summaryrefslogtreecommitdiffstats
path: root/mfbt/LinkedList.h
blob: a099d7597a4be8d4de60a975c7bf45bea413412f (plain)
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
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/* A type-safe doubly-linked list class. */

/*
 * The classes LinkedList<T> and LinkedListElement<T> together form a
 * convenient, type-safe doubly-linked list implementation.
 *
 * The class T which will be inserted into the linked list must inherit from
 * LinkedListElement<T>.  A given object may be in only one linked list at a
 * time.
 *
 * A LinkedListElement automatically removes itself from the list upon
 * destruction, and a LinkedList will fatally assert in debug builds if it's
 * non-empty when it's destructed.
 *
 * For example, you might use LinkedList in a simple observer list class as
 * follows.
 *
 *   class Observer : public LinkedListElement<Observer>
 *   {
 *   public:
 *     void observe(char* aTopic) { ... }
 *   };
 *
 *   class ObserverContainer
 *   {
 *   private:
 *     LinkedList<Observer> list;
 *
 *   public:
 *     void addObserver(Observer* aObserver)
 *     {
 *       // Will assert if |aObserver| is part of another list.
 *       list.insertBack(aObserver);
 *     }
 *
 *     void removeObserver(Observer* aObserver)
 *     {
 *       // Will assert if |aObserver| is not part of some list.
 *       aObserver.remove();
 *       // Or, will assert if |aObserver| is not part of |list| specifically.
 *       // aObserver.removeFrom(list);
 *     }
 *
 *     void notifyObservers(char* aTopic)
 *     {
 *       for (Observer* o = list.getFirst(); o != nullptr; o = o->getNext()) {
 *         o->observe(aTopic);
 *       }
 *     }
 *   };
 *
 * Additionally, the class AutoCleanLinkedList<T> is a LinkedList<T> that will
 * remove and delete each element still within itself upon destruction. Note
 * that because each element is deleted, elements must have been allocated
 * using |new|.
 */

#ifndef mozilla_LinkedList_h
#define mozilla_LinkedList_h

#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/Move.h"
#include "mozilla/RefPtr.h"

#ifdef __cplusplus

namespace mozilla {

template<typename T>
class LinkedListElement;

namespace detail {

/**
 * LinkedList supports refcounted elements using this adapter class. Clients
 * using LinkedList<RefPtr<T>> will get a data structure that holds a strong
 * reference to T as long as T is in the list.
 */
template<typename T>
struct LinkedListElementTraits
{
  typedef T* RawType;
  typedef const T* ConstRawType;
  typedef T* ClientType;
  typedef const T* ConstClientType;

  // These static methods are called when an element is added to or removed from
  // a linked list. It can be used to keep track ownership in lists that are
  // supposed to own their elements. If elements are transferred from one list
  // to another, no enter or exit calls happen since the elements still belong
  // to a list.
  static void enterList(LinkedListElement<T>* elt) {}
  static void exitList(LinkedListElement<T>* elt) {}
};

template<typename T>
struct LinkedListElementTraits<RefPtr<T>>
{
  typedef T* RawType;
  typedef const T* ConstRawType;
  typedef RefPtr<T> ClientType;
  typedef RefPtr<const T> ConstClientType;

  static void enterList(LinkedListElement<RefPtr<T>>* elt) { elt->asT()->AddRef(); }
  static void exitList(LinkedListElement<RefPtr<T>>* elt) { elt->asT()->Release(); }
};

} /* namespace detail */

template<typename T>
class LinkedList;

template<typename T>
class LinkedListElement
{
  typedef typename detail::LinkedListElementTraits<T> Traits;
  typedef typename Traits::RawType RawType;
  typedef typename Traits::ConstRawType ConstRawType;
  typedef typename Traits::ClientType ClientType;
  typedef typename Traits::ConstClientType ConstClientType;

  /*
   * It's convenient that we return nullptr when getNext() or getPrevious()
   * hits the end of the list, but doing so costs an extra word of storage in
   * each linked list node (to keep track of whether |this| is the sentinel
   * node) and a branch on this value in getNext/getPrevious.
   *
   * We could get rid of the extra word of storage by shoving the "is
   * sentinel" bit into one of the pointers, although this would, of course,
   * have performance implications of its own.
   *
   * But the goal here isn't to win an award for the fastest or slimmest
   * linked list; rather, we want a *convenient* linked list.  So we won't
   * waste time guessing which micro-optimization strategy is best.
   *
   *
   * Speaking of unnecessary work, it's worth addressing here why we wrote
   * mozilla::LinkedList in the first place, instead of using stl::list.
   *
   * The key difference between mozilla::LinkedList and stl::list is that
   * mozilla::LinkedList stores the mPrev/mNext pointers in the object itself,
   * while stl::list stores the mPrev/mNext pointers in a list element which
   * itself points to the object being stored.
   *
   * mozilla::LinkedList's approach makes it harder to store an object in more
   * than one list.  But the upside is that you can call next() / prev() /
   * remove() directly on the object.  With stl::list, you'd need to store a
   * pointer to its iterator in the object in order to accomplish this.  Not
   * only would this waste space, but you'd have to remember to update that
   * pointer every time you added or removed the object from a list.
   *
   * In-place, constant-time removal is a killer feature of doubly-linked
   * lists, and supporting this painlessly was a key design criterion.
   */

private:
  LinkedListElement* mNext;
  LinkedListElement* mPrev;
  const bool mIsSentinel;

public:
  LinkedListElement()
    : mNext(this),
      mPrev(this),
      mIsSentinel(false)
  { }

  /*
   * Moves |aOther| into |*this|. If |aOther| is already in a list, then
   * |aOther| is removed from the list and replaced by |*this|.
   */
  LinkedListElement(LinkedListElement<T>&& aOther)
    : mIsSentinel(aOther.mIsSentinel)
  {
    adjustLinkForMove(Move(aOther));
  }

  LinkedListElement& operator=(LinkedListElement<T>&& aOther)
  {
    MOZ_ASSERT(mIsSentinel == aOther.mIsSentinel, "Mismatch NodeKind!");
    MOZ_ASSERT(!isInList(),
               "Assigning to an element in a list messes up that list!");
    adjustLinkForMove(Move(aOther));
    return *this;
  }

  ~LinkedListElement()
  {
    if (!mIsSentinel && isInList()) {
      remove();
    }
  }

  /*
   * Get the next element in the list, or nullptr if this is the last element
   * in the list.
   */
  RawType getNext()            { return mNext->asT(); }
  ConstRawType getNext() const { return mNext->asT(); }

  /*
   * Get the previous element in the list, or nullptr if this is the first
   * element in the list.
   */
  RawType getPrevious()            { return mPrev->asT(); }
  ConstRawType getPrevious() const { return mPrev->asT(); }

  /*
   * Insert aElem after this element in the list.  |this| must be part of a
   * linked list when you call setNext(); otherwise, this method will assert.
   */
  void setNext(RawType aElem)
  {
    MOZ_ASSERT(isInList());
    setNextUnsafe(aElem);
  }

  /*
   * Insert aElem before this element in the list.  |this| must be part of a
   * linked list when you call setPrevious(); otherwise, this method will
   * assert.
   */
  void setPrevious(RawType aElem)
  {
    MOZ_ASSERT(isInList());
    setPreviousUnsafe(aElem);
  }

  /*
   * Remove this element from the list which contains it.  If this element is
   * not currently part of a linked list, this method asserts.
   */
  void remove()
  {
    MOZ_ASSERT(isInList());

    mPrev->mNext = mNext;
    mNext->mPrev = mPrev;
    mNext = this;
    mPrev = this;

    Traits::exitList(this);
  }

  /*
   * Remove this element from the list containing it.  Returns a pointer to the
   * element that follows this element (before it was removed).  This method
   * asserts if the element does not belong to a list.
   */
  ClientType removeAndGetNext()
  {
    ClientType r = getNext();
    remove();
    return r;
  }

  /*
   * Remove this element from the list containing it.  Returns a pointer to the
   * previous element in the containing list (before the removal).  This method
   * asserts if the element does not belong to a list.
   */
  ClientType removeAndGetPrevious()
  {
    ClientType r = getPrevious();
    remove();
    return r;
  }

  /*
   * Identical to remove(), but also asserts in debug builds that this element
   * is in aList.
   */
  void removeFrom(const LinkedList<T>& aList)
  {
    aList.assertContains(asT());
    remove();
  }

  /*
   * Return true if |this| part is of a linked list, and false otherwise.
   */
  bool isInList() const
  {
    MOZ_ASSERT((mNext == this) == (mPrev == this));
    return mNext != this;
  }

private:
  friend class LinkedList<T>;
  friend struct detail::LinkedListElementTraits<T>;

  enum class NodeKind {
    Normal,
    Sentinel
  };

  explicit LinkedListElement(NodeKind nodeKind)
    : mNext(this),
      mPrev(this),
      mIsSentinel(nodeKind == NodeKind::Sentinel)
  { }

  /*
   * Return |this| cast to T* if we're a normal node, or return nullptr if
   * we're a sentinel node.
   */
  RawType asT()
  {
    return mIsSentinel ? nullptr : static_cast<RawType>(this);
  }
  ConstRawType asT() const
  {
    return mIsSentinel ? nullptr : static_cast<ConstRawType>(this);
  }

  /*
   * Insert aElem after this element, but don't check that this element is in
   * the list.  This is called by LinkedList::insertFront().
   */
  void setNextUnsafe(RawType aElem)
  {
    LinkedListElement *listElem = static_cast<LinkedListElement*>(aElem);
    MOZ_ASSERT(!listElem->isInList());

    listElem->mNext = this->mNext;
    listElem->mPrev = this;
    this->mNext->mPrev = listElem;
    this->mNext = listElem;

    Traits::enterList(aElem);
  }

  /*
   * Insert aElem before this element, but don't check that this element is in
   * the list.  This is called by LinkedList::insertBack().
   */
  void setPreviousUnsafe(RawType aElem)
  {
    LinkedListElement<T>* listElem = static_cast<LinkedListElement<T>*>(aElem);
    MOZ_ASSERT(!listElem->isInList());

    listElem->mNext = this;
    listElem->mPrev = this->mPrev;
    this->mPrev->mNext = listElem;
    this->mPrev = listElem;

    Traits::enterList(aElem);
  }

  /*
   * Adjust mNext and mPrev for implementing move constructor and move
   * assignment.
   */
  void adjustLinkForMove(LinkedListElement<T>&& aOther)
  {
    if (!aOther.isInList()) {
      mNext = this;
      mPrev = this;
      return;
    }

    if (!mIsSentinel) {
      Traits::enterList(this);
    }

    MOZ_ASSERT(aOther.mNext->mPrev == &aOther);
    MOZ_ASSERT(aOther.mPrev->mNext == &aOther);

    /*
     * Initialize |this| with |aOther|'s mPrev/mNext pointers, and adjust those
     * element to point to this one.
     */
    mNext = aOther.mNext;
    mPrev = aOther.mPrev;

    mNext->mPrev = this;
    mPrev->mNext = this;

    /*
     * Adjust |aOther| so it doesn't think it's in a list.  This makes it
     * safely destructable.
     */
    aOther.mNext = &aOther;
    aOther.mPrev = &aOther;

    if (!mIsSentinel) {
      Traits::exitList(&aOther);
    }
  }

  LinkedListElement& operator=(const LinkedListElement<T>& aOther) = delete;
  LinkedListElement(const LinkedListElement<T>& aOther) = delete;
};

template<typename T>
class LinkedList
{
private:
  typedef typename detail::LinkedListElementTraits<T> Traits;
  typedef typename Traits::RawType RawType;
  typedef typename Traits::ConstRawType ConstRawType;
  typedef typename Traits::ClientType ClientType;
  typedef typename Traits::ConstClientType ConstClientType;

  LinkedListElement<T> sentinel;

public:
  class Iterator {
    RawType mCurrent;

  public:
    explicit Iterator(RawType aCurrent) : mCurrent(aCurrent) {}

    RawType operator *() const {
      return mCurrent;
    }

    const Iterator& operator++() {
      mCurrent = mCurrent->getNext();
      return *this;
    }

    bool operator!=(Iterator& aOther) const {
      return mCurrent != aOther.mCurrent;
    }
  };

  LinkedList() : sentinel(LinkedListElement<T>::NodeKind::Sentinel) { }

  LinkedList(LinkedList<T>&& aOther)
    : sentinel(mozilla::Move(aOther.sentinel))
  { }

  LinkedList& operator=(LinkedList<T>&& aOther)
  {
    MOZ_ASSERT(isEmpty(), "Assigning to a non-empty list leaks elements in that list!");
    sentinel = mozilla::Move(aOther.sentinel);
    return *this;
  }

  ~LinkedList() {
    MOZ_ASSERT(isEmpty(),
               "failing this assertion means this LinkedList's creator is "
               "buggy: it should have removed all this list's elements before "
               "the list's destruction");
  }

  /*
   * Add aElem to the front of the list.
   */
  void insertFront(RawType aElem)
  {
    /* Bypass setNext()'s this->isInList() assertion. */
    sentinel.setNextUnsafe(aElem);
  }

  /*
   * Add aElem to the back of the list.
   */
  void insertBack(RawType aElem)
  {
    sentinel.setPreviousUnsafe(aElem);
  }

  /*
   * Get the first element of the list, or nullptr if the list is empty.
   */
  RawType getFirst()            { return sentinel.getNext(); }
  ConstRawType getFirst() const { return sentinel.getNext(); }

  /*
   * Get the last element of the list, or nullptr if the list is empty.
   */
  RawType getLast()            { return sentinel.getPrevious(); }
  ConstRawType getLast() const { return sentinel.getPrevious(); }

  /*
   * Get and remove the first element of the list.  If the list is empty,
   * return nullptr.
   */
  ClientType popFirst()
  {
    ClientType ret = sentinel.getNext();
    if (ret) {
      static_cast<LinkedListElement<T>*>(RawType(ret))->remove();
    }
    return ret;
  }

  /*
   * Get and remove the last element of the list.  If the list is empty,
   * return nullptr.
   */
  ClientType popLast()
  {
    ClientType ret = sentinel.getPrevious();
    if (ret) {
      static_cast<LinkedListElement<T>*>(RawType(ret))->remove();
    }
    return ret;
  }

  /*
   * Return true if the list is empty, or false otherwise.
   */
  bool isEmpty() const
  {
    return !sentinel.isInList();
  }

  /*
   * Remove all the elements from the list.
   *
   * This runs in time linear to the list's length, because we have to mark
   * each element as not in the list.
   */
  void clear()
  {
    while (popFirst()) {
      continue;
    }
  }

  /*
   * Allow range-based iteration:
   *
   *     for (MyElementType* elt : myList) { ... }
   */
  Iterator begin() {
    return Iterator(getFirst());
  }
  Iterator end() {
    return Iterator(nullptr);
  }

  /*
   * Measures the memory consumption of the list excluding |this|.  Note that
   * it only measures the list elements themselves.  If the list elements
   * contain pointers to other memory blocks, those blocks must be measured
   * separately during a subsequent iteration over the list.
   */
  size_t sizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const
  {
    size_t n = 0;
    for (const T* t = getFirst(); t; t = t->getNext()) {
      n += aMallocSizeOf(t);
    }
    return n;
  }

  /*
   * Like sizeOfExcludingThis(), but measures |this| as well.
   */
  size_t sizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
  {
    return aMallocSizeOf(this) + sizeOfExcludingThis(aMallocSizeOf);
  }

  /*
   * In a debug build, make sure that the list is sane (no cycles, consistent
   * mNext/mPrev pointers, only one sentinel).  Has no effect in release builds.
   */
  void debugAssertIsSane() const
  {
#ifdef DEBUG
    const LinkedListElement<T>* slow;
    const LinkedListElement<T>* fast1;
    const LinkedListElement<T>* fast2;

    /*
     * Check for cycles in the forward singly-linked list using the
     * tortoise/hare algorithm.
     */
    for (slow = sentinel.mNext,
         fast1 = sentinel.mNext->mNext,
         fast2 = sentinel.mNext->mNext->mNext;
         slow != &sentinel && fast1 != &sentinel && fast2 != &sentinel;
         slow = slow->mNext, fast1 = fast2->mNext, fast2 = fast1->mNext) {
      MOZ_ASSERT(slow != fast1);
      MOZ_ASSERT(slow != fast2);
    }

    /* Check for cycles in the backward singly-linked list. */
    for (slow = sentinel.mPrev,
         fast1 = sentinel.mPrev->mPrev,
         fast2 = sentinel.mPrev->mPrev->mPrev;
         slow != &sentinel && fast1 != &sentinel && fast2 != &sentinel;
         slow = slow->mPrev, fast1 = fast2->mPrev, fast2 = fast1->mPrev) {
      MOZ_ASSERT(slow != fast1);
      MOZ_ASSERT(slow != fast2);
    }

    /*
     * Check that |sentinel| is the only node in the list with
     * mIsSentinel == true.
     */
    for (const LinkedListElement<T>* elem = sentinel.mNext;
         elem != &sentinel;
         elem = elem->mNext) {
      MOZ_ASSERT(!elem->mIsSentinel);
    }

    /* Check that the mNext/mPrev pointers match up. */
    const LinkedListElement<T>* prev = &sentinel;
    const LinkedListElement<T>* cur = sentinel.mNext;
    do {
        MOZ_ASSERT(cur->mPrev == prev);
        MOZ_ASSERT(prev->mNext == cur);

        prev = cur;
        cur = cur->mNext;
    } while (cur != &sentinel);
#endif /* ifdef DEBUG */
  }

private:
  friend class LinkedListElement<T>;

  void assertContains(const RawType aValue) const
  {
#ifdef DEBUG
    for (ConstRawType elem = getFirst(); elem; elem = elem->getNext()) {
      if (elem == aValue) {
        return;
      }
    }
    MOZ_CRASH("element wasn't found in this list!");
#endif
  }

  LinkedList& operator=(const LinkedList<T>& aOther) = delete;
  LinkedList(const LinkedList<T>& aOther) = delete;
};

template <typename T>
class AutoCleanLinkedList : public LinkedList<T>
{
public:
  ~AutoCleanLinkedList()
  {
    while (T* element = this->popFirst()) {
      delete element;
    }
  }
};

} /* namespace mozilla */

#endif /* __cplusplus */

#endif /* mozilla_LinkedList_h */