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       1                 :            : // Copyright (c) 2023 The Bitcoin Core developers
       2                 :            : // Distributed under the MIT software license, see the accompanying
       3                 :            : // file COPYING or http://www.opensource.org/licenses/mit-license.php.
       4                 :            : 
       5                 :            : #ifndef BITCOIN_KERNEL_DISCONNECTED_TRANSACTIONS_H
       6                 :            : #define BITCOIN_KERNEL_DISCONNECTED_TRANSACTIONS_H
       7                 :            : 
       8                 :            : #include <primitives/transaction.h>
       9                 :            : #include <util/hasher.h>
      10                 :            : 
      11                 :            : #include <list>
      12                 :            : #include <unordered_map>
      13                 :            : #include <vector>
      14                 :            : 
      15                 :            : /** Maximum bytes for transactions to store for processing during reorg */
      16                 :            : static const unsigned int MAX_DISCONNECTED_TX_POOL_BYTES{20'000'000};
      17                 :            : /**
      18                 :            :  * DisconnectedBlockTransactions
      19                 :            : 
      20                 :            :  * During the reorg, it's desirable to re-add previously confirmed transactions
      21                 :            :  * to the mempool, so that anything not re-confirmed in the new chain is
      22                 :            :  * available to be mined. However, it's more efficient to wait until the reorg
      23                 :            :  * is complete and process all still-unconfirmed transactions at that time,
      24                 :            :  * since we expect most confirmed transactions to (typically) still be
      25                 :            :  * confirmed in the new chain, and re-accepting to the memory pool is expensive
      26                 :            :  * (and therefore better to not do in the middle of reorg-processing).
      27                 :            :  * Instead, store the disconnected transactions (in order!) as we go, remove any
      28                 :            :  * that are included in blocks in the new chain, and then process the remaining
      29                 :            :  * still-unconfirmed transactions at the end.
      30                 :            :  *
      31                 :            :  * Order of queuedTx:
      32                 :            :  * The front of the list should be the most recently-confirmed transactions (transactions at the
      33                 :            :  * end of vtx of blocks closer to the tip). If memory usage grows too large, we trim from the front
      34                 :            :  * of the list. After trimming, transactions can be re-added to the mempool from the back of the
      35                 :            :  * list to the front without running into missing inputs.
      36                 :            :  */
      37                 :            : class DisconnectedBlockTransactions {
      38                 :            : private:
      39                 :            :     /** Cached dynamic memory usage for the `CTransactionRef`s */
      40                 :        151 :     uint64_t cachedInnerUsage = 0;
      41                 :            :     const size_t m_max_mem_usage;
      42                 :            :     std::list<CTransactionRef> queuedTx;
      43                 :            :     using TxList = decltype(queuedTx);
      44                 :            :     std::unordered_map<uint256, TxList::iterator, SaltedTxidHasher> iters_by_txid;
      45                 :            : 
      46                 :            :     /** Trim the earliest-added entries until we are within memory bounds. */
      47                 :            :     std::vector<CTransactionRef> LimitMemoryUsage();
      48                 :            : 
      49                 :            : public:
      50 [ +  - ][ +  - ]:        302 :     DisconnectedBlockTransactions(size_t max_mem_usage)
      51                 :        151 :         : m_max_mem_usage{max_mem_usage} {}
      52                 :            : 
      53                 :            :     ~DisconnectedBlockTransactions();
      54                 :            : 
      55                 :            :     size_t DynamicMemoryUsage() const;
      56                 :            : 
      57                 :            :     /** Add transactions from the block, iterating through vtx in reverse order. Callers should call
      58                 :            :      * this function for blocks in descending order by block height.
      59                 :            :      * We assume that callers never pass multiple transactions with the same txid, otherwise things
      60                 :            :      * can go very wrong in removeForBlock due to queuedTx containing an item without a
      61                 :            :      * corresponding entry in iters_by_txid.
      62                 :            :      * @returns vector of transactions that were evicted for size-limiting.
      63                 :            :      */
      64                 :            :     [[nodiscard]] std::vector<CTransactionRef> AddTransactionsFromBlock(const std::vector<CTransactionRef>& vtx);
      65                 :            : 
      66                 :            :     /** Remove any entries that are in this block. */
      67                 :            :     void removeForBlock(const std::vector<CTransactionRef>& vtx);
      68                 :            : 
      69                 :            :     size_t size() const { return queuedTx.size(); }
      70                 :            : 
      71                 :            :     void clear();
      72                 :            : 
      73                 :            :     /** Clear all data structures and return the list of transactions. */
      74                 :            :     std::list<CTransactionRef> take();
      75                 :            : };
      76                 :            : #endif // BITCOIN_KERNEL_DISCONNECTED_TRANSACTIONS_H