by quite a bit since we last came |
| 1334 | // in here |
| 1335 | int size = holders.size(); |
| 1336 | if (position >= size) |
| 1337 | position = size - 1; |
| 1338 | |
| 1339 | innerscan: |
| 1340 | // go from position (the last cached item in the holder array |
| 1341 | // to 0 (the first). Otherwise, if we go from 0 to |
| 1342 | // position, some other thread may come in and shrink items |
| 1343 | // which are between 0 and position. Since a shrink moves all |
| 1344 | // items up, we may skip some items without cleaning. |
| 1345 | for ( ; position >= 0; position--, item = null) { |
| 1346 | |
| 1347 | item = (CachedItem) holders.get(position); |
| 1348 | |
| 1349 | if (!item.isValid()) |
| 1350 | continue innerscan; |
| 1351 | |
| 1352 | if (!item.getEntry().isDirty()) |
| 1353 | continue innerscan; |
| 1354 | |
| 1355 | if (partialKey != null) { |
| 1356 | |
| 1357 | Object key = item.getEntry().getIdentity(); |
| 1358 | |
| 1359 | if (!partialKey.match(key)) |
| 1360 | continue; |
| 1361 | } |
| 1362 | |
| 1363 | item.keepForClean(); |
| 1364 | break innerscan; |
| 1365 | } |
| 1366 | } // end of synchronized block |
| 1367 | |
| 1368 | if (position < 0) |
| 1369 | { |
| 1370 | return; |
| 1371 | } |
| 1372 | |
| 1373 | try { |
| 1374 | |
| 1375 | item.clean(false); |
| 1376 | } finally { |
| 1377 | release(item); |
| 1378 | } |
| 1379 | position--; |
| 1380 | |
| 1381 | } // for (;;) |
| 1382 | } |
| 1383 | |
| 1384 | |
| 1385 | protected long shrinkSize(long currentSize) { |
| 1386 | |
| 1387 | long maxSize = getMaximumSize(); |
| 1388 | |
| 1389 | long toShrink = currentSize - maxSize; |
| 1390 | if (toShrink <= 0) |
| 1391 | return 0; |
| 1392 | |
| 1393 | // only shrink 10% of the maximum size |
| 1394 | long shrinkLimit = maxSize / 10; |
| 1395 | if (shrinkLimit == 0) |
| 1396 | shrinkLimit = 2; |
| 1397 | |
| 1398 | if (toShrink < shrinkLimit) |
| 1399 | return toShrink; |
| 1400 | else |
| 1401 | return shrinkLimit; |
| 1402 | } |
| 1403 | |
| 1404 | /** |
| 1405 | The background cleaner tries to make sure that there are serveral |
| 1406 | cleaned or invalied buffers ahead of the clock hand so that when they |
| 1407 | are evicted, they don't need to be cleaned. |
| 1408 | |
| 1409 | The way this routine work is as follows, starting at the current clock |
| 1410 | hand position, go forward around the cache buffers, moving the same |
| 1411 | route that the clock hand moves. It keep tracks of the number of |
| 1412 | invalid or not recently used buffers it sees along the way. If it sees |
| 1413 | a not recently used buffer, it will clean it. After it has seen N |
| 1414 | invalid or not recently used buffers, or it has gone around and visited |
| 1415 | all buffers in the cache, it finished. |
| 1416 | |
| 1417 | It does not clean recently used buffers. |
| 1418 | |
| 1419 | <P>MT - must be MT-safe. It takes a snapshot of the current clock hand |
| 1420 | position (a synchronous call). Getting and looking at the next |
| 1421 | serveral cached item is synchronized on this (RESOLVE: probably doesn't |
| 1422 | need to be). Cleaning of the cacheable is handle by the cacheable itself. |
| 1423 | |
| 1424 | */ |
| 1425 | protected int performWork(boolean shrinkOnly) |
| 1426 | { |
| 1427 | long target; |
| 1428 | long toShrink; |
| 1429 | int maxLooks; |
| 1430 | |
| 1431 | synchronized(this) |
| 1432 | { |
| 1433 | if (!active) { |
| 1434 | needService = false; |
| 1435 | return Serviceable.DONE; |
| 1436 | } |
| 1437 | else { |
| 1438 | long currentSize = getCurrentSize(); |
| 1439 | target = currentSize / 20; // attempt to get 5% of the cache clean |
| 1440 | toShrink = wokenToClean ? 0 : shrinkSize(currentSize); |
| 1441 | } |
| 1442 | |
| 1443 | if (target == 0) { |
| 1444 | wokenToClean = false; |
| 1445 | needService = false; |
| 1446 | return Serviceable.DONE; |
| 1447 | } |
| 1448 | |
| 1449 | if (!wokenToClean && (toShrink <= 0)) { |
| 1450 | needService = false; |
| 1451 | return Serviceable.DONE; |
| 1452 | } |
| 1453 | |
| 1454 | maxLooks = useByteCount ? (holders.size()/10) : (int) (target * 2); |
| 1455 | } |
| 1456 | |
| 1457 | // try to clean the next N (target) cached item, |
| 1458 | long clean = 0; |
| 1459 | int cleaned = 0; // only used in debug |
| 1460 | CachedItem item = null; |
| 1461 | int currentPosition = 0; |
| 1462 | |
| 1463 | String ThreadName = null; |
| 1464 | |
| 1465 | if (SanityManager.DEBUG) { |
| 1466 | if (SanityManager.DEBUG_ON(DaemonService.DaemonTrace)) |
| 1467 | { |
| 1468 | ThreadName = Thread.currentThread().getName(); |
| 1469 | SanityManager.DEBUG(DaemonService.DaemonTrace, ThreadName + " Cleaning " + name + " clientNumber " + myClientNumber); |
| 1470 | } |
| 1471 | } |
| 1472 | |
| 1473 | |
| 1474 | synchronized(this) |
| 1475 | { |
| 1476 | int itemCount = holders.size(); |
| 1477 | currentPosition = clockHand; |
| 1478 | |
| 1479 | // see if the cache needs to shrink |
| 1480 | boolean shrunk = false; |
| 1481 | long currentSize = getCurrentSize(); |
| 1482 | |
| 1483 | for (; shrinkOnly ? (currentSize > maximumSize && toShrink > 0) : (clean < target); item = null) |
| 1484 | { |
| 1485 | if (++currentPosition >= itemCount) { |
| 1486 | if (itemCount == 0) |
| 1487 | break; |
| 1488 | |
| 1489 | currentPosition = 0; |
| 1490 | |
| 1491 | } |
| 1492 | |
| 1493 | if (maxLooks-- <= 0) |
| 1494 | { |
| 1495 | if (SanityManager.DEBUG) { |
| 1496 | if (SanityManager.DEBUG_ON(DaemonService.DaemonTrace)) { |
| 1497 | SanityManager.DEBUG(DaemonService.DaemonTrace, ThreadName + " done one round of " + name); |
| 1498 | } |
| 1499 | } |
| 1500 | |
| 1501 | break; // done one round |
| 1502 | } |
| 1503 | |
| 1504 | item = (CachedItem) holders.get(currentPosition); |
| 1505 | |
| 1506 | if (item.isKept()) |
| 1507 | continue; |
| 1508 | |
| 1509 | if (!item.isValid()) |
| 1510 | { |
| 1511 | if (toShrink > 0) { |
| 1512 | |
| 1513 | if (SanityManager.DEBUG) { |
| 1514 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) { |
| 1515 | SanityManager.DEBUG(ClockFactory.CacheTrace, name + |
| 1516 | " shrinking item " + item + " at position " + currentPosition); |
| 1517 | } |
| 1518 | } |
| 1519 | |
| 1520 | toShrink -= currentSize; |
| 1521 | holders.remove(currentPosition); |
| 1522 | if( useByteCount) |
| 1523 | currentByteCount -= getItemSize( item); |
| 1524 | currentSize = getCurrentSize(); |
| 1525 | toShrink += currentSize; |
| 1526 | itemCount--; |
| 1527 | |
| 1528 | // account for the fact all the items have shifted down |
| 1529 | currentPosition--; |
| 1530 | |
| 1531 | shrunk = true; |
| 1532 | } |
| 1533 | continue; |
| 1534 | } |
| 1535 | |
| 1536 | if (item.recentlyUsed()) |
| 1537 | continue; |
| 1538 | |
| 1539 | // found a valid, not kept, and not recently used item |
| 1540 | // this item will be cleaned |
| 1541 | int itemSize = getItemSize( item); |
| 1542 | clean += itemSize; |
| 1543 | if (!item.getEntry().isDirty()) { |
| 1544 | |
| 1545 | if (toShrink > 0) { |
| 1546 | if (SanityManager.DEBUG) { |
| 1547 | if (SanityManager.DEBUG_ON(ClockFactory.CacheTrace)) { |
| 1548 | SanityManager.DEBUG(ClockFactory.CacheTrace, name + |
| 1549 | " shrinking item " + item + " at position " + currentPosition); |
| 1550 | } |
| 1551 | } |
| 1552 | |
| 1553 | toShrink -= currentSize; |
| 1554 | removeIdentity(item); |
| 1555 | holders.remove(currentPosition); |
| 1556 | if( useByteCount) |
| 1557 | currentByteCount -= getItemSize( item); |
| 1558 | currentSize = getCurrentSize(); |
| 1559 | toShrink += currentSize; |
| 1560 | itemCount--; |
| 1561 | shrunk = true; |
| 1562 | |
| 1563 | // account for the fact all the items have shifted down |
| 1564 | currentPosition--; |
| 1565 | } |
| 1566 | continue; |
| 1567 | } |
| 1568 | |
| 1569 | if (shrinkOnly) |
| 1570 | continue; |
| 1571 | |
| 1572 | // found one that needs cleaning, keep it to clean |
| 1573 | item.keepForClean(); |
| 1574 | break; |
| 1575 | } // end of for loop |
| 1576 | |
| 1577 | if (shrunk) |
| 1578 | trimToSize(); |
| 1579 | |
| 1580 | if (item == null) { |
| 1581 | wokenToClean = false; |
| 1582 | needService = false; |
| 1583 | return Serviceable.DONE; |
| 1584 | } |
| 1585 | } // end of sync block |
| 1586 | |
| 1587 | try |
| 1588 | { |
| 1589 | if (SanityManager.DEBUG) { |
| 1590 | if (SanityManager.DEBUG_ON(DaemonService.DaemonTrace)) { |
| 1591 | SanityManager.DEBUG(DaemonService.DaemonTrace, ThreadName + " cleaning entry in " + name); |
| 1592 | } |
| 1593 | } |
| 1594 | |
| 1595 | item.clean(false); |
| 1596 | if (SanityManager.DEBUG) // only need stats for debug |
| 1597 | cleaned++; |
| 1598 | |
| 1599 | } catch (StandardException se) { |
| 1600 | // RESOLVE - should probably throw the error into the log. |
| 1601 | } |
| 1602 | finally |
| 1603 | { |
| 1604 | release(item); |
| 1605 | item = null; |
| 1606 | } |
| 1607 | |
| 1608 | if (SanityManager.DEBUG) { |
| 1609 | if (SanityManager.DEBUG_ON(DaemonService.DaemonTrace)) { |
| 1610 | SanityManager.DEBUG(DaemonService.DaemonTrace, ThreadName + " Found " + clean + " clean items, cleaned " + |
| 1611 | cleaned + " items in " + name ); |
| 1612 | } |
| 1613 | } |
| 1614 | |
| 1615 | needService = true; |
| 1616 | return Serviceable.REQUEUE; // return is actually ignored. |
| 1617 | } // end of performWork |
| 1618 | |
| 1619 | private int getItemSize( CachedItem item) |
| 1620 | { |
| 1621 | if( ! useByteCount) |
| 1622 | return 1; |
| 1623 | SizedCacheable entry = (SizedCacheable) item.getEntry(); |
| 1624 | if( null == entry) |
| 1625 | return 0; |
| 1626 | return entry.getSize(); |
| 1627 | } // end of getItemSize |
| 1628 | |
| 1629 | /** |
| 1630 | Return statistics about cache that may be implemented. |
| 1631 | **/ |
| 1632 | public synchronized long[] getCacheStats() |
| 1633 | { |
| 1634 | stat.currentSize = getCurrentSize(); |
| 1635 | return stat.getStats(); |
| 1636 | } |
| 1637 | |
| 1638 | /** |
| 1639 | Reset the statistics to 0. |
| 1640 | **/ |
| 1641 | public void resetCacheStats() |
| 1642 | { |
| 1643 | stat.reset(); |
| 1644 | } |
| 1645 | |
| 1646 | /** |
| 1647 | * @return the current maximum size of the cache. |
| 1648 | */ |
| 1649 | public synchronized long getMaximumSize() |
| 1650 | { |
| 1651 | return maximumSize; |
| 1652 | } |
| 1653 | |
| 1654 | /** |
| 1655 | * Change the maximum size of the cache. If the size is decreased then cache entries |
| 1656 | * will be thrown out. |
| 1657 | * |
| 1658 | * @param newSize the new maximum cache size |
| 1659 | * |
| 1660 | * @exception StandardException Cloudscape Standard error policy |
| 1661 | */ |
| 1662 | public void resize( long newSize) throws StandardException |
| 1663 | { |
| 1664 | boolean shrink; |
| 1665 | |
| 1666 | synchronized( this) |
| 1667 | { |
| 1668 | maximumSize = newSize; |
| 1669 | stat.maxSize = maximumSize; |
| 1670 | shrink = ( shrinkSize( getCurrentSize()) > 0); |
| 1671 | } |
| 1672 | if( shrink) |
| 1673 | { |
| 1674 | performWork(true /* shrink only */); |
| 1675 | /* performWork does not remove recently used entries nor does it mark them as |
| 1676 | * not recently used. Therefore if the cache has not shrunk enough we will call rotateClock |
| 1677 | * to free up some entries. |
| 1678 | */ |
| 1679 | if( shrinkSize( getCurrentSize()) > 0) |
| 1680 | { |
| 1681 | CachedItem freeItem = rotateClock( (float) 2.0); |
| 1682 | /* rotateClock(2.0) means that the clock will rotate through the cache as much as |
| 1683 | * twice. If it does not find sufficient unused items the first time through it |
| 1684 | * will almost certainly find enough of them the second time through, because it |
| 1685 | * marked all the items as not recently used in the first pass. |
| 1686 | * |
| 1687 | * If the cache is very heavily used by other threads then a lot of the items marked as |
| 1688 | * unused in the first pass may be used before rotateClock passes over them again. In this |
| 1689 | * unlikely case rotateClock( 2.0) may not be able to clear out enough space to bring the |
| 1690 | * current size down to the maximum. However the cache size should come down as rotateClock |
| 1691 | * is called in the normal course of operation. |
| 1692 | */ |
| 1693 | if( freeItem != null) |
| 1694 | freeItem.unkeepForCreate(); |
| 1695 | } |
| 1696 | } |
| 1697 | |
| 1698 | } // end of resize; |
| 1699 | |
| 1700 | private synchronized long getCurrentSize() |
| 1701 | { |
| 1702 | if( ! useByteCount) |
| 1703 | return holders.size(); |
| 1704 | return currentByteCount + holders.size()*ITEM_OVERHEAD; |
| 1705 | } |
| 1706 | |
| 1707 | /** |
| 1708 | * Perform an operation on (approximately) all entries that matches the filter, |
| 1709 | * or all entries if the filter is null. Entries that are added while the |
| 1710 | * cache is being scanned might or might not be missed. |
| 1711 | * |
| 1712 | * @param filter |
| 1713 | * @param operator |
| 1714 | */ |
| 1715 | public void scan( Matchable filter, Operator operator) |
| 1716 | { |
| 1717 | int itemCount = 1; |
| 1718 | Cacheable entry = null; |
| 1719 | CachedItem item = null; |
| 1720 | |
| 1721 | // Do not call the operator while holding the synchronization lock. |
| 1722 | // However we cannot access an item's links without holding the synchronization lock, |
| 1723 | // nor can we assume that an item is still in the cache unless we hold the synchronization |
| 1724 | // lock or the item is marked as kept. |
| 1725 | for( int position = 0;; position++) |
| 1726 | { |
| 1727 | synchronized( this) |
| 1728 | { |
| 1729 | if( null != item) |
| 1730 | { |
| 1731 | release( item); |
| 1732 | item = null; |
| 1733 | } |
| 1734 | |
| 1735 | for( ; position < holders.size(); position++) |
| 1736 | { |
| 1737 | item = (CachedItem) holders.get( position); |
| 1738 | if( null != item) |
| 1739 | { |
| 1740 | try |
| 1741 | { |
| 1742 | entry = item.use(); |
| 1743 | } |
| 1744 | catch( StandardException se) |
| 1745 | { |
| 1746 | continue; |
| 1747 | } |
| 1748 | |
| 1749 | if( null != entry && (null == filter || filter.match( entry))) |
| 1750 | { |
| 1751 | item.keepForClean(); |
| 1752 | break; |
| 1753 | } |
| 1754 | } |
| 1755 | } |
| 1756 | if( position >= holders.size()) |
| 1757 | return; |
| 1758 | |
| 1759 | } // end of synchronization |
| 1760 | operator.operate( entry); |
| 1761 | // Do not release the item until we have re-acquired the synchronization lock. |
| 1762 | // Otherwise the item may be removed and its next link invalidated. |
| 1763 | } |
| 1764 | } // end of scan |
| 1765 | |
| 1766 | private int trimRequests = 0; |
| 1767 | |
| 1768 | /* Trim out invalid items from holders if there are a lot of them. This is expensive if |
| 1769 | * holders is large. |
| 1770 | * The caller must hold the cache synchronization lock. |
| 1771 | */ |
| 1772 | private void trimToSize() |
| 1773 | { |
| 1774 | int size = holders.size(); |
| 1775 | |
| 1776 | // Trimming is expensive, don't do it often. |
| 1777 | trimRequests++; |
| 1778 | if( trimRequests < size/8) |
| 1779 | return; |
| 1780 | trimRequests = 0; |
| 1781 | |
| 1782 | // move invalid items to the end. |
| 1783 | int endPosition = size - 1; |
| 1784 | |
| 1785 | int invalidCount = 0; |
| 1786 | for (int i = 0; i <= endPosition; i++) |
| 1787 | { |
| 1788 | CachedItem item = (CachedItem) holders.get(i); |
| 1789 | |
| 1790 | if (item.isKept()) |
| 1791 | continue; |
| 1792 | |
| 1793 | if (item.isValid()) |
| 1794 | continue; |
| 1795 | |
| 1796 | invalidCount++; |
| 1797 | |
| 1798 | // swap with an item later in the list |
| 1799 | // try to keep free items at the end of the holders array. |
| 1800 | for (; endPosition > i; endPosition--) { |
| 1801 | CachedItem last = (CachedItem) holders.get(endPosition); |
| 1802 | if (last.isValid()) { |
| 1803 | holders.set(i, last); |
| 1804 | holders.set(endPosition, item); |
| 1805 | endPosition--; |
| 1806 | break; |
| 1807 | } |
| 1808 | } |
| 1809 | } |
| 1810 | // small cache - don't shrink. |
| 1811 | if (size < 32) |
| 1812 | return; |
| 1813 | |
| 1814 | // now decide if we need to shrink the holder array or not. |
| 1815 | int validItems = size - invalidCount; |
| 1816 | |
| 1817 | // over 75% entries used, don't shrink. |
| 1818 | if (validItems > ((3 * size) / 4)) |
| 1819 | return; |
| 1820 | |
| 1821 | // keep 10% new items. |
| 1822 | int newSize = validItems + (validItems / 10); |
| 1823 | |
| 1824 | if (newSize >= size) |
| 1825 | return; |
| 1826 | |
| 1827 | // remove items, starting at the end, where |
| 1828 | // hopefully most of the free items are. |
| 1829 | for (int r = size - 1; r > newSize; r--) { |
| 1830 | CachedItem remove = (CachedItem) holders.get(r); |
| 1831 | if (remove.isKept() || remove.isValid()) { |
| 1832 | continue; |
| 1833 | } |
| 1834 | |
| 1835 | if (useByteCount) { |
| 1836 | currentByteCount -= getItemSize(remove); |
| 1837 | } |
| 1838 | |
| 1839 | holders.remove(r); |
| 1840 | } |
| 1841 | |
| 1842 | holders.trimToSize(); |
| 1843 | // move the clock hand to the start of the invalid items. |
| 1844 | clockHand = validItems + 1; |
| 1845 | |
| 1846 | } // end of trimToSize |
| 1847 | } |