src/base/freelist.h

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#ifndef MOZC_BASE_FREELIST_H_
#define MOZC_BASE_FREELIST_H_

#include <vector>
#include "base/port.h"

namespace mozc {

// Note: The program will be crashed in the following code;
//   FreeList<int> freelist(10);
//   freelist.Alloc(5);
//   freelist.set_size(100);
//   int* array = freelist.Alloc(10);
//   array[8] = 0;  // crashed.
// Also this class runs unneeded T's constructor along with the memory chunk
// allocation.
// Please do take care to use this class.
template <class T> class FreeList {
 public:
  explicit FreeList(size_t size)
      : current_index_(0), chunk_index_(0), size_(size) {
  }

  ~FreeList() {
    for (size_t i = 0; i < pool_.size(); ++i) {
      delete [] pool_[i];
    }
  }

  void Reset() {
    chunk_index_ = current_index_ = 0;
  }

  void Free() {
    for (size_t i = 1; i < pool_.size(); ++i) {
      delete [] pool_[i];
    }
    if (pool_.size() > 1) {
      pool_.resize(1);
    }
    current_index_ = 0;
    chunk_index_ = 0;
  }

  T* Alloc() {
    return Alloc(static_cast<size_t>(1));
  }

  T* Alloc(size_t len) {
    if ((current_index_ + len) >= size_) {
      chunk_index_++;
      current_index_ = 0;
    }

    if (chunk_index_ == pool_.size()) {
      pool_.push_back(new T[size_]);
    }

    T* r = pool_[chunk_index_] + current_index_;
    current_index_ += len;
    return r;
  }

  void set_size(size_t size) {
    size_ = size;
  }

 private:
  vector<T *> pool_;
  size_t current_index_;
  size_t chunk_index_;
  size_t size_;

  DISALLOW_COPY_AND_ASSIGN(FreeList);
};

template <class T> class ObjectPool {
 public:
  explicit ObjectPool(int size): freelist_(size) {
  }

  ~ObjectPool() {
  }

  void Free() {
    released_.clear();
    freelist_.Free();
  }

  T* Alloc() {
    if (!released_.empty()) {
      T *result = released_.back();
      released_.pop_back();
      return result;
    }
    return freelist_.Alloc(1);
  }

  void Release(T *ptr) {
    released_.push_back(ptr);
  }

  void set_size(int size) {
    freelist_.set_size(size);
  }

 private:
  vector<T *> released_;
  FreeList<T> freelist_;

  DISALLOW_COPY_AND_ASSIGN(ObjectPool);
};

}  // namespace mozc

#endif  // MOZC_BASE_FREELIST_H_