js引擎v8源码解析之list（基于0.1.5）

THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

#ifndef V8_LIST_H_
#define V8_LIST_H_

namespace v8 { namespace internal {


// ----------------------------------------------------------------------------
// The list is a template for very light-weight lists. We are not
// using the STL because we want full control over space and speed of
// the code. This implementation is based on code by Robert Griesemer
// and Rob Pike.
//
// The list is parameterized by the type of its elements (T) and by an
// allocation policy (P). The policy is used for allocating lists in
// the C free store or the zone; see zone.h.

// Forward defined as
// template <typename T, class P = FreeStoreAllocationPolicy> class List;
template <typename T, class P>
class List {
 public:
  // 构造函数，申请一块内存
  INLINE(explicit List(int capacity)) { Initialize(capacity); }
  // 析构函数，是否内存
  INLINE(~List()) { DeleteData(data_); }
  // 分配内存，P是内存管理的类，如FreeStoreAllocationPolicy，见allocation.h
  INLINE(void* operator new(size_t size)) { return P::New(size); }
  // 释放内存
  INLINE(void operator delete(void* p, size_t)) { return P::Delete(p); }
  // 重载[]运算符，返回对应索引的元素
  inline T& operator[](int i) const  {
    ASSERT(0 <= i && i < length_);
    return data_[i];
  }
  // 取某个索引对应的元素
  inline T& at(int i) const  { return this->operator[](i); }
  // 取最后一个元素
  INLINE(const T& last() const)  {
    ASSERT(!is_empty());
    return this->at(length_ - 1);
  }
  // 判空
  INLINE(bool is_empty() const) { return length_ == 0; }
  // 容量
  INLINE(int length() const) { return length_; }
  // 转成Vector，见utils.h
  Vector<T> ToVector() { return Vector<T>(data_, length_); }

  // Adds a copy of the given 'element' to the end of the list,
  // expanding the list if necessary.
  // 追加元素
  T& Add(const T& element);

  // Added 'count' elements with the value 'value' and returns a
  // vector that allows access to the elements.  The vector is valid
  // until the next change is made to this list.
  Vector<T> AddBlock(const T& value, int count);

  // Removes the i'th element without deleting it even if T is a
  // pointer type; moves all elements above i "down". Returns the
  // removed element.
  T Remove(int i);

  // Removes the last element without deleting it even if T is a
  // pointer type. Returns the removed element.
  INLINE(T RemoveLast()) { return Remove(length_ - 1); }

  // Clears the list by setting the length to zero. Even if T is a
  // pointer type, clearing the list doesn't delete the entries.
  INLINE(void Clear());

  // Drops all but the first 'pos' elements from the list.
  INLINE(void Rewind(int pos));

  // Iterate through all list entries, starting at index 0.
  void Iterate(void (*callback)(T* x));

  // Sort all list entries (using QuickSort)
  void Sort(int (*cmp)(const T* x, const T* y));

  INLINE(void Initialize(int capacity));

 private:
  // 指向数组的首地址
  T* data_;
  // 最多可以存储多少个元素
  int capacity_;
  // 已经存储了多少个元素
  int length_;

  INLINE(T* NewData(int n))  { return static_cast<T*>(P::New(n * sizeof(T))); }
  INLINE(void DeleteData(T* data))  { P::Delete(data); }

  DISALLOW_EVIL_CONSTRUCTORS(List);
};


} }  // namespace v8::internal

#endif  // V8_LIST_H_

#ifndef V8_LIST_INL_H_
#define V8_LIST_INL_H_

#include "list.h"

namespace v8 { namespace internal {


template<typename T, class P>
T& List<T, P>::Add(const T& element) {
  // 没有足够的空间了，重新申请一块新的更大的内存
  if (length_ >= capacity_) {
    // Grow the list capacity by 50%, but make sure to let it grow
    // even when the capacity is zero (possible initial case).
    // 多扩展50% + 1的空间，加一是兼容capacity_为0的情况
    int new_capacity = 1 + capacity_ + (capacity_ >> 1);
    // 申请一块内存
    T* new_data = NewData(new_capacity);
    // 把原来的复制过去
    memcpy(new_data, data_, capacity_ * sizeof(T));
    // 删除原来的
    DeleteData(data_);
    // 更新属性
    data_ = new_data;
    capacity_ = new_capacity;
  }
  // 赋值
  return data_[length_++] = element;
}


template<typename T, class P>
// 新增count个element元素到list，转成Vector返回
Vector<T> List<T, P>::AddBlock(const T& element, int count) {
  int start = length_;
  for (int i = 0; i < count; i++)
    Add(element);
  return Vector<T>(&data_[start], count);
}


template<typename T, class P>
// 删除某个元素，后续的元素补位
T List<T, P>::Remove(int i) {
  // 取出i对应的元素
  T element = at(i);
  // 长度减一
  length_--;
  // 如果删除的不是最后一个元素，则i后面的元素要往前补位
  while (i < length_) {
    data_[i] = data_[i + 1];
    i++;
  }
  return element;
}


template<typename T, class P>
// 清空list，释放内存
void List<T, P>::Clear() {
  DeleteData(data_);
  Initialize(0);
}

// 改变list的长度 
template<typename T, class P>
void List<T, P>::Rewind(int pos) {
  length_ = pos;
}

// 迭代list
template<typename T, class P>
void List<T, P>::Iterate(void (*callback)(T* x)) {
  for (int i = 0; i < length_; i++) callback(&data_[i]);
}

// 排序
template<typename T, class P>
void List<T, P>::Sort(int (*cmp)(const T* x, const T* y)) {
  qsort(data_,
        length_,
        sizeof(T),
        reinterpret_cast<int (*)(const void*, const void*)>(cmp));
#ifdef DEBUG
  for (int i = 1; i < length_; i++)
    ASSERT(cmp(&data_[i - 1], &data_[i]) <= 0);
#endif
}


template<typename T, class P>
void List<T, P>::Initialize(int capacity) {
  ASSERT(capacity >= 0);
  // 分配一块内存
  data_ = (capacity > 0) ? NewData(capacity) : NULL;
  // 容量
  capacity_ = capacity;
  // 已分配元素个数
  length_ = 0;
}


} }  // namespace v8::internal

#endif  // V8_LIST_INL_H_