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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 <core_memusage.h>
#include <memusage.h>
#include <primitives/transaction.h>
#include <util/hasher.h>
#include <list>
#include <unordered_map>
/**
* 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 CTransactions (memory for the shared pointers is
* included in the container calculations). */
uint64_t cachedInnerUsage = 0;
std::list<CTransactionRef> queuedTx;
using TxList = decltype(queuedTx);
std::unordered_map<uint256, TxList::iterator, SaltedTxidHasher> iters_by_txid;
public:
// 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());
assert(iters_by_txid.empty());
assert(cachedInnerUsage == 0);
}
size_t DynamicMemoryUsage() const {
return cachedInnerUsage + memusage::DynamicUsage(iters_by_txid) + memusage::DynamicUsage(queuedTx);
}
/** 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.
*/
void AddTransactionsFromBlock(const std::vector<CTransactionRef>& vtx)
{
iters_by_txid.reserve(iters_by_txid.size() + vtx.size());
for (auto block_it = vtx.rbegin(); block_it != vtx.rend(); ++block_it) {
auto it = queuedTx.insert(queuedTx.end(), *block_it);
iters_by_txid.emplace((*block_it)->GetHash(), it);
cachedInnerUsage += RecursiveDynamicUsage(**block_it);
}
}
/** Remove any entries that are in this block. */
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 (const auto& tx : vtx) {
auto iter = iters_by_txid.find(tx->GetHash());
if (iter != iters_by_txid.end()) {
auto list_iter = iter->second;
iters_by_txid.erase(iter);
cachedInnerUsage -= RecursiveDynamicUsage(**list_iter);
queuedTx.erase(list_iter);
}
}
}
/** Remove the first entry and update memory usage. */
CTransactionRef take_first()
{
CTransactionRef first_tx;
if (!queuedTx.empty()) {
first_tx = queuedTx.front();
cachedInnerUsage -= RecursiveDynamicUsage(*queuedTx.front());
iters_by_txid.erase(queuedTx.front()->GetHash());
queuedTx.pop_front();
}
return first_tx;
}
size_t size() const { return queuedTx.size(); }
void clear()
{
cachedInnerUsage = 0;
iters_by_txid.clear();
queuedTx.clear();
}
/** Clear all data structures and return the list of transactions. */
std::list<CTransactionRef> take()
{
std::list<CTransactionRef> ret = std::move(queuedTx);
clear();
return ret;
}
};
#endif // BITCOIN_KERNEL_DISCONNECTED_TRANSACTIONS_H
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