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
13namespace v8 {
14namespace 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 */
25template <typename T, int growth_factor = 2, int max_growth = 1 * MB>
26class 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 */
180template <typename T, int growth_factor = 2, int max_growth = 1 * MB>
181class 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;
213 this->Collector<T, growth_factor, max_growth>::Reset();
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.
224 this->Collector<T, growth_factor, max_growth>::NewChunk(new_capacity);
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_
249