text: 
  // Copyright (c) 2014-2019, The Monero Project
  // All rights reserved.
  //
  // Redistribution and use in source and binary forms, with or without modification, are
  // permitted provided that the following conditions are met:
  //
  // 1. Redistributions of source code must retain the above copyright notice, this list of
  //    conditions and the following disclaimer.
  //
  // 2. Redistributions in binary form must reproduce the above copyright notice, this list
  //    of conditions and the following disclaimer in the documentation and/or other
  //    materials provided with the distribution.
  //
  // 3. Neither the name of the copyright holder nor the names of its contributors may be
  //    used to endorse or promote products derived from this software without specific
  //    prior written permission.
  //
  // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY
  // EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
  // MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL
  // THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  // PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
  // INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
  // STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF
  // THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  
  #include <db_cxx.h>
  
  #include "blockchain_db/blockchain_db.h"
  #include "cryptonote_basic/blobdatatype.h" // for type blobdata
  
  #include <unordered_map>
  #include <condition_variable>
  
  // ND: Enables multi-threaded bulk reads for when getting indices.
  //     TODO: Disabled for now, as it doesn't seem to provide noticeable improvements (??. Reason: TBD.
  // #define BDB_BULK_CAN_THREAD
  namespace cryptonote
  {
  
  struct bdb_txn_safe
  {
    bdb_txn_safe() : m_txn(NULL) { }
    ~bdb_txn_safe()
    {
      LOG_PRINT_L3("bdb_txn_safe: destructor");
  
      if (m_txn != NULL)
        abort();
    }
  
    void commit(std::string message = "")
    {
      if (message.size() == 0)
      {
        message = "Failed to commit a transaction to the db";
      }
  
      if (m_txn->commit(0))
      {
        m_txn = NULL;
        LOG_PRINT_L0(message);
        throw DB_ERROR(message.c_str());
      }
      m_txn = NULL;
    }
  
    void abort()
    {
      LOG_PRINT_L3("bdb_txn_safe: abort()");
      if(m_txn != NULL)
      {
        m_txn->abort();
        m_txn = NULL;
      }
      else
      {
        LOG_PRINT_L0("WARNING: bdb_txn_safe: abort() called, but m_txn is NULL");
      }
    }
  
    operator DbTxn*()
    {
      return m_txn;
    }
  
    operator DbTxn**()
    {
      return &m_txn;
    }
  private:
    DbTxn* m_txn;
  };
  
  // ND: Class to handle buffer management when doing bulk queries
  // (DB_MULTIPLE). Allocates buffers then handles thread queuing
  // so a fixed set of buffers can be used (instead of allocating
  // every time a bulk query is needed).
  template <typename T>
  class bdb_safe_buffer
  {
    // limit the number of buffers to 8
    const size_t MaxAllowedBuffers = 8;
  public:
      bdb_safe_buffer(size_t num_buffers, size_t count)
      {
        if(num_buffers > MaxAllowedBuffers)
          num_buffers = MaxAllowedBuffers;
  
        set_count(num_buffers);
        for (size_t i = 0; i < num_buffers; i++)
          m_buffers.push_back((T) malloc(sizeof(T) * count));
        m_buffer_count = count;
      }
  
      ~bdb_safe_buffer()
      {
          for (size_t i = 0; i < m_buffers.size(); i++)
          {
              if (m_buffers[i])
              {
                  free(m_buffers[i]);
                  m_buffers[i] = nullptr;
              }
          }
  
          m_buffers.resize(0);
      }
  
      T acquire_buffer()
      {
          boost::unique_lock<boost::mutex> lock(m_lock);
          m_cv.wait(lock, [&]{ return m_count > 0; });
  
          --m_count;
          size_t index = -1;
          for (size_t i = 0; i < m_open_slot.size(); i++)
          {
              if (m_open_slot[i])
              {
                  m_open_slot[i] = false;
                  index = i;
                  break;
              }
          }
  
          assert(index >= 0);
  
          T buffer = m_buffers[index];
          m_buffer_map.emplace(buffer, index);
          return buffer;
      }
  
      void release_buffer(T buffer)
      {
          boost::unique_lock<boost::mutex> lock(m_lock);
  
          assert(buffer != nullptr);
          auto it = m_buffer_map.find(buffer);
          if (it != m_buffer_map.end())
          {
              auto index = it->second;
  
              assert(index < m_open_slot.size());
              assert(m_open_slot[index] == false);
              assert(m_count < m_open_slot.size());
  
              ++m_count;
              m_open_slot[index] = true;
              m_buffer_map.erase(it);
              m_cv.notify_one();
          }
      }
  
      size_t get_buffer_size() const
      {
          return m_buffer_count * sizeof(T);
      }
  
      size_t get_buffer_count() const
      {
          return m_buffer_count;
      }
  
      typedef T type;
  
  private:
      void set_count(size_t count)
      {
          assert(count > 0);
          m_open_slot.resize(count, true);
          m_count = count;
      }
  
      std::vector<T> m_buffers;
      std::unordered_map<T, size_t> m_buffer_map;
  
      boost::condition_variable m_cv;
      std::vector<bool> m_open_slot;
      size_t m_count;
      boost::mutex m_lock;
  
      size_t m_buffer_count;
  };
  
  template <typename T>
  class bdb_safe_buffer_autolock
  {
  public:
      bdb_safe_buffer_autolock(T &safe_buffer, typename T::type &buffer) :
          m_safe_buffer(safe_buffer), m_buffer(nullptr)
      {
          m_buffer = m_safe_buffer.acquire_buffer();
          buffer = m_buffer;
      }
  
      ~bdb_safe_buffer_autolock()
      {
          if (m_buffer != nullptr)
          {
              m_safe_buffer.release_buffer(m_buffer);
              m_buffer = nullptr;
          }
      }
  private:
      T &m_safe_buffer;
      typename T::type m_buffer;
  };
  
  class BlockchainBDB : public BlockchainDB
  {
  public:
    BlockchainBDB(bool batch_transactions=false);
    ~BlockchainBDB();
  
    virtual void open(const std::string& filename, const int db_flags);
  
    virtual void close();
  
    virtual void sync();
  
    virtual void reset();
  
    virtual std::vector<std::string> get_filenames() const;
  
    virtual bool remove_data_file(const std::string& folder);
  
    virtual std::string get_db_name() const;
  
    virtual bool lock();
  
    virtual void unlock();
  
    virtual bool block_exists(const crypto::hash& h, uint64_t *height = NULL) const;
  
    virtual block get_block(const crypto::hash& h) const;
  
    virtual uint64_t get_block_height(const crypto::hash& h) const;
  
    virtual block_header get_block_header(const crypto::hash& h) const;
  
    virtual block get_block_from_height(const uint64_t& height) const;
  
    virtual uint64_t get_block_timestamp(const uint64_t& height) const;
  
    virtual uint64_t get_top_block_timestamp() const;
  
    virtual size_t get_block_weight(const uint64_t& height) const;
  
    virtual difficulty_type get_block_cumulative_difficulty(const uint64_t& height) const;
  
    virtual difficulty_type get_block_difficulty(const uint64_t& height) const;
  
    virtual uint64_t get_block_already_generated_coins(const uint64_t& height) const;
  
    virtual crypto::hash get_block_hash_from_height(const uint64_t& height) const;
  
    virtual std::vector<block> get_blocks_range(const uint64_t& h1, const uint64_t& h2) const;
  
    virtual std::vector<crypto::hash> get_hashes_range(const uint64_t& h1, const uint64_t& h2) const;
  
    virtual crypto::hash top_block_hash() const;
  
    virtual block get_top_block() const;
  
    virtual uint64_t height() const;
  
    virtual bool tx_exists(const crypto::hash& h) const;
  
    virtual uint64_t get_tx_unlock_time(const crypto::hash& h) const;
  
    virtual transaction get_tx(const crypto::hash& h) const;
  
    virtual uint64_t get_tx_count() const;
  
    virtual std::vector<transaction> get_tx_list(const std::vector<crypto::hash>& hlist) const;
  
    virtual uint64_t get_tx_block_height(const crypto::hash& h) const;
  
    virtual uint64_t get_num_outputs(const uint64_t& amount) const;
  
    virtual uint64_t get_indexing_base() const { return 1; }
  
    virtual output_data_t get_output_key(const uint64_t& amount, const uint64_t& index);
    virtual void get_output_key(const uint64_t &amount, const std::vector<uint64_t> &offsets, std::vector<output_data_t> &outputs);
  
    virtual tx_out_index get_output_tx_and_index_from_global(const uint64_t& index) const;
    virtual void get_output_tx_and_index_from_global(const std::vector<uint64_t> &global_indices,
            std::vector<tx_out_index> &tx_out_indices) const;
  
    virtual tx_out_index get_output_tx_and_index(const uint64_t& amount, const uint64_t& index);
    virtual void get_output_tx_and_index(const uint64_t& amount, const std::vector<uint64_t> &offsets, std::vector<tx_out_index> &indices);
  
    virtual std::vector<uint64_t> get_tx_output_indices(const crypto::hash& h) const;
    virtual std::vector<uint64_t> get_tx_amount_output_indices(const crypto::hash& h) const;
  
    virtual bool has_key_image(const crypto::key_image& img) const;
  
    virtual uint64_t add_block( const block& blk
                              , size_t block_weight
                              , const difficulty_type& cumulative_difficulty
                              , const uint64_t& coins_generated
                              , const std::vector<transaction>& txs
                              );
  
    virtual void set_batch_transactions(bool batch_transactions);
    virtual bool batch_start(uint64_t batch_num_blocks=0);
    virtual void batch_commit();
    virtual void batch_stop();
    virtual void batch_abort();
  
    virtual void block_txn_start(bool readonly);
    virtual void block_txn_stop();
    virtual void block_txn_abort();
  
    virtual void pop_block(block& blk, std::vector<transaction>& txs);
  
  #if defined(BDB_BULK_CAN_THREAD)
    virtual bool can_thread_bulk_indices() const { return true; }
  #else
    virtual bool can_thread_bulk_indices() const { return false; }
  #endif
  
    /**
     * @brief return a histogram of outputs on the blockchain
     *
     * @param amounts optional set of amounts to lookup
     *
     * @return a set of amount/instances
     */
    std::map<uint64_t, uint64_t> get_output_histogram(const std::vector<uint64_t> &amounts) const;
  
  private:
    virtual void add_block( const block& blk
                  , size_t block_weight
                  , const difficulty_type& cumulative_difficulty
                  , const uint64_t& coins_generated
                  , const crypto::hash& block_hash
                  );
  
    virtual void remove_block();
  
    virtual void add_transaction_data(const crypto::hash& blk_hash, const transaction& tx, const crypto::hash& tx_hash, const crypto::hash& tx_prunable_hash);
  
    virtual void remove_transaction_data(const crypto::hash& tx_hash, const transaction& tx);
  
    virtual void add_output(const crypto::hash& tx_hash, const tx_out& tx_output, const uint64_t& local_index, const uint64_t unlock_time, const rct::key *commitment);
  
    virtual void remove_output(const tx_out& tx_output);
  
    void remove_tx_outputs(const crypto::hash& tx_hash, const transaction& tx);
  
    void remove_output(const uint64_t& out_index, const uint64_t amount);
    void remove_amount_output_index(const uint64_t amount, const uint64_t global_output_index);
  
    virtual void add_spent_key(const crypto::key_image& k_image);
  
    virtual void remove_spent_key(const crypto::key_image& k_image);
  
    void get_output_global_indices(const uint64_t& amount, const std::vector<uint64_t> &offsets, std::vector<uint64_t> &global_indices);
  
    virtual bool for_all_key_images(std::function<bool(const crypto::key_image&)>) const;
    virtual bool for_all_blocks(std::function<bool(uint64_t, const crypto::hash&, const cryptonote::block&)>) const;
    virtual bool for_all_transactions(std::function<bool(const crypto::hash&, const cryptonote::transaction&)>, bool pruned) const;
    virtual bool for_all_outputs(std::function<bool(uint64_t amount, const crypto::hash &tx_hash, size_t tx_idx)> f) const;
  
    // Hard fork related storage
    virtual void set_hard_fork_version(uint64_t height, uint8_t version);
    virtual uint8_t get_hard_fork_version(uint64_t height) const;
    virtual void check_hard_fork_info();
    virtual void drop_hard_fork_info();
  
    /**
     * @brief convert a tx output to a blob for storage
     *
     * @param output the output to convert
     *
     * @return the resultant blob
     */
    blobdata output_to_blob(const tx_out& output) const;
  
    /**
     * @brief convert a tx output blob to a tx output
     *
     * @param blob the blob to convert
     *
     * @return the resultant tx output
     */
    tx_out output_from_blob(const blobdata& blob) const;
  
    /**
     * @brief get the global index of the index-th output of the given amount
     *
     * @param amount the output amount
     * @param index the index into the set of outputs of that amount
     *
     * @return the global index of the desired output
     */
    uint64_t get_output_global_index(const uint64_t& amount, const uint64_t& index);
    output_data_t get_output_key(const uint64_t& global_index) const;
    void checkpoint_worker() const;
    void check_open() const;
  
    virtual bool is_read_only() const;
  
    //
    // fix up anything that may be wrong due to past bugs
    virtual void fixup();
  
    bool m_run_checkpoint;
    std::unique_ptr<boost::thread> m_checkpoint_thread;
    typedef bdb_safe_buffer<void *> bdb_safe_buffer_t;
    bdb_safe_buffer_t m_buffer;
  
    DbEnv* m_env;
  
    Db* m_blocks;
    Db* m_block_heights;
    Db* m_block_hashes;
    Db* m_block_timestamps;
    Db* m_block_sizes;
    Db* m_block_diffs;
    Db* m_block_coins;
  
    Db* m_txs;
    Db* m_tx_unlocks;
    Db* m_tx_heights;
    Db* m_tx_outputs;
  
    Db* m_output_txs;
    Db* m_output_indices;
    Db* m_output_amounts;
    Db* m_output_keys;
  
    Db* m_spent_keys;
  
    Db* m_hf_starting_heights;
    Db* m_hf_versions;
  
    Db* m_properties;
  
    uint64_t m_height;
    uint64_t m_num_outputs;
    std::string m_folder;
    bdb_txn_safe *m_write_txn;
  
    bool m_batch_transactions; // support for batch transactions
  };
  
  }  // namespace cryptonote
  