array_array.h

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/*
The MIT License (MIT)

Copyright (c) 2015 University of Central Florida's Computer Software Engineering
Scalable & Secure Systems (CSE - S3) Lab

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/
#ifndef __TERVEL_CONTAINERS_WF_VECTOR_VECTOR_ARRAY_ARRAY_H
#define __TERVEL_CONTAINERS_WF_VECTOR_VECTOR_ARRAY_ARRAY_H

#include <tervel/util/util.h>

#include <tervel/containers/wf/vector/vector_array.h>

namespace tervel {
namespace containers {
namespace wf {
namespace vector {

template<typename T>
class ArrayArray : public VectorArray<T> {
  typedef std::atomic<T> ArrayElement;
  typedef ArrayElement * ArraySegment;
 public:
  ArrayArray(size_t capacity, T default_value = nullptr)
      : default_value_(default_value) {
    if (capacity < 2) {
      capacity = 2;
    }
    offset_pow_ = tervel::util::round_to_next_power_of_two(capacity);
    offset_ = std::pow(2, offset_pow_);

    array_of_arrays[0].store(allocate_array_segment(offset_));
    current_capacity_.store(offset_);
  }

  ~ArrayArray() {
    for (size_t i = 0; i < k_max_array_segments_; i++) {
      delete [] array_of_arrays[i];
    }
  }

  ArraySegment add_segment(const size_t pos) {
    ArraySegment cur_seg = array_of_arrays[pos].load();

    if (cur_seg == nullptr) {
      size_t seg_cap = 0x1 << (offset_pow_ + pos);
      ArraySegment new_seg = allocate_array_segment(seg_cap);

      if (array_of_arrays[pos].compare_exchange_strong(cur_seg, new_seg)) {
        current_capacity_.fetch_add(seg_cap);
        return new_seg;
      } else {
        delete [] new_seg;
        return cur_seg;
      }
    }  // if cur_seg == nullprt
    return cur_seg;
  };  // add_segment


  ArrayElement * get_spot(const size_t raw_pos, const bool no_add = false) {
    if (raw_pos < offset_) {
      ArraySegment seg = array_of_arrays[0].load();
      return &(seg[raw_pos]);
    } else {
      static const int nobits = (sizeof(unsigned int) << 3) - 1;
      size_t pos = raw_pos + offset_;
      size_t num = nobits - __builtin_clz(pos);

      size_t elem_pos = pos ^ (1 << num);
      size_t seg_num = num - offset_pow_;

      ArraySegment seg = array_of_arrays[seg_num].load();
      if (seg == nullptr && !no_add) {
        seg = add_segment(seg_num);
        assert(seg != NULL);
      }

      if (seg != nullptr) {
        return &(seg[elem_pos]);
      } else {
        return nullptr;
      }
    }  // else it is first array
  }  // get_pos

  ArrayElement *allocate_array_segment(const size_t capacity) {
    ArrayElement * temp = new ArrayElement[capacity];
    for (uint64_t i = 0; i < capacity; i++) {
      temp[i] = default_value_;
    }
    return temp;
  }

  size_t capacity() {
    return current_capacity_.load();
  }

 private:
  const T default_value_ {nullptr};
  static const size_t k_max_array_segments_ {64};

  std::atomic<ArraySegment> array_of_arrays[k_max_array_segments_];
  size_t offset_, offset_pow_;

  std::atomic<size_t> current_capacity_;
};  // class Vector Array
}  // namespace vector
}  // namespace wf
}  // namespace containers
}  // namespace tervel

#endif  // __TERVEL_CONTAINERS_WF_VECTOR_VECTOR_