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// Copyright (c) 2023 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_KERNEL_DISCONNECTED_TRANSACTIONS_H
#define BITCOIN_KERNEL_DISCONNECTED_TRANSACTIONS_H
#include <primitives/transaction.h>
#include <util/hasher.h>
#include <list>
#include <unordered_map>
#include <vector>
/** Maximum bytes for transactions to store for processing during reorg */
static const unsigned int MAX_DISCONNECTED_TX_POOL_BYTES{20'000'000};
/**
* DisconnectedBlockTransactions
* During the reorg, it's desirable to re-add previously confirmed transactions
* to the mempool, so that anything not re-confirmed in the new chain is
* available to be mined. However, it's more efficient to wait until the reorg
* is complete and process all still-unconfirmed transactions at that time,
* since we expect most confirmed transactions to (typically) still be
* confirmed in the new chain, and re-accepting to the memory pool is expensive
* (and therefore better to not do in the middle of reorg-processing).
* Instead, store the disconnected transactions (in order!) as we go, remove any
* that are included in blocks in the new chain, and then process the remaining
* still-unconfirmed transactions at the end.
*
* Order of queuedTx:
* The front of the list should be the most recently-confirmed transactions (transactions at the
* end of vtx of blocks closer to the tip). If memory usage grows too large, we trim from the front
* of the list. After trimming, transactions can be re-added to the mempool from the back of the
* list to the front without running into missing inputs.
*/
class DisconnectedBlockTransactions {
private:
/** Cached dynamic memory usage for the `CTransactionRef`s */
uint64_t cachedInnerUsage = 0;
const size_t m_max_mem_usage;
std::list<CTransactionRef> queuedTx;
using TxList = decltype(queuedTx);
std::unordered_map<uint256, TxList::iterator, SaltedTxidHasher> iters_by_txid;
/** Trim the earliest-added entries until we are within memory bounds. */
std::vector<CTransactionRef> LimitMemoryUsage();
public:
DisconnectedBlockTransactions(size_t max_mem_usage)
: m_max_mem_usage{max_mem_usage} {}
~DisconnectedBlockTransactions();
size_t DynamicMemoryUsage() const;
/** Add transactions from the block, iterating through vtx in reverse order. Callers should call
* this function for blocks in descending order by block height.
* We assume that callers never pass multiple transactions with the same txid, otherwise things
* can go very wrong in removeForBlock due to queuedTx containing an item without a
* corresponding entry in iters_by_txid.
* @returns vector of transactions that were evicted for size-limiting.
*/
[[nodiscard]] std::vector<CTransactionRef> AddTransactionsFromBlock(const std::vector<CTransactionRef>& vtx);
/** Remove any entries that are in this block. */
void removeForBlock(const std::vector<CTransactionRef>& vtx);
size_t size() const { return queuedTx.size(); }
void clear();
/** Clear all data structures and return the list of transactions. */
std::list<CTransactionRef> take();
};
#endif // BITCOIN_KERNEL_DISCONNECTED_TRANSACTIONS_H
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