// 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 "src/checks.h"
#include "src/list-inl.h"
#include "src/vector.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_ = Vector<T>::New(initial_capacity);
}
virtual ~Collector() {
// Free backing store (in reverse allocation order).
current_chunk_.Dispose();
for (int i = chunks_.length() - 1; i >= 0; i--) {
chunks_.at(i).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 Vector<T> AddBlock(int size, T initial_value) {
DCHECK(size > 0);
if (size > current_chunk_.length() - index_) {
Grow(size);
}
T* position = current_chunk_.start() + index_;
index_ += size;
size_ += size;
for (int i = 0; i < size; i++) {
position[i] = initial_value;
}
return 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 Vector<T> AddBlock(Vector<const T> source) {
if (source.length() > current_chunk_.length() - index_) {
Grow(source.length());
}
T* position = current_chunk_.start() + index_;
index_ += source.length();
size_ += source.length();
for (int i = 0; i < source.length(); i++) {
position[i] = source[i];
}
return Vector<T>(position, source.length());
}
// Write the contents of the collector into the provided vector.
void WriteTo(Vector<T> destination) {
DCHECK(size_ <= destination.length());
int position = 0;
for (int i = 0; i < chunks_.length(); i++) {
Vector<T> chunk = chunks_.at(i);
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).
Vector<T> ToVector() {
Vector<T> new_store = Vector<T>::New(size_);
WriteTo(new_store);
return new_store;
}
// Resets the collector to be empty.
virtual void Reset() {
for (int i = chunks_.length() - 1; i >= 0; i--) {
chunks_.at(i).Dispose();
}
chunks_.Rewind(0);
index_ = 0;
size_ = 0;
}
// Total number of elements added to collector so far.
inline int size() { return size_; }
protected:
static const int kMinCapacity = 16;
List<Vector<T> > chunks_;
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(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) {
Vector<T> new_chunk = Vector<T>::New(new_capacity);
if (index_ > 0) {
chunks_.Add(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) {}
virtual ~SequenceCollector() {}
void StartSequence() {
DCHECK(sequence_start_ == kNoSequence);
sequence_start_ = this->index_;
}
Vector<T> EndSequence() {
DCHECK(sequence_start_ != kNoSequence);
int sequence_start = sequence_start_;
sequence_start_ = kNoSequence;
if (sequence_start == this->index_) return 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(sequence_start_ != kNoSequence);
int sequence_length = this->index_ - sequence_start_;
this->index_ = sequence_start_;
this->size_ -= sequence_length;
sequence_start_ = kNoSequence;
}
virtual void Reset() {
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.
virtual void NewChunk(int new_capacity) {
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_;
Vector<T> new_chunk = 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_.Add(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_