Marcel Offermans | faaed47 | 2010-09-08 10:07:32 +0000 | [diff] [blame^] | 1 | package org.apache.felix.dm.tracker; |
Marcel Offermans | c854d1a | 2009-11-24 15:41:41 +0000 | [diff] [blame] | 2 | /* |
| 3 | * Copyright (c) OSGi Alliance (2007, 2008). All Rights Reserved. |
| 4 | * |
| 5 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 6 | * you may not use this file except in compliance with the License. |
| 7 | * You may obtain a copy of the License at |
| 8 | * |
| 9 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 10 | * |
| 11 | * Unless required by applicable law or agreed to in writing, software |
| 12 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 13 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 14 | * See the License for the specific language governing permissions and |
| 15 | * limitations under the License. |
| 16 | */ |
| 17 | |
| 18 | import java.util.ArrayList; |
| 19 | import java.util.HashMap; |
| 20 | import java.util.LinkedList; |
| 21 | import java.util.List; |
| 22 | import java.util.Map; |
| 23 | |
| 24 | /** |
| 25 | * Abstract class to track items. If a Tracker is reused (closed then reopened), |
| 26 | * then a new AbstractTracked object is used. This class acts a map of tracked |
| 27 | * item -> customized object. Subclasses of this class will act as the listener |
| 28 | * object for the tracker. This class is used to synchronize access to the |
| 29 | * tracked items. This is not a public class. It is only for use by the |
| 30 | * implementation of the Tracker class. |
| 31 | * |
| 32 | * @ThreadSafe |
| 33 | * @version $Revision: 5871 $ |
| 34 | * @since 1.4 |
| 35 | */ |
| 36 | abstract class AbstractTracked { |
| 37 | /* set this to true to compile in debug messages */ |
| 38 | private static final boolean DEBUG = false; |
| 39 | |
| 40 | /** |
| 41 | * Map of tracked items to customized objects. |
| 42 | * |
| 43 | * @GuardedBy this |
| 44 | */ |
| 45 | private final Map tracked; |
| 46 | |
| 47 | /** |
| 48 | * Modification count. This field is initialized to zero and incremented by |
| 49 | * modified. |
| 50 | * |
| 51 | * @GuardedBy this |
| 52 | */ |
| 53 | private int trackingCount; |
| 54 | |
| 55 | /** |
| 56 | * List of items in the process of being added. This is used to deal with |
| 57 | * nesting of events. Since events may be synchronously delivered, events |
| 58 | * can be nested. For example, when processing the adding of a service and |
| 59 | * the customizer causes the service to be unregistered, notification to the |
| 60 | * nested call to untrack that the service was unregistered can be made to |
| 61 | * the track method. |
| 62 | * |
| 63 | * Since the ArrayList implementation is not synchronized, all access to |
| 64 | * this list must be protected by the same synchronized object for |
| 65 | * thread-safety. |
| 66 | * |
| 67 | * @GuardedBy this |
| 68 | */ |
| 69 | private final List adding; |
| 70 | |
| 71 | /** |
| 72 | * true if the tracked object is closed. |
| 73 | * |
| 74 | * This field is volatile because it is set by one thread and read by |
| 75 | * another. |
| 76 | */ |
| 77 | volatile boolean closed; |
| 78 | |
| 79 | /** |
| 80 | * Initial list of items for the tracker. This is used to correctly process |
| 81 | * the initial items which could be modified before they are tracked. This |
| 82 | * is necessary since the initial set of tracked items are not "announced" |
| 83 | * by events and therefore the event which makes the item untracked could be |
| 84 | * delivered before we track the item. |
| 85 | * |
| 86 | * An item must not be in both the initial and adding lists at the same |
| 87 | * time. An item must be moved from the initial list to the adding list |
| 88 | * "atomically" before we begin tracking it. |
| 89 | * |
| 90 | * Since the LinkedList implementation is not synchronized, all access to |
| 91 | * this list must be protected by the same synchronized object for |
| 92 | * thread-safety. |
| 93 | * |
| 94 | * @GuardedBy this |
| 95 | */ |
| 96 | private final LinkedList initial; |
| 97 | |
| 98 | /** |
| 99 | * AbstractTracked constructor. |
| 100 | */ |
| 101 | AbstractTracked() { |
| 102 | tracked = new HashMap(); |
| 103 | trackingCount = 0; |
| 104 | adding = new ArrayList(6); |
| 105 | initial = new LinkedList(); |
| 106 | closed = false; |
| 107 | } |
| 108 | |
| 109 | /** |
| 110 | * Set initial list of items into tracker before events begin to be |
| 111 | * received. |
| 112 | * |
| 113 | * This method must be called from Tracker's open method while synchronized |
| 114 | * on this object in the same synchronized block as the add listener call. |
| 115 | * |
| 116 | * @param list The initial list of items to be tracked. <code>null</code> |
| 117 | * entries in the list are ignored. |
| 118 | * @GuardedBy this |
| 119 | */ |
| 120 | void setInitial(Object[] list) { |
| 121 | if (list == null) { |
| 122 | return; |
| 123 | } |
| 124 | int size = list.length; |
| 125 | for (int i = 0; i < size; i++) { |
| 126 | Object item = list[i]; |
| 127 | if (item == null) { |
| 128 | continue; |
| 129 | } |
| 130 | if (DEBUG) { |
| 131 | System.out.println("AbstractTracked.setInitial: " + item); //$NON-NLS-1$ |
| 132 | } |
| 133 | initial.add(item); |
| 134 | } |
| 135 | } |
| 136 | |
| 137 | /** |
| 138 | * Track the initial list of items. This is called after events can begin to |
| 139 | * be received. |
| 140 | * |
| 141 | * This method must be called from Tracker's open method while not |
| 142 | * synchronized on this object after the add listener call. |
| 143 | * |
| 144 | */ |
| 145 | void trackInitial() { |
| 146 | while (true) { |
| 147 | Object item; |
| 148 | synchronized (this) { |
| 149 | if (closed || (initial.size() == 0)) { |
| 150 | /* |
| 151 | * if there are no more initial items |
| 152 | */ |
| 153 | return; /* we are done */ |
| 154 | } |
| 155 | /* |
| 156 | * move the first item from the initial list to the adding list |
| 157 | * within this synchronized block. |
| 158 | */ |
| 159 | item = initial.removeFirst(); |
| 160 | if (tracked.get(item) != null) { |
| 161 | /* if we are already tracking this item */ |
| 162 | if (DEBUG) { |
| 163 | System.out |
| 164 | .println("AbstractTracked.trackInitial[already tracked]: " + item); //$NON-NLS-1$ |
| 165 | } |
| 166 | continue; /* skip this item */ |
| 167 | } |
| 168 | if (adding.contains(item)) { |
| 169 | /* |
| 170 | * if this item is already in the process of being added. |
| 171 | */ |
| 172 | if (DEBUG) { |
| 173 | System.out |
| 174 | .println("AbstractTracked.trackInitial[already adding]: " + item); //$NON-NLS-1$ |
| 175 | } |
| 176 | continue; /* skip this item */ |
| 177 | } |
| 178 | adding.add(item); |
| 179 | } |
| 180 | if (DEBUG) { |
| 181 | System.out.println("AbstractTracked.trackInitial: " + item); //$NON-NLS-1$ |
| 182 | } |
| 183 | trackAdding(item, null); /* |
| 184 | * Begin tracking it. We call trackAdding |
| 185 | * since we have already put the item in the |
| 186 | * adding list. |
| 187 | */ |
| 188 | } |
| 189 | } |
| 190 | |
| 191 | /** |
| 192 | * Called by the owning Tracker object when it is closed. |
| 193 | */ |
| 194 | void close() { |
| 195 | closed = true; |
| 196 | } |
| 197 | |
| 198 | /** |
| 199 | * Begin to track an item. |
| 200 | * |
| 201 | * @param item Item to be tracked. |
| 202 | * @param related Action related object. |
| 203 | */ |
| 204 | void track(final Object item, final Object related) { |
| 205 | final Object object; |
| 206 | synchronized (this) { |
| 207 | if (closed) { |
| 208 | return; |
| 209 | } |
| 210 | object = tracked.get(item); |
| 211 | if (object == null) { /* we are not tracking the item */ |
| 212 | if (adding.contains(item)) { |
| 213 | /* if this item is already in the process of being added. */ |
| 214 | if (DEBUG) { |
| 215 | System.out |
| 216 | .println("AbstractTracked.track[already adding]: " + item); //$NON-NLS-1$ |
| 217 | } |
| 218 | return; |
| 219 | } |
| 220 | adding.add(item); /* mark this item is being added */ |
| 221 | } |
| 222 | else { /* we are currently tracking this item */ |
| 223 | if (DEBUG) { |
| 224 | System.out |
| 225 | .println("AbstractTracked.track[modified]: " + item); //$NON-NLS-1$ |
| 226 | } |
| 227 | modified(); /* increment modification count */ |
| 228 | } |
| 229 | } |
| 230 | |
| 231 | if (object == null) { /* we are not tracking the item */ |
| 232 | trackAdding(item, related); |
| 233 | } |
| 234 | else { |
| 235 | /* Call customizer outside of synchronized region */ |
| 236 | customizerModified(item, related, object); |
| 237 | /* |
| 238 | * If the customizer throws an unchecked exception, it is safe to |
| 239 | * let it propagate |
| 240 | */ |
| 241 | } |
| 242 | } |
| 243 | |
| 244 | /** |
| 245 | * Common logic to add an item to the tracker used by track and |
| 246 | * trackInitial. The specified item must have been placed in the adding list |
| 247 | * before calling this method. |
| 248 | * |
| 249 | * @param item Item to be tracked. |
| 250 | * @param related Action related object. |
| 251 | */ |
| 252 | private void trackAdding(final Object item, final Object related) { |
| 253 | if (DEBUG) { |
| 254 | System.out.println("AbstractTracked.trackAdding: " + item); //$NON-NLS-1$ |
| 255 | } |
| 256 | Object object = null; |
| 257 | boolean becameUntracked = false; |
| 258 | /* Call customizer outside of synchronized region */ |
| 259 | try { |
| 260 | object = customizerAdding(item, related); |
| 261 | /* |
| 262 | * If the customizer throws an unchecked exception, it will |
| 263 | * propagate after the finally |
| 264 | */ |
| 265 | } |
| 266 | finally { |
| 267 | boolean needToCallback = false; |
| 268 | synchronized (this) { |
| 269 | if (adding.remove(item) && !closed) { |
| 270 | /* |
| 271 | * if the item was not untracked during the customizer |
| 272 | * callback |
| 273 | */ |
| 274 | if (object != null) { |
| 275 | tracked.put(item, object); |
| 276 | modified(); /* increment modification count */ |
| 277 | notifyAll(); /* notify any waiters */ |
| 278 | needToCallback = true; /* marrs: invoke added callback */ |
| 279 | } |
| 280 | } |
| 281 | else { |
| 282 | becameUntracked = true; |
| 283 | } |
| 284 | } |
| 285 | if (needToCallback) { |
| 286 | customizerAdded(item, related, object); |
| 287 | } |
| 288 | } |
| 289 | /* |
| 290 | * The item became untracked during the customizer callback. |
| 291 | */ |
| 292 | if (becameUntracked && (object != null)) { |
| 293 | if (DEBUG) { |
| 294 | System.out |
| 295 | .println("AbstractTracked.trackAdding[removed]: " + item); //$NON-NLS-1$ |
| 296 | } |
| 297 | /* Call customizer outside of synchronized region */ |
| 298 | customizerRemoved(item, related, object); |
| 299 | /* |
| 300 | * If the customizer throws an unchecked exception, it is safe to |
| 301 | * let it propagate |
| 302 | */ |
| 303 | } |
| 304 | } |
| 305 | |
| 306 | /** |
| 307 | * Discontinue tracking the item. |
| 308 | * |
| 309 | * @param item Item to be untracked. |
| 310 | * @param related Action related object. |
| 311 | */ |
| 312 | void untrack(final Object item, final Object related) { |
| 313 | final Object object; |
| 314 | synchronized (this) { |
| 315 | if (initial.remove(item)) { /* |
| 316 | * if this item is already in the list |
| 317 | * of initial references to process |
| 318 | */ |
| 319 | if (DEBUG) { |
| 320 | System.out |
| 321 | .println("AbstractTracked.untrack[removed from initial]: " + item); //$NON-NLS-1$ |
| 322 | } |
| 323 | return; /* |
| 324 | * we have removed it from the list and it will not be |
| 325 | * processed |
| 326 | */ |
| 327 | } |
| 328 | |
| 329 | if (adding.remove(item)) { /* |
| 330 | * if the item is in the process of |
| 331 | * being added |
| 332 | */ |
| 333 | if (DEBUG) { |
| 334 | System.out |
| 335 | .println("AbstractTracked.untrack[being added]: " + item); //$NON-NLS-1$ |
| 336 | } |
| 337 | return; /* |
| 338 | * in case the item is untracked while in the process of |
| 339 | * adding |
| 340 | */ |
| 341 | } |
| 342 | object = tracked.remove(item); /* |
| 343 | * must remove from tracker before |
| 344 | * calling customizer callback |
| 345 | */ |
| 346 | if (object == null) { /* are we actually tracking the item */ |
| 347 | return; |
| 348 | } |
| 349 | modified(); /* increment modification count */ |
| 350 | } |
| 351 | if (DEBUG) { |
| 352 | System.out.println("AbstractTracked.untrack[removed]: " + item); //$NON-NLS-1$ |
| 353 | } |
| 354 | /* Call customizer outside of synchronized region */ |
| 355 | customizerRemoved(item, related, object); |
| 356 | /* |
| 357 | * If the customizer throws an unchecked exception, it is safe to let it |
| 358 | * propagate |
| 359 | */ |
| 360 | } |
| 361 | |
| 362 | /** |
| 363 | * Returns the number of tracked items. |
| 364 | * |
| 365 | * @return The number of tracked items. |
| 366 | * |
| 367 | * @GuardedBy this |
| 368 | */ |
| 369 | int size() { |
| 370 | return tracked.size(); |
| 371 | } |
| 372 | |
| 373 | /** |
| 374 | * Return the customized object for the specified item |
| 375 | * |
| 376 | * @param item The item to lookup in the map |
| 377 | * @return The customized object for the specified item. |
| 378 | * |
| 379 | * @GuardedBy this |
| 380 | */ |
| 381 | Object getCustomizedObject(final Object item) { |
| 382 | return tracked.get(item); |
| 383 | } |
| 384 | |
| 385 | /** |
| 386 | * Return the list of tracked items. |
| 387 | * |
| 388 | * @param list An array to contain the tracked items. |
| 389 | * @return The specified list if it is large enough to hold the tracked |
| 390 | * items or a new array large enough to hold the tracked items. |
| 391 | * @GuardedBy this |
| 392 | */ |
| 393 | Object[] getTracked(final Object[] list) { |
| 394 | return tracked.keySet().toArray(list); |
| 395 | } |
| 396 | |
| 397 | /** |
| 398 | * Increment the modification count. If this method is overridden, the |
| 399 | * overriding method MUST call this method to increment the tracking count. |
| 400 | * |
| 401 | * @GuardedBy this |
| 402 | */ |
| 403 | void modified() { |
| 404 | trackingCount++; |
| 405 | } |
| 406 | |
| 407 | /** |
| 408 | * Returns the tracking count for this <code>ServiceTracker</code> object. |
| 409 | * |
| 410 | * The tracking count is initialized to 0 when this object is opened. Every |
| 411 | * time an item is added, modified or removed from this object the tracking |
| 412 | * count is incremented. |
| 413 | * |
| 414 | * @GuardedBy this |
| 415 | * @return The tracking count for this object. |
| 416 | */ |
| 417 | int getTrackingCount() { |
| 418 | return trackingCount; |
| 419 | } |
| 420 | |
| 421 | /** |
| 422 | * Call the specific customizer adding method. This method must not be |
| 423 | * called while synchronized on this object. |
| 424 | * |
| 425 | * @param item Item to be tracked. |
| 426 | * @param related Action related object. |
| 427 | * @return Customized object for the tracked item or <code>null</code> if |
| 428 | * the item is not to be tracked. |
| 429 | */ |
| 430 | abstract Object customizerAdding(final Object item, final Object related); |
| 431 | |
| 432 | /** marrs: Call the specific customizer added method. */ |
| 433 | abstract void customizerAdded(final Object item, final Object related, final Object object); |
| 434 | |
| 435 | /** |
| 436 | * Call the specific customizer modified method. This method must not be |
| 437 | * called while synchronized on this object. |
| 438 | * |
| 439 | * @param item Tracked item. |
| 440 | * @param related Action related object. |
| 441 | * @param object Customized object for the tracked item. |
| 442 | */ |
| 443 | abstract void customizerModified(final Object item, final Object related, |
| 444 | final Object object); |
| 445 | |
| 446 | /** |
| 447 | * Call the specific customizer removed method. This method must not be |
| 448 | * called while synchronized on this object. |
| 449 | * |
| 450 | * @param item Tracked item. |
| 451 | * @param related Action related object. |
| 452 | * @param object Customized object for the tracked item. |
| 453 | */ |
| 454 | abstract void customizerRemoved(final Object item, final Object related, |
| 455 | final Object object); |
| 456 | } |