txmempool.h

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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2020 The Bitcoin Core 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 <atomic>
#include <map>
#include <optional>
#include <set>
#include <string>
#include <utility>
#include <vector>
 
#include <amount.h>
#include <coins.h>
#include <indirectmap.h>
#include <policy/feerate.h>
#include <policy/packages.h>
#include <primitives/transaction.h>
#include <random.h>
#include <sync.h>
#include <util/epochguard.h>
#include <util/hasher.h>
 
#include <boost/multi_index_container.hpp>
#include <boost/multi_index/hashed_index.hpp>
#include <boost/multi_index/ordered_index.hpp>
#include <boost/multi_index/sequenced_index.hpp>
 
class CBlockIndex;
class CChainState;
extern RecursiveMutex cs_main;
 
static const uint32_t MEMPOOL_HEIGHT = 0x7FFFFFFF;
 
struct LockPoints {
    // Will be set to the blockchain height and median time past
    // values that would be necessary to satisfy all relative locktime
    // constraints (BIP68) of this tx given our view of block chain history
    int height{0};
    int64_t time{0};
    // As long as the current chain descends from the highest height block
    // containing one of the inputs used in the calculation, then the cached
    // values are still valid even after a reorg.
    CBlockIndex* maxInputBlock{nullptr};
};
 
struct CompareIteratorByHash {
    // SFINAE for T where T is either a pointer type (e.g., a txiter) or a reference_wrapper<T>
    // (e.g. a wrapped CTxMemPoolEntry&)
    template <typename T>
    bool operator()(const std::reference_wrapper<T>& a, const std::reference_wrapper<T>& b) const
    {
        return a.get().GetTx().GetHash() < b.get().GetTx().GetHash();
    }
    template <typename T>
    bool operator()(const T& a, const T& b) const
    {
        return a->GetTx().GetHash() < b->GetTx().GetHash();
    }
};
 
class CTxMemPoolEntry
{
public:
    typedef std::reference_wrapper<const CTxMemPoolEntry> CTxMemPoolEntryRef;
    // two aliases, should the types ever diverge
    typedef std::set<CTxMemPoolEntryRef, CompareIteratorByHash> Parents;
    typedef std::set<CTxMemPoolEntryRef, CompareIteratorByHash> Children;
 
private:
    const CTransactionRef tx;
    mutable Parents m_parents;
    mutable Children m_children;
    const CAmount nFee;             
    const size_t nTxWeight;         
    const size_t nUsageSize;        
    const int64_t nTime;            
    const unsigned int entryHeight; 
    const bool spendsCoinbase;      
    const int64_t sigOpCost;        
    int64_t feeDelta{0};            
    LockPoints lockPoints;     
 
    // 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.
    uint64_t nCountWithDescendants{1}; 
    uint64_t nSizeWithDescendants;   
    CAmount nModFeesWithDescendants; 
 
    // Analogous statistics for ancestor transactions
    uint64_t nCountWithAncestors{1};
    uint64_t nSizeWithAncestors;
    CAmount nModFeesWithAncestors;
    int64_t nSigOpCostWithAncestors;
 
public:
    CTxMemPoolEntry(const CTransactionRef& tx, CAmount fee,
                    int64_t time, unsigned int entry_height,
                    bool spends_coinbase,
                    int64_t sigops_cost, LockPoints lp);
 
    const CTransaction& GetTx() const { return *this->tx; }
    CTransactionRef GetSharedTx() const { return this->tx; }
    const CAmount& GetFee() const { return nFee; }
    size_t GetTxSize() const;
    size_t GetTxWeight() const { return nTxWeight; }
    std::chrono::seconds GetTime() const { return std::chrono::seconds{nTime}; }
    unsigned int GetHeight() const { return entryHeight; }
    int64_t GetSigOpCost() const { return sigOpCost; }
    int64_t GetModifiedFee() const { return nFee + feeDelta; }
    size_t DynamicMemoryUsage() const { return nUsageSize; }
    const LockPoints& GetLockPoints() const { return lockPoints; }
 
    // Adjusts the descendant state.
    void UpdateDescendantState(int64_t modifySize, CAmount modifyFee, int64_t modifyCount);
    // Adjusts the ancestor state
    void UpdateAncestorState(int64_t modifySize, CAmount modifyFee, int64_t modifyCount, int64_t modifySigOps);
    // Updates the fee delta used for mining priority score, and the
    // modified fees with descendants.
    void UpdateFeeDelta(int64_t feeDelta);
    // Update the LockPoints after a reorg
    void UpdateLockPoints(const LockPoints& lp);
 
    uint64_t GetCountWithDescendants() const { return nCountWithDescendants; }
    uint64_t GetSizeWithDescendants() const { return nSizeWithDescendants; }
    CAmount GetModFeesWithDescendants() const { return nModFeesWithDescendants; }
 
    bool GetSpendsCoinbase() const { return spendsCoinbase; }
 
    uint64_t GetCountWithAncestors() const { return nCountWithAncestors; }
    uint64_t GetSizeWithAncestors() const { return nSizeWithAncestors; }
    CAmount GetModFeesWithAncestors() const { return nModFeesWithAncestors; }
    int64_t GetSigOpCostWithAncestors() const { return nSigOpCostWithAncestors; }
 
    const Parents& GetMemPoolParentsConst() const { return m_parents; }
    const Children& GetMemPoolChildrenConst() const { return m_children; }
    Parents& GetMemPoolParents() const { return m_parents; }
    Children& GetMemPoolChildren() const { return m_children; }
 
    mutable size_t vTxHashesIdx; 
    mutable Epoch::Marker m_epoch_marker; 
};
 
// 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.UpdateDescendantState(modifySize, modifyFee, modifyCount); }
 
    private:
        int64_t modifySize;
        CAmount modifyFee;
        int64_t modifyCount;
};
 
struct update_ancestor_state
{
    update_ancestor_state(int64_t _modifySize, CAmount _modifyFee, int64_t _modifyCount, int64_t _modifySigOpsCost) :
        modifySize(_modifySize), modifyFee(_modifyFee), modifyCount(_modifyCount), modifySigOpsCost(_modifySigOpsCost)
    {}
 
    void operator() (CTxMemPoolEntry &e)
        { e.UpdateAncestorState(modifySize, modifyFee, modifyCount, modifySigOpsCost); }
 
    private:
        int64_t modifySize;
        CAmount modifyFee;
        int64_t modifyCount;
        int64_t modifySigOpsCost;
};
 
struct update_fee_delta
{
    explicit update_fee_delta(int64_t _feeDelta) : feeDelta(_feeDelta) { }
 
    void operator() (CTxMemPoolEntry &e) { e.UpdateFeeDelta(feeDelta); }
 
private:
    int64_t feeDelta;
};
 
struct update_lock_points
{
    explicit update_lock_points(const LockPoints& _lp) : lp(_lp) { }
 
    void operator() (CTxMemPoolEntry &e) { e.UpdateLockPoints(lp); }
 
private:
    const LockPoints& lp;
};
 
// extracts a transaction hash from CTxMemPoolEntry or CTransactionRef
struct mempoolentry_txid
{
    typedef uint256 result_type;
    result_type operator() (const CTxMemPoolEntry &entry) const
    {
        return entry.GetTx().GetHash();
    }
 
    result_type operator() (const CTransactionRef& tx) const
    {
        return tx->GetHash();
    }
};
 
// extracts a transaction witness-hash from CTxMemPoolEntry or CTransactionRef
struct mempoolentry_wtxid
{
    typedef uint256 result_type;
    result_type operator() (const CTxMemPoolEntry &entry) const
    {
        return entry.GetTx().GetWitnessHash();
    }
 
    result_type operator() (const CTransactionRef& tx) const
    {
        return tx->GetWitnessHash();
    }
};
 
 
class CompareTxMemPoolEntryByDescendantScore
{
public:
    bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) const
    {
        double a_mod_fee, a_size, b_mod_fee, b_size;
 
        GetModFeeAndSize(a, a_mod_fee, a_size);
        GetModFeeAndSize(b, b_mod_fee, b_size);
 
        // Avoid division by rewriting (a/b > c/d) as (a*d > c*b).
        double f1 = a_mod_fee * b_size;
        double f2 = a_size * b_mod_fee;
 
        if (f1 == f2) {
            return a.GetTime() >= b.GetTime();
        }
        return f1 < f2;
    }
 
    // Return the fee/size we're using for sorting this entry.
    void GetModFeeAndSize(const CTxMemPoolEntry &a, double &mod_fee, double &size) const
    {
        // Compare feerate with descendants to feerate of the transaction, and
        // return the fee/size for the max.
        double f1 = (double)a.GetModifiedFee() * a.GetSizeWithDescendants();
        double f2 = (double)a.GetModFeesWithDescendants() * a.GetTxSize();
 
        if (f2 > f1) {
            mod_fee = a.GetModFeesWithDescendants();
            size = a.GetSizeWithDescendants();
        } else {
            mod_fee = a.GetModifiedFee();
            size = a.GetTxSize();
        }
    }
};
 
class CompareTxMemPoolEntryByScore
{
public:
    bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) const
    {
        double f1 = (double)a.GetFee() * b.GetTxSize();
        double f2 = (double)b.GetFee() * a.GetTxSize();
        if (f1 == f2) {
            return b.GetTx().GetHash() < a.GetTx().GetHash();
        }
        return f1 > f2;
    }
};
 
class CompareTxMemPoolEntryByEntryTime
{
public:
    bool operator()(const CTxMemPoolEntry& a, const CTxMemPoolEntry& b) const
    {
        return a.GetTime() < b.GetTime();
    }
};
 
class CompareTxMemPoolEntryByAncestorFee
{
public:
    template<typename T>
    bool operator()(const T& a, const T& b) const
    {
        double a_mod_fee, a_size, b_mod_fee, b_size;
 
        GetModFeeAndSize(a, a_mod_fee, a_size);
        GetModFeeAndSize(b, b_mod_fee, b_size);
 
        // Avoid division by rewriting (a/b > c/d) as (a*d > c*b).
        double f1 = a_mod_fee * b_size;
        double f2 = a_size * b_mod_fee;
 
        if (f1 == f2) {
            return a.GetTx().GetHash() < b.GetTx().GetHash();
        }
        return f1 > f2;
    }
 
    // Return the fee/size we're using for sorting this entry.
    template <typename T>
    void GetModFeeAndSize(const T &a, double &mod_fee, double &size) const
    {
        // Compare feerate with ancestors to feerate of the transaction, and
        // return the fee/size for the min.
        double f1 = (double)a.GetModifiedFee() * a.GetSizeWithAncestors();
        double f2 = (double)a.GetModFeesWithAncestors() * a.GetTxSize();
 
        if (f1 > f2) {
            mod_fee = a.GetModFeesWithAncestors();
            size = a.GetSizeWithAncestors();
        } else {
            mod_fee = a.GetModifiedFee();
            size = a.GetTxSize();
        }
    }
};
 
// Multi_index tag names
struct descendant_score {};
struct entry_time {};
struct ancestor_score {};
struct index_by_wtxid {};
 
class CBlockPolicyEstimator;
 
struct TxMempoolInfo
{
    CTransactionRef tx;
 
    std::chrono::seconds m_time;
 
    CAmount fee;
 
    size_t vsize;
 
    int64_t nFeeDelta;
};
 
enum class MemPoolRemovalReason {
    EXPIRY,      
    SIZELIMIT,   
    REORG,       
    BLOCK,       
    CONFLICT,    
    REPLACED,    
};
 
class CTxMemPool
{
protected:
    const int m_check_ratio; 
    std::atomic<unsigned int> nTransactionsUpdated{0}; 
    CBlockPolicyEstimator* const minerPolicyEstimator;
 
    uint64_t totalTxSize GUARDED_BY(cs);      
    CAmount m_total_fee GUARDED_BY(cs);       
    uint64_t cachedInnerUsage GUARDED_BY(cs); 
 
    mutable int64_t lastRollingFeeUpdate GUARDED_BY(cs);
    mutable bool blockSinceLastRollingFeeBump GUARDED_BY(cs);
    mutable double rollingMinimumFeeRate GUARDED_BY(cs); 
    mutable Epoch m_epoch GUARDED_BY(cs);
 
    // In-memory counter for external mempool tracking purposes.
    // This number is incremented once every time a transaction
    // is added or removed from the mempool for any reason.
    mutable uint64_t m_sequence_number GUARDED_BY(cs){1};
 
    void trackPackageRemoved(const CFeeRate& rate) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    bool m_is_loaded GUARDED_BY(cs){false};
 
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::hashed_unique<mempoolentry_txid, SaltedTxidHasher>,
            // sorted by wtxid
            boost::multi_index::hashed_unique<
                boost::multi_index::tag<index_by_wtxid>,
                mempoolentry_wtxid,
                SaltedTxidHasher
            >,
            // sorted by fee rate
            boost::multi_index::ordered_non_unique<
                boost::multi_index::tag<descendant_score>,
                boost::multi_index::identity<CTxMemPoolEntry>,
                CompareTxMemPoolEntryByDescendantScore
            >,
            // sorted by entry time
            boost::multi_index::ordered_non_unique<
                boost::multi_index::tag<entry_time>,
                boost::multi_index::identity<CTxMemPoolEntry>,
                CompareTxMemPoolEntryByEntryTime
            >,
            // sorted by fee rate with ancestors
            boost::multi_index::ordered_non_unique<
                boost::multi_index::tag<ancestor_score>,
                boost::multi_index::identity<CTxMemPoolEntry>,
                CompareTxMemPoolEntryByAncestorFee
            >
        >
    > indexed_transaction_set;
 
    mutable RecursiveMutex cs;
    indexed_transaction_set mapTx GUARDED_BY(cs);
 
    using txiter = indexed_transaction_set::nth_index<0>::type::const_iterator;
    std::vector<std::pair<uint256, txiter>> vTxHashes GUARDED_BY(cs); 
 
    typedef std::set<txiter, CompareIteratorByHash> setEntries;
 
    uint64_t CalculateDescendantMaximum(txiter entry) const EXCLUSIVE_LOCKS_REQUIRED(cs);
private:
    typedef std::map<txiter, setEntries, CompareIteratorByHash> cacheMap;
 
 
    void UpdateParent(txiter entry, txiter parent, bool add) EXCLUSIVE_LOCKS_REQUIRED(cs);
    void UpdateChild(txiter entry, txiter child, bool add) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    std::vector<indexed_transaction_set::const_iterator> GetSortedDepthAndScore() const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    std::set<uint256> m_unbroadcast_txids GUARDED_BY(cs);
 
 
    bool CalculateAncestorsAndCheckLimits(size_t entry_size,
                                          size_t entry_count,
                                          setEntries& setAncestors,
                                          CTxMemPoolEntry::Parents &staged_ancestors,
                                          uint64_t limitAncestorCount,
                                          uint64_t limitAncestorSize,
                                          uint64_t limitDescendantCount,
                                          uint64_t limitDescendantSize,
                                          std::string &errString) const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
public:
    indirectmap<COutPoint, const CTransaction*> mapNextTx GUARDED_BY(cs);
    std::map<uint256, CAmount> mapDeltas GUARDED_BY(cs);
 
    explicit CTxMemPool(CBlockPolicyEstimator* estimator = nullptr, int check_ratio = 0);
 
    void check(CChainState& active_chainstate) const EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
    // 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.
    // Note that addUnchecked is ONLY called from ATMP outside of tests
    // and any other callers may break wallet's in-mempool tracking (due to
    // lack of CValidationInterface::TransactionAddedToMempool callbacks).
    void addUnchecked(const CTxMemPoolEntry& entry, bool validFeeEstimate = true) EXCLUSIVE_LOCKS_REQUIRED(cs, cs_main);
    void addUnchecked(const CTxMemPoolEntry& entry, setEntries& setAncestors, bool validFeeEstimate = true) EXCLUSIVE_LOCKS_REQUIRED(cs, cs_main);
 
    void removeRecursive(const CTransaction& tx, MemPoolRemovalReason reason) EXCLUSIVE_LOCKS_REQUIRED(cs);
    void removeForReorg(CChainState& active_chainstate, int flags) EXCLUSIVE_LOCKS_REQUIRED(cs, cs_main);
    void removeConflicts(const CTransaction& tx) EXCLUSIVE_LOCKS_REQUIRED(cs);
    void removeForBlock(const std::vector<CTransactionRef>& vtx, unsigned int nBlockHeight) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    void clear();
    void _clear() EXCLUSIVE_LOCKS_REQUIRED(cs); //lock free
    bool CompareDepthAndScore(const uint256& hasha, const uint256& hashb, bool wtxid=false);
    void queryHashes(std::vector<uint256>& vtxid) const;
    bool isSpent(const COutPoint& outpoint) const;
    unsigned int GetTransactionsUpdated() const;
    void AddTransactionsUpdated(unsigned int n);
    bool HasNoInputsOf(const CTransaction& tx) const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    void PrioritiseTransaction(const uint256& hash, const CAmount& nFeeDelta);
    void ApplyDelta(const uint256& hash, CAmount &nFeeDelta) const EXCLUSIVE_LOCKS_REQUIRED(cs);
    void ClearPrioritisation(const uint256& hash) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    const CTransaction* GetConflictTx(const COutPoint& prevout) const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    std::optional<txiter> GetIter(const uint256& txid) const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    setEntries GetIterSet(const std::set<uint256>& hashes) const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    void RemoveStaged(setEntries& stage, bool updateDescendants, MemPoolRemovalReason reason) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    void UpdateTransactionsFromBlock(const std::vector<uint256>& vHashesToUpdate) EXCLUSIVE_LOCKS_REQUIRED(cs, cs_main) LOCKS_EXCLUDED(m_epoch);
 
    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) const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    bool CheckPackageLimits(const Package& package,
                            uint64_t limitAncestorCount,
                            uint64_t limitAncestorSize,
                            uint64_t limitDescendantCount,
                            uint64_t limitDescendantSize,
                            std::string &errString) const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    void CalculateDescendants(txiter it, setEntries& setDescendants) const EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    CFeeRate GetMinFee(size_t sizelimit) const;
 
    void TrimToSize(size_t sizelimit, std::vector<COutPoint>* pvNoSpendsRemaining = nullptr) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    int Expire(std::chrono::seconds time) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    void GetTransactionAncestry(const uint256& txid, size_t& ancestors, size_t& descendants, size_t* ancestorsize = nullptr, CAmount* ancestorfees = nullptr) const;
 
    bool IsLoaded() const;
 
    void SetIsLoaded(bool loaded);
 
    unsigned long size() const
    {
        LOCK(cs);
        return mapTx.size();
    }
 
    uint64_t GetTotalTxSize() const EXCLUSIVE_LOCKS_REQUIRED(cs)
    {
        AssertLockHeld(cs);
        return totalTxSize;
    }
 
    CAmount GetTotalFee() const EXCLUSIVE_LOCKS_REQUIRED(cs)
    {
        AssertLockHeld(cs);
        return m_total_fee;
    }
 
    bool exists(const GenTxid& gtxid) const
    {
        LOCK(cs);
        if (gtxid.IsWtxid()) {
            return (mapTx.get<index_by_wtxid>().count(gtxid.GetHash()) != 0);
        }
        return (mapTx.count(gtxid.GetHash()) != 0);
    }
    bool exists(const uint256& txid) const { return exists(GenTxid{false, txid}); }
 
    CTransactionRef get(const uint256& hash) const;
    txiter get_iter_from_wtxid(const uint256& wtxid) const EXCLUSIVE_LOCKS_REQUIRED(cs)
    {
        AssertLockHeld(cs);
        return mapTx.project<0>(mapTx.get<index_by_wtxid>().find(wtxid));
    }
    TxMempoolInfo info(const uint256& hash) const;
    TxMempoolInfo info(const GenTxid& gtxid) const;
    std::vector<TxMempoolInfo> infoAll() const;
 
    size_t DynamicMemoryUsage() const;
 
    void AddUnbroadcastTx(const uint256& txid)
    {
        LOCK(cs);
        // Sanity check the transaction is in the mempool & insert into
        // unbroadcast set.
        if (exists(txid)) m_unbroadcast_txids.insert(txid);
    };
 
    void RemoveUnbroadcastTx(const uint256& txid, const bool unchecked = false);
 
    std::set<uint256> GetUnbroadcastTxs() const
    {
        LOCK(cs);
        return m_unbroadcast_txids;
    }
 
    bool IsUnbroadcastTx(const uint256& txid) const EXCLUSIVE_LOCKS_REQUIRED(cs)
    {
        AssertLockHeld(cs);
        return m_unbroadcast_txids.count(txid) != 0;
    }
 
    uint64_t GetAndIncrementSequence() const EXCLUSIVE_LOCKS_REQUIRED(cs) {
        return m_sequence_number++;
    }
 
    uint64_t GetSequence() const EXCLUSIVE_LOCKS_REQUIRED(cs) {
        return m_sequence_number;
    }
 
private:
    void UpdateForDescendants(txiter updateIt,
            cacheMap &cachedDescendants,
            const std::set<uint256> &setExclude) EXCLUSIVE_LOCKS_REQUIRED(cs);
    void UpdateAncestorsOf(bool add, txiter hash, setEntries &setAncestors) EXCLUSIVE_LOCKS_REQUIRED(cs);
    void UpdateEntryForAncestors(txiter it, const setEntries &setAncestors) EXCLUSIVE_LOCKS_REQUIRED(cs);
    void UpdateForRemoveFromMempool(const setEntries &entriesToRemove, bool updateDescendants) EXCLUSIVE_LOCKS_REQUIRED(cs);
    void UpdateChildrenForRemoval(txiter entry) EXCLUSIVE_LOCKS_REQUIRED(cs);
 
    void removeUnchecked(txiter entry, MemPoolRemovalReason reason) EXCLUSIVE_LOCKS_REQUIRED(cs);
public:
    bool visited(const txiter it) const EXCLUSIVE_LOCKS_REQUIRED(cs, m_epoch)
    {
        return m_epoch.visited(it->m_epoch_marker);
    }
 
    bool visited(std::optional<txiter> it) const EXCLUSIVE_LOCKS_REQUIRED(cs, m_epoch)
    {
        assert(m_epoch.guarded()); // verify guard even when it==nullopt
        return !it || visited(*it);
    }
};
 
class CCoinsViewMemPool : public CCoinsViewBacked
{
    std::unordered_map<COutPoint, Coin, SaltedOutpointHasher> m_temp_added;
protected:
    const CTxMemPool& mempool;
 
public:
    CCoinsViewMemPool(CCoinsView* baseIn, const CTxMemPool& mempoolIn);
    bool GetCoin(const COutPoint &outpoint, Coin &coin) const override;
    void PackageAddTransaction(const CTransactionRef& tx);
};
 
// multi_index tag names
struct txid_index {};
struct insertion_order {};
 
struct DisconnectedBlockTransactions {
    typedef boost::multi_index_container<
        CTransactionRef,
        boost::multi_index::indexed_by<
            // sorted by txid
            boost::multi_index::hashed_unique<
                boost::multi_index::tag<txid_index>,
                mempoolentry_txid,
                SaltedTxidHasher
            >,
            // sorted by order in the blockchain
            boost::multi_index::sequenced<
                boost::multi_index::tag<insertion_order>
            >
        >
    > indexed_disconnected_transactions;
 
    // It's almost certainly a logic bug if we don't clear out queuedTx before
    // destruction, as we add to it while disconnecting blocks, and then we
    // need to re-process remaining transactions to ensure mempool consistency.
    // For now, assert() that we've emptied out this object on destruction.
    // This assert() can always be removed if the reorg-processing code were
    // to be refactored such that this assumption is no longer true (for
    // instance if there was some other way we cleaned up the mempool after a
    // reorg, besides draining this object).
    ~DisconnectedBlockTransactions() { assert(queuedTx.empty()); }
 
    indexed_disconnected_transactions queuedTx;
    uint64_t cachedInnerUsage = 0;
 
    // Estimate the overhead of queuedTx to be 6 pointers + an allocation, as
    // no exact formula for boost::multi_index_contained is implemented.
    size_t DynamicMemoryUsage() const {
        return memusage::MallocUsage(sizeof(CTransactionRef) + 6 * sizeof(void*)) * queuedTx.size() + cachedInnerUsage;
    }
 
    void addTransaction(const CTransactionRef& tx)
    {
        queuedTx.insert(tx);
        cachedInnerUsage += RecursiveDynamicUsage(tx);
    }
 
    // Remove entries based on txid_index, and update memory usage.
    void removeForBlock(const std::vector<CTransactionRef>& vtx)
    {
        // Short-circuit in the common case of a block being added to the tip
        if (queuedTx.empty()) {
            return;
        }
        for (auto const &tx : vtx) {
            auto it = queuedTx.find(tx->GetHash());
            if (it != queuedTx.end()) {
                cachedInnerUsage -= RecursiveDynamicUsage(*it);
                queuedTx.erase(it);
            }
        }
    }
 
    // Remove an entry by insertion_order index, and update memory usage.
    void removeEntry(indexed_disconnected_transactions::index<insertion_order>::type::iterator entry)
    {
        cachedInnerUsage -= RecursiveDynamicUsage(*entry);
        queuedTx.get<insertion_order>().erase(entry);
    }
 
    void clear()
    {
        cachedInnerUsage = 0;
        queuedTx.clear();
    }
};
 
#endif // BITCOIN_TXMEMPOOL_H