// Copyright 2016 the V8 project authors. All rights reserved. // Use of this source code is governed by a BSD-style license that can be // found in the LICENSE file. #ifndef V8_COLLECTOR_H_ #define V8_COLLECTOR_H_ #include <vector> #include "src/base/vector.h" #include "src/common/checks.h" namespace v8 { namespace internal { /* * A class that collects values into a backing store. * Specialized versions of the class can allow access to the backing store * in different ways. * There is no guarantee that the backing store is contiguous (and, as a * consequence, no guarantees that consecutively added elements are adjacent * in memory). The collector may move elements unless it has guaranteed not * to. */ template <typename T, int growth_factor = 2, int max_growth = 1 * MB> class Collector { public: explicit Collector(int initial_capacity = kMinCapacity) : index_(0), size_(0) { current_chunk_ = base::Vector<T>::New(initial_capacity); } virtual ~Collector() { // Free backing store (in reverse allocation order). current_chunk_.Dispose(); for (auto rit = chunks_.rbegin(); rit != chunks_.rend(); ++rit) { rit->Dispose(); } } // Add a single element. inline void Add(T value) { if (index_ >= current_chunk_.length()) { Grow(1); } current_chunk_[index_] = value; index_++; size_++; } // Add a block of contiguous elements and return a Vector backed by the // memory area. // A basic Collector will keep this vector valid as long as the Collector // is alive. inline base::Vector<T> AddBlock(int size, T initial_value) { DCHECK_GT(size, 0); if (size > current_chunk_.length() - index_) { Grow(size); } T* position = current_chunk_.begin() + index_; index_ += size; size_ += size; for (int i = 0; i < size; i++) { position[i] = initial_value; } return base::Vector<T>(position, size); } // Add a contiguous block of elements and return a vector backed // by the added block. // A basic Collector will keep this vector valid as long as the Collector // is alive. inline base::Vector<T> AddBlock(base::Vector<const T> source) { if (source.length() > current_chunk_.length() - index_) { Grow(source.length()); } T* position = current_chunk_.begin() + index_; index_ += source.length(); size_ += source.length(); for (int i = 0; i < source.length(); i++) { position[i] = source[i]; } return base::Vector<T>(position, source.length()); } // Write the contents of the collector into the provided vector. void WriteTo(base::Vector<T> destination) { DCHECK(size_ <= destination.length()); int position = 0; for (const base::Vector<T>& chunk : chunks_) { for (int j = 0; j < chunk.length(); j++) { destination[position] = chunk[j]; position++; } } for (int i = 0; i < index_; i++) { destination[position] = current_chunk_[i]; position++; } } // Allocate a single contiguous vector, copy all the collected // elements to the vector, and return it. // The caller is responsible for freeing the memory of the returned // vector (e.g., using Vector::Dispose). base::Vector<T> ToVector() { base::Vector<T> new_store = base::Vector<T>::New(size_); WriteTo(new_store); return new_store; } // Resets the collector to be empty. virtual void Reset() { for (auto rit = chunks_.rbegin(); rit != chunks_.rend(); ++rit) { rit->Dispose(); } chunks_.clear(); index_ = 0; size_ = 0; } // Total number of elements added to collector so far. inline int size() { return size_; } protected: static const int kMinCapacity = 16; std::vector<base::Vector<T>> chunks_; base::Vector<T> current_chunk_; // Block of memory currently being written into. int index_; // Current index in current chunk. int size_; // Total number of elements in collector. // Creates a new current chunk, and stores the old chunk in the chunks_ list. void Grow(int min_capacity) { DCHECK_GT(growth_factor, 1); int new_capacity; int current_length = current_chunk_.length(); if (current_length < kMinCapacity) { // The collector started out as empty. new_capacity = min_capacity * growth_factor; if (new_capacity < kMinCapacity) new_capacity = kMinCapacity; } else { int growth = current_length * (growth_factor - 1); if (growth > max_growth) { growth = max_growth; } new_capacity = current_length + growth; if (new_capacity < min_capacity) { new_capacity = min_capacity + growth; } } NewChunk(new_capacity); DCHECK(index_ + min_capacity <= current_chunk_.length()); } // Before replacing the current chunk, give a subclass the option to move // some of the current data into the new chunk. The function may update // the current index_ value to represent data no longer in the current chunk. // Returns the initial index of the new chunk (after copied data). virtual void NewChunk(int new_capacity) { base::Vector<T> new_chunk = base::Vector<T>::New(new_capacity); if (index_ > 0) { chunks_.push_back(current_chunk_.SubVector(0, index_)); } else { current_chunk_.Dispose(); } current_chunk_ = new_chunk; index_ = 0; } }; /* * A collector that allows sequences of values to be guaranteed to * stay consecutive. * If the backing store grows while a sequence is active, the current * sequence might be moved, but after the sequence is ended, it will * not move again. * NOTICE: Blocks allocated using Collector::AddBlock(int) can move * as well, if inside an active sequence where another element is added. */ template <typename T, int growth_factor = 2, int max_growth = 1 * MB> class SequenceCollector : public Collector<T, growth_factor, max_growth> { public: explicit SequenceCollector(int initial_capacity) : Collector<T, growth_factor, max_growth>(initial_capacity), sequence_start_(kNoSequence) {} ~SequenceCollector() override = default; void StartSequence() { DCHECK_EQ(sequence_start_, kNoSequence); sequence_start_ = this->index_; } base::Vector<T> EndSequence() { DCHECK_NE(sequence_start_, kNoSequence); int sequence_start = sequence_start_; sequence_start_ = kNoSequence; if (sequence_start == this->index_) return base::Vector<T>(); return this->current_chunk_.SubVector(sequence_start, this->index_); } // Drops the currently added sequence, and all collected elements in it. void DropSequence() { DCHECK_NE(sequence_start_, kNoSequence); int sequence_length = this->index_ - sequence_start_; this->index_ = sequence_start_; this->size_ -= sequence_length; sequence_start_ = kNoSequence; } void Reset() override { sequence_start_ = kNoSequence; this->Collector<T, growth_factor, max_growth>::Reset(); } private: static const int kNoSequence = -1; int sequence_start_; // Move the currently active sequence to the new chunk. void NewChunk(int new_capacity) override { if (sequence_start_ == kNoSequence) { // Fall back on default behavior if no sequence has been started. this->Collector<T, growth_factor, max_growth>::NewChunk(new_capacity); return; } int sequence_length = this->index_ - sequence_start_; base::Vector<T> new_chunk = base::Vector<T>::New(sequence_length + new_capacity); DCHECK(sequence_length < new_chunk.length()); for (int i = 0; i < sequence_length; i++) { new_chunk[i] = this->current_chunk_[sequence_start_ + i]; } if (sequence_start_ > 0) { this->chunks_.push_back( this->current_chunk_.SubVector(0, sequence_start_)); } else { this->current_chunk_.Dispose(); } this->current_chunk_ = new_chunk; this->index_ = sequence_length; sequence_start_ = 0; } }; } // namespace internal } // namespace v8 #endif // V8_COLLECTOR_H_