V8 API Reference, 7.2.502.16 (for Deno 0.2.4)
collector.h
1 // Copyright 2016 the V8 project authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4 
5 #ifndef V8_COLLECTOR_H_
6 #define V8_COLLECTOR_H_
7 
8 #include <vector>
9 
10 #include "src/checks.h"
11 #include "src/vector.h"
12 
13 namespace v8 {
14 namespace internal {
15 
16 /*
17  * A class that collects values into a backing store.
18  * Specialized versions of the class can allow access to the backing store
19  * in different ways.
20  * There is no guarantee that the backing store is contiguous (and, as a
21  * consequence, no guarantees that consecutively added elements are adjacent
22  * in memory). The collector may move elements unless it has guaranteed not
23  * to.
24  */
25 template <typename T, int growth_factor = 2, int max_growth = 1 * MB>
26 class Collector {
27  public:
28  explicit Collector(int initial_capacity = kMinCapacity)
29  : index_(0), size_(0) {
30  current_chunk_ = Vector<T>::New(initial_capacity);
31  }
32 
33  virtual ~Collector() {
34  // Free backing store (in reverse allocation order).
35  current_chunk_.Dispose();
36  for (auto rit = chunks_.rbegin(); rit != chunks_.rend(); ++rit) {
37  rit->Dispose();
38  }
39  }
40 
41  // Add a single element.
42  inline void Add(T value) {
43  if (index_ >= current_chunk_.length()) {
44  Grow(1);
45  }
46  current_chunk_[index_] = value;
47  index_++;
48  size_++;
49  }
50 
51  // Add a block of contiguous elements and return a Vector backed by the
52  // memory area.
53  // A basic Collector will keep this vector valid as long as the Collector
54  // is alive.
55  inline Vector<T> AddBlock(int size, T initial_value) {
56  DCHECK_GT(size, 0);
57  if (size > current_chunk_.length() - index_) {
58  Grow(size);
59  }
60  T* position = current_chunk_.start() + index_;
61  index_ += size;
62  size_ += size;
63  for (int i = 0; i < size; i++) {
64  position[i] = initial_value;
65  }
66  return Vector<T>(position, size);
67  }
68 
69  // Add a contiguous block of elements and return a vector backed
70  // by the added block.
71  // A basic Collector will keep this vector valid as long as the Collector
72  // is alive.
73  inline Vector<T> AddBlock(Vector<const T> source) {
74  if (source.length() > current_chunk_.length() - index_) {
75  Grow(source.length());
76  }
77  T* position = current_chunk_.start() + index_;
78  index_ += source.length();
79  size_ += source.length();
80  for (int i = 0; i < source.length(); i++) {
81  position[i] = source[i];
82  }
83  return Vector<T>(position, source.length());
84  }
85 
86  // Write the contents of the collector into the provided vector.
87  void WriteTo(Vector<T> destination) {
88  DCHECK(size_ <= destination.length());
89  int position = 0;
90  for (const Vector<T>& chunk : chunks_) {
91  for (int j = 0; j < chunk.length(); j++) {
92  destination[position] = chunk[j];
93  position++;
94  }
95  }
96  for (int i = 0; i < index_; i++) {
97  destination[position] = current_chunk_[i];
98  position++;
99  }
100  }
101 
102  // Allocate a single contiguous vector, copy all the collected
103  // elements to the vector, and return it.
104  // The caller is responsible for freeing the memory of the returned
105  // vector (e.g., using Vector::Dispose).
106  Vector<T> ToVector() {
107  Vector<T> new_store = Vector<T>::New(size_);
108  WriteTo(new_store);
109  return new_store;
110  }
111 
112  // Resets the collector to be empty.
113  virtual void Reset() {
114  for (auto rit = chunks_.rbegin(); rit != chunks_.rend(); ++rit) {
115  rit->Dispose();
116  }
117  chunks_.clear();
118  index_ = 0;
119  size_ = 0;
120  }
121 
122  // Total number of elements added to collector so far.
123  inline int size() { return size_; }
124 
125  protected:
126  static const int kMinCapacity = 16;
127  std::vector<Vector<T>> chunks_;
128  Vector<T> current_chunk_; // Block of memory currently being written into.
129  int index_; // Current index in current chunk.
130  int size_; // Total number of elements in collector.
131 
132  // Creates a new current chunk, and stores the old chunk in the chunks_ list.
133  void Grow(int min_capacity) {
134  DCHECK_GT(growth_factor, 1);
135  int new_capacity;
136  int current_length = current_chunk_.length();
137  if (current_length < kMinCapacity) {
138  // The collector started out as empty.
139  new_capacity = min_capacity * growth_factor;
140  if (new_capacity < kMinCapacity) new_capacity = kMinCapacity;
141  } else {
142  int growth = current_length * (growth_factor - 1);
143  if (growth > max_growth) {
144  growth = max_growth;
145  }
146  new_capacity = current_length + growth;
147  if (new_capacity < min_capacity) {
148  new_capacity = min_capacity + growth;
149  }
150  }
151  NewChunk(new_capacity);
152  DCHECK(index_ + min_capacity <= current_chunk_.length());
153  }
154 
155  // Before replacing the current chunk, give a subclass the option to move
156  // some of the current data into the new chunk. The function may update
157  // the current index_ value to represent data no longer in the current chunk.
158  // Returns the initial index of the new chunk (after copied data).
159  virtual void NewChunk(int new_capacity) {
160  Vector<T> new_chunk = Vector<T>::New(new_capacity);
161  if (index_ > 0) {
162  chunks_.push_back(current_chunk_.SubVector(0, index_));
163  } else {
164  current_chunk_.Dispose();
165  }
166  current_chunk_ = new_chunk;
167  index_ = 0;
168  }
169 };
170 
171 /*
172  * A collector that allows sequences of values to be guaranteed to
173  * stay consecutive.
174  * If the backing store grows while a sequence is active, the current
175  * sequence might be moved, but after the sequence is ended, it will
176  * not move again.
177  * NOTICE: Blocks allocated using Collector::AddBlock(int) can move
178  * as well, if inside an active sequence where another element is added.
179  */
180 template <typename T, int growth_factor = 2, int max_growth = 1 * MB>
181 class SequenceCollector : public Collector<T, growth_factor, max_growth> {
182  public:
183  explicit SequenceCollector(int initial_capacity)
184  : Collector<T, growth_factor, max_growth>(initial_capacity),
185  sequence_start_(kNoSequence) {}
186 
187  ~SequenceCollector() override = default;
188 
189  void StartSequence() {
190  DCHECK_EQ(sequence_start_, kNoSequence);
191  sequence_start_ = this->index_;
192  }
193 
194  Vector<T> EndSequence() {
195  DCHECK_NE(sequence_start_, kNoSequence);
196  int sequence_start = sequence_start_;
197  sequence_start_ = kNoSequence;
198  if (sequence_start == this->index_) return Vector<T>();
199  return this->current_chunk_.SubVector(sequence_start, this->index_);
200  }
201 
202  // Drops the currently added sequence, and all collected elements in it.
203  void DropSequence() {
204  DCHECK_NE(sequence_start_, kNoSequence);
205  int sequence_length = this->index_ - sequence_start_;
206  this->index_ = sequence_start_;
207  this->size_ -= sequence_length;
208  sequence_start_ = kNoSequence;
209  }
210 
211  void Reset() override {
212  sequence_start_ = kNoSequence;
214  }
215 
216  private:
217  static const int kNoSequence = -1;
218  int sequence_start_;
219 
220  // Move the currently active sequence to the new chunk.
221  void NewChunk(int new_capacity) override {
222  if (sequence_start_ == kNoSequence) {
223  // Fall back on default behavior if no sequence has been started.
225  return;
226  }
227  int sequence_length = this->index_ - sequence_start_;
228  Vector<T> new_chunk = Vector<T>::New(sequence_length + new_capacity);
229  DCHECK(sequence_length < new_chunk.length());
230  for (int i = 0; i < sequence_length; i++) {
231  new_chunk[i] = this->current_chunk_[sequence_start_ + i];
232  }
233  if (sequence_start_ > 0) {
234  this->chunks_.push_back(
235  this->current_chunk_.SubVector(0, sequence_start_));
236  } else {
237  this->current_chunk_.Dispose();
238  }
239  this->current_chunk_ = new_chunk;
240  this->index_ = sequence_length;
241  sequence_start_ = 0;
242  }
243 };
244 
245 } // namespace internal
246 } // namespace v8
247 
248 #endif // V8_COLLECTOR_H_
Definition: libplatform.h:13