oxen-core/src/cryptonote_core/tx_pool.h

// Copyright (c) 2014-2019, The Monero Project
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// Parts of this file are originally copyright (c) 2012-2013 The Cryptonote developers

#pragma once

#include <boost/serialization/version.hpp>
#include <functional>
#include <queue>
#include <set>
#include <unordered_map>
#include <unordered_set>

#include "blockchain_db/blockchain_db.h"
#include "common/periodic_task.h"
#include "crypto/hash.h"
#include "cryptonote_basic/cryptonote_basic_impl.h"
#include "cryptonote_basic/verification_context.h"
#include "epee/string_tools.h"
#include "oxen_economy.h"
#include "tx_blink.h"

namespace cryptonote {
class Blockchain;
/************************************************************************/
/*                                                                      */
/************************************************************************/

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

class txCompare {
  public:
    bool operator()(
            const tx_by_fee_and_receive_time_entry& a,
            const tx_by_fee_and_receive_time_entry& b) const {
        // Sort order:         non-standard txes,     fee (descending),      arrival time, hash
        return std::make_tuple(
                       !std::get<0>(a.first),
                       -std::get<1>(a.first),
                       std::get<2>(a.first),
                       a.second) <
               std::make_tuple(
                       !std::get<0>(b.first),
                       -std::get<1>(b.first),
                       std::get<2>(b.first),
                       b.second);
    }
};

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

/// Argument passed into add_tx specifying different requires on the transaction
struct tx_pool_options {
    bool kept_by_block = false;  ///< has this transaction been in a block?
    bool relayed = false;        ///< was this transaction from the network or a local client?
    bool do_not_relay = false;   ///< to avoid relaying the transaction to the network
    bool approved_blink =
            false;  ///< signals that this is a blink tx and so should be accepted even if it
                    ///< conflicts with mempool or recent txes in non-immutable block; typically
                    ///< specified indirectly (via core.handle_incoming_txs())
    uint64_t fee_percent = 100;  ///< the required miner tx fee in percent relative to the base
                                 ///< required miner tx fee; must be >= 100.
    uint64_t burn_fixed =
            0;  ///< a required minimum amount that must be burned (in atomic currency)
    uint64_t burn_percent = 0;  ///< a required amount as a percentage of the base required miner tx
                                ///< fee that must be burned (additive with burn_fixed, if both > 0)

    static tx_pool_options from_block() {
        tx_pool_options o;
        o.kept_by_block = true;
        o.relayed = true;
        return o;
    }
    static tx_pool_options from_peer() {
        tx_pool_options o;
        o.relayed = true;
        return o;
    }
    static tx_pool_options new_tx(bool do_not_relay = false) {
        tx_pool_options o;
        o.do_not_relay = do_not_relay;
        return o;
    }
    static tx_pool_options new_blink(bool approved, hf hf_version) {
        tx_pool_options o;
        o.do_not_relay = !approved;
        o.approved_blink = approved;
        o.fee_percent = oxen::BLINK_MINER_TX_FEE_PERCENT;

        o.burn_percent = oxen::BLINK_BURN_TX_FEE_PERCENT_V18;
        o.burn_fixed = oxen::BLINK_BURN_FIXED;
        return o;
    }
};

/**
 * @brief Transaction pool, handles transactions which are not part of a block
 *
 * This class handles all transactions which have been received, but not as
 * part of a block.
 *
 * This handling includes:
 *   storing the transactions
 *   organizing the transactions by fee per weight unit
 *   taking/giving transactions to and from various other components
 *   saving the transactions to disk on shutdown
 *   helping create a new block template by choosing transactions for it
 *
 */
class tx_memory_pool {
  public:
    /**
     * @brief Constructor
     *
     * @param bchs a Blockchain class instance, for getting chain info
     */
    tx_memory_pool(Blockchain& bchs);

    // Non-copyable
    tx_memory_pool(const tx_memory_pool&) = delete;
    tx_memory_pool& operator=(const tx_memory_pool&) = delete;

    /**
     * @copydoc add_tx(transaction&, tx_verification_context&, const tx_pool_options &, hf)
     *
     * @param id the transaction's hash
     * @param tx_weight the transaction's weight
     * @param blink_rollback_height if tx is a blink that conflicts with a recent (non-immutable)
     * block tx then set this pointer to the required new height: that is, all blocks with height
     * `block_rollback_height` and above must be removed.
     */
    bool add_tx(
            transaction& tx,
            const crypto::hash& id,
            const std::string& blob,
            size_t tx_weight,
            tx_verification_context& tvc,
            const tx_pool_options& opts,
            hf hf_version,
            uint64_t* blink_rollback_height = nullptr);

    /**
     * @brief add a transaction to the transaction pool
     *
     * Most likely the transaction will come from the network, but it is
     * also possible for transactions to come from popped blocks during
     * a reorg, or from local clients creating a transaction and
     * submitting it to the network
     *
     * @param tx the transaction to be added
     * @param tvc return-by-reference status about the transaction verification
     * @param opts the options controlling how this tx will be accepted/added
     * @param hf_version the hard fork version used to create the transaction
     *
     * @return true if the transaction passes validations, otherwise false
     */
    bool add_tx(
            transaction& tx,
            tx_verification_context& tvc,
            const tx_pool_options& opts,
            hf hf_version);

    /**
     * @brief attempts to add a blink transaction to the transaction pool.
     *
     * This method must be called without a held blink lock.
     *
     * This is only for use for new transactions that should not exist yet on the chain or mempool
     * (and will fail if already does).  See `add_existing_blink` instead to add blink data about a
     * transaction that already exists.  This is only meant to be called during the SN blink signing
     * phase (and requires that the `tx` transaction be properly set to a full transaction);
     * ordinary nodes receiving a blink tx from the network should be going through
     * core.handle_incoming_blinks instead.
     *
     * Whether or not the transaction is added to the known blinks or marked for relaying depends on
     * whether the passed-in transaction has an `.approved()` status: if it does, the transaction is
     * set for relaying and added to the active blinks immediately; otherwise it is not added to the
     * known blinks and will not be relayed.
     *
     * The transaction is *not* added to the known blinks or marked for relaying unless it is passed
     * in with an `.approved()` status.
     *
     * @param blink - a shared_ptr to the blink details
     * @param tvc - the verification results
     * @param blink_exists - will be set to true if the addition fails because the blink tx already
     * exists
     *
     * @return true if the tx passes validations and has been added to the tx pool.
     */
    bool add_new_blink(
            const std::shared_ptr<blink_tx>& blink,
            tx_verification_context& tvc,
            bool& blink_exists);

    /**
     * @brief attempts to add blink transaction information about an existing blink transaction
     *
     * You *must* already hold a blink_unique_lock().
     *
     * This method takes an approved blink_tx and records it in the known blinks data.  No check is
     * done that the transaction actually exists on the blockchain or mempool.  It is assumed that
     * the given shared_ptr is a new blink that is not yet shared between threads (and thus doesn't
     * need locking): sharing is expected only after it is added to the blinks via this method.
     *
     * NB: this function assumes that the given blink tx is valid and approved (signed) but does
     * *not* check it (except as an assert when compiling in debug mode).
     *
     * @param blink the blink_tx shared_ptr
     *
     * @return true if the blink data was recorded, false if the given blink was already known.
     */
    bool add_existing_blink(std::shared_ptr<blink_tx> blink);

    /**
     * @brief accesses blink tx details if the given tx hash is a known, approved blink tx, nullptr
     * otherwise.
     *
     * You *must* already hold a blink_shared_lock() or blink_unique_lock().
     *
     * @param tx_hash the hash of the tx to access
     */
    std::shared_ptr<blink_tx> get_blink(const crypto::hash& tx_hash) const;

    /**
     * Equivalent to `(bool) get_blink(...)`, but slightly more efficient when the blink information
     * isn't actually needed beyond an existance test (as it avoids copying the shared_ptr).
     *
     * You *must* already hold a blink_shared_lock() or blink_unique_lock().
     */
    bool has_blink(const crypto::hash& tx_hash) const;

    /**
     * @brief modifies a vector of tx hashes to remove any that have known valid blink signatures
     *
     * Must not currently hold a blink lock.
     *
     * @param txs the tx hashes to check
     */
    void keep_missing_blinks(std::vector<crypto::hash>& tx_hashes) const;

    /**
     * @brief returns checksums of blink txes included in recently mined blocks and in the mempool
     *
     * Must not currently hold a blink lock.
     *
     * The returned map consists of height => hashsum pairs where the height is the height in which
     * the blink transactions were mined and the hashsum is a checksum of all the blink txes mined
     * at that height.  Unmined mempool blink txes are included at a height of 0.  Only heights
     * since the immutable checkpoint block are included.  Any block height (including the special
     * "0" height) that has no blink tx in it is not included.
     */
    std::map<uint64_t, crypto::hash> get_blink_checksums() const;

    /**
     * @brief returns the hashes of any non-immutable blink transactions mined in the given heights.
     * A height of 0 is allowed: it indicates blinks in the mempool.
     *
     * Must not currently hold a blink lock.
     *
     * Note that this returned hashes by MINED HEIGHTS, not BLINK HEIGHTS where are a different
     * concept.
     *
     * @param set of heights
     *
     * @return vector of hashes
     */
    std::vector<crypto::hash> get_mined_blinks(const std::set<uint64_t>& heights) const;

    /**
     * @brief takes a transaction with the given hash from the pool
     *
     * @param id the hash of the transaction
     * @param tx return-by-reference the transaction taken
     * @param txblob return-by-reference the transaction as a blob
     * @param tx_weight return-by-reference the transaction's weight
     * @param fee the transaction fee
     * @param relayed return-by-reference was transaction relayed to us by the network?
     * @param do_not_relay return-by-reference is transaction not to be relayed to the network?
     * @param double_spend_seen return-by-reference was a double spend seen for that transaction?
     *
     * @return true unless the transaction cannot be found in the pool
     */
    bool take_tx(
            const crypto::hash& id,
            transaction& tx,
            std::string& txblob,
            size_t& tx_weight,
            uint64_t& fee,
            bool& relayed,
            bool& do_not_relay,
            bool& double_spend_seen);

    /**
     * @brief checks if the pool has a transaction with the given hash
     *
     * @param id the hash to look for
     *
     * @return true if the transaction is in the pool, otherwise false
     */
    bool have_tx(const crypto::hash& id) const;

    /**
     * @brief determines whether the given tx hashes are in the mempool
     *
     * @param hashes vector of tx hashes
     *
     * @return vector of the same size as `hashes` of true (1) or false (0) values.  (Not using
     * std::vector<bool> because it is broken by design).
     */
    std::vector<uint8_t> have_txs(const std::vector<crypto::hash>& hashes) const;

    /**
     * @brief action to take when notified of a block added to the blockchain
     *
     * @param new_block_height the height of the blockchain after the change
     * @param top_block_id the hash of the new top block
     *
     * @return true
     */
    bool on_blockchain_inc(block const& blk);

    /**
     * @brief action to take when notified of a block removed from the blockchain
     *
     * @param new_block_height the height of the blockchain after the change
     * @param top_block_id the hash of the new top block
     *
     * @return true
     */
    bool on_blockchain_dec();

    /**
     * @brief action to take periodically
     *
     * Currently checks transaction pool for stale ("stuck") transactions
     */
    void on_idle();

    /**
     * Specifies a callback to invoke when one or more transactions is added to the mempool.  Note
     * that, because incoming blocks have their transactions added to the mempool, this *does*
     * trigger for txes that arrive in new blocks.
     *
     * It does not, however, trigger for transactions that fail verification, that are flagged
     * do-not-relay, or that are returned to the pool from a block (i.e. when doing a reorg).
     */
    void add_notify(std::function<
                    void(const crypto::hash&,
                         const transaction&,
                         const std::string& blob,
                         const tx_pool_options&)> notify);

    /**
     * @brief locks the transaction pool
     */
    void lock() const { m_transactions_lock.lock(); }

    /**
     * @brief unlocks the transaction pool
     */
    void unlock() const { m_transactions_lock.unlock(); }

    /**
     * @briefs does a non-blocking attempt to lock the transaction pool
     */
    bool try_lock() const { return m_transactions_lock.try_lock(); }

    /**
     * @brief obtains a unique lock on the approved blink tx pool
     */
    template <typename... Args>
    auto blink_unique_lock(Args&&... args) const {
        return std::unique_lock{m_blinks_mutex, std::forward<Args>(args)...};
    }

    /**
     * @brief obtains a shared lock on the approved blink tx pool
     */
    template <typename... Args>
    auto blink_shared_lock(Args&&... args) const {
        return std::shared_lock{m_blinks_mutex, std::forward<Args>(args)...};
    }

    // load/store operations

    /**
     * @brief loads pool state (if any) from disk, and initializes pool
     *
     * @param max_txpool_weight the max weight in bytes
     *
     * @return true
     */
    bool init(size_t max_txpool_weight = 0);

    /**
     * @brief attempts to save the transaction pool state to disk
     *
     * Currently fails (returns false) if the data directory from init()
     * does not exist and cannot be created, but returns true even if
     * saving to disk is unsuccessful.
     *
     * @return true in most cases (see above)
     */
    bool deinit();

    /**
     * @brief Chooses transactions for a block to include
     *
     * @param bl return-by-reference the block to fill in with transactions
     * @param median_weight the current median block weight
     * @param already_generated_coins the current total number of coins "minted"
     * @param total_weight return-by-reference the total weight of the new block
     * @param raw_fee return-by-reference the total of fees from the included transactions.  Note
     * that this does not subtract any large block penalty fees; this is just the raw sum of fees of
     * included txes.
     * @param expected_reward return-by-reference the total reward awarded to the block producer
     * finding this block, including transaction fees and, if applicable, a large block reward
     * penalty.
     * @param version hard fork version to use for consensus rules
     *
     * @return true
     */
    bool fill_block_template(
            block& bl,
            size_t median_weight,
            uint64_t already_generated_coins,
            size_t& total_weight,
            uint64_t& raw_fee,
            uint64_t& expected_reward,
            hf version,
            uint64_t height);

    /**
     * @brief get a list of all transactions in the pool
     *
     * @param txs return-by-reference the list of transactions
     * @param include_unrelayed_txes include unrelayed txes in the result
     *
     */
    void get_transactions(std::vector<transaction>& txs, bool include_unrelayed_txes = true) const;

    /**
     * @brief get a list of all transaction hashes in the pool
     *
     * @param txs return-by-reference the list of transactions
     * @param include_unrelayed_txes include unrelayed txes in the result
     *
     */
    void get_transaction_hashes(
            std::vector<crypto::hash>& txs,
            bool include_unrelayed_txes = true,
            bool include_only_blinked = false) const;

    /// Return type of get_transaction_stats()
    struct tx_stats {
        uint64_t bytes_total;      ///< Total size of all transactions in pool.
        uint32_t bytes_min;        ///< Min transaction size in pool.
        uint32_t bytes_max;        ///< Max transaction size in pool.
        uint32_t bytes_med;        ///< Median transaction size in pool.
        uint64_t fee_total;        ///< Total fee's in pool in atomic units.
        uint64_t oldest;           ///< Unix time of the oldest transaction in the pool.
        uint32_t txs_total;        ///< Total number of transactions.
        uint32_t num_failing;      ///< Bumber of failing transactions.
        uint32_t num_10m;          ///< Number of transactions in pool for more than 10 minutes.
        uint32_t num_not_relayed;  ///< Number of non-relayed transactions.
        uint64_t histo_98pc;       ///< the time 98% of txes are "younger" than.
        std::vector<std::pair<uint32_t, uint64_t>>
                histo;  ///< List of txpool histo [number of txes, size in bytes] pairs.
        uint32_t num_double_spends;  ///< Number of double spend transactions.
    };

    /**
     * @brief get a summary statistics of all transaction hashes in the pool
     *
     * @param include_unrelayed_txes include unrelayed txes in the result
     *
     * @return txpool_stats struct of pool statistics
     */
    tx_stats get_transaction_stats(bool include_unrelayed_txes = true) const;

    /**
     * @brief check for presence of key images in the pool
     *
     * @param key_images [in] vector of key images to check
     * @param spent [out] vector of bool to return
     *
     * @return true
     */
    bool check_for_key_images(
            const std::vector<crypto::key_image>& key_images, std::vector<bool>& spent) const;

    /**
     * @brief get a specific transaction from the pool
     *
     * @param h the hash of the transaction to get
     * @param tx return-by-reference the transaction blob requested
     *
     * @return true if the transaction is found, otherwise false
     */
    bool get_transaction(const crypto::hash& h, std::string& txblob) const;

    /**
     * @brief get specific transactions from the pool
     *
     * @param hashes - tx hashes of desired transactions
     * @param txblobs - vector of std::string (i.e. std::strings) to which found blobs should be
     * appended.  The vector is *not* cleared of existing values.
     *
     * @return number of transactions added to txblobs
     */
    int find_transactions(
            const std::unordered_set<crypto::hash>& tx_hashes,
            std::vector<std::string>& txblobs) const;

    /**
     * @brief get a list of all relayable transactions and their hashes
     *
     * "relayable" in this case means:
     *   nonzero fee -or- a zero-fee SN state change tx
     *   hasn't been relayed too recently
     *   isn't old enough that relaying it is considered harmful
     *   doesn't have do_not_relay set
     *
     * @param txs return-by-reference the transactions and their hashes
     *
     * @return true
     */
    bool get_relayable_transactions(std::vector<std::pair<crypto::hash, std::string>>& txs) const;

    /**
     * @brief clear transactions' `do_not_relay` flags (if set) so that they can start being
     * relayed.  (Note that it still must satisfy the other conditions of
     * `get_relayable_transactions` to actually be relayable).
     *
     * @return the number of txes that were found with an active `do_not_relay` flag that was
     * cleared.
     */
    int set_relayable(const std::vector<crypto::hash>& tx_hashes);

    /**
     * @brief tell the pool that certain transactions were just relayed
     *
     * @param txs the list of transactions (and their hashes)
     */
    void set_relayed(const std::vector<std::pair<crypto::hash, std::string>>& txs);

    /**
     * @brief get the total number of transactions in the pool
     *
     * @return the number of transactions in the pool
     */
    size_t get_transactions_count(bool include_unrelayed_txes = true) const;

    /**
     * @brief remove transactions from the pool which are no longer valid
     *
     * With new versions of the currency, what conditions render a transaction
     * invalid may change.  This function clears those which were received
     * before a version change and no longer conform to requirements.
     *
     * @param version the version the transactions must conform to
     *
     * @return the number of transactions removed
     */
    size_t validate(hf version);

    /**
     * @brief return the cookie
     *
     * @return the cookie
     */
    uint64_t cookie() const { return m_cookie; }

    /**
     * @brief get the cumulative txpool weight in bytes
     *
     * @return the cumulative txpool weight in bytes
     */
    size_t get_txpool_weight() const;

    /**
     * @brief set the max cumulative txpool weight in bytes
     *
     * @param bytes the max cumulative txpool weight in bytes
     */
    void set_txpool_max_weight(size_t bytes);

    // TODO: confirm the below comments and investigate whether or not this
    //       is the desired behavior
    //! map key images to transactions which spent them
    /*! this seems odd, but it seems that multiple transactions can exist
     *  in the pool which both have the same spent key.  This would happen
     *  in the event of a reorg where someone creates a new/different
     *  transaction on the assumption that the original will not be in a
     *  block again.
     */
    using key_images_container =
            std::unordered_map<crypto::key_image, std::unordered_set<crypto::hash>>;

    /// Returns a copy of the map of key images -> set of transactions which spent them.
    ///
    /// \param already_locked can be passed as true if the caller already has a lock on the
    /// blockchain and mempool objects; otherwise a new lock will be obtained by the call.
    key_images_container get_spent_key_images(bool already_locked = false);

  private:
    /**
     * @brief insert key images into m_spent_key_images
     *
     * @return true on success, false on error
     */
    bool insert_key_images(
            const transaction_prefix& tx, const crypto::hash& txid, bool kept_by_block);

    /**
     * @brief remove old transactions from the pool
     *
     * After a certain time, it is assumed that a transaction which has not
     * yet been mined will likely not be mined.  These transactions are removed
     * from the pool to avoid buildup.
     *
     * @return true
     */
    bool remove_stuck_transactions();

    /**
     * @brief check if a transaction in the pool has a given spent key image
     *
     * @param key_im the spent key image to look for
     *
     * @return true if the spent key image is present, otherwise false
     */
    bool have_tx_keyimg_as_spent(const crypto::key_image& key_im) const;

    /**
     * @brief check if a tx that does not have a key-image component has a duplicate in the pool

     * @return true if it already exists
     *
     */
    bool have_duplicated_non_standard_tx(transaction const& tx, hf version) const;

    /**
     * @brief check if any spent key image in a transaction is in the pool
     *
     * Checks if any of the spent key images in a given transaction are present
     * in any of the transactions in the transaction pool.
     *
     * @note see tx_pool::have_tx_keyimg_as_spent
     *
     * @param tx the transaction to check spent key images of
     * @param found if specified, append the hashes of all conflicting mempool txes here
     *
     * @return true if any spent key images are present in the pool, otherwise false
     */
    bool have_tx_keyimges_as_spent(
            const transaction& tx, std::vector<crypto::hash>* conflicting = nullptr) const;

    /**
     * @brief forget a transaction's spent key images
     *
     * Spent key images are stored separately from transactions for
     * convenience/speed, so this is part of the process of removing
     * a transaction from the pool.
     *
     * @param tx the transaction
     * @param txid the transaction's hash
     *
     * @return false if any key images to be removed cannot be found, otherwise true
     */
    bool remove_transaction_keyimages(const transaction_prefix& tx, const crypto::hash& txid);

    /**
     * @brief check if a transaction is a valid candidate for inclusion in a block
     *
     * @param txd the transaction to check (and info about it)
     * @param txid the txid of the transaction to check
     * @param txblob the transaction blob to check
     * @param tx the parsed transaction, if successful
     *
     * @return true if the transaction is good to go, otherwise false
     */
    bool is_transaction_ready_to_go(
            txpool_tx_meta_t& txd,
            const crypto::hash& txid,
            const std::string& txblob,
            transaction& tx) const;

    /**
     * @brief mark all transactions double spending the one passed
     */
    void mark_double_spend(const transaction& tx);

    /**
     * @brief remove a transaction from the mempool
     *
     * This is called when pruning the mempool to reduce its size, and when deleting transactions
     * from the mempool because of a conflicting blink transaction arriving.  Transactions lock and
     * blockchain lock must be held by the caller.
     *
     * @param txid the transaction id to remove
     * @param meta optional pointer to txpool_tx_meta_t; will be looked up if omitted
     * @param stc_it an optional iterator to the tx's entry in m_txs_by_fee_and_receive_time to save
     * a (linear) scan to find it when already available.  The given iterator will be invalidated if
     * removed.
     *
     * @return true if the transaction was removed, false on failure.
     */
    bool remove_tx(
            const crypto::hash& txid,
            const txpool_tx_meta_t* meta = nullptr,
            const sorted_tx_container::iterator* stc_it = nullptr);

    /**
     * @brief prune lowest fee/byte txes till we're not above bytes
     *
     * @param skip don't prune the given ID this time (because it was just added)
     */
    void prune(const crypto::hash& skip);

    /**
     * @brief Attempt to add a blink tx "by force", removing conflicting non-blink txs
     *
     * The given transactions are removed from the mempool, if possible, to make way for this blink
     * transactions.  In order for any removal to happen, all the conflicting txes must be non-blink
     * transactions, and must either:
     * - be a mempool transaction
     * - be a mined, non-blink transaction in the recent (mutable) section of the chain
     *
     * If all conflicting txs satisfy the above then conflicting mempool txs are removed and the
     * blink_rollback_height pointer is updated to the required rollback height to eject any mined
     * txs (if not already at that height or lower).  True is returned.
     *
     * If any txs are found that do not satisfy the above then nothing is removed and false is
     * returned.
     *
     * @param the id of the incoming blink tx
     * @param conflict_txs vector of conflicting transaction hashes that are preventing the blink tx
     * @param blink_rollback_height a pointer to update to the new required height if a chain
     * rollback is needed for the blink tx.  (That is, all blocks with height >=
     * blink_rollback_height need to be popped).
     *
     * This method is *not* called with a blink lock held.
     *
     * @return true if the conflicting transactions have been removed (and/or the rollback height
     * set), false if tx removal and/or rollback are insufficient to eliminate conflicting txes.
     */
    bool remove_blink_conflicts(
            const crypto::hash& id,
            const std::vector<crypto::hash>& conflict_txs,
            uint64_t* blink_rollback_height);

    mutable std::recursive_mutex m_transactions_lock;  //!< mutex for the pool

    //! 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
    tools::periodic_task m_remove_stuck_tx_interval{30s};

    // 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::atomic<uint64_t> m_cookie;  //!< incremented at each change

    /// Callbacks for new tx notifications
    std::vector<std::function<void(
            const crypto::hash&,
            const transaction&,
            const std::string& blob,
            const tx_pool_options&)>>
            m_tx_notify;

    /**
     * @brief get an iterator to a transaction in the sorted container
     *
     * @param id the hash of the transaction to look for
     *
     * @return an iterator, possibly to the end of the container if not found
     */
    sorted_tx_container::iterator find_tx_in_sorted_container(const crypto::hash& id) const;

    //! cache/call Blockchain::check_tx_inputs results
    bool check_tx_inputs(
            const std::function<cryptonote::transaction&()>& get_tx,
            const crypto::hash& txid,
            uint64_t& max_used_block_height,
            crypto::hash& max_used_block_id,
            tx_verification_context& tvc,
            bool kept_by_block = false,
            uint64_t* blink_rollback_height = nullptr) const;

    //! transactions which are unlikely to be included in blocks
    /*! These transactions are kept in RAM in case they *are* included
     *  in a block eventually, but this container is not saved to disk.
     */
    std::unordered_set<crypto::hash> m_timed_out_transactions;

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

    size_t m_txpool_max_weight;
    size_t m_txpool_weight;

    mutable std::unordered_map<
            crypto::hash,
            std::tuple<bool, tx_verification_context, uint64_t, crypto::hash>>
            m_input_cache;

    std::unordered_map<crypto::hash, transaction> m_parsed_tx_cache;

    mutable std::shared_mutex m_blinks_mutex;

    // Contains blink metadata for approved blink transactions. { txhash => blink_tx, ... }.
    mutable std::unordered_map<crypto::hash, std::shared_ptr<cryptonote::blink_tx>> m_blinks;

    // Helper method: retrieves hashes and mined heights of blink txes since the immutable block;
    // mempool blinks are included with a height of 0.  Also takes care of cleaning up any blinks
    // that have become immutable.  Blink lock must not be already held.
    std::pair<std::vector<crypto::hash>, std::vector<uint64_t>> get_blink_hashes_and_mined_heights()
            const;
};
}  // namespace cryptonote