text: // Copyright (c) 2009-2010 Satoshi Nakamoto
  // Copyright (c) 2009-2014 The Bitcoin developers
  // Copyright (c) 2016-2020 The PIVX developers
  // Copyright (C) 2019-2020 The ucacoin developers
  // Distributed under the MIT software license, see the accompanying
  // file COPYING or http://www.opensource.org/licenses/mit-license.php.
  
  #ifndef BITCOIN_TXMEMPOOL_H
  #define BITCOIN_TXMEMPOOL_H
  
  #include <list>
  #include <set>
  
  #include "amount.h"
  #include "coins.h"
  #include "primitives/transaction.h"
  #include "sync.h"
  #include "random.h"
  
  #include "boost/multi_index_container.hpp"
  #include "boost/multi_index/ordered_index.hpp"
  
  class CAutoFile;
  
  inline double AllowFreeThreshold()
  {
      return COIN * 1440 / 250;
  }
  
  inline bool AllowFree(double dPriority)
  {
      // Large (in bytes) low-priority (new, small-coin) transactions
      // need a fee.
      return dPriority > AllowFreeThreshold();
  }
  
  
  /** Fake height value used in CCoins to signify they are only in the memory pool (since 0.8) */
  static const unsigned int MEMPOOL_HEIGHT = 0x7FFFFFFF;
  
  class CTxMemPool;
  
  /** \class CTxMemPoolEntry
   *
   * CTxMemPoolEntry stores data about the correponding transaction, as well
   * as data about all in-mempool transactions that depend on the transaction
   * ("descendant" transactions).
   *
   * When a new entry is added to the mempool, we update the descendant state
   * (nCountWithDescendants, nSizeWithDescendants, and nFeesWithDescendants) for
   * all ancestors of the newly added transaction.
   *
   * If updating the descendant state is skipped, we can mark the entry as
   * "dirty", and set nSizeWithDescendants/nFeesWithDescendants to equal nTxSize/
   * nTxFee. (This can potentially happen during a reorg, where we limit the
   * amount of work we're willing to do to avoid consuming too much CPU.)
   *
   */
  class CTxMemPoolEntry
  {
  private:
      CTransaction tx;
      CAmount nFee;         //! Cached to avoid expensive parent-transaction lookups
      size_t nTxSize;       //! ... and avoid recomputing tx size
      size_t nModSize;      //! ... and modified size for priority
      size_t nUsageSize;    //! ... and total memory usage
      CFeeRate feeRate;     //! ... and fee per kB
      int64_t nTime;        //! Local time when entering the mempool
      double entryPriority;     //! Priority when entering the mempool
      unsigned int entryHeight; //! Chain height when entering the mempool
      bool hadNoDependencies; //! Not dependent on any other txs when it entered the mempool
      CAmount inChainInputValue; //! Sum of all txin values that are already in blockchain
      bool spendsCoinbaseOrCoinstake; //! keep track of transactions that spend a coinbase or a coinstake
  
      // Information about descendants of this transaction that are in the
      // mempool; if we remove this transaction we must remove all of these
      // descendants as well.  if nCountWithDescendants is 0, treat this entry as
      // dirty, and nSizeWithDescendants and nFeesWithDescendants will not be
      // correct.
      uint64_t nCountWithDescendants; //! number of descendant transactions
      uint64_t nSizeWithDescendants;  //! ... and size
      CAmount nFeesWithDescendants;  //! ... and total fees (all including us)
  
  public:
      CTxMemPoolEntry(const CTransaction& _tx, const CAmount& _nFee,
              int64_t _nTime, double _entryPriority, unsigned int _entryHeight,
              bool poolHasNoInputsOf, CAmount _inChainInputValue, bool _spendsCoinbaseOrCoinstake);
      CTxMemPoolEntry(const CTxMemPoolEntry& other);
  
      const CTransaction& GetTx() const { return this->tx; }
      /**
       * Fast calculation of lower bound of current priority as update
       * from entry priority. Only inputs that were originally in-chain will age.
       */
      double GetPriority(unsigned int currentHeight) const;
      const CAmount& GetFee() const { return nFee; }
      size_t GetTxSize() const { return nTxSize; }
      int64_t GetTime() const { return nTime; }
      unsigned int GetHeight() const { return entryHeight; }
      bool WasClearAtEntry() const { return hadNoDependencies; }
      size_t DynamicMemoryUsage() const { return nUsageSize; }
  
      // Adjusts the descendant state, if this entry is not dirty.
      void UpdateState(int64_t modifySize, CAmount modifyFee, int64_t modifyCount);
  
      /** We can set the entry to be dirty if doing the full calculation of in-
       *  mempool descendants will be too expensive, which can potentially happen
       *  when re-adding transactions from a block back to the mempool.
       */
      void SetDirty();
      bool IsDirty() const { return nCountWithDescendants == 0; }
  
      uint64_t GetCountWithDescendants() const { return nCountWithDescendants; }
      uint64_t GetSizeWithDescendants() const { return nSizeWithDescendants; }
      CAmount GetFeesWithDescendants() const { return nFeesWithDescendants; }
  
      bool GetSpendsCoinbaseOrCoinstake() const { return spendsCoinbaseOrCoinstake; }
  };
  
  // Helpers for modifying CTxMemPool::mapTx, which is a boost multi_index.
  struct update_descendant_state
  {
      update_descendant_state(int64_t _modifySize, CAmount _modifyFee, int64_t _modifyCount) :
          modifySize(_modifySize), modifyFee(_modifyFee), modifyCount(_modifyCount)
      {}
  
      void operator() (CTxMemPoolEntry &e)
          { e.UpdateState(modifySize, modifyFee, modifyCount); }
  
      private:
          int64_t modifySize;
          CAmount modifyFee;
          int64_t modifyCount;
  };
  
  struct set_dirty
  {
      void operator() (CTxMemPoolEntry &e)
          { e.SetDirty(); }
  };
  
  // extracts a TxMemPoolEntry's transaction hash
  struct mempoolentry_txid
  {
      typedef uint256 result_type;
      result_type operator() (const CTxMemPoolEntry &entry) const
      {
          return entry.GetTx().GetHash();
      }
  };
  
  /** \class CompareTxMemPoolEntryByFee
   *
   *  Sort an entry by max(feerate of entry's tx, feerate with all descendants).
   */
  class CompareTxMemPoolEntryByFee
  {
  public:
      bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) const
      {
          bool fUseADescendants = UseDescendantFeeRate(a);
          bool fUseBDescendants = UseDescendantFeeRate(b);
  
          double aFees = fUseADescendants ? a.GetFeesWithDescendants() : a.GetFee();
          double aSize = fUseADescendants ? a.GetSizeWithDescendants() : a.GetTxSize();
  
          double bFees = fUseBDescendants ? b.GetFeesWithDescendants() : b.GetFee();
          double bSize = fUseBDescendants ? b.GetSizeWithDescendants() : b.GetTxSize();
  
          // Avoid division by rewriting (a/b > c/d) as (a*d > c*b).
          double f1 = aFees * bSize;
          double f2 = aSize * bFees;
  
          if (f1 == f2) {
              return a.GetTime() >= b.GetTime();
          }
          return f1 < f2;
      }
  
      // Calculate which feerate to use for an entry (avoiding division).
      bool UseDescendantFeeRate(const CTxMemPoolEntry &a) const
      {
          double f1 = (double)a.GetFee() * a.GetSizeWithDescendants();
          double f2 = (double)a.GetFeesWithDescendants() * a.GetTxSize();
          return f2 > f1;
      }
  };
  
  
  class CompareTxMemPoolEntryByEntryTime
  {
  public:
      bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) const
      {
          return a.GetTime() < b.GetTime();
      }
  };
  
  
  class CBlockPolicyEstimator;
  
  /** An inpoint - a combination of a transaction and an index n into its vin */
  class CInPoint
  {
  public:
      const CTransaction* ptx;
      uint32_t n;
  
      CInPoint() { SetNull(); }
      CInPoint(const CTransaction* ptxIn, uint32_t nIn)
      {
          ptx = ptxIn;
          n = nIn;
      }
      void SetNull()
      {
          ptx = NULL;
          n = (uint32_t)-1;
      }
      bool IsNull() const { return (ptx == NULL && n == (uint32_t)-1); }
      size_t DynamicMemoryUsage() const { return 0; }
  };
  
  /**
   * CTxMemPool stores valid-according-to-the-current-best-chain
   * transactions that may be included in the next block.
   *
   * Transactions are added when they are seen on the network
   * (or created by the local node), but not all transactions seen
   * are added to the pool: if a new transaction double-spends
   * an input of a transaction in the pool, it is dropped,
   * as are non-standard transactions.
   *
   * CTxMemPool::mapTx, and CTxMemPoolEntry bookkeeping:
   *
   * mapTx is a boost::multi_index that sorts the mempool on 3 criteria:
   * - transaction hash
   * - feerate [we use max(feerate of tx, feerate of tx with all descendants)]
   * - time in mempool
   *
   * Note: the term "descendant" refers to in-mempool transactions that depend on
   * this one, while "ancestor" refers to in-mempool transactions that a given
   * transaction depends on.
   *
   * In order for the feerate sort to remain correct, we must update transactions
   * in the mempool when new descendants arrive.  To facilitate this, we track
   * the set of in-mempool direct parents and direct children in mapLinks.  Within
   * each CTxMemPoolEntry, we track the size and fees of all descendants.
   *
   * Usually when a new transaction is added to the mempool, it has no in-mempool
   * children (because any such children would be an orphan).  So in
   * addUnchecked(), we:
   * - update a new entry's setMemPoolParents to include all in-mempool parents
   * - update the new entry's direct parents to include the new tx as a child
   * - update all ancestors of the transaction to include the new tx's size/fee
   *
   * When a transaction is removed from the mempool, we must:
   * - update all in-mempool parents to not track the tx in setMemPoolChildren
   * - update all ancestors to not include the tx's size/fees in descendant state
   * - update all in-mempool children to not include it as a parent
   *
   * These happen in UpdateForRemoveFromMempool().  (Note that when removing a
   * transaction along with its descendants, we must calculate that set of
   * transactions to be removed before doing the removal, or else the mempool can
   * be in an inconsistent state where it's impossible to walk the ancestors of
   * a transaction.)
   *
   * In the event of a reorg, the assumption that a newly added tx has no
   * in-mempool children is false.  In particular, the mempool is in an
   * inconsistent state while new transactions are being added, because there may
   * be descendant transactions of a tx coming from a disconnected block that are
   * unreachable from just looking at transactions in the mempool (the linking
   * transactions may also be in the disconnected block, waiting to be added).
   * Because of this, there's not much benefit in trying to search for in-mempool
   * children in addUnchecked().  Instead, in the special case of transactions
   * being added from a disconnected block, we require the caller to clean up the
   * state, to account for in-mempool, out-of-block descendants for all the
   * in-block transactions by calling UpdateTransactionsFromBlock().  Note that
   * until this is called, the mempool state is not consistent, and in particular
   * mapLinks may not be correct (and therefore functions like
   * CalculateMemPoolAncestors() and CalculateDescendants() that rely
   * on them to walk the mempool are not generally safe to use).
   *
   * Computational limits:
   *
   * Updating all in-mempool ancestors of a newly added transaction can be slow,
   * if no bound exists on how many in-mempool ancestors there may be.
   * CalculateMemPoolAncestors() takes configurable limits that are designed to
   * prevent these calculations from being too CPU intensive.
   *
   * Adding transactions from a disconnected block can be very time consuming,
   * because we don't have a way to limit the number of in-mempool descendants.
   * To bound CPU processing, we limit the amount of work we're willing to do
   * to properly update the descendant information for a tx being added from
   * a disconnected block.  If we would exceed the limit, then we instead mark
   * the entry as "dirty", and set the feerate for sorting purposes to be equal
   * the feerate of the transaction without any descendants.
   *
   */
  class CTxMemPool
  {
  private:
      uint32_t nCheckFrequency; //! Value n means that n times in 2^32 we check.
      unsigned int nTransactionsUpdated;
      CBlockPolicyEstimator* minerPolicyEstimator;
  
      CFeeRate minRelayFee; //! Passed to constructor to avoid dependency on main
      uint64_t totalTxSize; //! sum of all mempool tx' byte sizes
      uint64_t cachedInnerUsage; //! sum of dynamic memory usage of all the map elements (NOT the maps themselves)
  
      CFeeRate minReasonableRelayFee;
  
      mutable int64_t lastRollingFeeUpdate;
      mutable bool blockSinceLastRollingFeeBump;
      mutable double rollingMinimumFeeRate; //! minimum fee to get into the pool, decreases exponentially
  
      void trackPackageRemoved(const CFeeRate& rate);
  
  public:
  
      static const int ROLLING_FEE_HALFLIFE = 60 * 60 * 12; // public only for testing
  
      typedef boost::multi_index_container<
          CTxMemPoolEntry,
          boost::multi_index::indexed_by<
              // sorted by txid
              boost::multi_index::ordered_unique<mempoolentry_txid>,
              // sorted by fee rate
              boost::multi_index::ordered_non_unique<
                  boost::multi_index::identity<CTxMemPoolEntry>,
                  CompareTxMemPoolEntryByFee
              >,
              // sorted by entry time
              boost::multi_index::ordered_non_unique<
                  boost::multi_index::identity<CTxMemPoolEntry>,
                  CompareTxMemPoolEntryByEntryTime
              >
          >
      > indexed_transaction_set;
  
      /**
       * This mutex needs to be locked when accessing `mapTx` or other members
       * that are guarded by it.
       *
       * @par Consistency guarantees
       *
       * By design, it is guaranteed that:
       *
       * 1. Locking both `cs_main` and `mempool.cs` will give a view of mempool
       *    that is consistent with current chain tip (`::ChainActive()` and
       *    `CoinsTip()`) and is fully populated. Fully populated means that if the
       *    current active chain is missing transactions that were present in a
       *    previously active chain, all the missing transactions will have been
       *    re-added to the mempool and should be present if they meet size and
       *    consistency constraints.
       *
       * 2. Locking `mempool.cs` without `cs_main` will give a view of a mempool
       *    consistent with some chain that was active since `cs_main` was last
       *    locked, and that is fully populated as described above. It is ok for
       *    code that only needs to query or remove transactions from the mempool
       *    to lock just `mempool.cs` without `cs_main`.
       *
       * To provide these guarantees, it is necessary to lock both `cs_main` and
       * `mempool.cs` whenever adding transactions to the mempool and whenever
       * changing the chain tip. It's necessary to keep both mutexes locked until
       * the mempool is consistent with the new chain tip and fully populated.
       */
      mutable RecursiveMutex cs;
      indexed_transaction_set mapTx;
      typedef indexed_transaction_set::nth_index<0>::type::iterator txiter;
      struct CompareIteratorByHash {
          bool operator()(const txiter &a, const txiter &b) const {
              return a->GetTx().GetHash() < b->GetTx().GetHash();
          }
      };
      typedef std::set<txiter, CompareIteratorByHash> setEntries;
  
  private:
      typedef std::map<txiter, setEntries, CompareIteratorByHash> cacheMap;
  
      struct TxLinks {
          setEntries parents;
          setEntries children;
      };
  
      typedef std::map<txiter, TxLinks, CompareIteratorByHash> txlinksMap;
      txlinksMap mapLinks;
  
      const setEntries & GetMemPoolParents(txiter entry) const;
      const setEntries & GetMemPoolChildren(txiter entry) const;
      void UpdateParent(txiter entry, txiter parent, bool add);
      void UpdateChild(txiter entry, txiter child, bool add);
  
  public:
      std::map<COutPoint, CInPoint> mapNextTx;
      std::map<uint256, std::pair<double, CAmount> > mapDeltas;
  
      /** Create a new CTxMemPool.
       *  minReasonableRelayFee should be a feerate which is, roughly, somewhere
       *  around what it "costs" to relay a transaction around the network and
       *  below which we would reasonably say a transaction has 0-effective-fee.
       */
      CTxMemPool(const CFeeRate& _minReasonableRelayFee);
      ~CTxMemPool();
  
      /**
       * If sanity-checking is turned on, check makes sure the pool is
       * consistent (does not contain two transactions that spend the same inputs,
       * all inputs are in the mapNextTx array). If sanity-checking is turned off,
       * check does nothing.
       */
      void check(const CCoinsViewCache *pcoins) const;
      void setSanityCheck(double dFrequency = 1.0) { nCheckFrequency = dFrequency * 4294967295.0; }
  
      // addUnchecked must updated state for all ancestors of a given transaction,
      // to track size/count of descendant transactions.  First version of
      // addUnchecked can be used to have it call CalculateMemPoolAncestors(), and
      // then invoke the second version.
      bool addUnchecked(const uint256& hash, const CTxMemPoolEntry& entry, bool fCurrentEstimate = true);
      bool addUnchecked(const uint256& hash, const CTxMemPoolEntry &entry, setEntries &setAncestors, bool fCurrentEstimate = true);
      void remove(const CTransaction& tx, std::list<CTransaction>& removed, bool fRecursive = false);
      void removeForReorg(const CCoinsViewCache* pcoins, unsigned int nMemPoolHeight, int flags);
      void removeConflicts(const CTransaction& tx, std::list<CTransaction>& removed);
      void removeForBlock(const std::vector<CTransaction>& vtx, unsigned int nBlockHeight, std::list<CTransaction>& conflicts, bool fCurrentEstimate = true);
      void clear();
      void _clear();  // lock-free
      void queryHashes(std::vector<uint256>& vtxid);
      void getTransactions(std::set<uint256>& setTxid);
      void pruneSpent(const uint256& hash, CCoins& coins);
      unsigned int GetTransactionsUpdated() const;
      void AddTransactionsUpdated(unsigned int n);
      /**
       * Check that none of this transactions inputs are in the mempool, and thus
       * the tx is not dependent on other mempool transactions to be included in a block.
       */
      bool HasNoInputsOf(const CTransaction& tx) const;
  
      /** Affect CreateNewBlock prioritisation of transactions */
      void PrioritiseTransaction(const uint256 hash, const std::string strHash, double dPriorityDelta, const CAmount& nFeeDelta);
      void ApplyDeltas(const uint256 hash, double& dPriorityDelta, CAmount& nFeeDelta) const;
      void ClearPrioritisation(const uint256 hash);
  
      /** Remove a set of transactions from the mempool.
       *  If a transaction is in this set, then all in-mempool descendants must
       *  also be in the set.*/
      void RemoveStaged(setEntries &stage);
  
      /** When adding transactions from a disconnected block back to the mempool,
       *  new mempool entries may have children in the mempool (which is generally
       *  not the case when otherwise adding transactions).
       *  UpdateTransactionsFromBlock() will find child transactions and update the
       *  descendant state for each transaction in hashesToUpdate (excluding any
       *  child transactions present in hashesToUpdate, which are already accounted
       *  for).  Note: hashesToUpdate should be the set of transactions from the
       *  disconnected block that have been accepted back into the mempool.
       */
      void UpdateTransactionsFromBlock(const std::vector<uint256> &hashesToUpdate);
  
      /** Try to calculate all in-mempool ancestors of entry.
       *  (these are all calculated including the tx itself)
       *  limitAncestorCount = max number of ancestors
       *  limitAncestorSize = max size of ancestors
       *  limitDescendantCount = max number of descendants any ancestor can have
       *  limitDescendantSize = max size of descendants any ancestor can have
       *  errString = populated with error reason if any limits are hit
       *  fSearchForParents = whether to search a tx's vin for in-mempool parents, or
       *    look up parents from mapLinks. Must be true for entries not in the mempool
       */
      bool CalculateMemPoolAncestors(const CTxMemPoolEntry &entry, setEntries &setAncestors, uint64_t limitAncestorCount, uint64_t limitAncestorSize, uint64_t limitDescendantCount, uint64_t limitDescendantSize, std::string &errString, bool fSearchForParents = true);
  
      /** The minimum fee to get into the mempool, which may itself not be enough
       *  for larger-sized transactions.
       *  The minReasonableRelayFee constructor arg is used to bound the time it
       *  takes the fee rate to go back down all the way to 0. When the feerate
       *  would otherwise be half of this, it is set to 0 instead.
       */
      CFeeRate GetMinFee(size_t sizelimit) const;
  
      /** Remove transactions from the mempool until its dynamic size is <= sizelimit. */
      void TrimToSize(size_t sizelimit);
  
      /** Expire all transaction (and their dependencies) in the mempool older than time. Return the number of removed transactions. */
      int Expire(int64_t time);
  
      unsigned long size()
      {
          LOCK(cs);
          return mapTx.size();
      }
      uint64_t GetTotalTxSize()
      {
          LOCK(cs);
          return totalTxSize;
      }
  
      bool exists(uint256 hash) const
      {
          LOCK(cs);
          return (mapTx.count(hash) != 0);
      }
  
      bool lookup(uint256 hash, CTransaction& result) const;
  
      /** Estimate fee rate needed to get into the next nBlocks */
      CFeeRate estimateFee(int nBlocks) const;
  
      /** Estimate priority needed to get into the next nBlocks */
      double estimatePriority(int nBlocks) const;
  
      /** Write/Read estimates to disk */
      bool WriteFeeEstimates(CAutoFile& fileout) const;
      bool ReadFeeEstimates(CAutoFile& filein);
  
      size_t DynamicMemoryUsage() const;
  
  private:
      /** UpdateForDescendants is used by UpdateTransactionsFromBlock to update
       *  the descendants for a single transaction that has been added to the
       *  mempool but may have child transactions in the mempool, eg during a
       *  chain reorg.  setExclude is the set of descendant transactions in the
       *  mempool that must not be accounted for (because any descendants in
       *  setExclude were added to the mempool after the transaction being
       *  updated and hence their state is already reflected in the parent
       *  state).
       *
       *  If updating an entry requires looking at more than maxDescendantsToVisit
       *  transactions, outside of the ones in setExclude, then give up.
       *
       *  cachedDescendants will be updated with the descendants of the transaction
       *  being updated, so that future invocations don't need to walk the
       *  same transaction again, if encountered in another transaction chain.
       */
      bool UpdateForDescendants(txiter updateIt,
              int maxDescendantsToVisit,
              cacheMap &cachedDescendants,
              const std::set<uint256> &setExclude);
      /** Update ancestors of hash to add/remove it as a descendant transaction. */
      void UpdateAncestorsOf(bool add, txiter hash, setEntries &setAncestors);
      /** For each transaction being removed, update ancestors and any direct children. */
      void UpdateForRemoveFromMempool(const setEntries &entriesToRemove);
      /** Sever link between specified transaction and direct children. */
      void UpdateChildrenForRemoval(txiter entry);
      /** Populate setDescendants with all in-mempool descendants of hash.
       *  Assumes that setDescendants includes all in-mempool descendants of anything
       *  already in it.  */
      void CalculateDescendants(txiter it, setEntries &setDescendants);
  
      /** Before calling removeUnchecked for a given transaction,
       *  UpdateForRemoveFromMempool must be called on the entire (dependent) set
       *  of transactions being removed at the same time.  We use each
       *  CTxMemPoolEntry's setMemPoolParents in order to walk ancestors of a
       *  given transaction that is removed, so we can't remove intermediate
       *  transactions in a chain before we've updated all the state for the
       *  removal.
       */
      void removeUnchecked(txiter entry);
  };
  
  /** 
   * CCoinsView that brings transactions from a memorypool into view.
   * It does not check for spendings by memory pool transactions.
   */
  class CCoinsViewMemPool : public CCoinsViewBacked
  {
  protected:
      CTxMemPool& mempool;
  
  public:
      CCoinsViewMemPool(CCoinsView* baseIn, CTxMemPool& mempoolIn);
      bool GetCoins(const uint256& txid, CCoins& coins) const;
      bool HaveCoins(const uint256& txid) const;
  };
  
  #endif // BITCOIN_TXMEMPOOL_H
  