Class BatchAllocator

external/jsoncpp/jsoncpp.cpp:1074–1160

 */
template <typename AllocatedType, const unsigned int objectPerAllocation>
class BatchAllocator {
public:
  BatchAllocator(unsigned int objectsPerPage = 255)
      : freeHead_(0), objectsPerPage_(objectsPerPage) {
    //      printf( "Size: %d => %s\n", sizeof(AllocatedType),
    // typeid(AllocatedType).name() );
    assert(sizeof(AllocatedType) * objectPerAllocation >=
           sizeof(AllocatedType *)); // We must be able to store a slist in the
                                     // object free space.
    assert(objectsPerPage >= 16);
    batches_ = allocateBatch(0); // allocated a dummy page
    currentBatch_ = batches_;
  }

  ~BatchAllocator() {
    for (BatchInfo *batch = batches_; batch;) {
      BatchInfo *nextBatch = batch->next_;
      free(batch);
      batch = nextBatch;
    }
  }

  /// allocate space for an array of objectPerAllocation object.
  /// @warning it is the responsability of the caller to call objects
  /// constructors.
  AllocatedType *allocate() {
    if (freeHead_) // returns node from free list.
    {
      AllocatedType *object = freeHead_;
      freeHead_ = *(AllocatedType **)object;
      return object;
    }
    if (currentBatch_->used_ == currentBatch_->end_) {
      currentBatch_ = currentBatch_->next_;
      while (currentBatch_ && currentBatch_->used_ == currentBatch_->end_)
        currentBatch_ = currentBatch_->next_;

      if (!currentBatch_) // no free batch found, allocate a new one
      {
        currentBatch_ = allocateBatch(objectsPerPage_);
        currentBatch_->next_ = batches_; // insert at the head of the list
        batches_ = currentBatch_;
      }
    }
    AllocatedType *allocated = currentBatch_->used_;
    currentBatch_->used_ += objectPerAllocation;
    return allocated;
  }

  /// Release the object.
  /// @warning it is the responsability of the caller to actually destruct the
  /// object.
  void release(AllocatedType *object) {
    assert(object != 0);
    *(AllocatedType **)object = freeHead_;
    freeHead_ = object;
  }