File: SyncCollection.java

package info (click to toggle)
concurrent-dfsg 1.3.4-4
  • links: PTS, VCS
  • area: main
  • in suites: buster, jessie, jessie-kfreebsd, squeeze, stretch, wheezy
  • size: 976 kB
  • ctags: 2,018
  • sloc: java: 10,704; xml: 49; makefile: 12
file content (509 lines) | stat: -rw-r--r-- 13,812 bytes parent folder | download | duplicates (3)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
/*
  File: SyncCollection.java

  Originally written by Doug Lea and released into the public domain.
  This may be used for any purposes whatsoever without acknowledgment.
  Thanks for the assistance and support of Sun Microsystems Labs,
  and everyone contributing, testing, and using this code.

  History:
  Date       Who                What
   1Aug1998  dl               Create public version
*/

package EDU.oswego.cs.dl.util.concurrent;
import java.util.*;

/**
 * SyncCollections wrap Sync-based control around java.util.Collections.
 * They are similar in operation to those provided
 * by java.util.Collection.synchronizedCollection, but have
 * several extended capabilities.
 * <p>
 * The Collection interface is conceptually broken into two
 * parts for purposes of synchronization control. The  purely inspective
 * reader operations are:
 * <ul>
 *  <li> size
 *  <li> isEmpty
 *  <li> toArray
 *  <li> contains
 *  <li> containsAll
 *  <li> iterator
 * </ul>
 * The possibly mutative writer operations (which are also
 * the set of operations that are allowed to throw 
 * UnsupportedOperationException) are:
 * <ul>
 *  <li> add
 *  <li> addAll
 *  <li> remove
 *  <li> clear
 *  <li> removeAll
 *  <li> retainAll
 * </ul>
 *  
 * <p>
 * SyncCollections can be used with either Syncs or ReadWriteLocks.
 * When used with
 * single Syncs, the same lock is used as both the reader and writer lock.
 * The SyncCollection class cannot itself guarantee that using
 * a pair of read/write locks will always correctly protect objects, since
 * Collection implementations are not precluded from internally
 * performing hidden unprotected state changes within conceptually read-only
 * operations. However, they do work with current java.util implementations.
 * (Hopefully, implementations that do not provide this natural
 * guarantee will be clearly documentented as such.)
 * <p>
 * This class provides a straight implementation of Collections interface.
 * In order to conform to this interface, sync failures
 * due to interruption do NOT result in InterruptedExceptions. 
 * Instead, upon detection of interruption, 
 * <ul>
 *  <li> All mutative operations convert the interruption to
 *    an UnsupportedOperationException, while also propagating
 *    the interrupt status of the thread. Thus, unlike normal
 *    java.util.Collections, SyncCollections can <em>transiently</em>
 *    behave as if mutative operations are not supported.
 *  <li> All read-only operations 
 *     attempt to return a result even upon interruption. In some contexts,
 *     such results will be meaningless due to interference, but 
 *     provide best-effort status indications that can be useful during
 *     recovery. The cumulative number of synchronization failures encountered
 *     during such operations is accessible using method 
 *     <code>synchronizationFailures()</code>.  
 *     Non-zero values may indicate serious program errors.
 * </ul>
 * <p>
 * The iterator() method returns a SyncCollectionIterator with 
 * properties and methods that are analogous to those of SyncCollection
 * itself: hasNext and next are read-only, and remove is mutative.
 * These methods allow fine-grained controlled access, but do <em>NOT</em>
 * preclude concurrent modifications from being interleaved with traversals,
 * which may lead to ConcurrentModificationExceptions.
 * However, the class also supports method <code>unprotectedIterator</code>
 * that can be used in conjunction with the <code>readerSync</code> or
 * <code>writerSync</code> methods to perform locked traversals. For example,
 * to protect a block of reads:
 * <pre>
 *    Sync lock = coll.readerSync();
 *    try {
 *      lock.acquire();
 *      try {
 *        Iterator it = coll.unprotectedIterator();
 *        while (it.hasNext()) 
 *          System.out.println(it.next());
 *      }
 *      finally {
 *        lock.release();
 *      }
 *   }
 *   catch (InterruptedException ex) { ... }
 * </pre>
 * If you need to protect blocks of writes, you must use some
 * form of <em>reentrant</em> lock (for example <code>ReentrantLock</code>
 * or <code>ReentrantWriterPreferenceReadWriteLock</code>) as the Sync 
 * for the collection in order to allow mutative methods to proceed
 * while the current thread holds the lock. For example, you might
 * need to hold a write lock during an initialization sequence:
 * <pre>
 *   Collection c = new SyncCollection(new ArrayList(), 
 *                                     new ReentrantWriterPreferenceReadWriteLock());
 *   // ...
 *   c.writeLock().acquire();
 *   try {
 *     for (...) {
 *       Object x = someStream.readObject();
 *       c.add(x); // would block if writeLock not reentrant
 *     }
 *   }
 *   catch (IOException iox) {
 *     ...
 *   }
 *   finally {
 *     c.writeLock().release();
 *   }
 *   catch (InterruptedException ex) { ... }
 * </pre>
 * <p>
 * (It would normally be better practice here to not make the
 * collection accessible until initialization is complete.)
 * <p>
 * This class does not specifically support use of
 * timed synchronization through the attempt method. However,
 * you can obtain this effect via
 * the TimeoutSync class. For example:
 * <pre>
 * Mutex lock = new Mutex();
 * TimeoutSync timedLock = new TimeoutSync(lock, 1000); // 1 sec timeouts
 * Collection c = new SyncCollection(new HashSet(), timedlock);
 * </pre>
 * <p>
 * The same can be done with read-write locks:
 * <pre>
 * ReadWriteLock rwl = new WriterPreferenceReadWriteLock();
 * Sync rlock = new TimeoutSync(rwl.readLock(), 100);
 * Sync wlock = new TimeoutSync(rwl.writeLock(), 100);
 * Collection c = new SyncCollection(new HashSet(), rlock, wlock);
 * </pre>
 * <p>
 * In addition to synchronization control, SyncCollections
 * may be useful in any context requiring before/after methods
 * surrounding collections. For example, you can use ObservableSync
 * to arrange notifications on method calls to collections, as in:
 * <pre>
 * class X {
 *   Collection c;
 *
 *   static class CollectionObserver implements ObservableSync.SyncObserver {
 *     public void onAcquire(Object arg) {
 *       Collection coll = (Collection) arg;
 *       System.out.println("Starting operation on" + coll);
 *       // Other plausible responses include performing integrity
 *       //   checks on the collection, updating displays, etc
 *     }
 *     public void onRelease(Object arg) {
 *       Collection coll = (Collection) arg;
 *       System.out.println("Finished operation on" + coll);
 *     }
 *   }
 *
 *   X() {
 *     ObservableSync s = new ObservableSync();
 *     c = new SyncCollection(new HashSet(), s);
 *     s.setNotificationArgument(c);
 *     CollectionObserver obs = new CollectionObserver();
 *     s.attach(obs);
 *   }
 *   ...
 * }
 * </pre>
 *
 * <p>[<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>]
 * @see LayeredSync
 * @see TimeoutSync
**/


public class SyncCollection implements Collection {
  protected final Collection c_;	   // Backing Collection
  protected final Sync rd_;  //  sync for read-only methods
  protected final Sync wr_;  //  sync for mutative methods

  protected final SynchronizedLong syncFailures_ = new SynchronizedLong(0);

  /**
   * Create a new SyncCollection protecting the given collection,
   * and using the given sync to control both reader and writer methods.
   * Common, reasonable choices for the sync argument include
   * Mutex, ReentrantLock, and Semaphores initialized to 1.
   * <p>
   * <b>Sample Usage</b>
   * <pre>
   * Collection c = new SyncCollection(new ArrayList(), new Mutex()); 
   * </pre>
   **/
  public SyncCollection(Collection collection, Sync sync) {
    this (collection, sync, sync);
  }


  /**
   * Create a new SyncCollection protecting the given collection,
   * and using the given ReadWriteLock to control reader and writer methods.
   * <p>
   * <b>Sample Usage</b>
   * <pre>
   * Collection c = new SyncCollection(new HashSet(), 
   *                                   new WriterPreferenceReadWriteLock());
   * </pre>
   **/
  public SyncCollection(Collection collection, ReadWriteLock rwl) {
    this (collection, rwl.readLock(), rwl.writeLock());
  }

  /**
   * Create a new SyncCollection protecting the given collection,
   * and using the given pair of locks to control reader and writer methods.
   **/
  public SyncCollection(Collection collection, Sync readLock, Sync writeLock) {
    c_ = collection; 
    rd_ = readLock;
    wr_ = writeLock;
  }

  /** 
   * Return the Sync object managing read-only operations
   **/
      
  public Sync readerSync() {
    return rd_;
  }

  /** 
   * Return the Sync object managing mutative operations
   **/

  public Sync writerSync() {
    return wr_;
  }

  /**
   * Return the number of synchronization failures for read-only operations
   **/
  public long syncFailures() {
    return syncFailures_.get();
  }


  /** Try to acquire sync before a reader operation; record failure **/
  protected boolean beforeRead() {
    try {
      rd_.acquire();
      return false;
    }
    catch (InterruptedException ex) { 
      syncFailures_.increment();
      return true; 
    }
  }

  /** Clean up after a reader operation **/
  protected void afterRead(boolean wasInterrupted) {
    if (wasInterrupted) {
      Thread.currentThread().interrupt();
    }
    else
      rd_.release();
  }



  public int size() {
    boolean wasInterrupted = beforeRead();
    try {
      return c_.size();
    }
    finally {
      afterRead(wasInterrupted);
    }
  }

  public boolean isEmpty() {
    boolean wasInterrupted = beforeRead();
    try {
      return c_.isEmpty();
    }
    finally {
      afterRead(wasInterrupted);
    }
  }

  public boolean contains(Object o) {
    boolean wasInterrupted = beforeRead();
    try {
      return c_.contains(o);
    }
    finally {
      afterRead(wasInterrupted);
    }
  }

  public Object[] toArray() {
    boolean wasInterrupted = beforeRead();
    try {
      return c_.toArray();
    }
    finally {
      afterRead(wasInterrupted);
    }
  }

  public Object[] toArray(Object[] a) {
    boolean wasInterrupted = beforeRead();
    try {
      return c_.toArray(a);
    }
    finally {
      afterRead(wasInterrupted);
    }
  }

  public boolean containsAll(Collection coll) {
    boolean wasInterrupted = beforeRead();
    try {
      return c_.containsAll(coll);
    }
    finally {
      afterRead(wasInterrupted);
    }
  }


  public boolean add(Object o) {
    try {
      wr_.acquire();
      try {
        return c_.add(o);
      }
      finally {
        wr_.release();
      }
    }
    catch (InterruptedException ex) {
      Thread.currentThread().interrupt();
      throw new UnsupportedOperationException();
    }
  }

  public boolean remove(Object o) {
    try {
      wr_.acquire();
      try {
        return c_.remove(o);
      }
      finally {
        wr_.release();
      }
    }
    catch (InterruptedException ex) {
      Thread.currentThread().interrupt();
      throw new UnsupportedOperationException();
    }
  }

  public boolean addAll(Collection coll) {
    try {
      wr_.acquire();
      try {
        return c_.addAll(coll);
      }
      finally {
        wr_.release();
      }
    }
    catch (InterruptedException ex) {
      Thread.currentThread().interrupt();
      throw new UnsupportedOperationException();
    }
  }

  public boolean removeAll(Collection coll) {
    try {
      wr_.acquire();
      try {
        return c_.removeAll(coll);
      }
      finally {
        wr_.release();
      }
    }
    catch (InterruptedException ex) {
      Thread.currentThread().interrupt();
      throw new UnsupportedOperationException();
    }
  }


  public boolean retainAll(Collection coll) {
    try {
      wr_.acquire();
      try {
        return c_.retainAll(coll);
      }
      finally {
        wr_.release();
      }
    }
    catch (InterruptedException ex) {
      Thread.currentThread().interrupt();
      throw new UnsupportedOperationException();
    }
  }

	
  public void clear() {
    try {
      wr_.acquire();
      try {
        c_.clear();
      }
      finally {
        wr_.release();
      }
    }
    catch (InterruptedException ex) {
      Thread.currentThread().interrupt();
      throw new UnsupportedOperationException();
    }
  }


  /** Return the base iterator of the underlying collection **/
  public Iterator unprotectedIterator() {
    boolean wasInterrupted = beforeRead();
    try {
      return c_.iterator(); 
    }
    finally {
      afterRead(wasInterrupted);
    }
  }

  public Iterator iterator() {
    boolean wasInterrupted = beforeRead();
    try {
      return new SyncCollectionIterator(c_.iterator()); 
    }
    finally {
      afterRead(wasInterrupted);
    }
  }

  public class SyncCollectionIterator implements Iterator {
    protected final Iterator baseIterator_;

    SyncCollectionIterator(Iterator baseIterator) {
      baseIterator_ = baseIterator;
    }

    public boolean hasNext() {
      boolean wasInterrupted = beforeRead();
      try {
        return baseIterator_.hasNext();
      }
      finally {
        afterRead(wasInterrupted);
      }
    }

    public Object next() {
      boolean wasInterrupted = beforeRead();
      try {
        return baseIterator_.next();
      }
      finally {
        afterRead(wasInterrupted);
      }
    }

    public void remove() {
      try {
        wr_.acquire();
        try {
           baseIterator_.remove();
        }
        finally {
          wr_.release();
        }
      }
      catch (InterruptedException ex) {
        Thread.currentThread().interrupt();
        throw new UnsupportedOperationException();
      }
    }

  }
}