1// Copyright (c) 2023-present 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 <cstddef>
12#include <cstdint>
13#include <list>
14#include <unordered_map>
15#include <vector>
16
17/** Maximum bytes for transactions to store for processing during reorg */
18inline constexpr unsigned int MAX_DISCONNECTED_TX_POOL_BYTES{20'000'000};
19/**
20 * DisconnectedBlockTransactions
21
22 * During the reorg, it's desirable to re-add previously confirmed transactions
23 * to the mempool, so that anything not re-confirmed in the new chain is
24 * available to be mined. However, it's more efficient to wait until the reorg
25 * is complete and process all still-unconfirmed transactions at that time,
26 * since we expect most confirmed transactions to (typically) still be
27 * confirmed in the new chain, and re-accepting to the memory pool is expensive
28 * (and therefore better to not do in the middle of reorg-processing).
29 * Instead, store the disconnected transactions (in order!) as we go, remove any
30 * that are included in blocks in the new chain, and then process the remaining
31 * still-unconfirmed transactions at the end.
32 *
33 * Order of queuedTx:
34 * The front of the list should be the most recently-confirmed transactions (transactions at the
35 * end of vtx of blocks closer to the tip). If memory usage grows too large, we trim from the front
36 * of the list. After trimming, transactions can be re-added to the mempool from the back of the
37 * list to the front without running into missing inputs.
38 */
39class DisconnectedBlockTransactions {
40private:
41    /** Cached dynamic memory usage for the `CTransactionRef`s */
42    uint64_t cachedInnerUsage = 0;
43    const size_t m_max_mem_usage;
44    std::list<CTransactionRef> queuedTx;
45    using TxList = decltype(queuedTx);
46    std::unordered_map<Txid, TxList::iterator, SaltedTxidHasher> iters_by_txid;
47
48    /** Trim the earliest-added entries until we are within memory bounds. */
49    std::vector<CTransactionRef> LimitMemoryUsage();
50
51public:
52    DisconnectedBlockTransactions(size_t max_mem_usage)
53        : m_max_mem_usage{max_mem_usage} {}
54
55    ~DisconnectedBlockTransactions();
56
57    size_t DynamicMemoryUsage() const;
58
59    /** Add transactions from the block, iterating through vtx in reverse order. Callers should call
60     * this function for blocks in descending order by block height.
61     * We assume that callers never pass multiple transactions with the same txid, otherwise things
62     * can go very wrong in removeForBlock due to queuedTx containing an item without a
63     * corresponding entry in iters_by_txid.
64     * @returns vector of transactions that were evicted for size-limiting.
65     */
66    [[nodiscard]] std::vector<CTransactionRef> AddTransactionsFromBlock(const std::vector<CTransactionRef>& vtx);
67
68    /** Remove any entries that are in this block. */
69    void removeForBlock(const std::vector<CTransactionRef>& vtx);
70
71    size_t size() const { return queuedTx.size(); }
72
73    void clear();
74
75    /** Clear all data structures and return the list of transactions. */
76    std::list<CTransactionRef> take();
77};
78#endif // BITCOIN_KERNEL_DISCONNECTED_TRANSACTIONS_H
79