tx_pool

  //! pair of <transaction fee, transaction hash> for organization
  typedef std::pair<std::pair<double, std::time_t>, crypto::hash> tx_by_fee_and_receive_time_entry;

  //! container for sorting transactions by fee per unit size
  typedef std::set<tx_by_fee_and_receive_time_entry, txCompare> sorted_tx_container;

    /**
     * @brief information about a single transaction
     */
    struct tx_details
    {
      transaction tx;  //!< the transaction
      size_t blob_size;  //!< the transaction's size
      uint64_t fee;  //!< the transaction's fee amount
      crypto::hash max_used_block_id;  //!< the hash of the highest block referenced by an input
      uint64_t max_used_block_height;  //!< the height of the highest block referenced by an input

      //! whether or not the transaction has been in a block before
      /*! if the transaction was returned to the pool from the blockchain
       *  due to a reorg, then this will be true
       */
      bool kept_by_block;  

      //! the highest block the transaction referenced when last checking it failed
      /*! if verifying a transaction's inputs fails, it's possible this is due
       *  to a reorg since it was created (if it used recently created outputs
       *  as inputs).
       */
      uint64_t last_failed_height;  

      //! the hash of the highest block the transaction referenced when last checking it failed
      /*! if verifying a transaction's inputs fails, it's possible this is due
       *  to a reorg since it was created (if it used recently created outputs
       *  as inputs).
       */
      crypto::hash last_failed_id;

      time_t receive_time;  //!< the time when the transaction entered the pool

      time_t last_relayed_time;  //!< the last time the transaction was relayed to the network
      bool relayed;  //!< whether or not the transaction has been relayed to the network
      bool do_not_relay; //!< to avoid relay this transaction to the network

      bool double_spend_seen; //!< true iff another tx was seen double spending this one
    };

    typedef std::unordered_map<crypto::key_image, std::unordered_set<crypto::hash> > key_images_container;

    //! container for spent key images from the transactions in the pool
    key_images_container m_spent_key_images;  

    //TODO: this time should be a named constant somewhere, not hard-coded
    //! interval on which to check for stale/"stuck" transactions
    epee::math_helper::once_a_time_seconds<30> m_remove_stuck_tx_interval;

    //TODO: look into doing this better
    //!< container for transactions organized by fee per size and receive time
    sorted_tx_container m_txs_by_fee_and_receive_time;

    std::unordered_set<crypto::hash> m_timed_out_transactions;

    Blockchain& m_blockchain;  //!< reference to the Blockchain object

    size_t m_txpool_max_size;
    size_t m_txpool_size;